Spain leads the way on reserve power capability

SPAIN: Spanish utility and wind operator Iberdrola is leading a €8.15 million project called Syserwind, aimed at demonstrating that wind, like conventional sources, could contribute to the reserve power European electricity systems need at times of increased demand.

Iberdrola's national control centre in Toledo
Iberdrola's national control centre in Toledo

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The capability, known as secondary frequency control, enables the transmission system operator (TSO) to handle unexpected fluctuations in demand, notably by an injection of power when demand rises above TSO expected levels.

"This is not R&D," says Carlos Lozano, R&D coordinator at renewables division Iberdrola Renovables. "It is a demonstrator – by definition, to demonstrate something can work. And we have no doubt it will."

By 2011, Iberdrola hopes to have reserve power capability across three of its wind plant clusters totalling 480MW from 250 individual turbines. All three clusters are in the southern region of Andalucía and connected directly to the national transmission network.

Iberdrola’s partners in Syserwind are TSO Red Eléctrica de España (REE), Gamesa and Madrid’s public Institute for Technology Research (IIT), which will process the findings of the demonstrator.

The project falls under the European-wide "Twenties" programme, which is running six projects to demonstrate how wind power can contribute to grid stability across Europe and be instrumental in the EU’s objective of sourcing 20% of total energy consumption from renewables by 2020.
Frequency control

On European networks, the frequency of electricity generated by individual plant alternates at 50 cycles per second, or 50 Hertz (Hz).

When supply matches demand, overall combined frequency across the system is stable (at 50Hz). A surge of demand above supply will cause frequency to drop; a drop in demand will cause frequency to rise.

Changes in frequency are therefore both a symptom and an accurate measure of imbalances in power supply-demand.

For the small, inevitable variations in the operator’s hourly programming between supply against actual spot demand, power stations and the TSO control rooms respond in seconds, stepping output up or down accordingly.

That is known as primary frequency regulation and is provided by large conventional generators able to act quickly.

For more pronounced frequency drops, when spot power demand exceeds expected demand, smaller generators step in.

This is secondary frequency control, or secondary power regulation, and requires power stations to respond in ten seconds to 15 minutes.

That gives emergency cover while extra power from conventional plant can be cranked up if demand keeps rising beyond the 15 minutes. In secondary regulation, smaller generators may also be called upon to reduce power due to a drop in demand.

Wind is different

To date, wind power has been exempt from frequency control capability.

It is produced only when the wind blows, and is prioritised, meaning the grid must take all power from wind turbines regardless of spot electricity demand.

The rest of the system must therefore be balanced not just for varying demand but also for varying wind production.

Syserwind aims to prove that wind can provide secondary frequency regulation, thus contributing to grid stability and reducing demand on conventional generation.

If the project works as well as Iberdrola hopes, wind plants and turbines could be certified for the secondary regulation market, in which extra earnings can be made by selling reserve power.

For wind to offer extra power on demand, turbine output would have to be kept somewhere below its full potential in order to keep some power in reserve, translating to lost production earnings.

But in secondary regulation, a price is also established for reducing production on demand.

That means that wind could, for the first time, earn money for not generating.

How it works

The project’s key facilities are Iberdrola’s national control centre for renewable energy (CORE) in Toledo, controlling the company’s turbines, and REE’s renewables control centre in Madrid.

The two will be responsible for two-way communications regarding production needs and output. CORE will issue orders to the wind plants, which, in turn, will remotely issue orders to the individual turbines.

The increase or reduction in production will be achieved by pitch control of turbines, says Roberto Veguillas, Iberdrola’s coordinator of wind turbines, referring to the motors varying the angle, or pitch, of each blade against the wind.

If reduction of pitch reaches a maximum, the system may shut off individual turbines, although Veguillas says this option is not ideal since a restarted machine needs a few seconds to return to its previous speed.

Lozano says the main technological upgrades needed for success will be speedier communications and control, particularly algorithm software governing real-time communications from turbine to REE and for continuously calculating how much capacity to keep in reserve.

For that, wind prediction methods, obligatory for all Spanish wind producers since 2004, will need to be further sharpened.

Assessing whether earnings from the secondary regulation market will compensate the losses – either from not selling all potential wind power or from extra wear and tear – is "one of our secondary objectives" says Lozano.

"Our primary aim is to show it can work. The rest is up to the follow-up analysis."

Lozano is confident participation in secondary frequency control will "open the way for further wind penetration".

He explains: "If the Spanish electricity system needed up to 1GW of reserve conventional capacity when there were 15GW of installed wind capacity, with the 30GW expected by 2015, it will need around 2GW." If wind participates, he believes the demands on conventional reserve may be halved.

Other European nations will watch closely when, after 2014, the Danish renewables research institute Riso assesses the potential of Syserwind’s work for continental grids.

Alberto Ceña, technical director of Spanish wind body Asociación Empresarial Eólica, says: "With British, German, Spanish and other TSOs keen to pull wind into secondary regulation, the demonstrator conclusions will not come a moment too soon."

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