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Taking the wind out of their sails

News analysis Wind energy

The future of wind energy is in doubt following Ireland's emergency decision to stop new wind farm projects. Mark Hansford finds out what has gone wrong.

ON 4 December last year the Irish electricity regulator placed a moratorium on new connection licences for wind generators. It took immediate effect.

The drastic decision was taken reluctantly, and following urgent warnings from Irish grid operator ESB National Grid that a 'recent rapid rise in the amount of wind generation proposed for connection to the power system poses an increased risk to the security and stability of the power system which exceeds the level normally likely to be accepted by a prudent system operator.'

ESB said a number of outstanding technical issues needed to be addressed before further wind capacity is connected to the grid. Technical problems stem from the intermittent nature of wind as an energy source.

Power is there when the wind is blowing, but it ebbs away to nothing when it is not.

After a swift review of the situation Ireland's Commission for Energy Regulation (CER) was forced to agree. It banned any further connections of wind turbines to the Irish grid until the end of the year. To the chagrin of wind generators this moratorium has since been extended for three months to allow technical issues 'to be urgently resolved'.

British wind energy developers will be looking on with concern, as the two systems are comparable.

Both are stand-alone island grids - interconnection to neighbouring European grids is limited. Both are attempting to support bold targets for renewable energy.

Fortunately for the developers the British grid is larger, so the issue will take longer to surface.

Indeed, they have only come up in Ireland now because the number of connections to Ireland's grid is set to explode in next three years.

Since 1995 wind-generated power has gently increased from 20MW to 166MW - a small enough percentage of Ireland's 7,000MW total generation for inherent technical shortcomings to be overlooked.

But in the last year alone connection agreements for over 400MW of wind generation have been granted. The total amount of committed wind generation - either connected or with signed connection agreements - is now 700MW and, taking account of applications in process, this figure could rise to 1,200MW. Around 800MW is expected to be online by 2005, way ahead of Ireland's Kyoto obligations and its own target of 500MW.

And at this level of generation, the ESB argues that technical problems can no longer be ignored. They must be addressed before any further connections are made.

Wind generators, on the other hand, argue that they can easily be dealt with as the programme develops. 'There are no technical issues which cannot be addressed and resolved well in advance of the current connection offers becoming operational, ' says renewable energy firm Airtricity chief executive Paddy O'Kane.

'They are all soluble and can be dealt with in parallel in the issuing of grid connections.'

Intermittency has two effects on the grid.

First, increased wind generation affects other power sources. As the output from wind farms increases the output of conventional generation running must be reduced. Like an idling car engine, eventually output from these other sources will reach a limit below which it cannot be reduced. When this limit is reached, the output from wind generators must be cut back instead.

A report last year by wind power expert Garrad Hassan & Partners and ESB on behalf of CER said this point will be reached when wind generation hits 800MW in 2005, at first when full wind output coincides with low demand periods such as summer nights.

Ahead of this, systems to cut back wind such as control infrastructure and contractual agreements are essential, the report argues. Wind developers, such as O'Kane, argue that this is a worst case scenario, and in any case is easily solvable.

The Hassan report admits that the initial effect is 'very small' in economic terms.

The second effect is more complex and relates to the ability of a generator, whatever the power source, to cope with fluctuations in the grid.

The requirements are set out in Ireland's wind code and demand that generators connected to the grid can handle the voltage depressions caused by the loss of at least one line or generator (news last week).

The Hassan report says that this approach is 'unrealistically restrictive' for wind generators, which use capacitors to smooth peaks and troughs in energy output. However, if output falls off sharply these capacitors accelerate the voltage shortfall by drawing in power from the rest of the grid, rapidly leading to system collapse.

Control systems can be retrofitted to resolve this problem, but it would be expensive. Instead, the Hassan report recommends that a 'remedial action scheme' be adopted. Automatic protection equipment detects disturbances and automatically disconnects wind generation in that area. This would be enough to hold up the system, the report concludes.

Adopting this method would be a departure from the current code, but it is already under review. CER hopes to have a new Grid Code for Wind ready by summer to tackle these technical glitches.

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