The assertion made by the CEPA consultants commissioned by DETI was that a tiering system was not required in Northern Ireland because the cost of wood pellets - the fuel used in biomass boilers - was higher than the subsidy on offer through the RHI scheme.

If a boiler owner had to pay more for the fuel than they were receiving in subsidies there would be no burn-to-earn incentive.

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CEPA's basis for that suggestion will be a key focus for the inquiry, says Mr Scoffield.

But crucially, he says, when CEPA produced its second report for DETI, the subsidy on offer actually was higher than the cost of the fuel.