Selected Solar Glossary
AC:
Stands for ‘alternating current’ - an electrical current in which the polarity is constantly alternating. The UK power network has AC with a frequency of 50 Hz. AC is generated in a solar plant using an inverter.
Anti-reflective layer:
A layer only a few millionths of a millimeter thick that consists of silicon nitride (SiN) and minimises reflection losses. In solar cells, the anti-reflective layer increases the light yield and the efficiency (light reflected from the surface of a solar cell can’t be absorbed, and so doesn’t contribute to the generation of electricity).
Carbon dioxide:
CO2 - a colourless, odourless incombustible gas formed during respiration, combustion and organic decomposition. It makes up about 0.3 % of the air and is generated when coal, oil and gas (non-renewable resources) are burned. In the last two centuries, man has burned increasing volumes of these fossil fuels, so increasing the concentration of CO2 in the atmosphere and creating a greenhouse effect in which average temperatures increase.
Carbon footprint
Commonly used to describe the total set/amount of greenhouse gas emissions that are caused by or result from an organisation and its operations, a building, event, product, individual, etc. To simplify reporting, it is often expressed in terms of the amount of carbon dioxide (or its equivalent in other greenhouse gases) that has been or will be emitted.
Climate change:
Climate change can be defined as any change in global temperatures and precipitation and/or other weather patterns over time due to natural variability or to human activity; often commonly used as an umbrella term for (sometime controversial) theories and/or evidence around global warming. Global climate change is being effected by the accumulation of greenhouse gases in the lower atmosphere. The concentration of these gases is increasing, mainly due to human activities, like the combustion of fossil fuels (which release carbon dioxide) and deforestation (forests remove carbon from the atmosphere). The atmospheric concentration of CO2, the main greenhouse gas, has increased by 30% since preindustrial times.
Crystalline silicon / Crystalline silicon modules:
Polycrystalline silicon is a key component of solar panel construction; most solar modules are currently produced from silicon PV cells; these are typically categorised into either monocrystalline or multicrystalline modules. Growth of the photovoltaic solar industry is limited by the supply of the polysilicon material. In the natural world, silicon occurs only as silicon dioxide or in silicate minerals such as sand (i.e. a contaminated state). For photovoltaics (solar energy usage) it must be processed into crystalline silicon with a purity of over 99.99 %.
Efficiency:
The efficiency of a solar cell or module (η pronounced ‘eta’) is defined as the ratio between the power output (clean electricity produced) and the power input (the light absorbed from the sun) – it is an indicator of how well the cell is converting light into power.
Greenhouse effect:
The phenomenon by which the Earth’s atmosphere traps solar radiation; caused by the presence in our atmosphere of gases like carbon dioxide, water vapour and methane that allow incoming sunlight to pass through but absorb heat radiated back from the Earth's surface. The atmosphere heats up as a result, with knock-on effects.
Grid:
An interconnected system for the distribution of electricity and/or electromagnetic signals over a wide area, especially a network of high-tension cables and power stations.
Inverter:
Photovoltaic modules generate DC (direct current). An inverter is used as part of the solar electricity system to transform DC into AC (alternating current), suitable for the UK power network; this means the cleaner energy generated by solar PV can be used by consumers at 230v of alternating voltage, or the electricity can be fed in to the public power network. Large photovoltaic systems use central inverters, small photovoltaic systems use string inverters.
Kilowatt (kW):
Unit of power equal to 1,000 watts (equivalent to around 1.34 horsepower). The electrical output produced by a solar plant is measured in kilowatts.
Kilowatt peak (kWp):
This is a measure of power output, most often used in relation to photovoltaic solar energy device; the value refers to the nominal capacity of a photovoltaic cell or a photovoltaic module and is measured under standardised test conditions that make a direct comparison of the output of different modules possible.
Kilowatt hour (kWh):
A unit of electric energy equal to the work done by one kilowatt acting for one hour; energy produced by a solar plant is typically shown by the amount of electricity in watts that is produced per hour.
Megawatt (MW):
A unit of power: one million watts. 1 megawatt = 1,000 kilowatts or 1,000,000 watts.
Megawatt Peak (MWp):
1 megawatt peak equals 1,000 kilowatts peak.
Photons:
Light energy from the sun arrives as photons. Solar panels use photons to generate electricity through the photovoltaic effect (the photo-electric effect).
Photovoltaics:
The conversion of radiation energy, in particular solar energy, into electrical energy. Solar PV cells convert energy from the sun into clean power. The photovoltaic effect refers to photons of light knocking electrons into a higher state of energy to create the electricity.
Photovoltaic array:
Because a single photovoltaic module can only produce a limited amount of power, many installations contain several modules or panels; this is known as a photovoltaic array.
Photovoltaic module:
A PV module or photovoltaic panel is a packaged inter-connected assembly of photovoltaic cells, also known as solar cells. More commonly known as a solar panel. PV modules are normally attached inside a frame on the roof or to a supporting frame.
Photovoltaic installation:
This typically includes an array of photovoltaic modules or panels, an inverter, batteries and interconnection wiring.
Thin film technology/optics:
A microscopically thin layer of material deposited onto a metal, ceramic, semiconductor or plastic base. Usually less than one micron thick, thin films can be conductive or dielectric (non-conductive) and are used in many applications. Thin films of photovoltaic material using silicon, cadmium telluride and other elements are used to make solar panels.
Watt:
International System unit of power equal to one joule per second, recognised in 1889. Unit of the energy output of photovoltaic plants - used to measure its performance.
