Suppliers are obliged to fund the Feed In Tariff (FIT) scheme, which is administered by Ofgem, but Colorado Energy, Igloo Energy Supply, Neon Reef, Whoop Energy and Symbio Energy have so far failed to do so for this year.
They owe a collective £765,000 to the scheme, with Igloo alone responsible for nearly half of the total.
The FIT scheme was first introduced in 2010 as a way to encourage property managers and organisations to generate their own renewable electricity using technology such as solar panels or wind turbines, and feeds any surplus back to the grid.
The Government has estimated that FITs support small-scale low-carbon generation that would cost £8.6bn up to 2030 and produce monetised carbon savings worth £0.42bn.
The scheme was closed to new entrants in 2019, but those already part of it are still being funded by the levy on energy firms.
“If the suppliers fail to comply with the order made against them, Ofgem may take further enforcement...