Which is the better investment – solar PV or solar thermal?

Solar power has become an affordable, cost-effective way to produce your own energy, and there are two obvious options for your home. One is solar PV, where the sun’s energy is turned into electricity. The other is solar thermal, where the heat from the sun is used to directly heat water, which is then used to heat your hot water cylinder.

Over half a million homes in the UK now have solar PV, but thousands of homes also have solar thermal too – which has seen a surge in popularity since the RHI was launched last year.  So in this blog we want to consider which is the better investment, if you had to buy one of these systems, which system should you go for – solar PV or a solar thermal system – read on to find out our thoughts!

Cylinder for solar thermal

Solar PV takes up a lot of space on the roof. Not every house will have a suitable roof to fit a reasonably-sized system, whereas solar thermal is much more compact and even the smallest roof can potentially accommodate a solar thermal system, as long as it is sunny enough!

Solar thermal is an RHI qualifying measure

Solar thermal is an RHI qualifying measure

Whilst solar PV generally takes up more space on the roof, solar thermal requires more space in the house. You will always need to have a hot water cylinder for solar thermal – which is a bulky annoyance in your home, unless you have a good spot to put it in. Of course, if you already have a cylinder, this might not be an issue for you, but remember if you need to add a cylinder it will seriously increase the cost of the installation.

Solar PV can create hot water too

Whilst solar thermal is limited to heating your hot water, PV can provide you with electricity and hot water. All you need is to use a solar optimiser to divert excess electricity to your water cylinder.

So in a way PV could be considered as more flexible.

Solar thermal better in cloudy weather

It is a myth that solar technology doesn’t work in cloudy weather, but it is true that performance dips considerably. PV is much more sensitive to the sunlight and as such, solar thermal will provide more return in cloudy weather than PV does.

Solar thermal could leak – Solar PV can’t!

It may seem obvious, but because solar thermal heats water directly, it needs lots of pipes running from the roof into the house. Now hopefully, if it has been installed well, you shouldn’t have any leaks, but there is always that risk with a wet system like solar thermal. Solar PV is a dry system, so no danger of any ‘accidents’!


On the other hand solar thermal has a really important advantage – you can store the energy you produce – you don’t need to use it as it is produced. Solar PV will need a power diverter to store the energy produced in your cylinder, and that means an extra cost of £300 or so. Otherwise you need to use the electricity as it is generated.

Solar thermal gets the RHI…

The RHI is relatively new, but pays you for generating heat from solar thermal, amongst other technologies.

…Solar PV gets the Feed in Tariff

The Feed in Tariff is paid for generation, with an additional payment for exporting energy to the grid. Find current rates here.

Bigger savings with PV

Whilst solar thermal certainly has its advantages, you will see bigger savings on your energy bills with PV. A typical solar system could save you £100-200 a year, whereas a 3kW PV system is likely to save you £300 or more.

Cost of installation

It is not possible to say one is cheaper than the other, as it depends on the size of the system you are installing. A solar thermal system could set you back £4,000 on a typical install, whilst a PV system will cost around £1,750 per kW. Each kW is the equivalent of around 4 panels.

Which is better?

It really does depend on your needs. There are plenty of advantages and disadvantages to both. If you go purely on payback, we believe PV pays back quicker. Solar PV may well be more practical for smaller properties however, and it tends to have a lower base cost. Just make sure you take the time to weigh up which system is more practical for you.

Interested in solar PV, or solar thermal? Get in touch below!

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