Essential technical jargon for solar PV
Are you new to solar power or do you feel like your solar installer might as well be speaking another language when it comes to developing your solar projects? Here are some of the most common terms used in the industry and their meanings.
Irradiance – the power of electromagnetic radiation per unit area expressed in Watts per square metre (W/M2). Solar irradiance calculations are used to estimate the amount of power a system will generate in a given location.
PV (photovoltaic) – a method for generating electricity from solar radiation using semiconductors. Photovoltaic materials include monocrystalline silicon, polycrystalline silicon, amorphous silicon, cadmium telluride and copper indium gallium selenide.
Solar cell – the wafers of photovoltaic material that are assembled to make a module (panel).
Module – the combination of solar cells forms a module or solar panel.
String – strings of modules are connected to form a solar PV system. The string is linked to an inverter.
Inverter – a solar inverter converts direct current (DC) from the PV panels into alternating current (AC) that can be fed into the grid or used by a local network.
Microinverter – an inverter that converts the electricity from a single panel. This allows each panel to operate independently improving the efficiency of the system as well as allowing the detection of a single faulty panel. Microinverters are often a popular choice for smaller sized systems.
String inverter – the most commonly used inverter offers flexibility where there are areas of shading or unusual structural requirements. With an inverter connected to a string there are fewer potential points of failure making string inverters ideal for larger systems.
Central inverter – a large-scale inverter for a large sized solar PV system. Central inverters are cost-effective but are also large in size and limit the system to just a single potential point of failure.
Maximum Power Point Tracking (MPPT) – used in inverters to maximise the efficiency of the solar PV system.
Thin film solar cell (TFSC) – a solar cell made by depositing layers of photovoltaic material on a substrate. TFSC are often lighter weight and perform well in a hot climate, however, the cells are more costly than crystalline cells and usually require a larger area because the cells are less efficient.
Crystalline silicon cell – a solar cell made from mono or polycrystalline silicon. 150mm wafer cells are combined together in a circuit to make a module. These are offer a high efficiency and are the lowest cost form of module available. However, polycrystalline are often blue and can look bulky in small areas. The panels are a standard size, which reduces flexibility.
Distribution Network Operator (DNO) – all grid-connected systems require DNO approval, which must be obtained prior to installation for systems that are over 3.68kWp in size. Connection approval applications can vary in complexity and timescales.
kWp – Kilowatt peak, the maximum possible electricity generation from the installed system under full solar radiation (1,000 watts per square metre).
kWh – Kilowatt hours, the electricity generated (or consumed) every hour. The kWh per kWp generated from a system will vary between locations.
MWp and MWh – Megawatt peak and megawatt hours are equivalent to 1000 kilowatts, which in turn are equivalent to 1000 Watts.
Ballasted mount – on a flat roof it is possible to fit solar panels on a ballasted mount that angles the panels toward the sun. This increases the yield and system efficiency whilst allowing space between modules to minimise shading.
MCS – Microgeneration Certification Scheme is an industry standard for renewable energy installers supported by the Department of Energy and Climate Change. It is also an eligibility requirement for government subsidies like the Feed in Tariff.
Feed in Tariff (FiT) – a government subsidy that pays owners of renewable energy systems for every kWh of electricity they generate. The rate is variable according to the size of the system and once approved is guaranteed for 20 years and RPI linked. The Feed in Tariff is only available for systems that are less than 5MWp in size, although this is a mammoth sized system!
ROC (renewable obligation certificate) – a trading scheme for renewable energy that enables electricity suppliers to meet their renewables targets under the Renewables Obligation. The scheme is generally more suited to large-scale systems upward of 250kWp and only systems that are greater than 50kWp are eligible. It allows system owners to obtain a certain number of ROCs for every MWh of electricity produced. These ROCs can then be sold to the highest bidder.
Contracts for Difference (CfDs) – a new trading scheme for large systems (+5MW) that will soon operate alongside the Feed in Tariff and ROCs systems. Unlike the ROCs scheme the CfD scheme will include a minimum strike price for every MWh of electricity. This has initially been agreed at £125 / MWh for solar electricity.