AC —alternating current (AC) — A type of electrical current, the direction of which is reversed at regular intervals or cycles. In the United States, the standard is 120 reversals or 60 cycles per second. Electricity transmission networks use AC because voltage can be controlled with relative ease.
array — See photovoltaic (PV) array.
azimuth angle — The angle between true south and the point on the horizon directly below the sun.
bird droppings – Avian poo! Rain is often not sufficient to wash away the mess, and it requires manual cleaning. Unlike dirt particulate matter, it only affects one or two cells at a time but the cells it does impact are substantially blocked. Due to the series connection of cells within a panel, the one impacted cell could knock out the cell string or the entire module if bypass diodes are not present. The best advice is to clean off the panel quickly.
cell (battery) — A single unit of an electrochemical device capable of producing direct voltage by converting chemical energy into electrical energy. A battery usually consists of several cells electrically connected together to produce higher voltages. (Sometimes the terms cell and battery are used interchangeably). See also photovoltaic (PV) cell.
cloud enhancement — The increase in solar intensity caused by reflected irradiance from nearby clouds.
converter — A unit that converts a direct current (dc) voltage to another dc voltage.
current — See electric current.
DC — See direct current.
direct current (DC) — A type of electricity transmission and distribution by which electricity flows in one direction through the conductor, usually relatively low voltage and high current. To be used for typical 120 volt or 220 volt household appliances, DC must be converted to alternating current, its opposite.
disconnect — Switch gear used to connect or disconnect components in a photovoltaic system.
electric circuit — The path followed by electrons from a power source (generator or battery), through an electrical system, and returning to the source.
electric current — The flow of electrical energy (electricity) in a conductor, measured in amperes.
electrical grid — An integrated system of electricity distribution, usually covering a large area.
electricity — Energy resulting from the flow of charge particles, such as electrons or ions.
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. The movement of electrons in an electrical conductor constitutes an electric 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.
fixed tilt array — A photovoltaic array set in at a fixed angle with respect to horizontal.
flat-plate array — A photovoltaic (PV) array that consists of non-concentrating PV modules.
frequency — The number of repetitions per unit time of a complete waveform, expressed in Hertz (Hz).
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).
gigawatt (GW) — A unit of power equal to 1 billion Watts; 1 million kilowatts, or 1,000 megawatts.
grid — See electrical grid.
grid-connected system — A solar electric or photovoltaic (PV) system in which the PV array acts like a central generating plant, supplying power to the grid.
high voltage disconnect — The voltage at which a charge controller will disconnect the photovoltaic array from the batteries to prevent overcharging.
hybrid system — A solar electric or photovoltaic system that includes other sources of electricity generation, such as wind or diesel generators.
incident light — Light that shines onto the face of a solar cell or module.
input voltage — This is determined by the total power required by the alternating current loads and the voltage of any direct current loads. Generally, the larger the load, the higher the inverter input voltage. This keeps the current at levels where switches and other components are readily available.
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. See also diffuse insolation and direct insolation.
interconnect — A conductor within a module or other means of connection that provides an electrical interconnection between the solar cells.
inverter — A device that converts direct current electricity to alternating current either for stand-alone systems or to supply power to an 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. Usually expressed in kilowatts per square meter. Irradiance multiplied by time equals insolation.
joule — A metric unit of energy or work; 1 joule per second equals 1 watt or 0.737 foot-pounds; 1 Btu equals 1,055 joules.
junction box — A photovoltaic (PV) generator junction box is an enclosure on the module where PV strings are electrically connected and where protection devices can be located, if necessary
kilowatt (kW) — A standard unit of electrical power equal to 1000 watts, or to the energy consumption at a rate of 1000 joules per second.
kilowatt-hour (kWh) — 1,000 thousand watts acting over a period of 1 hour. The kWh is a unit of energy. 1 kWh=3600 kJ.
life — The period during which a system is capable of operating above a specified performance level.
life-cycle cost — The estimated cost of owning and operating a photovoltaic system for the period of its useful life.
load — The demand on an energy producing system; the energy consumption or requirement of a piece or group of equipment. Usually expressed in terms of amperes or watts in reference to electricity.
megawatt (MW) — 1,000 kilowatts, or 1 million watts; standard measure of electric power plant generating capacity.
megawatt-hour — 1,000 kilowatt-hours or 1 million watt-hours.
module — See photovoltaic (PV) module.
National Electrical Code (NEC) — Contains guidelines for all types of electrical installations. The 1984 and later editions of the NEC contain Article 690, “Solar Photovoltaic Systems” which should be followed when installing a PV system.
National Electrical Manufacturers Association (NEMA) — This organization sets standards for some non-electronic products like junction boxes.
NEC — See National Electrical Code.
NEMA — See National Electrical Manufacturers Association.
ohm — 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.
one-axis tracking — A system capable of rotating about one axis.
orientation — Placement with respect to the cardinal directions, N, S, E, W; azimuth is the measure of orientation from north.
panel — See photovoltaic (PV) panel.
parallel connection — A way of joining solar cells or photovoltaic modules by connecting positive leads together and negative leads together; such a configuration increases the current, but not the voltage.
particulates – Reflect and dissipate sunlight, leading to a loss of efficiency and generation and if unchecked to overheating (hot spots) and eventual panel loss.
peak power tracking — See maximum power tracking.
peak sun hours — The equivalent number of hours per day when solar irradiance averages 1,000 w/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 1,000 w/m2.
peak watt — A unit used to rate the performance of solar cells, modules, or arrays; the maximum nominal output of a photovoltaic device, in watts (Wp) under standardized test conditions, usually 1,000 watts per square meter of sunlight with other conditions, such as temperature specified.
photocurrent — An electric current induced by radiant energy.
photon — A particle of light that acts as an individual unit of energy.
photovoltaic(s) (PV) — Pertaining to the direct conversion of light into electricity.
photovoltaic (PV) array — An interconnected system of PV modules that function as a single electricity-producing unit. The modules are assembled as a discrete structure, with common support or mounting. In smaller systems, an array can consist of a single module.
photovoltaic (PV) cell — The smallest semiconductor element within a PV module to perform the immediate conversion of light into electrical energy (direct current voltage and current). Also called a solar cell.
photovoltaic (PV) 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) 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 semiconductor materials including silicon, cadmium sulfide, cadmium telluride, and gallium arsenide, and in single crystalline, multicrystalline, or amorphous forms.
photovoltaic (PV) effect — 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, current will flow and electric power will be available.
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.
photovoltaic (PV) generator — The total of all PV strings of a PV power supply system, which are electrically interconnected.
photovoltaic (PV) module — The smallest environmentally protected, essentially planar assembly of solar cells and ancillary parts, such as interconnections, terminals, (and protective devices such as diodes) intended to generate direct current power under unconcentrated sunlight. The structural (load carrying) member of a module can either be the top layer (superstrate) or the back layer (substrate).
photovoltaic (PV) panel — often used interchangeably 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) system — A complete set of components for converting sunlight into electricity by the photovoltaic process, including the array and balance of system components.
photovoltaic-thermal (PV/T) system — A photovoltaic system that, in addition to converting sunlight into electricity, collects the residual heat energy and delivers both heat and electricity in usable form. Also called a total energy system or solar thermal system.
power — The amount of electrical energy available for doing work, measured in horsepower, Watts, or Btu per hour.
power conversion efficiency — The ratio of output power to input power of the inverter.
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.
PV — See photovoltaic(s).
rated power — Rated power of the inverter. However, some units cannot produce rated power continuously.
resistance (R) — The property of a conductor, which opposes the flow of an electric current resulting in the generation of heat in the conducting material. The measure of the resistance of a given conductor is the electromotive force needed for a unit current flow. The unit of resistance is ohms.
safe solar clean — Provides safe, efficient, mechanized cleaning for energy generation at full capacity. More power to your solar.
series connection — A way of joining photovoltaic cells by connecting positive leads to negative leads; such a configuration increases the voltage.
soiling – The amount of sunlight that is blocked by dirt and debris that accumulate on solar panels over time. Just like a car’s windshield, small amounts of dust and dirt can accumulate and scatter light.
solar cell — See photovoltaic (PV) cell.
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 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 noon — The time of the day, at a specific location, when the sun reaches its highest, apparent point in the sky.
solar panel — See photovoltaic (PV) panel.
solar resource — The amount of solar insolation a site receives, usually measured in kWh/m2/day, which is equivalent to the number of peak sun hours.
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
string — A number of photovoltaic modules or panels interconnected electrically in series to produce the operating voltage required by the load.
tilt angle — The angle at which a photovoltaic array 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.
tracking array — A photovoltaic (PV) 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.
two-axis tracking — A photovoltaic array tracking system capable of rotating independently about two axes (e.g., vertical and horizontal).
volt (V) — 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.
voltage at maximum power (Vmp) — The voltage at which maximum power is available from a photovoltaic module.
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).
