Vocabulary

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ABSORBER
The absorber is that part of a solar thermal collector that receives the incident radiant energy and transforms it into heat energy.

ACTIVE SOLAR THERMAL SYSTEM
A system that traps the sun’s energy with solar collectors and uses an electromechanical subsystem to move that energy to its point of intended use for water heating, space heating, pool heating, industrial process heat, electrical generation and space cooling.

ALTERNATING CURRENT (AC)
An electrical current in which the direction of electron flow reverses periodically, usually many times per second. Most U.S. household electrical systems use AC current rated at 120 volts and 60 cycles per second.

ALTERNATOR
An mechanical device that generates alternating current electricity.

ALTITUDE ANGLE
The angle of the sun above the horizon, measured in degrees. In winter, the sun is at a low solar altitude, and in the summer, the sun is at a high solar altitude.

AMMETER
A device used for measuring the current (amperage) at any point in an electrical circuit.

AMORPHOUS SILICON
A thin-film PV silicon cell having no crystalline structure.

AMPACITY
Refers to the highest safe amount of electrical current through conductors, overcurrent devices, or other electrical equipment. Ampacity is determined by the cross-sectional area and the material of the conductor, or the manufacturer’s equipment rating.

AMPERE (AMP; A, I)
The rate of flow of electrical charge. Unit of electrical current. One volt across one ohm of resistance causes a current of one ampere. One ampere is equal to 6.235 x 10^18 electrons (one coulomb) per second passing a given point in a circuit.

AMPERE-HOUR (AMP-HOUR; AH)
A measure of electron flow over time, used to measure battery capacity and state of charge. For example, a current of 1 amp drawn from a battery for 10 hours would result in 10 amp-hours of charge cycling through the battery.

AMPERE-HOUR METER
An instrument that monitors electron flow over time. Amp-hours are the product of electron flow (in amperes) and time (in hours).

AMPLITUDE
Generally refers to the maximum and minimum voltage attained by an alternating or pulsed current in each complete cycle or pulse of that current.

ANGLE OF INCIDENCE
The angle between the sun’s rays and a line perpendicular to the active surface of a solar module or collector, in degrees.

ANGLE OF INCLINATION
The angle that a solar collector or PV module is positioned above horizontal.

ANODE
( Battery ) The electrode within a battery cell that undergoes the chemical process of oxidation. Electrically, the anode is the cell’s positive terminal.

(Water heater) An aluminum or magnesium sacrificial rod installed within steel tanks that is used to help prevent corrosion of the tank itself.

ARRAY
Any number of photovoltaic modules connected together electrically to provide a single electrical output.

AWG
American Wire Gauge, a set of standards in the U.S. specifying the diameter of wire. A higher number indicates smaller wire.

AZIMUTH
The angle between true south and a point on the horizon, measured in degrees east or west of true south.

BALANCE OF SYSTEMS (BOS)
Parts or components of a photovoltaic system other than the photovoltaic array or other generating equipment.

BALLAST
A circuit used to condition and stabilize an electric current, for example, in a fluorescent light.

BATCH SOLAR HOT WATER HEATER
The simplest of solar hot water systems. A tank of water within a glass-covered insulated enclosure aimed at the sun. Water is heated in the tank and then flows to the load or an auxiliary water heater.

BATTERY
Two or more electrochemical cells electrically interconnected in an appropriate series/parallel arrangement to provide the required operating voltage and capacity levels. Under common usage, the term battery also applies to a single cell if it constitutes the entire electrochemical storage system.

BATTERY CAPACITY
The total maximum charge, expressed in ampere-hours, that can be withdrawn from a cell or battery under a specific set of operating conditions including discharge rate, temperature, state of charge, age, and cutoff voltage.

BATTERY CELL
The simplest operating unit in a storage battery. It consists of one or more positive electrodes or plates, electrolyte that permits ionic conduction, one or more negative electrodes or plates, separators between plates of opposite polarity, a container for all the above, and posts or other terminals for electrical connection.

BATTERY CYCLE LIFE
The number of cycles, to a specified depth of discharge, that a cell or battery can undergo before failing to meet its specified capacity or efficiency performance criteria.

BATTERY LIFE
The period during which a cell or battery is capable of operating above a specified capacity or efficiency performance level. With lead-acid batteries, end-of-life is generally considered when a fully charged cell can deliver only 80 percent of its rated capacity. Beyond this state of aging, deterioration and loss of capacity begins to accelerate rapidly. Life may be measured in cycles or years, depending on the type of service for which the cell or battery is intended.

BETZ LIMIT
The theoretical maximum energy that a wind generator can extract from the wind—59.6 percent.

BIOMASS
Any organic matter available on a renewable basis, including agricultural crops, wastes, and residues; wood, wood wastes, and residues; animal wastes and municipal wastes; and aquatic plants.

BIOFUELS (BIOMASS FUELS)
Biomass converted directly to energy or converted to liquid or gaseous fuels, such as ethanol methane, and hydrogen.

BLADE
The energy-capturing, aerodynamically designed part of a wind turbine, which interacts directly with the wind.

BLOCKING DIODE
A semiconductor connected in series with a solar-electric cell or cells and a storage battery to keep the battery from discharging through the cell when there is no output, or low output, from the solar cell. It can be thought of as a one-way valve that allows electrons to flow forwards, but not backwards.

BRAKE
Device for stopping a wind turbine. This can be an electric brake that shorts the output of the turbine (dynamic braking), or a mechanical brake that physically stops the rotation, as with a brake drum and shoe.

BREAKER
A manually operable switching device that also automatically opens a circuit in the event of overcurrent.

BRITISH THERMAL UNIT (BTU)
The amount of heat required to raise the temperature of one pound (one pint) of water, one degree Fahrenheit. 1 watt-hour = 3.413 BTU.

BULK CHARGE
The initial phase of battery charging, when the largest amount of energy is put into the battery.

BUSS
An electrical connection component that can accept multiple cables or wires. Also bus, bus bar, or busbar

BYPASS DIODE
A semiconductor device connected in parallel with a series block of parallel PV strings to prevent current from flowing back through any shaded or failed modules in the same block.

CAPACITANCE
An electrical effect in AC circuits that results in amperage peaking before voltage.

CATHODE
The electrode within a battery cell that undergoes the chemical process of reduction. Electrically, the cathode is the negative terminal of the cell.

CATHODIC PROTECTION
Systems that protect metal from corrosion by running small electrical currents along the metal. Most often used to protect well heads, and oil, gas, and water pipelines.

CELL (battery)
A single unit of an electro-chemical device capable of producing an electrical current by converting chemical energy into electrical energy. The cell is the basic unit used to store energy in the battery. The cell contains an anode, a cathode, and the electrolyte. A battery usually consists of several cells electrically connected together to produce higher voltages. (Sometimes the terms cell and battery are used interchangeably).

CELL (solar)
The smallest, basic photovoltaic device that generates electricity when exposed to light.

CHARGE CONTROLLER
A component of photovoltaic systems that controls the charging of the battery to protect the batteries from overcharge and overdischarge. The charge controller may also indicate the system operational status. Standard charge controllers vary the current (A) based on preset voltage set points.

CHARGE RATE
The current applied to a cell or battery to restore its available capacity, specified in relation to total battery size. A C/20 rate is a charge rate that is 1/20th of the total battery capacity. Also called a “20-hour rate.”

CIRCUIT
A group of electrical components that make a complete electrical path, providing some function.

CIRCUIT BREAKER
See BREAKER.

CLOSED LOOP SYSTEM
A solar hot water system of which no part is vented to the atmosphere or fed with fresh liquid. The system liquid, usually some form of antifreeze solution, is recirculated. Closed loop solar systems are also known as glycol systems and indirect systems.

COB CONSTRUCTION
A traditional building technique using hand formed lumps of earth mixed with sand and straw.

COLLECTOR LOOP
The plumbing loop in a solar hot water system that includes the solar collectors. The collectors heat the fluid in the collector, and the heated fluid can be used directly (if water) or the heat can be exchanged to a potable water loop.

COMBINER BOX
A box where wires from individual PV modules or strings are combined into larger wires to run to the battery bank. Can also contain overcurrent protection devices.

COMPACT FLUORESCENT LIGHT (CFL)
A smaller version of standard fluorescent lamps that can directly replace incandescent lights. CFLs use 65 to 80 percent less energy, while producing the same lumens.

CONCENTRATOR
A photovoltaic module that includes optical components, such as lenses, to direct and concentrate sunlight onto a solar cell of smaller area. Most concentrator arrays must directly face or track the sun.

CONDUCTION
Heat transfer from a hot object to a colder object through direct contact.

CONDUCTOR
A material with relatively low resistance through which electricity will readily flow—wires, cables, busbars. The most common conductors are copper and aluminum.

CONDUIT
Metal or plastic tubing designed to protect electrical conductors.

CONTINUOUS OUTPUT RATING
The maximum amount of power an inverter may deliver to a load (or loads) for a sustained period of time.

CONVECTION

• Heat transfer by the movement of fluid (usually air or water).
• Heat transfer through either the natural or forced movement of air.CONVERTER
  An electronic device for DC power that steps up voltage and steps down current proportionally (or vice-versa).

CRYSTALLINE SILICON
A type of PV cell made from a single crystal or polycrystalline slice of silicon.

CURRENT
Flow rate of electrons. See AMPERE.

CUTOFF VOLTAGE
Electrical equipment setting for the voltage level at which a battery is considered to be empty, and the discharge process is terminated. Most commonly found in inverters and charge controllers that include a feature for low voltage disconnection.

CYCLE

• One complete charge/discharge cycle of a battery.
• An AC sine wave’s movement from zero to maximum positive, through zero, to maximum negative, and back to zero.

CYCLE LIFE
Cycle life is the number of cycles a cell or battery will undergo before being considered “worn out.” This point is usually defined as when the battery’s capacity has decreased to 80 percent of its initial rated capacity.