Eco expert Nigel Griffiths explores the pros and cons of these two routes to harnessing the sun’s energy, to help you decide which best fits your project goals

For the Education House (www.buildit.co.uk/ ourhouse), the Build It team selected an Easy Roof integrated mounting system from IRFTS (en.irfts.com)

There are two key solar technologies for self builders and renovators to consider. PV (photovoltaic) panels harness light from the sun in order to generate electricity. Solar thermal, meanwhile, uses the sun’s warmth to provide hot water for bathing, showering etc. Both options have their merits – but what if you have a limited budget, or limited roof space?

If you’re facing that situation, this article explores how you might choose between the two and the factors that could impact on your decision. The box-outs in this article give a quick insight into how each system works. If you want more in-depth advice on designing and installing them, check out my guides at www.self-build. co.uk/solar-pvand www.selfbuild.co.uk/solar-thermal.

Technical considerations

Both PV and solar thermal require an unobstructed southerly aspect, usually an area of roof space, for the collectors to be mounted. Based on typical sizes of systems installed for a family of four, a PV array requires over 25m2 of roof space, while a solar thermal system requires only 4m .

Inside the house, solar thermal generally requires a stored hot water system (as very few combi boilers can accept pre-heated water). Many self builders create larger houses with more than one shower installed, and a combi won’t serve this effectively, so stored water is normally planned in any case. The system will work best where the collectors are close to the cylinder, as this will minimise pipe runs and heat losses. So think carefully about its location in relation to the available roof space and the bathrooms.