The Department for Energy and Climate Change say on their website that they intend to introduce the RHI in April 2011. As with the FIT for electricity generating renewable technologies the tariff awarded and the length of time that the tariff is guaranteed for will vary for each technology and will be reduced for medium and large installations.
The consultation on the RHI ran from early February until late April this year and the consultation document can be found at the link at the bottom of this message. The information you are likely to want to know is the costs and lifetimes for domestic scale technologies (page 46) which currently looks like this:
Solid biomass (<45kW) = 9p/kWh for 15 years
Ground Source Heat Pump (<45kW) = 7p/kWh for 23 years
Air Source Heat Pump (<45kW) = 7.5p/kWh for 18 years
Solar thermal (<20kW) = 18p/kWh for 20 years
I hope this helps.
Chris Hunt (Ham and Petersham SolariHam)
www.decc.gov.uk/assets/decc/Consultations/RHI/1_20100204094844_e_@@_ConsultationonRenewableHeatIncentive.pdf