How to buy solar panels Solar panel jargon

Active Solar panel

'Active' solar power involves using a solar panel to capture the sun's energy

Buying solar panels can be confusing if you don't know what all the jargon means. Use our guide to help you understand solar PV and solar water heating terms.

Amorphous
A type of PV solar cell. Unlike multicrystalline and monocrystalline cells (see below), amorphous panels are not made from interconnected solar cells made from expensive crystalline silicon.  Instead, a very thin layer of silicon is sprayed on to a backing material to make solar roof tiles. As the silicon is much thinner than the silicon wafers in a typical crystalline solar cell, material costs are greatly reduced.
Active solar
Using a collector, e.g. solar panel, to capture the sun's energy and use it to heat water or convert it to electricity.
Drain-back system
A type of solar water heating system where the water inside the solar panel drains into a small back bottle when the pump switches off. This protects the system against damage caused by boiling and freezing, without the use of antifreeze.
Evacuated tubes
A type of solar water-heating panel. Evacuated glass tubes collect the sun's energy and heat water running through a container at the top of the tubes.
Feed-in tariff (FIT)
The Feed-in tariff (FIT) scheme allows you to receive payments in exchange for owning a solar photovoltaic system. It also pays you for excess electricity sold back to the national grid. For a detailed guide to the FIT, check our guide to the feed-in tariff.
'Free solar' or 'rent-a-roof' schemes
Schemes where companies pay for the cost of installing and maintaining solar panels on your roof, and then generally take all of your Feed-in tariff income. Householders still benefit from the electricity produced by the panels.
kWp
KiloWatt peak. The unit of measurement for the maximum amount of power your solar system can generate. On an overcast day, your system will produce less.
MCS
Microgeneration Certification Scheme. Certification scheme for products and installers of microgeneration technologies, including solar PV. To qualify for the Feed-in tariff, you must use MCS-certified products and installers.
Microgeneration
The term 'microgeneration' is used to refer to low-capacity electricity generation equipment, which covers generation of electricity up to 50 kW. Domestic-scale microgeneration embraces a range of technologies including small scale photovoltaic (PV) arrays, micro-hydro generation, small wind generators and domestic scale Combined Heat and Power (CHP) equipment.
Monocrystalline silicon cells
The most efficient and expensive PV cell. Cut from single crystals of silicon, this system can harness around 15% of the sun's energy that shines on it.
Multicrystalline silicon cells
PV system made from silicon cut into wafers. It's slightly less efficient than monocrystalline cells, but also slightly cheaper.
Passive solar
Capturing the sun's energy without a panel or collector, eg through large south-facing windows, and minimising heat loss through insulation.
Photovoltaic, PV
PV cells are thin layers of semi-conducting material (usually silicon). Electrical charges are generated when the silicon is exposed to light, which can be conducted away as direct current. Multiple cells are connected together (usually behind glass) to form a panel.
Pressurised system
Water is pumped through the solar panel and heated. This heated water flows through a heat exchanger, warming the water stored in your hot water cylinder. These systems typically use antifreeze.
REAL
Renewable Energy Assurance Limited. Its Consumer Code is the one installers of microgeneration technologies would have signed up to to get MCS certified. The Consumer Code sets out clear standards of consumer service, before, during and after a contract is signed.
Renewable Heat Incentive (RHI)
A financial support scheme that will be pay householders for generating heat, similar to the Feed-in tariff (which pays people for generating electricity). The RHI is due to be introduced in 2013. In the meantime RHI premium payments, which offer cash to people to help towards the cost of installing certainly heat-generating technologies, are available.
Solar tiles
Solar tiles use the same technology as photovoltaic cells, but are smaller and narrower than PV panels and look like roof tiles.
Solar water heating
Water is pumped through a solar panel and heated by solar energy. The heated water then flows through a heat exchanger, warming the water in your hot water cylinder.

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