Measuring heat output
The RHI tariffs are paid based on the heat output of the renewable energy system
There are two different approaches that can be used to measure the heat output of systems: metering (i.e. measuring) and 'deeming' (i.e. estimating the likely heat output).
The current proposals for non-residential systems require heat metering. It is possible that the future proposals for domestic systems will allow deeming, depending on the size of the system.
For phase 1 of the scheme all systems will have to meter the heat they produce and deliver. All payments will be made by calculating the metered number of kWh multiplied by the tariff per kWh.
Some systems are designated as 'complex metering'. This includes installations where any of the following apply:
- Heat is delivered by steam
- Combined heat and power systems
- Heat used in more than one building
- Ineligible heat uses on heating system
Similar requirements apply for systems above 1MWth.
These systems are more demanding in terms of the metering requirements, including the need for an Independent Report on Metering Arrangements.
Metering injected biomethane
In the original proposals it was suggested that for small domestic systems the levels of payment would be based on a 'deemed' output based on what the installed system would be expected to deliver if the property were well insulated.
If this approach were adopted in Phase 2, the RHI would define what 'well insulated' means (the consultation had proposed levels for minimum energy efficiency). The building's energy use woukld be assessed through the Standard Assessment Procedure (SAP)28 used for the energy rating of buildings. This identifies the appropriate heat demand of the building based on the assumption that the minimum energy efficiency measures will have been taken up alongside the renewable heat installation.
We don't know if this approach will still be used for domestic installations.