The government's plans for a massive expansion of the UK's offshore wind capacity have received a mixed welcome, with several of the renewable energy industry's leading figures questioning whether the target of generating 33 gigawatts (GW) from offshore wind by 2020 can be met.

Speaking yesterday to the European energy industry at a conference in Berlin, business secretary John Hutton said that the UK would open up much of its continental shelf to offshore wind farms capable of generating 33GW of energy by 2020, enough to power 25 million homes and meet a third of the UK's electricity demand.

However, experts questioned whether such a large-scale project can be delivered within 13 years and expressed concern that the focus on offshore wind could distract from other renewable energy technologies.

Leonie Greene of the Renewable Energy Association (REA) said that the announcement was extremely welcome, but said more information about the proposals was required beyond the current commitment to undertake a strategic environmental assessment. "The BWEA [British Wind Energy Association] has already been quoted as saying that the 33 gigawatt target is 'pie in the sky' and the government needs to make sure that it does not ignore the supply chain issues affecting the wind turbine market," she said.

Juliet Davenport, chief executive of green energy supplier Good Energy, warned that such a large-scale project would face considerable technical challenges. "Denmark has shown that you can get around 20 per cent of your energy from wind, based on the conventional gird management systems that make sure the lights stay on, but over 25 per cent and you start to move into the unknown," she said. "You will need significant investment to upgrade the transmission grid and my guess is there are a lot of people behind the scenes now asking how we are going to meet this target. "

The government has announced that it will instigate a new regulatory regime designed to streamline planning processes and make it easier for offshore wind farms to connect to the onshore grid. But experts remain unconvinced that the technical challenge of relying on inherently unreliable wind power for a large proportion of the UK's energy can be overcome without massive investment in the national grid.

Experts also voiced concerns that the focus on offshore wind would undermine investments in other renewable energy technologies, such as cheaper onshore wind farms.

Dale Vince, chief executive of green energy provider Ecotricity, which is engaged in building onshore wind farms, said that he supported the government's plans, but only if they are not to the detriment of onshore wind.

"It's dangerous to overlook the fantastic resource we have in this country – enough onshore wind to power the country three of four times over, enough to easily reach our target and at no extra cost," he said. "By our estimates, it will cost somewhere in the region of £40bn to build the 33 gigawatts of offshore power Hutton is proposing. We could do the same job onshore for £20bn. "

Vince argued that the offshore announcement could be interpreted as a "cop out" from the government and a way "of avoiding facing the noisy nimby minority who oppose onshore wind in this country".

Greene added that there was a risk that the government was "cherry picking" certain renewable technologies at the expense of others. "It's good that we are getting announcements such as the commitment to offshore and the plans for a Severn barrage, but what we want is an overall framework for the entire renewables industry," she said. "It can't just be about wind."