SINCE October sightseers on the hills above Edinburgh have gawped at a brand new landmark. Across the Firth of Forth, on a test site, stands the biggest wind turbine in Britain. The tips of its blades rise 196m above sea level. Its rotor sweeps an area twice as large as the London Eye. This monster and others like it are bound for the North Sea—part of the biggest and most ambitious offshore wind programme in the world.

1. Renewable energy –
Rueing the waves

3. SINCE October sightseers on the hills above
Edinburgh have gawped at a brand new landmark.
Across the Firth of Forth, on a test site, stands the
biggest wind turbine in Britain. The tips of its
blades rise 196m above sea level. Its rotor sweeps
an area twice as large as the London Eye. This
monster and others like it are bound for the North
Sea—part of the biggest and most ambitious
offshore wind programme in the world.

4. Britain gets more electricity from offshore wind farms than all
other countries combined. In 2012 it added nearly five times more
offshore capacity than Belgium, the next keenest nation, and ten
times more than Germany. Its waters already contain more than
1,000 turbines, and the government thinks capacity could triple in
six years. Boosters think Britain a global pioneer. Critics say
ministers are flogging a costly boondoggle.
Two things explain Britain's enthusiasm for offshore wind turbines.
First, the country is committed by European law to generate about
30% of its electricity from renewable sources by 2020, up from
about 13% now. Nuclear energy does not count and Britain is well
behind on solar power, which means lots more wind turbines and
biomass plants (mostly wood-burning power stations) will be
required.

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The simplest solution would be to put more
wind turbines on land. But they are unpopular
with locals: rural voters have harried several
Conservative MPs into outright opposition. So
Britain is building much of its new capacity at
sea. Offshore turbines supply less than 3% of
Britain's juice but about one-fifth of its
renewable power (see chart). That share is
rising.

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The second reason for ministers' enthusiasm is that
they spy a chance to conquer a growing global
market. Miles of shallow sea give Britain an
unrivalled opportunity to experiment with
technologies it may one day lucratively export,
much as North Sea oil has turned Scotland into a
hub of hydrocarbon expertise. China and Japan
have a growing appetite for offshore generators but
little capacity. America has only a single prototype
turbine.

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Unfortunately, offshore wind power is staggeringly
expensive. Dieter Helm, an economist at Oxford University,
describes it as "among the most expensive ways of
marginally reducing carbon emissions known to man".
Under a subsidy system unveiled late in 2013, the
government guarantees farms at sea £155 ($250) per
megawatt hour for their juice. That is three times the
current wholesale price of electricity and about 60% more
than is promised to onshore turbines. It is also more than
the £92.50 which Britain's new nuclear plant at Hinkley
Point will get—though that deal is for 35 years, not 15.

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Ten-metre waves and salty gales are just two of
the hazards that keep offshore costs high.
Second-world-war bombs on the seabed are
slowing new projects in Germany; in December
Scottish Power, an energy firm, scrapped plans
for 300 turbines on a site filled with basking
sharks.

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The government wants offshore generators to slash costs
by about one-third by 2020. The price of energy from
offshore farms has actually risen since Britain built its first
turbines at sea in the early 2000s, in part because
developers are putting them in ever deeper waters, farther
from land. But costs now appear to be stabilising.
Operators claim bigger turbines can bring prices down.
Simpler models that break less ought to help matters, too.
In some places floating wind farms could prove cheaper
than fixed foundations. To cut losses from outages, offshore
operators are investing in helicopters to whizz engineers to
stricken turbines when seas are too rough for boats.

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Another hitch is that much of the money
lavished on building offshore wind farms leaves
the country. Only about 25% of capital spending
flows through British companies, compared with
70% of the cash invested in North Sea oil and
gas. Almost all of the country's existing
offshore turbines were produced by two firms,
Siemens and Vestas, which manufacture them in
Denmark. Fleets from continental ports
commonly construct the farms.

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The government hopes British firms will one day
shoulder at least half of the work new offshore
farms require. Its industrial strategy, published in
August, tries to give small businesses a leg up. But
whereas local companies are already good at many
footling jobs, the real prize would be tempting a
turbine manufacturer to build a British factory.
Lacklustre facilities at ports near the farms are one
significant obstacle.

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The industry says offshore wind power would become
cheaper more quickly, and boost Britain's economy, if the
government agrees to build lots more offshore farms. The
Department of Energy and Climate Change (DECC) says
that 10 gigawatts (GW) of offshore capacity is "achievable"
by 2020. That is three times the amount already deployed,
and would provide about the same capacity as Britain's nine
nuclear power stations combined (although wind farms
produce power only about a third of the time). Still,
ministers once had loftier ambitions. Wind-farm operators
worry that the government will divert subsidies to other
kinds of low-carbon generation, such as nuclear and gasfired stations.

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The Institute for Public Policy Research, a think-tank, warns
that half-hearted investment in offshore power could leave
Britain in the "worst of all worlds"—a moderate amount of
offshore energy, supplied at whopping cost and to little
economic benefit. Enthusiasts want the government to boost
investment by setting a binding target for carbon emissions in
2030 and extending its support for new wind farms from 15
years to 25 years. In December, partly in response to such
concerns, DECC tweaked its subsidies to provide more cash to
offshore farms that begin construction at the end of the
decade. It reaffirmed that Britain could have over 40GW of
offshore capacity by 2030, if costs fall quickly. That would
mean offshore turbines supplying about a third of Britain's
power.

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Yet hefty subsidies will only get harder to defend as
bill-payers grow angrier about rising energy prices.
And Britain is not the only country questioning its
support for costly, complex offshore generation. In
2012 European offshore deployment fell 14%
behind its target; in November 2013 politicians in
Germany agreed to slash that country's objective
from 10GW in 2020 to 6.5GW. One day mammoth
offshore turbines might herald cheaper power. For
now they only supersize the gamble.