A new report on the capacity in the UK for offshore wind, wave and tidal power should be used to put pressure on ministers

Whenever you suggest that renewables could one day supply a large proportion of our electricity, scores of people jump up to denounce it as a pipedream, a fantasy, a dangerous delusion.

They insist that the energy resources don't exist; that the technologies are inefficient; that they can't be accommodated on the grid; that the variability of supply will cause constant blackouts.

I suspect that no amount of evidence will sway some of these people. There's a large contingent which seems to hate renewables come what may.

However often you point them to papers showing how a European supergrid, which could one day stretch from Iceland to North Africa, allows us to balance renewable resources against each other, ensuring constant supplies; however often you explain the potential of smart appliances, a smart grid and new energy storage technologies, they just clamp their fingers in their ears and shout: "No, no, no!"

I don't know how to explain this unreasoning antagonism, but it casts an interesting light on the oft-repeated myth that it is environmentalists who are hostile to new technologies.

But even the defeatists might be swayed by some of the findings of the Offshore Valuation report, just published by the Public Interest Research Centre (Pirc). It's the first time anyone has tried to work out how much electricity could be produced by offshore renewables in the UK, and the results are fascinating.

It examines only existing technologies – wind turbines with both fixed and floating foundations, wave machines, tidal range and tidal stream devices – and the contribution they can make by 2050.

It accepts the usual constraints on offshore renewables: maximum water depths, the need to avoid dense shipping lanes and other obstacles, the various technical limits. Having applied these constraints, it finds that the practical resource for offshore renewables in the UK is 2,130 terawatt hours per year. This is six times our current electricity demand.

Were we to use only 29% of the total resource, the UK would become a net electricity exporter. We would be generating energy equivalent to 1bn barrels of oil a year, which roughly corresponds to the average amount of North Sea oil and gas the UK has been producing over the past four decades.

The report estimates that this industry would directly employ 145,000 people and produce annual revenues of £62bn. The construction effort would be roughly similar to building the North Sea oil and gas infrastructure: eminently plausible, in other words, if propelled by strong government policy.

Were we to make use of 76% of the resource, the UK would become a net exporter of total energy. This is a tougher call, but not necessarily impossible: we'd be producing the equivalent of 150% of the energy output from UK's peak production year for oil and gas (1999).

It would mean building an average of 1,800 7.5 megawatt wind turbines every year. This is likely to stretch available manpower and construction capacity to the maximum, possibly beyond. But if enough investment is sunk into training, manufacturing and transport, the potential for creating both employment and income is enormous.

The national grid, the report estimates, could accommodate about 50% variable renewables (power sources whose output depends on the weather) by 2050, as long as it had 34 gigawatts of backup capacity, energy storage and interconnectors linking it with the continent. This is both plausible and affordable. (Backup, to address another persistent myth, does not mean that the necessary thermal power plants are kept running all the time, just that they are available if needed.)

There are some interesting implications. The UK could close its looming energy gap without using new sources of fossil fuels. It could do this without encountering the public hostility which often scuppers onshore windfarms.

The best wind resources are mostly way out of the sight of land: the further out to sea you go, the stronger the wind becomes. A recent study shows that offshore windfarms can greatly increase the abundance of fish and crabs. (My hope is that the foundations could be connected by a web of steel cables, so the windfarms could function as marine reserves which never needed to be policed, as trawling through them would be impossible.)

It also raises some important questions. If the offshore resource is so abundant and its deployment likely to cause hardly any political fuss, should we give up fighting for onshore windfarms? I don't know, but I would appreciate your views.

The report also makes me wonder whether, in the light of the damage they will do and of the far greater resources in the open sea, a Severn barrage and other tidal range devices are worth developing. The report suggests that the total practical resource for offshore wind is 1,939 terawatt hours per year, while the total tidal range resource is just 36 – and more expensive to deploy. Given the aggro tidal barrages will cause and the habitats they will destroy, are they worth developing?

If any of this is to happen, the big decisions will need to be taken in the next year or so. So if ever you meet ministers or officials, ask them these questions. Have they read the report? What do they intend to do about it?

monbiot.com