Solar water heating on trial

The market for solar water heating in the UK grew by over 18 per cent last year, to 73,640 kWth of installed capacity - both large and small installations were up.

This is in sharp contrast with a 13.1 per cent decrease across the rest of Europe as a result of the economic downturn.

It seems that, in the UK, the economy actually helped to fuel this area of growth because fuel prices are high and rising, and the proposed introduction of the Renewable Heat Incentive (RHI) acted as a stimulus.

However, the performance of solar thermal systems has been inconsistent leaving many end users disappointed.

Therefore, the Energy Saving Trust decided to carry out a comprehensive field trial to investigate where the problems lay and produce clear guidance and advice.

At the end of the trial, their main finding was that solar water heating systems can work very well in the UK when "installed properly and controlled adequately by the user".

In some cases, researchers found that the system was providing 60 per cent of a household’s hot water. However, by the same token, the trial also found examples where systems were not properly configured or used, and where the contribution from solar was as low as 9 per cent.

The average across all systems trialled was 39 per cent.

The EST called for better instruction to users about how to use their systems and suggested that the industry's installation standards be reviewed.

Householders are, in the main, happy with their solar water heating systems, according to the trial. 84 per cent were “satisfied” with their system, and over 50 per cent were “very satisfied”.

In the field trial, there was little difference between the total solar energy yield of those installations that used flat-plate solar collectors and those that used evacuated-tube solar collectors.

The trial found that the way householders use their solar water heating system is critical in achieving the best results. Better advice to users on how to control their systems (in terms of volume of hot water use, timing of back-up heating and hot water use, and temperatures required) is essential, the EST concluded.

Where mains electricity provided power to the pumps and controllers of systems in the trial, the amount of energy used was generally small compared with the overall heat delivered.

However, in a number of cases, the researchers found that insufficient insulation was installed on some hotwater storage cylinders and pipes. This significantly reduced the proportion of hot water provided by the system.

Typical savings from a well-installed and properly used system are £55/year when replacing gas and £80/year when replacing electric immersion heating.