Solar or Renewable Power Glossary
SOLAR or RENEWABLE POWER GLOSSARY
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.
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.
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.
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.
( 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.
Any number of photovoltaic modules connected together electrically to provide a single electrical output.
The angle between true south and a point on the horizon, measured in degrees east or west of true south.
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.
The total maximum charge, expressed in ampere-hours, that can be withdrawn from a cell or battery under a specific set of operating conditions including discharge rate, temperature, state of charge, age, and cutoff voltage.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 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.
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.
The initial phase of battery charging, when the largest amount of energy is put into the 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).
The smallest, basic photovoltaic device that generates electricity when exposed to light.
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.
A group of electrical components that make a complete electrical path, providing some function.
An electronic device for DC power that steps up voltage and steps down current proportionally (or vice-versa).
A type of PV cell made from a single crystal or polycrystalline slice of silicon.
Flow rate of electrons. See AMPERE.
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.
Direct current. A one-way flow of electrons. Typical sources of direct current are solar-electric cells, rectifiers, and direct current generators. To be used for typical 120 volt or 220 volt household appliances, DC must be converted to
AC (alternating current).
A battery designed to regularly discharge 50 to 80 percent of its capacity before recharging.
DIRECT CURRENT (DC)
An electrical current that moves in one direction only.
The rate at which energy is being drained from a battery.
Switch gear used to connect or disconnect components in a system.
EFFICIENCY (PV modules)
The ratio of power output of a photovoltaic cell to the incident power from the sun or simulated sun sources under specified standard insulation conditions. A solar cell that converts 1/10 of the sun’s energy that strikes its surface to electricity has an efficiency of 10 percent.
The effectiveness of a device to convert energy from one form to another, or to transfer energy from one body to another. An electric pump that is 60 percent efficient converts 60 percent of the input energy into work by pumping water. The remaining 40 percent becomes waste heat.
The amount of work that a system or entity can do (potential energy) or is doing (kinetic energy), measured in joules. The product of power and time, measured in watt-hours. 1,000 watt-hours = 1 kilowatt-hour (KWH).
The process of restoring all cells in a battery to an equal state-of-charge. For lead-acid batteries, this is a charging process designed to bring all cells to 100 percent state-of-charge.
The final stage of battery charging, when the battery is charged at a slow rate over a long period of time.
FLAT PLATE COLLECTOR
A solar thermal collector that converts the sun’s radiation into heat on a flat surface. Does not use reflecting surfaces or lens arrangements to concentrate the sun’s energy.
A trickle charge to keep a battery fully charged at a safe voltage level with minimal gassing.
The full sun condition is the amount of power density received at the surface of the earth at noon on a clear day– about 1 KW per m^2, or 1 Sun. Lower levels of sunlight are often expressed as 0.5 sun or 0.1 sun.
A electrical device that is designed to break a circuit by melting an internal conductor when the current in the circuit exceeds the maximum considered safe for the conductors or devices in the circuit.
The production of hydrogen and oxygen gas from one or more of the electrodes in the cells of a battery. Gassing commonly results from the electrolysis of water in the electrolyte during charging.
Transmission line network used to distribute electrical energy, generally by a commercial power utility.
Metallic contacts fused to the surface of a solar cell to provide a low resistance path for electrons to flow out to the cell interconnect wires.
A renewable energy system that is connected to the utility grid, selling excess energy back to the utility. Also called a utility-interactive system.
The connection of electrical components to the earth and/or each other for the purposes of dissipating static charge or protecting against a short circuit or lightning.
Unwanted current path to ground.
A photovoltaic (PV) rack designed to be installed on the ground or other flat surface.
GROUND ROD (ELECTRODE)
A metal rod (typically 5/8 inch diameter) that is driven into the earth (typically 8 feet deep) and is electrically connected to the negative conductor and/or any metal parts, wiring enclosures, or conduit of an electrical circuit.
Cycles per second. Generally refers to the number of complete cycles of the AC sine wave per second, or the frequency at which a radio or computer processor works.
INDUCTION MOTOR (AC)
A type of electric motor that requires a high surge to start, and a stable voltage supply, making it a challenge to run using a solar-electric system.
The amount of sunlight reaching an area. Usually expressed in watts per square meter.
A device that converts DC electricity (anywhere from 12 to 600 VDC) to AC electricity (typically 120/240 VAC).
One thousand watts.
One thousand watt-hours. Unit of energy used to perform work (energy and work are equivalent in units, energy being the potential value and work the achieved value).
A location’s distance north or south of the equator measured in degrees.
Refers to equipment that is powered by electricity. Usually expressed in terms of amperes or watts. Any device or appliance that uses energy (such as a light or pump).
MAXIMUM POWER POINT
The point on a PV module’s voltage/amperage curve where the product of current and voltage is a maximum (measured in watts).
MAXIMUM POWER POINT TRACKING (MPPT)
Electronically tracking the maximum power point of a PV module to achieve the highest possible output, by (in simplest terms) using surplus voltage to boost amperage.
The smallest non-divisible, self-contained, and environmentally protected physical structure housing interconnected photovoltaic cells and providing a single DC electrical output. Commonly called a “panel.”
State by state legislation that requires utilities to purchase renewable produced electricity at the same price that they sell it, until a building’s monthly or annual energy use is offset..
The period of low energy demand, as opposed to maximum or peak demand.
Energy supplied during periods of relatively high system demands as specified by the utility.
When an electrical circuit is interrupted by breaking the path at one or more points, stopping the electrons from flowing. A light switch opens an electrical circuit when it turns off the light.
OPEN CIRCUIT VOLTAGE (VOC)
The maximum possible voltage across a PV array, module, or cell. The voltage across the terminals of a photovoltaic cell, module, or array with no load applied when the cell is exposed to standard insulation conditions, measured with a voltmeter.
OPEN LOOP SYSTEM
A fresh water or “direct” solar hot water system, generally for use in freeze-free climates.
Placement according to the directions N, S, E, or W.
An electrical circuit with more than one possible path for electron flow. When wiring PV modules, this wiring configuration increases amperage (current), while voltage remains the same. Parallel wiring is positive to positive (+ to +) and negative to negative (- to -). Opposite of a series connection.
The period of time it takes for an energy generating device or system to pay for itself in fuel savings.
The maximum load or electrical power draw occurring in a given period of time.
PEAK SUN HOURS
The equivalent number of hours per day when solar irradiance averages 1,000 watts per meter squared.
A device that consumes energy even when its switch is off, such as the digital clock on a VCR.
The actual (physical) particle unit of light, as the electron is a particle of electric charge. Solar-electric modules use photons to generate electricity. Photons not captured by the cell are either reflected, pass through the panel, or are converted to heat in the solar array.
A collection of solar modules connected in series, parallel, or series-parallel combination to provide greater voltage, current, or power than can be furnished by a single solar module. Solar-electric arrays can be designed to furnish any desired voltage, current, or power.
A device composed of specially prepared semiconductor material or material combinations exhibiting the ability to convert incident solar energy directly into electrical energy.
The phenomenon that occurs when photons, the particles in a beam of light, knock electrons loose from the atoms they strike. When this property of light is combined with the properties of semiconductors, electrons flow in one direction across a junction, setting up a voltage. With the addition of circuitry, electrons will flow and electrical energy will be available.
A PV module consists of series and/or parallel wired cells typically made from layered silicon crystals that convert light energy to DC electricity. The number of modules in a given system varies depending on the combined load being powered.
A PV mount that is installed on the top or side of a pole usually set in concrete. Can be fixed or seasonally tilted.
A wafer of silicon with a multi-grained structure. All grains have the same atomic crystal lattice, however, each grain has a unique orientation in space, producing a unique reflection of light, resulting in a “patchy” mottled appearance. AKA multicrystalline cell.
Two or more photovoltaic modules wired in series or parallel.
The use of electricity directly from a photovoltaic array, without batteries or other electrical storage. Many solar water pumps work this way, using a tank to store water.
# RADIATION The sun’s energy that comes to earth in the form of direct, diffuse, and reflected rays.
# The transfer of heat through electromagnetic waves, without heating the air between objects.
A device that prevents overcharging of batteries by controlling the charge cycle, and usually adjustable to conform to specific battery needs. Regulators do not step the voltage down, but control the rate of charge so the battery stays at a specified voltage. Also called CHARGE CONTROLLER.
A PV or solar collector rack intended to be installed on a roof. For PVs, its elevation angle can be fixed or seasonally adjustable.
The tendency of all batteries to lose energy. Self-discharge represents energy lost to internal chemical reactions within the cell. This energy is not and cannot be used from the battery or cell’s output terminals.
A wiring configuration used to increase voltage from more than one supply. Series wiring is positive to negative (+ to -) or negative to positive (- to +). Opposite of parallel connection. Series circuits have only one possible path for electron flow.
A device that prevents overcharging of a battery by disconnecting the charging source as the battery voltage approaches some upper limit.
A group of PV modules or batteries wired in series.
A PV mount installed on the side of a pole. May be fixed or seasonally adjustable.
A nonmetallic element, which when specially treated, is sensitive to light and capable of transforming light into electricity. Silicon is the basic material of most beach sand, and is the raw material used to manufacture most photovoltaic cells.
SINGLE CRYSTAL CELL
A wafer of silicon that has a perfect, continuous, crystal lattice (on the atomic level).
An estimation of a location for its potential for solar, hydro, or wind power.
A system that operates independently of the utility lines. It may draw supplementary electricity from the utility, but is not capable of providing electricity to the utility.
The maximum amount of AC power an inverter may deliver to a load (or loads) for a short period of time, such as when starting a motor.
A fixed angle measured from the horizontal to which a solar array is tilted. The tilt angle is chosen to maximize the array output. Depending upon latitude, season, and time of day, the optimum angle will vary.
A mounting rack for a PV array that automatically tilts to follow the daily path of the sun through the sky. A “tracking array” will produce more energy through the course of the day than a “fixed array” (nontracking), particularly during the long days of summer. Some trackers are single-axis while others are dual-axis.
UTILITY-INTERTIE (UI) SYSTEM
See GRID-TIE SYSTEM.
The volt is the unit used in the measurement of electromotive force (electrical “pressure”). A standard electrical definition of the volt is: an electromotive force of 1 volt is necessary to move a current of 1 ampere through a 1 â„¦ resistor. It is often also referred to as electrical potential difference or potential difference.
Unit of power. Power is the rate of generating or using energy. One watt is the power developed or dissipated in a one volt circuit in which there is a current of one ampere (6.28 million million electrons per second). Watts = amps X volts.
A unit of measurement quantifying an amount of energy used or generated. A load that consumes 1 watt for 10 hours uses 10 watt-hours.
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