Periodic support payments for accredited RHI installations in simple systems in respect of which an application for accreditation was made before 24th September 2013
64.—(1) This regulation applies to an accredited RHI installation in respect of which an application for accreditation was made before 24th September 2013 and which—
(a)is generating and supplying heat solely for one or more eligible purposes used in one building;
(b)does not deliver heat by steam; and
(c)is not a CHP system.
(2) Subject to regulations 71 and 72, periodic support payments in respect of each quarterly period must be calculated in accordance with one of the following formulae, as applicable—
(b)where the installation is generating heat from the combustion of biogas, 
where—
A is the tariff determined in accordance with regulation 59;
B is the heat in kWhth generated by the installation during the relevant quarterly period; and
C is—
the heat in kWhth delivered in the relevant quarterly period to the biogas production plant which produced the biogas which is combusted (other than heat contained in any feedstock used to produce that biogas); or
such proportion (as may be chosen by the participant and agreed by the Authority) of that heat, provided that the proportion is no less than—
where—
x is the heat produced by that biogas which is used for eligible purposes; and
y is the energy content of all the biogas produced by that biogas production plant.