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FAQs - Renewable Energy

What is a solar photovoltaic (PV) system?

A Photovoltaic system converts the energy in light into electrical energy; this electricity is then used to power anything that would normally have been powered by the mains.

How much space does it take up?

Solar panels produce around 150w (watts) per m2- domestic systems range from around 1.5Kw to 4Kw (1Kw = 1000w) so a medium size domestic system of 2.5Kw would require around 17m2 of roof space. The solar panels are kept away from the edges of the roof by around 300mm as a minimum.

How much electricity will my system produce?

Typically a well designed system will produce about 800Kwh of electricity for every Kwp (Kilowatt of solar panel) per year. 1Kwh (kilowatt hour) is the amount of electricity required to keep a 100w bulb on for 10 hours or to run an electric kettle for 20 minutes.

How much will it cost?

Solar PV will normally cost about £3,750-£4,250 per Kw of solar panels installed, the cost of a system depends on the panels used and how they are to be installed. Generally a larger system will cost less per Kw than a small system. So a 2.5Kw solar PV will cost £8,250-£9,350. Currently a 2kW PV system will cost £12000

How long will it take to pay for itself?

A PV system should pay for itself in under 10 years. You can use the link to the Energy Saving Trust web site for a payback calculator.

What is the difference between PV and solar thermal?

Solar thermal is the system that uses the energy from the sun to heat water, this is done using solar thermal collectors normally mounted on the roof, the water flowing through the collectors heats the water in your hot water cylinder in the same way the boiler heats the cylinder.

What are the different types of PV panel available?

There are three main types of panel commonly available in the UK.

  1. Mono crystalline, this is made up of single crystalline silicone, almost black in colour.
  2. Polycrystalline, this is made up of mulitcrystaline silicone and have a marbled appearance.
  3. Amorphous or thin film, these are made using a thinner layer of silicone and usually have a brownish appearance.

Monocrystaline has the highest efficiency at 14-18% but is adversely affected by shading. Poly crystalline is 10-12% efficient but is less affected by limited shading. Amorphous panels are normally 6-8% efficient but tend to perform better in lower light conditions and in shading; they are cheaper but are about 50% bigger for the same output.

There are also some panels that are a hybrid monocrystaline/amorphous. These panels offer a higher output and efficiency along with better performance across the spectrum of light. They are however more expensive than the other panel types.

Where can the panels be installed?

Normally they are mounted onto an existing roof, but they can be mounted on a frame fixed to a vertical wall, on a ground mounting frame or pole mounted.

Do I need Planning Permission?

No; not normally for a roof a mounted system. It will require planning consent if it is on a listed building, in a conservation area, in an AONB, national park, ground mounted or over 4Kw. It is prudent to check with the local planning authority in all cases.

A guide to what requires planning permission can be found at

What is the life expectancy of a PV system?

The PV panels normally have a performance guarantee of 90% after 12 years and 80% after 25 years. The specific terms of the guarantee varies between manufacturers. The inverter is the other major component of the system and they usually have extendable guarantees available often up to 25 years.

Will having a PV system protect me from power cuts?

No- under the current regulations if a domestic system is connected to the mains then it must shut down when there is no mains power. This is to ensure that power is not feed back into the mains when it may have been cut off for maintenance or emergency repair. Systems are available for larger installations that enable the PV to be connected when the mains is cut off. It is a matter of time before these systems are domestically available and the regulations are amended to allow them.

Does PV work in the winter?

Yes. PV will work all year round; there will be a reduced yield during the winter due to shorter days and generally more overcast conditions. Although the panels will perform very well on cold clear days.

Can I add extra panels to my system later?

Yes, although it will probably mean that an additional or new inverter is required as in a well designed system the inverter will be sized to run at close to its full capacity. This is because the inverter is more efficient when running at close to full power.

What is the biggest PV system I can have?

There is no practical limit on the size of system, only the space available to install the system. The main constraint is that systems under 4Kw are eligible for the highest FIT and the connection process is simple. Systems over 4Kw receive less FIT and the application process for grid connection can be significantly more complicated.