Wind energy's erratic performance as a power source means the more it forms part of a power system, the more back-up supply is required and the less cost efficient it is, according to a report on renewable energy produced for Britain's House of Lords.
Some evidence put to the Science and Technology Committee which produced the report claimed wind energy needed a 100 per cent back-up to overcome the reliability issue. In other words 100 megawatts of wind power would require 100 mw of conventional power as a back-up for times the wind didn't blow.
However the committee rejected that argument saying winds' need for back-up could be balanced across the reliability of the whole power system.
As a result, the relative amount of back-up generation needed for wind would increase as wind's share in overall generation increased.
The report found that if wind were to provide 10 per cent of Britain's power needs it would require back-up generation equivalent to 72.5 per cent of its rated output. However if wind were to make up 20 per cent of power generation capacity it would need back-up generation amounting to 80 per cent of its potential output.
Regulators in South Australia estimate that wind generation demands a reserve margin of 92 per cent in back-up generation.
The British report found that regulators had not addressed the reserve margin issue. "We are . . . concerned that at the same time as Government policies are encouraging large-scale development of wind energy capacity, margins are at low levels," the report said.
It found that while there are no technical limitations on the amount of wind that can be introduced "penetration much beyond 10 per cent will become progressively more costly".