Depending configuration of system and the back up fuel you use (gas, oil, electricity) to heat water, a typical solar thermal system will save between 2000 and 3000kWh of energy a year. The calculation of this is complex taking into account the efficiency of the panels, hot water usage, and the seasonal efficiency of the back up heating source.
Further savings are generated through the simple act of fitting a new hot water cylinder. These are far better insulated than older ones, so the standing loss (the rate at which they cool down) is far less.
New performance calculation methods taking these factors into account will be published soon by the Microgeneration Certification Scheme.
The detail of the domestic Renewable Heat Incentive will be published in 2013 advance of its launch in 2014. Installations undertaken before launch will be eligible for the RHI.
In advance of the RHI, The Renewable Heat Premium Payment provides £600.00 towards the cost of your system. This is an advance payment from the Renewable Heat Incentive Scheme and will be deducted from it after its launch in 2014. All new systems installed under the RHPP will be eligible for the RHI.
Currently there are interest free loans offered by the Energy Savings Trust in Scotland which can be used towards the cost of installation