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Definitions
Below is a directory of terms used in discussions about solar power. Most of the terms have been reproduced from the International Energy Agency, the UN Environment Programme or the US Department of Energy.
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A
Active solar
Directly harnessing solar energy to produce either electricity or hot water.
Alternating current (AC)
A type of electrical current in which the movement of electric charge periodically reverses direction. AC is the form in which electricity is used in distribution grids.
B
Battery
Two or more electrochemical cells enclosed in a container and electrically interconnected to provide the required operating voltage and current.
C
Centralised energy
Where electricity is produced at large power plants and 'shipped' though transmission and distribution grids (known as the electrical grid) to consumers.
Charge controller
A component of a photovoltaic system that controls the flow of current to and from the battery to protect it from over-charge and over-discharge.
Concentrating solar power (CSP)
CSP systems use concentrators to convert solar energy into heat, which can be used to create steam to drive a generator or to power chemical processes such as hydrogen production. Also known as high temperature solar thermal systems. Concentrating solar power may also refer to a system that focuses solar rays on a photovoltaic cell to increase conversion efficiency.
Concentrator
A photovoltaic module, that includes optical components such as lenses or mirrors to direct and concentrate sunlight onto a smaller area. Most concentrator arrays directly face or track the sun. They can increase the power flux of sunlight hundreds of times.
Conversion efficiency
The percentage of the input energy of a process that is converted to energy of the desired type.
Converter
A unit that converts a direct current (DC) power to another voltage.
D
Decentralised energy
Where electricity is generated from many small energy sources. It uses systems that are installed at or near the location where the electricity is used. Also called distributed power, on-site generation or embedded generation. See off-grid system.
Direct current (DC)
A type of electrical current in which the movement of electric charge flows steadily in one direction. It is produced by solar cells and batteries and to be used for typical household appliances, DC must be converted to alternating current (AC).
E
Electrical grid
An integrated system of electricity distribution, usually covering a large area. Commonly referred to as 'the grid'.
Electricity
Energy resulting from the flow of charge particles, such as electrons or ions.
Electrification
The act of providing electricity.
F
Feed-in tariff
A policy mechanism to encourage the adoption of renewable energy sources, through which utility companies buy renewable energy at a fixed rate (set by the government). The energy is fed into the electrical grid by third parties such as private investors.
G
Grid-connected solar system
A solar system that is connected to the central electrical grid. This system does not require batteries and is mainly used to offset the energy supplied by the mains electricity grid, or to supply power to the grid. Also called on-grid system or grid-interactive system.
Grid parity
Occurs when the cost of electricity from a renewable energy source is equal to the cost of grid electricity at the point of connection.
H
Hybrid solar system
A solar system that includes other energy sources, such as wind or diesel generators.
I
Insolation
A measure of the amount of solar radiation falling on a particular surface at a specific time.
Inverter
A device that converts direct current (DC) electricity to alternating current (AC).
Investment tax credit
A policy mechanism that allows investments in renewable energy to be fully or partially deducted from tax obligations or taxable income.
K
Kerosene
A flammable hydrocarbon liquid that, in developing countries, is often used in cooking stoves, water heaters and as a light source (when burned in wick-fed lamps). Kerosene, when burned, emits pollutants that pose serious health risks, including respiratory or eye infections and kidney or liver problems. It is also a leading cause of house fires in the developing world. It is also known as paraffin.
Kilowatt hour (kWh)
A common unit of energy used to measure electricity use. It is equivalent to using 1000 watts of electricity for one full hour.
L
Lead-acid battery
A general type of battery that includes batteries with plates made of pure lead, lead-antimony, or lead-calcium immersed in an acid electrolyte. Lead-acid batteries are the oldest type of rechargeable battery.
Light emitting diodes (LEDs)
An electronic light source based on a semiconductor device that converts electrical energy directly into light. LEDs consume 80 per cent less energy than conventional incandescent bulbs.
M
Megawatt (MW)
A unit of power equal to one million watts.
Microfinance
The provision of very small loans to low-income people or groups, mostly in developing countries. Microfinance providers often require no collateral or down payment to assure repayment.
Monocrystalline cells
Single crystal solar photovoltaic (PV) cells, made from very thin silicone. They are the most efficient type of PV cells.
Multicrystalline cells
Solar photovoltaic cells made from silicon with variously oriented, small, individual crystals. These are less efficient than monocrystalline cells but are cheaper to produce. Also called polycrystalline or semicrystalline cells.
N
Net metering
An electricity policy where people generating small-scale electricity through, for example, solar systems, get paid for the electricity they produce over and above their domestic needs.
O
Off-grid system
An autonomous or hybrid solar system not connected to a grid. It often includes batteries to store excess energy for use when solar energy is not available — for example during cloud cover or at night. Also called stand-alone system.
P
Parabolic dish
A high-temperature (above 180 degrees Fahrenheit) solar thermal concentrator, generally bowl-shaped, used to collect or distribute energy.
Photovoltaic (PV) array
An interconnected system of PV modules that function as a single electricity-producing unit.
Photovoltaic (PV) cell
The smallest semiconductor element within a PV module to convert light into electrical energy. Also called a solar cell.
Photovoltaic (PV) module
The smallest complete environmentally protected assembly of interconnected PV cells. PV modules are generally installed in a frame on a rooftop or on a support mount. The most common type of PV module is a solar panel.
Photovoltaics (PV)
PV solar technology converts solar energy directly into electricity (as opposed to heat).
R
Renewable energy
Energy generated from resources that are naturally replenishing, including geothermal heat, sunlight, wind, rain and tidal action.
S
Satellite power system (SPS)
A concept for providing large amounts of electricity from one or more spaceborne satellites. A very large array of solar cells on each satellite would provide electricity, which would be converted to microwave energy and beamed to a receiving antenna on the ground. There, it would be reconverted into electricity and distributed through a grid.
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 photovoltaics.
Silicon (Si)
A semi-metallic chemical element that makes an excellent semiconductor material for photovoltaic devices. It is commonly found in sand and quartz.
Solar cell
A cell that converts solar energy into electricity. See photovoltaic (PV) cell.
Solar collector
A device that receives solar energy and converts it to useful energy forms. Collectors range from flat plates put on roofs to parabolic dishes, power towers or solar pyramids used in solar power plants.
Solar dish
See parabolic dish.
Solar energy
Electromagnetic energy transmitted from the sun and converted into usable thermal or electrical energy. The amount that reaches the earth is about 420 trillion kilowatt hours, equivalent to one billionth of total solar energy generated.
Solar farm
See solar photovoltaic power station.
Solar home system
The most commonly used solar photovoltaic system to provide small amounts of electricity to rural households in developing countries. A solar home system consists of a solar panel, connected to a battery and charge controller. It usually includes at least one light and a socket to power electrical equipment such as radios, televisions or mobile phone chargers.
Solar panel
A device that collects energy from the sun. See photovoltaic module.
Solar photovoltaic (PV) power station
A power station that uses PV modules to generate utility-scale electricity. Some PV power stations use tracking systems to follow the sun's path across the sky. PV power stations have no fuels costs or emissions.
Solar pond
A body of water that contains highly saline water that absorbs and traps solar energy. Solar ponds can be used to provide heat for industrial or agricultural processes, for heating and cooling buildings, and for generating electricity.
Solar power tower
A solar system that uses a large field of independently adjustable mirrors (heliostats) to focus solar rays on a small point on a fixed tower (receiver). The concentrated energy may be used to directly heat the working fluid of a generator or to heat an intermediary thermal storage medium (such as a molten salt).
Solar thermal
Technology that harnesses solar energy for thermal energy (heat).
T
Thin film cells
Solar cells made of a semiconductor material that is a few microns or less in thickness, such as copper indium diselenide or gallium arsenide, deposited on glass or aluminium. Thin film cells are more inefficient than polycrystalline cells but much cheaper to produce.
Tracking array
A photovoltaic (PV) array that follows the path of the sun to maximise the solar energy falling on the PV surface. They most commonly use a single axis to track the sun from east to west or two axes to point directly at the sun at all times.
W
Watt peak (Wp)
The power output of photovoltaic systems.
Watt (W)
A unit of power equal to one joule per second.
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