Labour is promising to build dozens of new state-owned offshore windfarms, at a cost of £83bn in public and private money. The plan comes as members prepare to debate the climate emergency at their party conference in what could be a fierce contest between heavyweight unions and grassroots campaigners.

On Tuesday, delegates will be asked to vote on the party’s target to cut the UK’s carbon emissions to net zero. Two motions are to be put to members, one with a target of net zero carbon emissions by 2030 – which would be much more stringent than the government’s current target of net zero by 2050 – and one backed by the GMB union, which does not set a date.

The motions emerged from the “compositing” process after 128 constituency parties sent climate-related motions to the conference. The 2030 motion came from the pressure group Labour for a Green New Deal and has the support of several smaller unions. Both motions could pass.

Lauren Townsend, trade unionist and spokesperson for Labour for a Green New Deal, said: “Delegates have a clear choice: they can vote to lead the way on climate, responding to youth strikers’ calls for a 2030 decarbonisation target, or they could vote for a motion which risks leaving Labour with the least ambitious climate target of any major party.”

The party leadership is focusing its efforts on the “green industrial revolution”, its strategy for reviving the economy, creating high-quality jobs and tackling the climate emergency, spearheaded by the shadow business secretary, Rebecca Long-Bailey.

She pointed to the proposals for new offshore windfarms as a prime example of how the strategy would work. The new farms, which would provide electricity for 57m homes, were needed because the construction of new turbines by the private sector was too slow, despite falling costs, she said. The profits from the power generation would be reinvested to benefit coastal communities and tackle the climate emergency.

Public ownership would ensure jobs and revenue stayed in the UK, she added. “[We can] learn from countries such as Norway and Sweden by owning what is already ours,” she said. “By taking a stake in offshore wind, we can collectively benefit from the profits, investing them back in our held-back coastal communities. Instead of jackets for windfarms in Scotland being made in Indonesia, we’ll bring those jobs back to Fife.”

Labour would invest £6.2bn from its proposed £250bn national transformation fund in the new windfarms, along with a matching amount from the regional energy agencies which would replace the renationalised National Grid. The remaining £70bn would be sought from private sector investors, and the new windfarms would be 51% owned by the public.

A projected £600m to £1bn a year in profits would go to coastal communities for amenities such as harbour fronts, parks, leisure centres and libraries, with the remainder invested in improvements to the energy system and measures to combat global heating.

Other “green industrial revolution” proposals include a £3.6bn national network of electric vehicle charging stations, solar panels for low-income and social housing tenants, and a programme of insulation for fuel-poor households.

Sue Ferns, senior deputy general secretary at the Prospect union, said: “This focus on how to drive up low-carbon generation while lowering costs and encouraging quality unionised UK jobs is welcome. It is essential that we retain the jobs and skills that we have in traditional [power] generation and create new jobs – a strong government role could be central to delivering that.”

Businesses have been more cautious on the green industrial plan. James Diggle, head of energy and climate change at the CBI employers’ organisation, said: “Firms will welcome the Labour party making growth in low-carbon technologies and green jobs a priority. The emphasis on increasing renewable energy is backed by the business [community]. To meet net zero emissions by 2050 we need ambitious policy. Labour’s proposals to invest in energy efficiency, introduce a zero-carbon homes policy and support uptake of low-emission vehicles all support this ambition.”

But he added: “In the huge push to reach net zero as fast and as cost-effectively as possible, renationalisation will disrupt the investment needed across water, rail and energy that all contribute to reducing emissions.”