Solar panel heating results revealedBad installation shown to cut savings in EST trial

13 October 2011

The Energy Saving Trust (EST) today reveals results of a long-running trial of 88 solar hot water systems, also known as solar thermal systems.

Solar thermal panels use the sun to heat water in homes, rather than generate power, as solar photovoltaic (PV) panels do.

The trial shows that proper installation, householders' behaviour and insulation of the pipes and water tank are all key in improving the performance of a solar hot water system, so you can save the most on your heating bills.

Solar thermal savings

The EST found that solar hot water systems normally provide 39 per cent of the hot water a home needs. Which? estimates that this equates to about £60-£90 savings on energy bills per year.

But the trials also found that if the system is well installed and used, it could provide 60%. But if not, it could provide as little as 9%.

Which? energy expert Dr Sylvia Baron says: 'The trials highlight how important it is that householders know how to make the best out of their system by insulating their tank and pipes, getting the right system size and setting up pumps and timers correctly.'

Solar payback time

With solar thermal systems costing about £3,000-£5,000, and savings of only £60-£90 a year, payback time is still an issue and might explain why there aren’t many systems installed in the UK. This is because there is currently very little financial support towards these technologies, unlike with solar PV systems. Under the government's feed-in tariff scheme, a solar PV system, which costs about £12,000, will pay for itself in about 10 years. 

Solar heating systems however qualify for the Renewable Heat Premium Payment scheme which runs until 31st March 2012. This provides a grant of £300 towards the cost of installing solar thermal. More detail are available from the Energy Saving Trust website.

Sylvia Baron says: 'Unless you want to install a solar hot water system for ecological reason, we would advise to wait until the details of the Renewable Heat Incentive (RHI) are announced to see what the level of the financial incentive will be for solar hot water systems and from which date you might be eligible.'

Which? will publish these details as soon as they become available. To find out more about the RHI, see our guide to RHI explained.

Solar thermal customer satisfaction

The EST found that, generally, solar thermal systems worked well and 84% of the people who took part in the trial were either fairly or very happy with their system.

Maximising benefits

One of the key finding of the report is that how the system is installed in the first place is key and also how it is used by the householders. System performances can be improved if the pumps and timers are set correctly. Also it found that in some houses, the lack of insulation on the hot water tank and the pipes led to lower performances because of losses.

Solar panels live Q&A

On 6 October, Which? ran a live Q&A on solar panels. You can replay the event. And there is more information about solar panels in Which? guide to solar panels.