Under existing regulations -- aimed at maintaining security of supply -- wind power production is not allowed to exceed 12% of the hourly demand for electricity. In compliance with this rule, REE has curtailed production from wind plant four times since Christmas, with three of the demands to switch off turbines coming since June. On the last two occasions, 7000 MWh was cut off across 30 wind plants.
The regulations came into force in 1985 when "wind technology was still in nappies," says Alberto Ceña from wind association Plataforma Eólica Empresarial (PEE). They are "obsolete" and "unnecessarily restrictive" and take no account of the considerable technology advances of the past two decades. A 12% production limit implies that no more than 13,000 MW of wind can be connected to Spain's transmission system -- a theoretical ceiling the government imposed in practice. At current growth rates, Spain will hit that ceiling in 2009.
Help is at hand, however. Changes at the top of REE following the election of a new government in Spain have also brought about rapid changes in its attitude to integrating wind power. The system operator has called on PEE to help it review the regulation, and PEE has called in power giant ABB as advisor. Of particular relevance is the ability of modern wind turbines to "ride through" grid faults, rather than tripping offline or being damaged if grid voltage drops or surges. By staying online, they add to grid stability rather than reducing it.
Specifically, the 1985 regulation requires that all wind turbines automatically trip offline if grid voltage drops to 85% of what it should be. As well as protecting the turbines, the aim was to avoid voltage strains on distribution networks caused by turbines absorbing reactive power as they got back to work. "Tripping prevents us from proving that we have developed much better technology and can support much bigger drops and contribute to grid security," says Ceña. Indeed, grid codes under discussion in the UK and Ireland are talking about requiring wind turbines to stay connected for drops right down to 15% of nominal voltage.
Under new leadership, REE is no longer disputing the point. With most wind plant today connecting directly into its transmission system rather than spread out at the level of the distribution network, large volumes of wind megawatts are being concentrated at single connection points. Under the existing regulation for automatic tripping of wind turbines to comply with the 12% rule, a relatively minor drop in voltage could cause a major loss of wind power supply. REE is now saying it wants wind turbines to ride-through drops in voltage that are right down to 20% of what it should be. REE is also asking wind plant to absorb zero reactive power during a fault and to provide it for a short period following the fault. These are similar to demands made by German transmission operator E.On Netz, "but even tougher," says Ceña.
We can do it
All the wind turbine manufacturers with significant activity in Spain say they can meet these demands -- and are willing to do so. Under Spain's new market rules for wind power, introduced in March, an incentive is on offer for wind generators to provide grid-support services. Those that do get a bonus payment equal to 5% of the average price of electricity sold to the consumer. From Ecotècnia, Antonio Martínez says his machines have been ready and waiting to prove ride-through capability in the field since February. First, however, the government needs to specify exactly what it requires of them.
The review by REE and PEE is expected to reach its conclusions before the end of the year, leading to the introduction of revised regulations sometime next year. This is not before time, says PEE. With ever more wind power coming online, wind will be pushing against the 12% penetration barrier with increasing frequency, especially during trough demand at weekends. About 1700 MW of wind capacity is now under construction in Spain, with the total now standing at more than 7000 MW (Windpower Monthly, October 2004).
Whether the 13,000 MW cap can be raised to 20,000, as loosely mentioned by some government departments over the summer, remains to be seen. PEE is making no promises. But it seems the government is waiting for the conclusions of the review before any announcements. PEE expects to see a new official target for wind power in Spain early in the new year.