The Renewable Heat Incentive (RHI) is a government incentive program which entitles users of renewable technology, which is used to heat their house, to a claim payments back over time.
Therefore when using solar thermal to heat water (unluckily not counting swimming pools) you can receive money back over time. The rate is 19p/KWH produced. The actual figure of energy produced which is used is based on an estimate and these payments are made over a period of seven years and the rates the same for that entire period.
This could mean that should you use a 6 square metre installation producing 2811 kWH per year you would receive £3778 as a result of RHI.