Twenty new gas-fired power stations are likely to be built in the UK, amounting to a massive increase in consumption of the fossil fuel, the climate and energy secretary, Ed Davey, has told the Guardian.

But Davey insisted the expansion – the biggest construction effort in the power sector for decades – would not harm the prospects for investment in renewable energy or in the government’s carbon reduction targets.

He said: “I strongly support more gas, just as I strongly support more renewable energy. We need a big expansion of renewable energy and of gas if we are to tackle our climate change challenges.”

Davey is expected to announce a new gas strategy this autumn, which will require the investment of hundreds of billions of pounds in new electricity generation capacity and dictate the shape and construction of the UK’s energy infrastructure for decades to come. But environmental groups and renewable energy investors are concerned that a new “dash for gas” would put carbon targets beyond reach and deter investment in renewables.

Joss Garman, political director of Greenpeace, said: “Green-lighting a whole fleet of new fossil fuel power stations would cause a huge jump in emissions and blow this autumn’s once-in-a-generation opportunity to replace dirty power stations with clean ones.”

Davey said the government was planning to add 20GW of electricity generation capacity from gas, between now and 2030. That is about ten times the current capacity for generating renewable energy from offshore windfarms. As of Thursday, when a new offshore windfarm was opened off the north Norfolk coast, the UK had 2GW offshore wind-generating capacity – more than any other country.

Davey said: “People who see the UK’s energy future as a competition between renewable and gas are misreading the next phase.”

However, this is in contrast to the arguments put forward by aides to George Osborne, the chancellor, who do see the two in competition – they have insisted that investment in renewable energy was in danger of crowding out investment in gas.

Each new gas-fired power plant is likely to have a useful life of about 25 years. Davey also supports a target of decarbonising the electricity sector by 2030, so this would imply fitting new gas-fired power stations with technology to capture and store carbon dioxide, either on construction or subsequently. There are no full-scale power stations currently running with CCS technology, which has suffered serious delays.

Greenpeace’s Garman said investment in renewable energy was the way to cut emissions: “Only days ago Ed Davey and Danny Alexander said they were fully committed to achieving completely carbon-free power in the UK by 2030. Nick Clegg can’t afford to make this another ‘sorry’.”

Davey attended the opening of the UK’s latest offshore windfarm off the north Norfolk coast on Thursday, a £1.2bn projected called Sheringham Shoal. The major investors in the project are from Norway, emphasising the strong trend for investment in the UK’s energy infrastructure to come mainly from overseas companies.

Christian Rynning-Tønnesen, chief executive of Statkraft, the Norwegian power utility that has invested in Sheringham Shoal, said the UK’s wind resources and regulatory regime made it the most attractive location in Europe for offshore wind investors.

The Norwegian company is looking at a huge expansion of offshore wind in the North Sea, along with the German utility RWE and Scottish and Southern Energy. The Dogger Bank could support up to 9GW of offshore windfarms, but this investment is likely to take more than a decade.

Rynning-Tønnesen said he was seeking new offshore windfarm projects to invest in. But he warned that if there were no suitable opportunities in the UK, the company would take its investment elsewhere. He added that the government’s plans for reforming the electricity market could work, but were still unclear.