After months of deliberation, the UK government has announced a range of illustrative figures for feed-in tariffs (FITs), which it's calling a Clean Energy Cashback scheme. FITs are fixed payments made to the owners of small generating stations for the electricity that they export to the grid. Micro-generators need high payments to justify their expensive investment in buying and installing green generation.

The proposed levels of FIT vary by the type of technology. The principal ones covered are biomass combustion (burning wood to generate electric power), hydro, solar photovoltaics, and wind turbines. Of these, the most appealing are likely to be wind and PV. If my estimates in the following paragraphs are correct, the government's proposal for payments to rooftop PV are too low to generate much new investment. On the other hand, the payments for rural wind are good enough to make decent returns. If the figures survive unchanged through (yet another) consultation process, we should see thousands of small wind turbines in windy British fields.

The proposal is for a FIT of 36.5 pence per kilowatt hour for a domestic rooftop system for installations in financial year 2010/2011. A typical UK installation is about '2 kilowatts peak', a figure for the maximum output in the middle of the day in mid-summer. Such an installation will generate about 1,800 kilowatt hours (kWh) a year in a sunny location in Devon or Cornwall on a south-facing roof. No more than half this electricity would be fed into the grid, the rest would be used in the home.