Glossary of Solar Terms

ALTERNATING CURRENT (AC): Electric current in which the direction of flow is reversed at frequent intervals: 100 or 120 times per second.

AMPERE (A) OR AMP: A unit of measure of electron flow rate in an electric circuit.

AMPERE-HOUR (AH): Quantity of electricity or measure of charge.

ARRAY: Total collection of PV modules connected together on an installation.

BLOCKING DIODE: A diode used to restrict or block reverse current from flowing backward through a module. Also, when connected in a series to a PV string it protects its modules from a reverse power flow and the risk of thermal destruction of solar cells.

CELL: The basic PV system unit that converts light energy into DC electric current.

CHARGE CONTROLLER: Controls the DC current from the panels into the battery bank while maintaining the charge rate based upon battery voltage.

COGENERATTON: Using the excess heat created by a conventional turbine electric generator for other purposes like space or water heating.

COMPACT FLUORESCENT LIGHTS: Lights that use a lot less energy than regular light bulbs.

DEEP DISCHARGE: Discharging a battery to 20% or less of its full charge.

DIRECT CURRENT (DC): An electric current in which electrons flow in one direction only, as from a battery or solar module.

DIRECT GAIN: Sunlight directly enters the home through windows and is absorbed and stored in massive floors or walls. These buildings are elongated in the east-west direction, and most windows are southern. The area devoted to south windows varies throughout the country. It could be as much as 20% of the floor area in sunny cold climates, where advanced glazings or moveable insulation are recommended to prevent heat loss at night. These buildings have high insulation levels and added thermal mass for heat storage.

ELECTRIC CURRENT: The flow of electrons measures in Amperes or Amps.

ELECTRICAL GRID: An interconnected system of electricity distribution wires and stations, usually covering a large area (state or country).

FLOAT CHARGE: Float charge is the voltage required to counteract the self-discharge of the battery at a certain temperature.

FOSSIL FUELS: Fuels formed in the ground from the remains of dead plants and animals. It takes millions of years to form fossil fuels. Oil, natural gas, and coal are fossil fuels.

FUEL CELL: A device that converts the energy of a fuel directly to electricity and heat, without combustion. Because there is no combustion, fuel cells give off few emissions; because there are no moving parts, fuel cells are quiet.

GEL-TYPE BATTERY: Lead-acid battery that the electrolyte is made of a silica gel matrix.

GREENHOUSE EFFECT: The effect of the Earth’s atmosphere, due to certain gases, in trapping heat from the sun; the atmosphere acts like a greenhouse.

GRID-CONNECTED (PV SYSTEM): A PV system that acts like a central generating plant, supplying power to the grid.

HYBRID SYSTEM: A PV system that includes other sources of electricity generation, such as wind or diesel generators.

INTERCONNECT: A conductor within a module or other connection, which provides an electrical interconnection between the solar cells.

INVERTERS: Devices that convert DC electricity into ac electricity (single or multiphase), either for stand-alone systems (not connected to the grid) or for utility-interactive systems.

KILOWATT (KW): 1000 watts.

LOAD: Anything in an electrical circuit that, when the circuit is turned on, draws power from that circuit.

MEGAWATT (MW): One million watts; 1000 kilowatts.

MODULE: The basic durable building block of a solar array, consisting of a circuit of solar cells connected in series to produce a useful voltage and current, protected from the environment by lamination and edge framing.

NONRENEWABLE FUELS: Fuels not re-generated naturally in a short period of time, such as coal, oil, natural gas, and nuclear materials like uranium (as different from 'renewable fuels').

OHM: The unit of resistance to the flow of an electric current.

PASSIVE SOLAR HOME: A house that stays warm or cold passively, using natural heat flows from sunlight, wind and the earth, without "active" devices like air conditioners or heaters.

PEAK POWER: Power generated by a utility to meet short-term high demand, usually from turbines normally on stand-by most of the time.

PHOTOVOLTAIC (PV): The direct conversion of light into electricity.

PHOTOVOLTAIC (PV) CELL: The smallest semiconductor element within a PV module to perform the immediate conversion of light into electrical energy (dc voltage and current).

PHOTOVOLTAIC (PV) PANEL: often used inter changeably with PV module (especially in one module systems), but more accurately used to refer to a physically connected collection of modules (i.e., a laminate string of modules used to achieve a required voltage and current).

PHOTOVOLTAIC (PV) PEAK WATT: Maximum "rated" output of a cell, module, or system.

REMOTE SYSTEMS: Systems off the utility grid.

SELF-DISCHARGE: Rate at which a battery, without a load, will lose its charge.

SINE WAVE INVERTER: An inverter that produces utility-quality, sine wave power forms.

SOLAR ENERGY: Energy from the sun, both in the form of heat and light.

SQUARE WAVE INVERTER: The inverter 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.

STAND-ALONE (PV SYSTEM): A photovoltaic power system not connected to a utility power grid, for example remote water pumping or remote power for telecommunications repeaters or remote homes (similar to "off-grid").

SULFATION: A condition that afflicts unused and discharged batteries; large crystals of lead sulfate grow on the plate, instead of the usual tiny crystals, making the battery extremely difficult to recharge.

SUNSPACE: A room that faces south, or a small structure attached to the south side of a house.

THERMAL MASS: Materials that store heat within a sunspace.

THERMAL STORAGE WALL (MASONRY OR WATER): A south-facing wall that is glazed on the outside. Solar heat strikes the glazing and is absorbed into the wall, which conducts the heat into the room over time. The thicker the wall, the less the indoor temperature fluctuates.

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

TRANSFORMER: Two wire coils with different number of windings, to allow alternating current (AC) power to be changed from one voltage and current into another, often used to raise voltage before transmission over long distances and reduce voltage to useful levels at final distribution points.

TRICKLE CHARGE: A charge at a low rate, balancing through self-discharge losses, to maintain a cell or battery in a fully charged condition.

VOLT (V): A unit of measure of the force, or 'push,' given the electrons in an electric circuit. One volt produces one ampere of current when acting a resistance of one ohm.

WATT (W): The unit of electric power, or amount of work (J), done in a unit of time. One ampere of current flowing at a potential of one volt produces one watt of power.