A

Active Power - The power (in Watts) used by a device to produce useful work. Also called input power.

Air Change - A measure of the rate at which the air in an interior space is replace by outside (or conditioned) air by ventilation and infiltration; usually measured in cubic feet per time interval (hour), divided by the volume of air in the room.

Air-Conditioning & Refrigeration Institute (ARI) - 320, 325, 330 - ARI heat pump classifications: 320 refers to a water-source heat pump; 325 refers to a ground water-source heat pump; 330 refers to a ground source closed-loop heat pump.

Air Infiltration Measurement - A building energy auditing technique used to determine and/or locate air leaks in a building shell or envelope.

Air Retarder/Barrier - A material or structural element that inhibits air flow into and out of a building's envelope or shell. This is a continuous sheet composed of polyethylene, polypropylene, or extruded polystyrene. The sheet is wrapped around the outside of a house during construction to reduce air in-and exfiltration, yet allow water to easily diffuse through it.

Albedo - The ratio of light reflected by a surface to the light falling on it.

Alternating Current - A type of electrical current, the direction of which is reversed at regular intervals or cycles; in the U.S. the standard is 120 reversals or 60 cycles per second; typically abbreviated as AC.

Ambient Air - The air external to a building or device.

Amorphous Semiconductor - A non-crystalline semiconductor material that has no long-range order.

Amorphous Silicon - An alloy of silica and hydrogen, with a disordered, noncrystalline internal atomic arrangement, that can be deposited in thin-layers (a few micrometers in thickness) by a number of deposition methods to produce thin-film photovoltaic cells on glass, metal, or plastic substrates.

Ampere - A unit of measure for an electrical current; the amount of current that flows in a circuit at an electromotive force of one Volt and at a resistance of one Ohm. Abbreviated as amp.

Amp-Hours - A measure of the flow of current (in amperes) over one hour.

Angle of Incidence - In reference to solar energy systems, the angle at which direct sunlight strikes a surface; the angle between the direction of the sun and the perpendicular to the surface. Sunlight with an incident angle of 90 degrees tends to be absorbed, while lower angles tend to be reflected.

Angle of Inclination - In reference to solar energy systems, the angle that a solar collector is positioned above horizontal.

Angstrom Unit - A unit of length named for A.J. Angstome, a Swedish spectroscopist, used in measuring electromagnetic radiation equal to 0.000,000,01 centimeters.

Annual Load Fraction - That fraction of annual energy demand supplied by a solar system.

Annual Solar Savings - The annual solar savings of a solar building is the energy savings attributable to a solar feature relative to the energy requirements of a non-solar building.

Annualized Growth Rates -Calculated as follows:

(xn / x1) 1/n ,

where x is the value under consideration and n is the number of periods.

Antireflection Coating - A thin coating of a material applied to a photovoltaic cell surface that reduces the light reflection and increases light transmission.

Aperture - An opening; in solar collectors, the area through which solar radiation is admitted and directed to the absorber.

Apparent Day - A solar day; an interval between successive transits of the sun's center across an observer's meridian; the time thus measured is not equal to clock time.

Apparent Power (kVA) - This is the voltage-ampere requirement of a device designed to convert electric energy to a non-electrical form.

Appliance - A device for converting one form of energy or fuel into useful energy or work.

Array (Solar) - Any number of solar photovoltaic modules or solar thermal collectors or reflectors connected together to provide electrical or thermal energy.

Audit (Energy) - The process of determining energy consumption, by various techniques, of a building or facility.

Automatic (or Remote) Meter Reading System - A system that records the consumption of electricity, gas, water, etc, and sends the data to a central data accumulation device.

Auxiliary Energy or System - Energy required to operate mechanical components of an energy system, or a source of energy or energy supply system to back-up another.

Availability Factor - A percentage representing the number of hours a generating unit is available to produce power (regardless of the amount of power) in a given period, compared to the number of hours in the period.

Average Demand - The demand on, or the power output of, an electrical system or any of its parts over an interval of time, as determined by the total number of kilowatt-hours divided by the units of time in the interval.

Average Cost - The total cost of production divided by the total quantity produced.

Azimuth (Solar) - The angle between true south and the point on the horizon directly below the sun.

B

[top]

Backup Energy System - A reserve appliance; for example, a stand-by generator for a home or commercial building.

Balance-of-System - In a renewable energy system, refers to all components other than the mechanism used to harvest the resource (such as photovoltaic panels or a wind turbine). Balance-of-system costs can include design, land, site preparation, system installation, support structures, power conditioning, operation and maintenance, and storage.

Band Gap Energy - The amount of energy (in electron volts) required to free an outer shell electron from its orbit about the nucleus to a free state, and thus promote it from the valence to the conduction level.

Base Power - Power generated by a power generator that operates at a very high capacity factor.

Battery - An energy storage device composed of one or more electrolyte cells.

Battery Energy Storage - Energy storage using electrochemical batteries. The three main applications for battery energy storage systems include spinning reserve at generating stations, load leveling at substations, and peak shaving on the customer side of the meter.

Beam Radiation - Solar radiation that is not scattered by dust or water droplets.

BIPV - Building-Integrated Photovoltaic

Biomass - Organic nonfossil material of biological origin constituting a renewable energy source.

Bioenergy - Useful, renewable energy produced from organic matter, which may either be used directly as a fuel or processed into liquids and gases.

Biomass gas (Biogas) - A medium Btu gas containing methane and carbon dioxide, resulting from the action of microorganisms on organic materials such as a landfill.

Blackbody - An ideal substance that absorbs all radiation falling on it, and reflecting nothing.

British Thermal Unit (Btu) - The amount of heat required to raise the temperature of one pound of water one degree Fahrenheit; equal to 252 calories.

Building Energy Ratio - The space-conditioning load of a building.

Building Envelope - The structural elements (walls, roof, floor, foundation) of a building that encloses conditioned space; the building shell.

Building Heat-Loss Factor - A measure of the heating requirements of a building expressed in Btu per degree-day.

Building Orientation - The relationship of a building to true south, as specified by the direction of its longest axis.

Building Overall Energy Loss Coefficient-Area Product - The factor, when multiplied by the monthly degree-days, that yields the monthly space heating load.

Building Overall Heat Loss Rate - The overall rate of heat loss from a building by means of transmission plus infiltration, expressed in Btu per hour, per degree temperature difference between the inside and outside.

C

Calorie - The amount of heat required to raise the temperature of a unit of water, at or near the temperature of maximum density, one degree Celsius (or Centigrade [C]); expressed as a "small calorie" (the amount of heat required to raise the temperature of 1 gram of water one degree C), or as a "large calorie" or "kilogram calorie" (the amount of heat required to raise one kilogram [1,000 grams] of water one degree C); capitalization of the word calorie indicates a kilogram-calorie.

Capability - The maximum load that a generating unit, power plant, or other electrical apparatus can carry under specified conditions for a given period of time, without exceeding its approved limits of temperature and stress.

Capability Margin - The difference between net electrical system capability and system maximum load requirements (peak load); the margin of capability available to provide for scheduled maintenance, emergency outages, system operating requirements and unforeseen loads.

Capacitor - An electrical device that adjusts the leading current of an applied alternating current to balance the lag of the circuit to provide a high power factor.

Capacity - The load that a power generation unit or other electrical apparatus or heating unit is rated by the manufacture to be able to meet or supply.

Capacity (Heating, of a material) - The amount of heat energy needed to raise the temperature of a given mass of a substance by one degree Celsius. The heat required to raise the temperature of 1 kg of water by 1 degree Celsius is 4186 Joules.

Capacity Factor - The ratio of the average load on (or power output of) a generating unit or system to the capacity rating of the unit or system over a specified period of time.

Capacity, Gross - The full-load continuous rating of a generator, prime mover, or other electric equipment under specified conditions as designated by the manufacturer. It is usually indicated on a nameplate attached to the equipment.

Capacity, Net Summer - See Net Summer Capacity.

Capital Cost - The cost of field development and plant construction and the equipment required for the generation of electricity.

Cast Silicon - Crystalline silicon obtained by pouring pure molten silicon into a vertical mold and adjusting the temperature gradient along the mold volume during cooling to obtain slow, vertically-advancing crystallization of the silicon. The polycrystalline ingot thus formed is composed of large, relatively parallel, interlocking crystals. The cast ingots are sawed into wafers for further fabrication into photovoltaic cells. Cast-silicon wafers and ribbon-silicon sheets fabricated into cells are usually referred to as polycrystalline photovoltaic cells.

Cathode - The negative pole or electrode of an electrolytic cell, vacuum tube, etc., where electrons enter (current leaves) the system; the opposite of an anode.

Cathodic Protection - A method of preventing oxidation of the exposed metal in structures by imposing between the structure and the ground a small electrical voltage.

Cell - A component of a electrochemical battery. A 'primary' cell consists of two dissimilar elements, known as 'electrodes,' immersed in a liquid or paste known as the 'electrolyte.' A direct current of 1-1.5 volts will be produced by this cell. A 'secondary' cell or accumulator is a similar design but is made useful by passing a direct current of correct strength through it in a certain direction. Each of these cells will produce 2 volts; a 12 volt car battery contains six cells.

Central Receiver Solar Power Plants - Also known as "power towers," these use fields of two-axis tracking mirrors known as heliostats. Each heliostat is individually positioned by a computer control system to reflect the sun's rays to a tower-mounted thermal receiver. The effect of many heliostats reflecting to a common point creates the combined energy of thousands of suns, which produces high-temperature thermal energy. In the receiver, molten nitrate salts absorb the heat energy. The hot salt is then used to boil water to steam, which is sent to a conventional steam turbine-generator to produce electricity.

Charge Controller - An electronic device that regulates the electrical charge stored in batteries so that unsafe, overcharge conditions for the batteries are avoided.

Circuit - A device, or system of devices, that allows electrical current to flow through it and allows voltage to occur across positive and negative terminals.

Circuit Breaker - A device used to interrupt or break an electrical circuit when an overload condition exists; usually installed in the positive circuit; used to protect electrical equipment.

Circuit Lag - As time increases from zero at the terminals of an inductor, the voltage comes to a particular value on the sine function curve ahead of the current. The voltage reaches its negative peak exactly 90 degrees before the current reaches its negative peak thus the current lags behind by 90 degrees.

Cleavage of Lateral Epitaxial Films for Transfer (CLEFT) - A process for making inexpensive Gallium Arsenide (GaAs) photovoltaic cells in which a thin film of GaAs is grown atop a thick, single-crystal GaAs (or other suitable material) substrate and then is cleaved from the substrate and incorporated into a cell, allowing the substrate to be reused to grow more thin-film GaAs.

Clerestory - A window located high in a wall near the eaves that allows daylight into a building interior, and may be used for ventilation and solar heat gain.

Climate - The prevailing or average weather conditions of a geographic region.

Coefficient of Heat Transmission (U-Value) - A value that describes the ability of a material to conduct heat. The number of Btu that flow through 1 square foot of material, in one hour. It is the reciprocal of the R-Value (U-Value = 1/R-Value).

Coefficient of Performance (COP) - A ratio of the work or useful energy output of a system versus the amount of work or energy inputted into the system as determined by using the same energy equivalents for energy in and out. Is used as a measure of the steady state performance or energy efficiency of heating, cooling, and refrigeration appliances. The COP is equal to the Energy Efficiency Ratio (EER) divided by 3.412. The higher the COP, the more efficient the device.

Cogeneration - See combined heat and power.

Coincidence Factor - The ratio of the coincident, maximum demand or two or more loads to the sum of their noncoincident maximum demand for a given period; the reciprocal of the diversity factor, and is always less than or equal to one.

Coincident Demand - The demand of a consumer of electricity at the time of a power supplier's peak system demand.

Collector - The component of a solar energy heating system that collects solar radiation, and that contains components to absorb solar radiation and transfer the heat to a heat transfer fluid (air or liquid).

Collector Efficiency - The ratio of solar radiation captured and transferred to the collector (heat transfer) fluid.

Collector Fluid - The fluid, liquid (water or water/antifreeze solution) or air, used to absorb solar energy and transfer it for direct use, indirect heating of interior air or domestic water, and/or to a heat storage medium.

Collector Tilt - The angle that a solar collector is positioned from horizontal.

Color Rendition (Rendering) Index (CRI) - A measure of light quality. The maximum CRI value of 100 is given to natural daylight and incandescent lighting. The closer a lamp's CRI rating is to 100, the better its ability to show true colors to the human eye.

Combined Heat and Power (CHP) Plant - A plant designed to produce both heat and electricity from a single heat source. Note: This term is being used in place of the term "cogenerator" that was used by EIA in the past. CHP better describes the facilities because some of the plants included do not produce heat and power in a sequential fashion and, as a result, do not meet the legal definition of cogeneration specified in the Public Utility Regulatory Policies Act (PURPA).

Commercial Building - A building with more than 50 percent of its floor space used for commercial activities, which include stores, offices, schools, churches, libraries, museums, health care facilities, warehouses, and government buildings except those on military bases.

Commercial Sector - An energy-consuming sector that consists of service-providing facilities and equipment of: businesses; Federal, State, and local governments; and other private and public organizations, such as religious, social, or fraternal groups. The commercial sector includes institutional living quarters. It also includes sewage treatment facilities. Common uses of energy associated with this sector include space heating, water heating, air conditioning, lighting, refrigeration, cooking, and running a wide variety of other equipment. Note: This sector includes generators that produce electricity and/or useful thermal output primarily to support the activities of the above-mentioned commercial establishments.

Compound Paraboloid Collector - A form of solar concentrating collector that does not track the sun.

Concentrator - A reflective or refractive device that focuses incident insolation onto an area smaller than the reflective or refractive surface, resulting in increased insolation at the point of focus.

Concentrating (Solar) Collector - A solar collector that uses reflective surfaces to concentrate sunlight onto a small area, where it is absorbed and converted to heat or, in the case of solar photovoltaic (PV) devices, into electricity. Concentrators can increase the power flux of sunlight hundreds of times. The principal types of concentrating collectors include: compound parabolic, parabolic trough, fixed reflector moving receiver, fixed receiver moving reflector, Fresnel lense, and central receiver. A PV concentrating module uses optical elements (Fresnel lense) to increase the amount of sunlight incident onto a PV cell. Concentrating PV modules/arrays must track the sun and use only the direct sunlight because the diffuse portion cannot be focused onto the PV cells. Concentrating collectors for home or small business solar water heating applications are usually parabolic troughs that concentrate the sun's energy on an absorber tube (called a receiver), which contains a heat-transfer fluid.

Conditioned Space - The interior space of a building that is heated or cooled.

Conduction - The transfer of heat through a material by the transfer of kinetic energy from particle to particle; the flow of heat between two materials of different temperatures that are in direct physical contact.

Conduction Band - An energy band in a semiconductor in which electrons can move freely in a solid, producing a net transport of charge.

Conductivity (Thermal) - This is a positive constant, k, that is a property of a substance and is used in the calculation of heat transfer rates for materials. It is the amount of heat that flows through a specified area and thickness of a material over a specified period of time when there is a temperature difference of one degree between the surfaces of the material.

Conductor - The material through which electricity is transmitted, such as an electrical wire, or transmission or distribution line.

Conduit - A tubular material used to encase and protect one or more electrical conductors.

Connected Load - The sum of the ratings of the electricity consuming apparatus connected to a generating system.

Conventional hydroelectric (hydropower) plant - A plant in which all of the power is produced from natural streamflow as regulated by available storage.

Conversion Efficiency - The amount of energy produced as a percentage of the amount of energy consumed.

Cooling Degree Day - A value used to estimate interior air cooling requirements (load) calculated as the number of degrees per day (over a specified period) that the daily average temperature is above 65 degrees Fahrenheit (or some other, specified base temperature). The daily average temperature is the mean of the maximum and minimum temperatures recorded for a specific location for a 24 hour period.

Cooling Load - That amount of cooling energy to be supplied (or heat and humidity removed) based on the sensible and latent loads.

Coulomb - A unit for the quantity of electricity transported in 1 second by a current of 1 ampere.

Crystalline Silicon Photovoltaic Cell - A type of photovoltaic cell made from a single crystal or a polycrystalline slice of silicon. Crystalline silicon cells can be joined together to form a module (or panel).

Current (Electrical) - The flow of electrical energy (electricity) in a conductor, measured in amperes.

Cycle - In alternating current, the current goes from zero potential or voltage to a maximum in one direction, back to zero, and then to a maximum potential or voltage in the other direction. The number of complete cycles per second determines the current frequency; in Canada the standard for alternating current is 60 cycles.

D

Daylighting - The use of direct, diffuse, or reflected sunlight to provide supplemental lighting for building interiors.

Decentralized (Energy) System - Energy systems supply individual, or small-groups, of energy loads.

Declination - The angular position of the sun at solar noon with respect to the plane of the equator.

Deep Discharge - Discharging a battery to 20 percent or less of its full charge capacity.

Degree Day - A unit for measuring the extent that the outdoor daily average temperature (the mean of the maximum and minimum daily dry-bulb temperatures) falls below (in the case of heating, see Heating Degree Day), or falls above (in the case of cooling, see Cooling Degree Day) an assumed base temperature, normally taken as 65 degrees Fahrenheit, unless otherwise stated. One degree day is counted for each degree below (for heating) or above (in the case of cooling) the base, for each calendar day on which the temperature goes below or above the base.

Degree Hour - The product of 1 hour, and usually the number of degrees Fahrenheit the hourly mean temperature is above a base point (usually 65 degrees Fahrenheit); used in roughly estimating or measuring the cooling load in cases where processes heat, heat from building occupants, and humidity are relatively unimportant compared to the dry-bulb temperature.

Demand - The rate at which electricity is delivered to or by a system, part of a system, or piece of equipment expressed in kilowatts, kilovoltamperes, or other suitable unit, at a given instant or averaged over a specified period of time.

Demand(ed) Factor - The ratio of the maximum demand on an electricity generating and distribution system to the total connected load on the system; usually expressed as a percentage.

Dendrite - A slender threadlike spike of pure crystalline material, such as silicon.

Dendritic Web Technique - A method for making sheets of polycrystalline silicon in which silicon dendrites are slowly withdrawn from a melt of silicon whereupon a web of silicon forms between the dendrites and solidifies as it rises from the melt and cools.

Dependable Capacity - The load-carrying ability of an electric power plant during a specific time interval and period when related to the characteristics of the load to be/being supplied; determined by capability, operating power factor, and the portion of the load the station is to supply.

Design Life - Period of time a system or appliance (or component of) is expected to function at its nominal or design capacity without major repair.

Design Temperature - The temperature that a system is designed to maintain (inside) or operate against (outside) under the most extreme conditions.

Design Voltage - The nominal voltage for which a conductor or electrical appliance is designed; the reference voltage for identification and not necessarily the precise voltage at which it operates.

Difference of Potential - The difference in electrical pressure (voltage) between any two points in an electrical system or between any point in an electrical system and the earth.

Differential Thermostat - A type of automatic thermostat (used on solar heating systems) that responds to temperature differences (between collectors and the storage components) so as to regulate the functioning of appliances (to switch transfer fluid pumps on and off).

Diffuse Solar Radiation - Sunlight scattered by atmospheric particles and gases so that it arrives at the earth's surface from all directions and can not be focused.

Diffusion - The movement of individual molecules through a material; permeation of water vapor through a material.

Diffusion Length - The mean distance a free electron or hole moves before recombining with another hole or electron.

Direct Beam Radiation - Solar radiation that arrives in a straight line from the sun.

Direct Current - A type of electricity transmission and distribution by which electricity flows in one direction through the conductor; usually relatively low voltage and high current; typically abbreviated as dc.

Direct-Gain - The process by which sunlight directly enters a building through the windows and is absorbed and stored in massive floors or walls.

Dispatchability - The ability to dispatch power.

Displacement Power - A source of power (electricity) that can displace power from another source so that source's power can be transmitted to more distant loads.

Distributed Generation (Distributed Energy Resources) - Refers to electricity provided by small, modular power generators (typically ranging in capacity from a few kilowatts to 50 megawatts) located at or near customer demand.

Distribution - The process of distributing electricity; usually defines that portion of a power provider's power lines between a power provider's power pole and transformer and a customer's point of connection/meter.

Distribution Line - One or more circuits of a distribution system on the same line or poles or supporting structures' usually operating at a lower voltage relative to the transmission line.

Distribution System - That portion of an electricity supply system used to deliver electricity from points on the transmission system to consumers.

Donor - In a solar photovoltaic device, an n-type dopant, such as phosphorus, that puts an additional electron into an energy level very near the conduction band; this electron is easily exited into the conduction band where it increases the electrical conductivity over than of an undoped semiconductor.

Dopant - A chemical element (impurity) added in small amounts to an otherwise pure semiconductor material to modify the electrical properties of the material. An n-dopant introduces more electrons. A p-dopant creates electron vacancies (holes).

Doping - The addition of dopants to a semiconductor.

Drainback (Solar) Systems - A closed-loop solar heating system in which the heat transfer fluid in the collector loop drains into a tank or reservoir whenever the booster pump stops to protect the collector loop from freezing.

Draindown (Solar) Systems - An open-loop solar heating system in which the heat transfer fluid from the collector loop and the piping drain into a drain whenever freezing conditions occur.

Duty Cycle - The duration and periodicity of the operation of a device.

E

Edge-Defined Film-Fed Growth (EFG) - A method for making sheets of polycrystalline silicon (for solar photovoltaic devices) in which molten silicon is drawn upward by capillary action through a mold.

Effective Capacity - The maximum load that a device is capable of carrying.

Efficiency - Under the First Law of Thermodynamics, efficiency is the ratio of work or energy output to work or energy input, and cannot exceed 100 percent. Efficiency under the Second Law of Thermodynamics is determined by the ratio of the theoretical minimum energy that is required to accomplish a task relative to the energy actually consumed to accomplish the task. Generally, the measured efficiency of a device, as defined by the First Law, will be higher than that defined by the Second Law.

Efficiency (Appliance) Ratings - A measure of the efficiency of an appliance's energy efficiency.

Electric power sector - An energy-consuming sector that consists of electricity only and combined heat and power(CHP) plants whose primary business is to sell electricity, or electricity and heat, to the public--i.e., North American Industry Classification System 22 plants.

Electric Utility - A corporation, person, agency, authority, or other legal entity or instrumentality aligned with distribution facilities for delivery of electric energy for use primarily by the public. Included are investor-owned electric utilities, municipal and State utilities, Federal electric utilities, and rural electric cooperatives. A few entities that are tariff based and corporately aligned with companies that own distribution facilities are also included.
Note: Due to the issuance of FERC Order 888 that required traditional electric utilities to functionally unbundle their
generation, transmission, and distribution operations, "electric utility" currently has inconsistent interpretations from State to State.

Electric Utility Restructuring - The introduction of competition into at least the generation phase of electricity production, with a corresponding decrease in regulatory control.

Electrical Energy - The energy of moving electrons.

Electrical Charge - A condition that results from an imbalance between the number of protons and the number of electrons in a substance.

Electrical System - All the conductors and electricity using devices that are connected to a source of electromotive force (or generator).

Electrical System Energy Losses - A measure of the amount of energy lost during the generation, transmission, and distribution of electricity.

Electric Circuit - The path followed by electrons from a generation source, through an electrical system, and returning to the source.

Electric Energy - The amount of work accomplished by electrical power, usually measured in kilowatt-hours (kWh). One kWh is 1,000 Watts and is equal to 3,413 Btu.

Electricity Generation - The process of producing electricity by transforming other forms or sources of energy into electrical energy; measured in kilowatt-hours.

Electric System Loss(es) - The total amount of electric energy loss in an electric system between the generation source and points of delivery.

Electrode - A conductor that is brought in conducting contact with a ground.

Electrolysis - A chemical change in a substance that results from the passage of an electric current through an electrolyte. The production of commercial hydrogen by separating the elements of water, hydrogen, and oxygen, by charging the water with an electrical current.

Electrolyte - A nonmetallic (liquid or solid) conductor that carries current by the movement of ions (instead of electrons) with the liberation of matter at the electrodes of an electrochemical cell.

Electron - An elementary particle of an atom with a negative electrical charge and a mass of 1/1837 of a proton; electrons surround the positively charged nucleus of an atom and determine the chemical properties of an atom.

Electron Volt - The amount of kinetic energy gained by an electron when accelerated through an electric potential difference of 1 Volt; equivalent to 1.603 x 10^-12; a unit of energy or work; abbreviated as eV.

Emissions - Anthropogenic releases of gases to the atmosphere. In the context of global climate change, they consist of radiatively important greenhouse gases (e.g., the release of carbon dioxide during fuel combustion).

Emissivity - The ratio of the radiant energy (heat) leaving (being emitted by) a surface to that of a black body at the same temperature and with the same area; expressed as a number between 0 and 1.

Energize(d) - To send electricity through a electricity transmission and distribution network; a conductor or power line that is carrying current.

Energy - The capability of doing work; different forms of energy can be converted to other forms, but the total amount of energy remains the same.

Energy Audit - A survey that shows how much energy you use in your house or apartment. It will help you find ways to use less energy.

Energy Contribution Potential - Recombination occurring in the emitter region of a photovoltaic cell.

Energy Efficiency Ratio (EER) - The measure of the instantaneous energy efficiency of room air conditioners; the cooling capacity in Btu/hr divided by the watts of power consumed at a specific outdoor temperature (usually 95 degrees Fahrenheit).

Energy Density - The ratio of available energy per pound; usually used to compare storage batteries.

Energy Intensity - The relative extent that energy is required for a process.

Energy Storage - The process of storing, or converting energy from one form to another, for later use; storage devices and systems include batteries, conventional and pumped storage hydroelectric, flywheels, compressed gas, and thermal mass.

Epitaxial Growth - In reference to solar photovoltaic devices, the growth of one crystal on the surface of another crystal. The growth of the deposited crystal is oriented by the lattice structure of the original crystal.

Equinox - The two times of the year when the sun crosses the equator and night and day are of equal length; usually occurs on March 21st (spring equinox) and September 23 (fall equinox).

Evacuated Tube - In a solar thermal collector, an absorber tube, which is contained in an evacuated glass cylinder, through which collector fluids flows.

Evaporation - The conversion of a liquid to a vapor (gas), usually by means of heat.

Exothermic - A reaction or process that produces heat; a combustion reaction.

F

Farad - A unit of electrical capacitance; the capacitance of a capacitor between the plates of which there appears a difference of 1 Volt when it is charged by one coulomb of electricity.

Fill Factor - The ratio of a photovoltaic cell's actual power to its power if both current and voltage were at their maxima. A key characteristic in evaluating cell performance.

Fin - A thin sheet of material (metal) of a heat exchanger that conducts heat to a fluid.

First Law of Thermodynamics - States that energy cannot be created or destroyed, but only changed from one form to another. First Law efficiency measures the fraction of energy supplied to a device or process that it delivers in its output. Also called the law of conservation of energy.

Flat Plate Pumped - A medium-temperature solar thermal collector that typically consists of a metal frame, glazing, absorbers (usually metal), and insulation and that uses a pump liquid as the heat-transfer medium: predominant use is in water heating applications.

Flat Plate Solar Photovoltaic Module - An arrangement of photovoltaic cells or material mounted on a rigid flat surface with the cells exposed freely to incoming sunlight.

Flat Roof - A slightly sloped roof, usually with a tar and gravel cover. Most commercial buildings use this kind of roof.

Float-Zone Process - In reference to solar photovoltaic cell manufacture, a method of growing a large-size, high-quality crystal whereby coils heat a polycrystalline ingot placed atop a single-crystal seed. As the coils are slowly raised the molten interface beneath the coils becomes a single crystal.

Flow Condition - In reference to solar thermal collectors, the condition where the heat transfer fluid is flowing through the collector loop under normal operating conditions.

Frequency - The number of cycles through which an alternating current passes per second; in Canada the standard for electricity generation is 60 cycles per second (60 Hertz).

Fresnel Lens - An optical device for concentrating light that is made of concentric rings that are faced at different angles so that light falling on any ring is focused to the same point.

Fuel Cells - One or more cells capable of generating an electrical current by converting the chemical energy of a fuel directly into electrical energy. Fuel cells differ from conventional electrical cells in that the active materials such as fuel and oxygen are not contained within the cell but are supplied from outside.

Full Sun - The amount of power density in sunlight received at the earth's surface at noon on a clear day (about 1,000 Watts/square meter).

Fuse - A safety device consisting of a short length of relatively fine wire, mounted in a holder or contained in a cartridge and connected as part of an electrical circuit. If the circuit source current exceeds a predetermined value, the fuse wire melts (i.e. the fuse 'blows') breaking the circuit and preventing damage to the circuit protected by the fuse.

G

Gallium Arsenide - A compound used to make certain types of solar photovoltaic cells.

Generation (Electricity) - The process of producing electric energy from other forms of energy; also, the amount of electric energy produced, expressed in watthours (Wh).

Geothermal Energy - As used at electric power plants, hot water or steam extracted from geothermal reservoirs in the Earth's crust that is supplied to steam turbines at electric power plants that drive generators to produce electricity.

Geothermal Plant - A plant in which a turbine is driven either from hot water or by natural steam that derives its energy from heat found in rocks or fluids at various depths beneath the surface of the earth. The fluids are extracted by drilling and/or pumping.

Giga - One billion.

Gigawatt (GW) - A unit of power equal to 1 billion Watts; 1 million kilowatts, or 1,000 megawatts.

Glazing - Transparent or translucent material (glass or plastic) used to admit light and/or to reduce heat loss; used for building windows, skylights, or greenhouses, or for covering the aperture of a solar collector.

Global Insolation (or Solar Radiation) - The total diffuse and direct insolation on a horizontal surface, averaged over a specified period of time.

Green Power - A popular term for energy produced from clean, renewable energy resources.

Green Pricing/Marketing - In the case of renewable electricity, green pricing represents a market solution to the various problems associated with regulatory valuation of the nonmarket benefits of renewables. Green pricing programs allow electricity customers to express their willingness to pay for renewable energy development through direct payments on their monthly utility bills.

Grid - The layout of an electrical distribution system.

Grid-Connected System - Independent power systems that are connected to an electricity transmission and distribution system (referred to as the electricity grid) such that the systems can draw on the grid's reserve capacity in times of need, and feed electricity back into the grid during times of excess production.

Ground - A device used to protect the user of any electrical system or appliance from shock.

Ground Reflection - Solar radiation reflected from the ground onto a solar collector.

Gross Generation - The total amount of electric energy produced by the generating units at a generating station or stations, measured at the generator terminals.

H

Hardwoods -Usually broad-leaved and deciduous trees.

Heat Absorbing Window Glass - A type of window glass that contains special tints that cause the window to absorb as much as 45% of incoming solar energy, to reduce heat gain in an interior space. Part of the absorbed heat will continue to be passed through the window by conduction and reradiation.

Heat Balance - Energy output from a system that equals energy input.

Heat Pump - A year-round heating and air-conditioning system employing a refrigeration cycle. In a refrigeration cycle, a refrigerant is compressed (as a liquid) and expanded (as a vapor) to absorb and reject heat. The heat pump transfers heat to a space to be heated during the winter period and by reversing the operation extracts (absorbs) heat from the same space to be cooled during the summer period. The refrigerant within the heat pump in the heating mode absorbs the heat to be supplied to the space to be heated from an outside medium (air, ground or ground water) and in the cooling mode absorbs heat from the space to be cooled to be rejected to the outside medium.

Heating Capacity (Also specific heat) - The quantity of heat necessary to raise the temperature of a specific mass of a substance by one degree.

Heating Degree Day(s) (HDD) - The number of degrees per day that the daily average temperature (the mean of the maximum and minimum recorded temperatures) is below a base temperature, usually 65 degrees Fahrenheit, unless otherwise specified; used to determine indoor space heating requirements and heating system sizing. Total HDD is the cumulative total for the year/heating season. The higher the HDD for a location, the colder the daily average temperature(s).

Heating Load - The rate of heat flow required to maintain a specific indoor temperature; usually measured in Btu per hour.

Heating Season - The coldest months of the year; months where average daily temperatures fall below 65 degrees Fahrenheit creating demand for indoor space heating.

Heat Loss - The heat that flows from the building interior, through the building envelope to the outside environment.

Heat Sink - A structure or media that absorbs heat.

Heat Source - A structure or media from which heat can be absorbed or extracted.

Heat Storage - A device or media that absorbs heat for storage for later use.

Heat Storage Capacity - The amount of heat that a material can absorb and store.

Heliodon - A device used to simulate the angle of the sun for assessing shading potentials of building structures or landscape features.

Heliostat - A device that tracks the movement of the sun; used to orient solar concentrating systems.

Heliothermometer - An instrument for measuring solar radiation.

Heliotropic - Any device (or plant) that follows the sun's apparent movement across the sky.

Hemispherical Bowl Technology - A solar energy concentrating technology that uses a linear receiver that tracks the focal area of a reflector or array of reflectors.

Hertz - A measure of the number of cycles or wavelengths of electrical energy per second; Canadian. electricity supply has a standard frequency of 60 hertz.

High-Temperature Collector - A solar thermal collector designed to operate at a temperature of 180 degrees Fahrenheit or higher.

Homojunction - The region between an n-layer and a p-layer in a single material, photovoltaic cell.

Hybrid System - A renewable energy system that includes two different types of technologies that produce the same type of energy; for e.g., a wind turbine and a solar photovoltaic array combined to meet a power demand.

I

Incentives - Subsidies and other Government actions where the Governments's financial assistance is indirect.

Incident Solar Radiation - The amount of solar radiation striking a surface per unit of time and area.

Independent Power Producer (IPP) - A corporation, person, agency, authority, or other legal entity or instrumentality that owns or operates facilities for the generation of electricity for use primarily by the public, and that is not an electric utility.

Indirect Solar Gain System - A passive solar heating system in which the sun warms a heat storage element, and the heat is distributed to the interior space by convection, conduction, and radiation.

Industrial Process Heat - The thermal energy used in an industrial process.

Industrial Sector - An energy-consuming sector that consists of all facilities and equipment used for producing, processing, or assembling goods. The industrial sector encompasses the following types of activity: manufacturing (NAICS codes 31-33); agriculture, forestry, and fisheries (NAICS code 11); mining, including oil and gas extraction (NAICS code 21); natural gas transmission (NAICS code 2212); and construction (NAICS code 23). Overall energy use in this sector is largely for process heat and cooling and powering machinery, with lesser amounts used for facility heating, air conditioning, and lighting. Fossil fuels are also used as raw material inputs to manufactured products. Note: This sector includes generators that produce electricity and/or useful thermal output primarily to support the above-mentioned industrial activities.

Insolation - The solar power density incident on a surface of stated area and orientation, usually expressed as Watts per square meter or Btu per square foot per hour.

Installed Capacity - The total capacity of electrical generation devices in a power station or system.

Instantaneous Efficiency (of a Solar Collector) - The amount of energy absorbed (or converted) by a solar collector (or photovoltaic cell or module) over a 15 minute period.

Internal Collector Storage (ICS) - A solar thermal collector in which incident solar radiation is absorbed by the storage medium.

Intrinsic Layer - A layer of semiconductor material (as used in a solar photovoltaic device) whose properties are essentially those of the pure, undoped, material.

Inverter - A device that converts direct current electricity (from for example a solar photovoltaic module or array) to alternating current for use directly to operate appliances or to supply power to a electricity grid.

Ion - An electrically charged atom or group of atoms that has lost or gained electrons; a loss makes the resulting particle positively charged; a gain makes the particle negatively charged.

Irradiance - The direct, diffuse, and reflected solar radiation that strikes a surface.

I-Type Semiconductor - A semiconductor material that is left intrinsic, or undoped so that the concentration of charge carriers is characteristic of the material itself rather than of added impurities.

I-V Curve - A graphical plot or representation the current and voltage output of a solar photovoltaic cell or module as a load on the device is increased from short circuit (no load) condition to the open circuit condition; used to characterize cell/module performance.

J

Joule - A metric unit of energy or work; the energy produced by a force of one Newton operating through a distance of one meter; 1 Joule per second equals 1 Watt or 0.737 foot-pounds; 1 Btu equals 1,055 Joules.

Joule's Law - The rate of heat production by a steady current in any part of an electrical circuit that is proportional to the resistance and to the square of the current, or, the internal energy of an ideal gas depends only on its temperature.

Junction - A region of transition between semiconductor layers, such as a p/n junction, which goes from a region that has a high concentration of acceptors (p-type) to one that has a high concentration of donors (n-type).

K

Kilovolt-Ampere (kVa) - A unit of apparent power, equal to 1,000 volt-amperes; the mathematical product of the volts and amperes in an electrical circuit.

Kilowatt (kW) - A standard unit of electrical power equal to one thousand watts, or to the energy consumption at a rate of 1000 Joules per second.

Kilowatt-hour - A unit or measure of electricity supply or consumption of 1,000 Watts over the period of one hour; equivalent to 3,412 Btu.

L

Langley - A unit or measure of solar radiation; 1 calorie per square centimeter or 3.69 Btu per square foot.

Lattice - The regular periodic arrangement of atoms or molecules in a crystal of semiconductor material.

Latent Cooling Load - The load created by moisture in the air, including from outside air infiltration and that from indoor sources such as occupants, plants, cooking, showering, etc.

Lead Acid Battery - An electrochemical battery that uses lead and lead oxide for electrodes and sulfuric acid for the electrolyte.

Leaking Electricity - Related to stand-by power, leaking electricity is the power needed for electrical equipment to remain ready for use while in a dormant mode or operation. Electricity is still used by many electrical devices, such as TVs, stereos, and computers, even when you think they are turned "off."

Levelized Life Cycle Cost - A total life cycle cost divided into equal amounts.

Levelized Cost - The present value of the total cost of building and operating a generating plant over its economic life, converted to equal annual payments. Costs are levelized in real dollars (i.e., adjusted to remove the impact of inflation).

Life Cycle Cost - The sum of all the costs both recurring and nonrecurring, related to a product, structure, system, or service during its life span or specified time period.

Light Trapping - The trapping of light inside a semiconductor material by refracting and reflecting the light at critical angles; trapped light will travel further in the material, greatly increasing the probability of absorption and hence of producing charge carriers.

Limited Liability Corporation (LLC) - A company that limits the liability of its participants to the assets they commit to the enterprise.

Line Loss (or Drop) - Electrical energy lost due to inherent inefficiencies in an electrical transmission and distribution system under specific conditions.

Liquid Collector - A medium-temperature solar thermal collector, employed predominantly in water heating, which uses pumped liquid as the heat-transfer medium.

Load - The power required to run a defined circuit or system, such as a refrigerator, building, or an entire electricity distribution system.

Load Analysis - Assessing and quantifying the discrete components that comprise a load. This analysis often includes time of day or season as a variable.

Load Duration Curve - A curve that displays load values on the horizontal axis in descending order of magnitude against the percent of time (on the vertical axis) that the load values are exceeded.

Load Factor - The ratio of average energy demand (load) to maximum demand (peak load) during a specific period.

Load Forecast - An estimate of power demand at some future period.

Load Leveling - The deferment of certain loads to limit electrical power demand, or the production of energy during off-peak periods for storage and use during peak demand periods.

Load Management - To influence the demand on a power source.

Load Profile or Shape - A curve on a chart showing power (kW) supplied (on the horizontal axis) plotted against time of occurrence (on the vertical axis) to illustrate the variance in a load in a specified time period.

Load Shedding - Turning off or disconnecting loads to limit peak demand.

Load Shifting - A load management objective that moves loads from on-peak periods to off-peak periods.

Local Solar Time - A system of astronomical time in which the sun crosses the true north-south meridian at 12 noon, and which differs from local time according to longitude, time zone, and equation of time.

Loss of Load Probability (LOLP) - A measure of the probability that a system demand will exceed capacity during a given period; often expressed as the estimated number of days over a long period, frequently 10 years or the life of the system.

Low-Temperature Collectors - Metallic or nonmetallic solar thermal collectors that generally operate at temperatures below 110 degrees Fahrenheit and use pumped liquid or air as the heat transfer medium. They usually contain no glazing and no insulation, and they are often made of plastic or rubber, although some are made of metal.

Lumen - An empirical measure of the quantity of light. It is based upon the spectral sensitivity of the photosensors in the human eye under high (daytime) light levels. Photometrically it is the luminous flux emitted with a solid angle (1 steradian) by a point source having a uniform luminous intensity of 1 candela.

Lumens/Watt (lpw) - A measure of the efficacy (efficiency) of lamps. It indicates the amount of light (lumens) emitted by the lamp for each unit of electrical power (Watts) used.

Lux - The unit of illuminance equivalent to 1lumen per square meter.

M

Marginal Cost - The change in cost associated with a unit change in quantity supplied or produced.

Medium-Temperature Collectors - Solar thermal col-lectors designed to operate in the temperature range of 140 degrees to 180 degrees Fahrenheit, but that can also operate at a temperature as low as 110 degrees Fahrenheit. The collector typically consists of a metal frame, metal absorption panels with integral flow channels (attached tubing for liquid collectors or integral ducting for air collectors), and glazing and insulation on the sides and back.

Megawatt - One thousand kilowatts, or 1 million watts; standard measure of electric power plant generating capacity.

Megawatt-hour - One thousand kilowatt-hours or 1 million watt-hours.

Microclimate - The local climate of specific place or habitat, as influenced by landscape features.

Microgroove - A small groove scribed into the surface of a solar photovoltaic cell which is filled with metal for contacts.

Minority Carrier - A current carrier, either an electron or a hole, that is in the minority in a specific layer of a semiconductor material; the diffusion of minority carriers under the action of the cell junction voltage is the current in a photovoltaic device.

Minority Carrier Lifetime - The average time a minority carrier exists before recombination.

Modified Degree-Day Method - A method used to estimate building heating loads by assuming that heat loss and gain is proportional to the equivalent heat-loss coefficient for the building envelope.

Monolithic - Fabricated as a single structure.

MSW (Municipal Solid Waste) - Residential solid waste and some nonhazardous commercial, institutional, and industrial wastes.

Multijunction Device - A high-efficiency photovoltaic device containing two or more cell junctions, each of which is optimized for a particular part of the solar spectrum.

N

Natural Cooling - Space cooling achieved by shading, natural (unassisted, as opposed to forced) ventilation, conduction control, radiation, and evaporation; also called passive cooling.

Natural Draft - Draft that is caused by temperature differences in the air.

Natural Ventilation - Ventilation that is created by the differences in the distribution of air pressures around a building. Air moves from areas of high pressure to areas of low pressure with gravity and wind pressure affecting the airflow. The placement and control of doors and windows alters natural ventilation patterns.

Net Energy Production (or Balance) - The amount of useful energy produced by a system less the amount of energy required to produce the fuel.

Net Generation - Gross generation less the electric energy consumed at the generating station for station's use.

Net Metering - The practice of using a single meter to measure consumption and generation of electricity by a small generation facility (such as a house with a wind or solar photovoltaic system). The net energy produced or consumed is purchased from or sold to the power provider, respectively.

Net Photovoltaic Cell Shipment - The difference between photovoltaic cell shipments and photovoltaic cell purchases.

Net Photovoltaic Module Shipment - The difference between photovoltaic module shipments and photovoltaic module purchases.

Net summer capacity - The maximum output, commonly expressed in megawatts (MW), that generating equipment can supply to system load, as demonstrated by a multi-hour test, at the time of summer peak demand (period of May 1 through October 31). This output reflects a reduction in capacity due to electricity use for station service or auxiliaries.

Nominal Capacity - The approximate energy producing capacity of a power plant, under specified conditions, usually during periods of highest load.

Nonutility Generation - Electric generation by nonutility power producers to supply electric power for industrial, commercial, and military operations, or sales to electric utilities. See Nonutility Power Producer.

Nonutility Power Producer - A corporation, person, agency, authority, or other legal entity or instrumentality that owns electric generating capacity and is not an electric utility. Nonutility power producers include qualifying cogenerators, qualifying small power producers, and other nonutility generators (including independent power producers) without a designated, franchised service area that do not file forms listed in the Code of Federal Regulations, Title 18, Part 141.

N-Type Semiconductor - A semiconductor produced by doping an intrinsic semiconductor with an electron-donor impurity (e.g., phosphorous in silicon).

O

Off-Peak - The period of low energy demand, as opposed to maximum, or peak, demand.

Ohms - A measure of the electrical resistance of a material equal to the resistance of a circuit in which the potential difference of 1 volt produces a current of 1 ampere.

Ohm's Law - In a given electrical circuit, the amount of current in amperes (i) is equal to the pressure in volts (V) divided by the resistance, in ohms (R).

One-Axis Tracking - A system capable of rotating about one axis.

One Sun - The maximum value of natural solar insolation.

On-Peak Energy - Energy supplied during periods of relatively high system demands as specified by the supplier.

On-Site Generation - Generation of energy at the location where all or most of it will be used.

Open-Circuit Voltage - The maximum possible voltage across a photovoltaic cell; the voltage across the cell in sunlight when no current is flowing.

Operation and Maintenance (O&M) Cost - Operating expenses are associated with operating a facility (i.e., supervising and engineering expenses). Maintenance expenses are that portion of expenses consisting of labor, materials, and other direct and indirect expenses incurred
for preserving the operating efficiency or physical condition of utility plants that are used for power production, transmission, and distribution of energy.

Orientation - The alignment of a building along a given axis to face a specific geographical direction. The alignment of a solar collector, in number of degrees east or west of true south.

Outage - A discontinuance of electric power supply.

Overload - To exceed the design capacity of a device.

Ovonic - A device that converts heat or sunlight directly to electricity, invented by Standford Ovshinsky, that has a unique glass composition that changes from an electrically non-conducting state to a semiconducting state.

P

Packing Factor - The ratio of solar collector array area to actual land area.

Panel (Solar) - A term generally applied to individual solar collectors, and typically to solar photovoltaic collectors or modules.

Parabolic Dish - A high-temperature (above 180 degrees Fahrenheit) solar thermal concentrator, generally bowl-shaped, with two-axis tracking.

Parabolic Trough - A high-temperature (above 180 degrees Fahrenheit) solar thermal concentrator with the capacity for tracking the sun using one axis of rotation.

Passive Solar (Building) Design - A building design that uses structural elements of a building to heat and cool a building, without the use of mechanical equipment, which requires careful consideration of the local climate and solar energy resource, building orientation, and landscape features, to name a few. The principal elements include proper building orientation, proper window sizing and placement and design of window overhangs to reduce summer heat gain and ensure winter heat gain, and proper sizing of thermal energy storage mass (for example a Trombe wall or masonry tiles). The heat is distributed primarily by natural convection and radiation, though fans can also be used to circulate room air or ensure proper ventilation.

Payback Period - The amount of time required before the savings resulting from your system equal the system cost.

Peak Clipping/Shaving - The process of implementing measures to reduce peak power demands on a system.

Peak Demand/Load - The maximum energy demand or load in a specified time period.

Peaking Capacity - Power generation equipment or system capacity to meet peak power demands.

Peak Power - Power generated that operates at a very low capacity factor; generally used to meet short-lived and variable high demand periods.

Peak Shifting - The process of moving existing loads to off-peak periods.

Peak Sun Hours - The equivalent number of hours per day when solar irradiance averages 1 kW/m2. For example, six peak sun hours means that the energy received during total daylight hours equals the energy that would have been received had the irradiance for six hours been 1 kW/m2.

Peak Watt - A unit used to rate the performance of a solar photovoltaic (PV) cells, modules, or arrays; the maximum nominal output of a PV device, in Watts (Wp) under standardized test conditions, usually 1000 Watts per square meter of sunlight with other conditions, such as temperature specified.

Performance Ratings - Solar collector thermal performance ratings based on collector efficiencies, usually expressed in Btu per hour for solar collectors under standard test or operating conditions for solar radiation intensity, inlet working fluid temperatures, and ambient temperatures.

Phantom Load - Any appliance that consumes power even when it is turned off. Examples of phantom loads include appliances with electronic clocks or timers, appliances with remote controls, and appliances with wall cubes (a small box that plugs into an AC outlet to power appliances).

Phase - Alternating current is carried by conductors and a ground to residential, commercial, or industrial consumers. The waveform of the phase power appears as a single continuous sine wave at the system frequency whose amplitude is the rated voltage of the power.

Photocurrent - An electric current induced by radiant energy.

Photoelectric Cell - A device for measuring light intensity that works by converting light falling on, or reach it, to electricity, and then measuring the current; used in photometers.

Photoelectrochemical Cell - A type of photovoltaic device in which the electricity induced in the cell is used immediately within the cell to produce a chemical, such as hydrogen, which can then be withdrawn for use.

Photogalvanic Processes - The production of electrical current from light.

Photon - A particle of light that acts as an individual unit of energy.

Photovoltaic (Conversion) Efficiency - The ratio of the electric power produced by a photovoltaic device to the power of the sunlight incident on the device.

Photovoltaic (PV; Solar) Array - A group of solar photovoltaic modules connected together.

Photovoltaic (PV) Cell - An electronic device consisting of layers of semiconductor materials fabricated to form a junction (adjacent layers of materials with different electronic characteristics) and electrical contacts and being capable of converting incident light directly into electricity (direct current).

Photovoltaic (Solar) Cell - Treated semiconductor material that converts solar irradiance to electricity.

Photovoltaic Device - A solid-state electrical device that converts light directly into direct current electricity of voltage-current characteristics that are a function of the characteristics of the light source and the materials in and design of the device. Solar photovoltaic devices are made of various semi-conductor materials including silicon, cadmium sulfide, cadmium telluride, and gallium arsenide, and in single crystalline, multi-crystalline, or amorphous forms.

Photovoltaic (Solar) Module or Panel - A solar photovoltaic product that generally consists of groups of PV cells electrically connected together to produce a specified power output under standard test conditions, mounted on a substrate, sealed with an encapsulant, and covered with a protective glazing. Maybe further mounted on an aluminum frame. A junction box, on the back or underside of the module is used to allow for connecting the module circuit conductors to external conductors.

Photovoltaic Peak Watt - see Peak Watt.

Photovoltaic (Solar) System - A complete PV power system composed of the module (or array), and balance-of-system (BOS) components including the array supports, electrical conductors/wiring, fuses, safety disconnects, and grounds, charge controllers, inverters, battery storage, etc.

P-I-N - A semiconductor (photovoltaic) device structure that layers an intrinsic semiconductor between a p-type semiconductor and an n-type semiconductor; this structure is most often used with amorphous silicon PV devices.

P/N - A semiconductor (photovoltaic) device structure in which the junction is formed between a p-type layer and an n-type layer.

Point-Contact Cell - A high efficiency silicon photovoltaic concentrator cell that employs light trapping techniques and point-diffused contacts on the rear surface for current collection.

Polycrystalline - A semiconductor (photovoltaic) material composed of variously oriented, small, individual crystals.

Power - Energy that is capable or available for doing work; the time rate at which work is performed, measured in horsepower, Watts, or Btu per hour. Electric power is the product of electric current and electromotive force.

Power Factor (PF) - The ratio of actual power being used in a circuit, expressed in watts or kilowatts, to the power that is apparently being drawn from a power source, expressed in volt-amperes or kilovolt-amperes.

Power Provider - A company or other organizational unit that sells and distributes electrical power (e.g., private or public electrical utility), either to other distribution and wholesale businesses or to end-users. Sometimes power providers also generate the power they sell.

Power (Solar) Tower - A term used to describe solar thermal, central receiver, power systems, where an array of reflectors focus sunlight onto a central receiver and absorber mounted on a tower.

Power Transmission Line - An electrical conductor/cable that carries electricity from a generator to other locations for distribution.

P-Type Semiconductor - A semiconductor in which holes carry the current; produced by doping an intrinsic semiconductor with an electron acceptor impurity (e.g., boron in silicon).

Process Heating - The direct process end use in which energy is used to raise the temperature of substances involved in the manufacturing process.

Production Tax Credit (PTC) - an inflation - adjusted 1.5 cents per kilowatthour payment for electricity produced using qualifying renewable energy sources.

Public Utility Regulatory Policies Act of 1978 (PURPA) - One part of the National Energy Act, PURPA contains measures designed to encourage the conservation of energy, more efficient use of resources, and equitable rates. Principal among these were suggested retail rate reforms and new incentives for production of electricity by cogenerators and users of renewable resources.

Pumped-storage hydroelectric plant - A plant that usually generates electric energy during peak load periods by using water previously pumped into an elevated storage reservoir during off-peak periods when excess generating capacity is available to do so. When additional generating capacity is needed, the water can be released from the reservoir through a conduit to turbine generators located in a power plant at a lower level.

Pulse - Width-Modulated (PWM) Wave Inverter - A type of power inverter that produce a high quality (nearly sinusoidal) voltage, at minimum current harmonics.

Pyranometer - A device used to measure total incident solar radiation (direct beam, diffuse, and reflected radiation) per unit time per unit area.

Pyrheliometer - A device that measures the intensity of direct beam solar radiation.

Q

Quad - One quadrillion Btu. (1,000,000,000,000,000 Btu)

Quadrillion Btu - Equivalent to 10 to the 15th power Btu.

Qualifying Facility (QF) - A cogeneration or small power production facility that meets certain ownership, operating, and efficiency criteria established by the Federal Energy Regulatory Commission (FERC) pursuant to the Public Utility Regulatory Policies Act of 1978 (PURPA). (See the Code of Federal Regulations, Title 18, Part 292.)

R

Rated Life - The length of time that a product or appliance is expected to meet a certain level of performance under nominal operating conditions; in a luminaire, the period after which the lumen depreciation and lamp failure is at 70% of its initial value.

Rated Power - The power output of a device under specific or nominal operating conditions.

Receiver - The component of a central receiver solar thermal system where reflected solar energy is absorbed and converted to thermal energy.

Reflectance - The amount (percent) of light that is reflected by a surface relative to the amount that strikes it.

Reflective Coatings - Materials with various qualities that are applied to glass windows before installation. These coatings reduce radiant heat transfer through the window and also reflects outside heat and a portion of the incoming solar energy, thus reducing heat gain. The most common type has a sputtered coating on the inside of a window unit. The other type is a durable "hard-coat" glass with a coating, baked into the glass surface.

Refraction - The change in direction of a ray of light when it passes through one media to another with differing optical densities.

Reliability - This is the concept of how long a device or process can operate properly without needing maintenance or replacement.

Renewable Energy Resources - Energy resources that are naturally replenishing but flow-limited. They are virtually inexhaustible in duration but limited in the amount of energy that is available per unit of time. Renewable energy resources include: biomass, hydro, geothermal, solar, wind, ocean thermal, wave action, and tidal action.

Renewable Portfolio Standard (RPS) - a mandate requiring that renewable energy provide a certain percentage of total energy generation or consumption.

Residential Sector - An energy-consuming sector that consists of living quarters for private households. Common uses of energy associated with this sector include space heating, water heating, air conditioning, lighting, refrigeration, cooking, and running a variety of other appliances. The residential sector excludes institutional living quarters.

Resistance - The inherent characteristic of a material to inhibit the transfer of energy. In electrical conductors, electrical resistance results in the generation of heat. Electrical resistance is measured in Ohms. The heat transfer resistance properties of insulation products are quantified as the R-value.

Resistive Voltage Drop - The voltage developed across a cell by the current flow through the resistance of the cell.

Resistor - An electrical device that resists electric current flow.

Retrofit - The process of modifying a building's structure.

Ribbon (Photovoltaic) Cells - A type of solar photovoltaic device made in a continuous process of pulling material from a molten bath of photovoltaic material, such as silicon, to form a thin sheet of material.

Ribbon Silicon - Single-crystal silicon derived by means of fabricating processes that produce sheets or ribbons of single-crystal silicon. These processes include edge-defined film-fed growth, dendritic web growth, and ribbon-to-ribbon growth.

Roundwood - Wood cut specifically for use as a fuel.

Roof - A building element that provides protection against the sun, wind, and precipitation.

R-Value - A measure of the capacity of a material to resist heat transfer. The R-Value is the reciprocal of the conductivity of a material (U-Value). The larger the R-Value of a material, the greater its insulating properties.

S

Safety Disconnect - An electronic (automatic or manual) switch that disconnects one circuit from another circuit. These are used to isolate power generation or storage equipment from conditions such as voltage spikes or surges, thus avoiding potential damage to equipment.

Salt Gradient Solar Ponds - Consist of three main layers. The top layer is near ambient and has low salt content. The bottom layer is hot, typically 160 F to 212 F (71 C to 100 C), and is very salty. The important gradient zone separates these zones. The gradient zone acts as a transparent insulator, permitting the sunlight to be trapped in the hot bottom layer (from which useful heat is withdrawn). This is because the salt gradient, which increases the brine density with depth, counteracts the buoyancy effect of the warmer water below (which would otherwise rise to the surface and lose its heat to the air). An organic Rankine cycle engine is used to convert the thermal energy to electricity.

Scribing - The cutting of a grid pattern of grooves in a semiconductor material, generally for the purpose of making interconnections.

Seasonal Performance Factor (SPF) - Ratio of useful energy output of a device to the energy input, averaged over an entire heating season.

Selectable Load - Any device, such as lights, televisions, and power tools, which is plugged into your central power source and used only intermittently.

Selective Absorber - A solar absorber surface that has high absorbence at wavelengths corresponding to that of the solar spectrum and low emittance in the infrared range.

Selective Surface Coating - A material with high absorbence and low emittance properties applied to or on solar absorber surfaces.

Semiconductor - Any material that has a limited capacity for conducting an electric current. Certain semiconductors, including silicon, gallium arsenide, copper indium diselenide, and cadmium telluride, are uniquely suited to the photovoltaic conversion process.

Shading Coefficient - A measure of window glazing performance that is the ratio of the total solar heat gain through a specific window to the total solar heat gain through a single sheet of double-strength glass under the same set of conditions; expressed as a number between 0 and 1.

Sheathing - A construction element used to cover the exterior of wall framing and roof trusses.

Short Circuit - An electric current taking a shorter or different path than intended.

Short Circuit Current - The current flowing freely through an external circuit that has no load or resistance; the maximum current possible.

Shunt Load - An electrical load used to safely use excess generated power when not needed for its primary uses. A shunt load in a residential photovoltaic system might be domestic water heating, such that when power is not needed for typical building loads, such as operating lights or running HVAC system fans and pumps, it still provides value and is used in a constructive, safe manner.

Silicon - A chemical element, of atomic number 14, that is semi-metallic, and an excellent semiconductor material used in solar photovoltaic devices; commonly found in sand.

Sine Wave - The type of alternative current generated by alternating current generators, rotary inverters, and solid-state inverters.

Single-Crystal Material - In reference to solar photovoltaic devices, a material that is composed of a single crystal or a few large crystals.

Single Crystal Silicon (Czochralski) - An extremely pure form of crystalline silicon produced by the Czochralski method of dipping a single crystal seed into a pool of molten silicon under high vacuum conditions and slowly withdrawing a solidifying single crystal boule rod of silicon. The boule is sawed into thin wafers and fabricated into single-crystal photovoltaic cells.

Single Glaze or Pane - One layer of glass in a window frame. It has very little insulating value (R-1) and provides only a thin barrier to the outside and can account for considerable heat loss and gain.

Sizing - The process of designing a solar system to meet a specified load given the solar resource and the nominal or rated energy output of the solar energy collection or conversion device.

Sludge - A dense, slushy, liquid-to-semifluid product that accumulates as an end result of an industrial or technological process designed to purify a substance. Industrial sludges are produced from the processing of energy-related raw materials, chemical products, water, mined ores, sewerage, and other natural and man-made products. Sludges can also form from natural processes, such as the run off produced by rain fall, and accumulate on the bottom of bogs, streams, lakes, and tidelands.

Solar Access or Rights - The legal issues related to protecting or ensuring access to sunlight to operate a solar energy system, or use solar energy for heating and cooling.

Solar Altitude Angle - The angle between a line from a point on the earth's surface to the center of the solar disc, and a line extending horizontally from the point.

Solar Array - A group of solar collectors or solar modules connected together.

Solar Azimuth - The angle between the sun's apparent position in the sky and true south, as measured on a horizontal plane.

Solar Cell - A solar photovoltaic device with a specified area.

Solar Constant - The average amount of solar radiation that reaches the earth's upper atmosphere on a surface perpendicular to the sun's rays; equal to 1353 Watts per square meter or 492 Btu per square foot.

Solar Declination - The apparent angle of the sun north or south of the earth's equatorial plane. The earth's rotation on its axis causes a daily change in the declination.

Solar Energy - Electromagnetic energy transmitted from the sun (solar radiation). The amount that reaches the earth is equal to one billionth of total solar energy generated, or the equivalent of about 420 trillion kilowatt-hours.

Solar Film - A window glazing coating, usually tinted bronze or gray, used to reduce building cooling loads, glare, and fabric fading.

Solar Fraction - The percentage of a building's seasonal energy requirements that can be met by a solar energy device(s) or system(s).

Solar Furnace - A device that achieves very high temperatures by the use of reflectors to focus and concentrate sunlight onto a small receiver.

Solar Gain - The amount of energy that a building absorbs due to solar energy striking its exterior and conducting to the interior or passing through windows and being absorbed by materials in the building.

Solar Irradiation - The amount of solar radiation, both direct and diffuse, received at any location.

Solar Mass - A term used for materials used to absorb and store solar energy.

Solar Module (Panel) - A solar photovoltaic device that produces a specified power output under defined test conditions, usually composed of groups of solar cells connected in series, in parallel, or in series-parallel combinations.

Solar Noon - The time of the day, at a specific location, when the sun reaches its highest, apparent point in the sky; equal to true or due, geographic south.

Solar Panel - See Photovoltaic Module.

Solar Radiation - A general term for the visible and near visible (ultraviolet and near-infrared) electromagnetic radiation that is emitted by the sun. It has a spectral, or wavelength, distribution that corresponds to different energy levels; short wavelength radiation has a higher energy than long-wavelength radiation.

Solar Simulator - An apparatus that replicates the solar spectrum, and used for testing solar energy conversion devices.

Solar Spectrum - The total distribution of electromagnetic radiation emanating from the sun. The different regions of the solar spectrum are described by their wavelength range. The visible region extends from about 390 to 780 nanometers (a nanometer is one billionth of one meter). About 99 percent of solar radiation is contained in a wavelength region from 300 nm (ultraviolet) to 3,000 nm (near-infrared). The combined radiation in the wavelength region from 280 nm to 4,000 nm is called the broadband, or total, solar radiation.

Solar Thermal Collector - A device designed to receive solar radiation and convert it into thermal energy. Normally, a solar thermal collector includes a frame, glazing, and an absorber, together with the appropriate insulation. The heat collected by the solar thermal collector may be used immediately or stored for later use.

Solar Thermal Collector, Special - An evacuated tube collector or a concentrating (focusing) collector. Special collectors operate in the temperature (low concentration for pool heating) to several hundred degrees Fahrenheit (high concentration for air conditioning and specialized industrial processes).

Solar Time - The period marked by successive crossing of the earth's meridian by the sun; the hour angle of the sun at a point of observance (apparent time) is corrected to true (solar) time by taking into account the variation in the earth's orbit and rate of rotation. Solar time and local standard time are usually different for any specific location.

Solar Transmittance - The amount of solar energy that passes through a glazing material, expressed as a percentage.

Spectral Energy Distribution - A curve illustrating the variation or spectral irradiance with wavelength.

Spectral Irradiance - The monochromatic irradiance of a surface per unit bandwidth at a particular wavelength, usually expressed in Watts per square meter-nanometer bandwidth.

Spectral Reflectance - The ratio of energy reflected from a surface in a given waveband to the energy incident in that waveband.

Spectrum - see Solar Spectrum above.

Spent liquor - The liquid residue left after an industrial process; can be a component of waste materials used as fuel.

Split Spectrum Photovoltaic Cell - A photovoltaic device where incident sunlight is split into different spectral regions, with an optical apparatus, that are directed to individual photovoltaic cells that are optimized for converting that spectrum to electricity.

Sputtering - A process used to apply photovoltaic semi-conductor material to a substrate by a physical vapor deposition process where high-energy ions are used to bombard elemental sources of semiconductor material, which eject vapors of atoms that are then deposited in thin layers on a substrate.

Square Wave Inverter - A type of inverter that produces square wave output.; consists of a DC source, four switches, and the load. The switches are power semiconductors that can carry a large current and withstand a high voltage rating. The switches are turned on and off at a correct sequence, at a certain frequency. The square wave inverter is the simplest and the least expensive to purchase, but it produces the lowest quality of power.

Staebler-Wronski effect - The tendency of the sunlight to electricity conversion efficiency of amorphous silicon photovoltaic devices to degrade (drop) upon initial exposure to light.

Stand-Alone Inverter - An inverter that operates independent of or is not connected to an electric transmission and distribution network.

Stand-Alone System - An system that operates independent of or is not connected to an electric transmission and distribution network.

Storage Capacity - The amount of energy an energy storage device or system can store.

Substrate - The physical material upon which a photovoltaic cell is applied.

Subsidy - Financial assistance granted by the Government to firms and individuals.

Sun Path Diagram - A circular projection of the sky vault onto a flat diagram used to determine solar positions and shading effects of landscape features on a solar energy system.

System Benefits Charge (SBC) - A non-bypassable fee on transmission interconnection; funds are allocated among public purposes, including the development and demonstration of renewable energy technologies.

T

Temperature Coefficient (of a solar photovoltaic cell) - The amount that the voltage, current, and/or power output of a solar cell changes due to a change in the cell temperature.

Thermal Resistance (R-Value) - This designates the resistance of a material to heat conduction. The greater the R-value the larger the number.

Thermocouple - A device consisting of two dissimilar conductors with their ends connected together. When the two junctions are at different temperatures, a small voltage is generated.

Thermophotovoltaic Cell - A device where sunlight concentrated onto a absorber heats it to a high temperature, and the thermal radiation emitted by the absorber is used as the energy source for a photovoltaic cell that is designed to maximize conversion efficiency at the wavelength of the thermal radiation.

Thermopile - A large number of thermocouples connected in series.

Thermosiphon System - A solar collector system for water heating in which circulation of the collection fluid
through the storage loop is provided solely by the temperature and density difference between the hot and cold fluids.

Thin-Film - A layer of semiconductor material, such as copper indium diselenide or gallium arsenide, a few microns or less in thickness, used to make solar photovoltaic cells.

Three-phase Current - Alternating current in which three separate pulses are present, identical in frequency and voltage, but separated 120 degrees in phase.

Tilt Angle (of a Solar Collector or Module) - The angle at which a solar collector or module is set to face the sun relative to a horizontal position. The tilt angle can be set or adjusted to maximize seasonal or annual energy collection.

Total Incident Radiation - The total radiation incident on a specific surface area over a time interval.

Total Internal Reflection - The trapping of light by refraction and reflection at critical angles inside a semiconductor device so that it cannot escape the device and must be eventually absorbed by the semiconductor.

Tracking Solar Array - A solar energy array that follows the path of the sun to maximize the solar radiation incident on the PV surface. The two most common orientations are (1) one axis where the array tracks the sun east to west and (2) two-axis tracking where the array points directly at the sun at all times. Tracking arrays use both the direct and diffuse sunlight. Two-axis tracking arrays capture the maximum possible daily energy.

Transformer - An electromagnetic device that changes the voltage of alternating current electricity. It consists of an induction coil having a primary and secondary winding and a closed iron core.

Transmission - The process of sending or moving electricity from one point to another; usually defines that part of an electric power provider's electric power lines from the power plant buss to the last transformer before the customer's connection.

Transmission System (Electric) - An interconnected group of electric transmission lines and associated equipment for moving or transferring electric energy in bulk between points of supply and points at which it is transformed for delivery over the distribution system lines to consumers, or is delivered to other electric systems.

Transmission Lines - Transmit high-voltage electricity from the transformer to the electric distribution system.

Transportation Sector - An energy-consuming sector that consists of all vehicles whose primary purpose is transporting people and/or goods from one physical location to another. Included are automobiles; trucks; buses; motorcycles; trains, subways, and other rail vehicles; aircraft; and ships, barges, and other waterborne vehicles. Vehicles whose primary purpose is not transportation (e.g., construction cranes and bulldozers, farming vehicles, and warehouse tractors and forklifts) are classified in the sector of their primary use.

Turbine - A machine for generating rotary mechanical power from the energy of a stream of fluid (such as water, steam, or hot gas). Turbines convert the kinetic energy of fluids to mechanical energy through the principles of impulse and reaction, or a mixture of the two.

Two-Axis Tracking - A solar array tracking system capable of rotating independently about two axes (e.g., vertical and horizontal).

U

V

Visible Light Transmittance - The amount of visible light that passes through the glazing material of a window, expressed as a percentage.

Visible Radiation - The visible portion of the electromagnetic spectrum with wavelengths from 0.4 to 0.76 microns

Volt - A unit of electrical force equal to that amount of electromotive force that will cause a steady current of one ampere to flow through a resistance of one ohm.

Voltage - The amount of electromotive force, measured in volts, that exists between two points.

Volt-Ampere - A unit of electrical measurement equal to the product of a volt and an ampere.

W

Wafer - A thin sheet of semiconductor (photovoltaic material) made by cutting it from a single crystal or ingot.

Watt - The rate of energy transfer equivalent to one ampere under an electrical pressure of one volt. One watt equals 1/746 horsepower, or one joule per second. It is the product of Voltage and Current (amperage).

Watt (Electric) - The electrical unit of power. The rate of energy transfer equivalent to 1 ampere of electric
current flowing under a pressure of 1 volt at unity power factor.

Watt (Thermal) - A unit of power in the metric system, expressed in terms of energy per second, equal to the work done at a rate of 1 joule per second.

Watt-hour - A unit of electricity consumption of one Watt over the period of one hour.

Wattmeter - A device for measuring power consumption.

Wave Form - The shape of the phase power at a certain frequency and amplitude.

Wavelength - The distance between similar points on successive waves.

Wire (Electrical) - A generic term for an electrical conductor.