Solar Thermal FAQ


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How much does a solar thermal system cost?

A typical domestic solar thermal system will cost between £3000 for a small to medium sized property, up to £5000 for a larger property or if your hot water cylinder requires replacement. These costs are guide only and are subject to a solar survey.

What is the life expectancy of a solar thermal system?

Generally a solar thermal system has a 20 years although the solar pump will usually require replacement at least once within this period.

Do I require planning permission?

Generally no. As with solar PV, Solar thermal systems are deemed permitted development if the solar panels project <200mm above the roof surface and do not rise above the ridgeline. You may need to gain permission if there are special conditions in place such as the property; is listed / in an area of outstanding natural beauty / in a conservation area. In addition, if you are aware of bats in the area a “bat survey” will be required.

How long does a solar hot water system take to install?

Domestic systems range from 1-3 days depending on where the solar collectors are to be situated and what other equipment being installed, such as hot water stores. A commercial system can take longer dependent on access arrangements, number of collectors and connection into the hot water system. In all cases GenFIT will give you a guide on installation time with your quotation.

What maintenance is required?

Solar thermal systems that contain antifreeze generally require maintenance every 2-3 years, although some components such as an unvented hot water cylinder (if installed) should be inspected annually. Systems without antifreeze, often referred to as “direct” systems have lower maintenance requirements, although in hard water areas it is essential – and prudent whatever hot/solar water system you have – to control water hardness with a softener, or other suitable form of control.

What is back up heating, and legionella control?

Back up heating is the regime of using your existing fossil fuel heater, such as gas boiler or immersion heater, to top up the hot water cylinder temperature to 60C if the solar thermal system has not reached it. This should be timed to ensure the whole cylinder reaches 60C for at least 1 hour each day (ideally to start after sunset, and stop after final hot water usage in the evening). GenFIT commercial solar thermal systems are designed to mitigate the back up heating requirement other than in the hot water cylinder. We install a dedicated solar thermal store, which preheats to a fossil fuel heated hot water cylinder or water heater. Thermal stores ensure there are very low volumes of “potable” (that which goes to the taps) stored water, which are regularly swept and temperatures are “topped” up by the back up heating source downstream before going to the point of use.

Flat plate or evacuated tube collectors?

Both perform well when sized correctly. The main choice between them is down to aesthetics, space and cost: Flat plates can be mounted on or in roofs and tend to look slightly better, whereas evacuated tubes inhabit less area but are more expensive. We can go through the Pro’s and Con’s of each system so you can decide which best suits your project.

What is the Renewable Heat Incentive (RHI)?

The RHI is similar to the feed in tariff scheme where qualifying installations benefit from payments for the heat energy generated by a renewable heat source. At present the RHI is only available for commercial systems >45kW, and pays 8.5p/kWh of useful energy generated by a solar thermal or biomass system. All energy must be metered and payments are made quarterly.

What is the Renewable Heat Premium Payment (RHPP)?

The RHPP is an interim grant arrangement available to solar thermal or biomass systems installed up until the 31st March 2012. To qualify properties must meet minimum energy efficiency requirements, and the system must have an MCS certificate. The RHPP will be replaced by the domestic RHI towards the end of 2012. To date the government are yet to announce whether any transition arrangements will be put in place in the interim.

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