Onshore wind farms will continue to play "a big role", Danny Alexander insisted as he denied that reducing Government subsidies was a response to Tory opposition to the controversial turbines.
The Liberal Democrat Chief Secretary to the Treasury said state help for onshore wind and solar was being reduced "slightly" in favour of offshore wind.
The latest "strike prices" for renewable energy - set well above the current market value to encourage investment - are due to be announced to the House of Commons later.
They are expected to be lower for onshore wind than suggested in a consultation earlier this year.
Rural wind farms have been a source of coalition tension, with many senior Conservatives staunchly opposed to the turbines, which Lib Dems say are needed to meet environmental objectives.
It is feared by Tory activists to be an issue on which they are losing support to the UK Independence Party, which is highly critical of the subsidies.
Mr Alexander said the switch in favour of offshore wind was based on "value for money" and, on Government estimates, could open the way for an extra 10 gigawatts of energy by 2020.
"Within the total envelope of money that we are able to make available to energy suppliers, we have looked in detail at how much it costs to do offshore windfarms and onshore windfarms and big solar schemes and we are reducing slightly the subsidy we are providing to onshore wind and to these big solar schemes because we think that's the best way to get value for money for the electricity consumer," he told BBC Radio 4's Today.
Asked if it was a politically-inspired move, he said: "No, it's not. Onshore wind is going to continue to play a big role.
"I believe passionately in meeting this country's obligations to tackle climate change and meeting our environmental commitments.
"But we should be doing so in the most cost-effective way we can and we should also be making sure that industries where the UK has a vast potential, like offshore wind, get the support they need really to take off.
"With the strike prices for offshore wind today that we are setting out, that will also I think enable, on Decc's (Department of Energy and Climate Change) analysis, at least 10 gigawatts of offshore wind between now and 2020.
"I hope that is also a big vote of confidence from the Government in that sector."