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Wind weakening system security -- Spain's isolated grid

Without incentives for wind developers and operators to improve the power quality of wind plant, Spain's grid will suffer increasing instability. National wind absorption capacity could stretch to 13,000 MW, given current turbine specifications, though areas with high and localised concentrations of wind plant, such as Galicia, are already posing technical challenges.

These were the main messages to the wind industry imparted last month by David Alvira from Spain's grid operator Red Eléctrica Española (REE). He was speaking at Madrid's third Jornadas Eólicas, an annual wind conference organised by the renewables producers association, Asociación de Pequeós Productores Autogeneradores (APPA) and electrical generation journal CV-Saypower. His presentation met with a mixed response.

Given current asynchronous wind turbine generation technology, wind power adds to problems arising out of unforeseen hazards on the grid, argued Alvira. Such hazards include lightning strikes, fallen lines, short-circuits or human error, any of which could see huge amounts of generation capacity -- such as that produced by a nuclear power station -- disappear instantly. If large amounts of wind power are also connected in the same area, instead of helping to maintain grid voltage, they also disconnect, exacerbating the problem. Disconnection happens due to the massive loss in voltage during the milliseconds before the grid system can re-establish a modicum of stability. REE controls all transmission above 220 kV.

Weak interconnections

Spain's condition as an "energy island," with extremely weak interconnections with the rest of Europe means that REE can import very little power to cover such huge drops in voltage. Wind power provides just 2% of Spain's electricity, compared with 18% in Denmark, but Denmark's interconnection capacity with the rest of Europe is 30% of the total, while Spain's connection via France is just 3%, according to Alvira. Even when interconnection is improved, Denmark cannot be used as a comparison because its wind power is thinly distributed compared to Spain's wind plant clusters, which often inject more than 100 MW within a small area. Wind prediction abilities are also more limited in Spain, compared with those in Denmark, due to its complex, mountainous geography.

While current legislation, which guarantees a fixed rate of pay for all wind energy, encourages developers to put up as much capacity as possible, regardless of the negative effects on the grid, the problem will grow, says Alvira. At the same time he insists that this is REE's problem as it must cope with whatever generation capacity is allowed to go up.

Adapting technology

Among the few delegates to agree with much of Alvira's thesis was Antonio de Lara, director of one of Spain's largest turbine manufacturers, MADE Tecnologías. He says turbine manufacturers are capable of adapting technology to enable wind to add to grid stability.

This is especially the case of existing turbines using synchronous generators, such as MADE's own 800 kW machine or the direct drive multi-pole turbines, such as those produced by Germany's Enercon. With simple adaptation there is no need for such turbines to disconnect during periods of voltage loss, he argued.

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