Controversial changes introduced to the FiT scheme mean that, from today, households and small businesses signing up will see earnings from energy they produce cut in half.
The letter urges the coalition government to "intervene and secure sufficient budget (or budget flexibility) to sustain the companies and jobs you have created in the solar power sector until the end of this Parliament".
The letter said: "Yesterday, the tariff levels for solar power were cut 50 per cent at six weeks’ notice and before the close of any consultation. Your ministers have signed off proposals which they anticipate could see the sector reduced to a tenth of its current size, at the cost of tens of thousands of jobs."
A survey published last week by the Renewable Energy Association and the Solar Trade Association claimed that 42 per cent of jobs in the solar industry are expected to be lost as a result of the changes to the tariff scheme.
The letter said: "Allowing the solar sector to collapse will waste both public investment to date and the opportunity to strengthen the UK’s position in this vital global industry."
Gaynor Hartnell, chief executive of the Renewable Energy Association, said: "We are calling on Cameron and Clegg to intervene to ensure a future for solar power beyond 1 April 2012.
"The cost of solar is falling so dramatically that in about five years’ time it should cost no more to generate one’s own solar power than to buy it from an electricity supply company. To get there we need commitment and stability, not boom and bust."
Announcing the cuts in October, energy minister Greg Barker said reduced rates for solar power under the FiT scheme, which guarantees a fixed price for each unit of electricity fed into the national grid from green energy equipment, are justified by the need to keep costs under control.
Under the proposals, FiT rates for the smallest schemes – those with a capacity of less than 4kW – would be more than halved, from 43.3 to 21p per kilowatt-hour. Larger devices up to 250kW would also see rates reduced.