The long-awaited renewable energy feed-in tariff scheme will pay households 40c a kilowatt hour for electricity exported into the power grid.

Details of the scheme, the funding for which was announced in the state budget last week, were unveiled by Energy Minister Peter Collier today.

However, they were immediately slammed as “ludicrous” by the Greens.

The payments will be made to householders with new and existing solar, wind and micro-hydro systems feeding into the South West Interconnected System and regional power grids.

The systems, which include tenanted properties, must be owned by the homeowner. Payments would be made for 10 years.

Synergy customers would be allowed systems up to 5kW, while that limit doubled for those covered by regional retailer Horizon.

Mr Collier said payments would be made from August, with registrations accepted from July.

However, the scheme has been widely criticised by conservation groups, who say that the net feed-in tariff, as opposed to gross feed-in, would mean little in the way of actual payments.

With a net scheme, only excess power above that required by a household is paid for, while with a gross scheme all power generated is paid for, with the householder still required to pay their full power bill.

Mr Collier said the tariff would be in addition to that paid under the existing renewable energy buyback scheme, so householders could receive at least 47c a kWh.

“This provides a genuine incentive for home owners to install renewable energy systems, which not only has a positive impact on the environment but it will also help householders manage their electricity bills,” he said.

A feasibility study was also being undertaken into the potential for a similar scheme for businesses.

But Greens MLC Robin Chapple said the scheme was “meaningless” for the “well-meaning people” who would consider installing small-scale systems.

“The Minister today has made ludicrous claims about the payback period under his scheme, but unless householders have more solar panels than they need the payback period is simple – never,” he said.

WA Sustainable Energy Association chief executive Ray Wills said the scheme would allow WA “to catch the pack” as all states tried to ramp up renewable energy use.