Analysis: Acciona plays the reserve game

SPAIN: Spanish wind operator Acciona claims to have turned the tables and provided reserve wind power on a commercial basis to fill a gap on the grid caused by conventional thermal power shortfalls.

Acciona's turbines in Spain provided an upward adjustment on the country's grid
Acciona's turbines in Spain provided an upward adjustment on the country's grid

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The group claimed this is the first instance of this anywhere in the world.

This delivery of reserve power — a service that national regulations had previously restricted to so-called controllable thermal and hydro generators — "quells misconceptions" regarding wind's controllability and "is an example for wind markets worldwide", said Alberto Ceña, CEO of wind engineering firm Bepte, and technical adviser to Spanish wind energy association AEE.

It is also a marketable capability on the power adjustment market. Since announcing the transaction, Acciona's lines have been abuzz with enquiries from power traders and wind companies at home and abroad, Acciona's operations director, Jorge Moreno, said.

Most are from big wind markets, such as Germany, Denmark and the US, "but other countries, including New Zealand, have enquired", he added.

Spain has been ahead in terms of grid integration since 2008, when it became the first country obliging wind operators to provide real-time monitoring and emergency override control of all installed wind capacity nationwide.

But, until now, that capability had been used exclusively for what is termed downward adjustment — reducing power output from a project.

Up instead of down

In contrast, Acciona's pioneering feat, performed on 28 February, provided "upward adjustment", taking advantage of new power services regulations in force since 10 February.

By purposely pitching turbine blades out of their usual optimal angle with the wind, the company kept power output below full potential output. This gives national grid operator Red Electrica de Espana (REE) a reserve of power to call upon when needed.

And on the night of 28 February REE did need it, because of technical restrictions on thermal capacity. Due to excess power across one grid connection hub, thermal capacity had been reduced locally to below the point where power can be rapidly ramped up again.

This situation left a generation shortfall across the entire grid, and Acciona filled the gap, "injecting up to 180MW of additional power, 150MW on average, over a three-hour period," said Moreno. The power was supplied from a number of Acciona-operated projects in Spain.


Acciona was able to do so profitably by participating in REE's adjustment markets using day-ahead wind forecasting — accurate to 96%, according to Moreno — coupled with continual adjustments every 15 minutes on the day of delivery.

"Participating on the adjustment market will always be a trade off for wind," said Ceña.

A thermal plant saves fuel when operating below full power. But a wind operator "wastes" wind by pulling back from operating at full capacity in order to keep some potential power in reserve. "The trick is to make sure you gain more from participating on the adjustment services market than you lose in power sales by holding back," added Ceña, "especially bearing in mind you may equally be called upon to reduce power output, not to increase it."

To ensure net gains, "the spot market electricity price has to be low", Moreno said. During the event on 28 February it was below €10/MWh.

Acciona's handling of the programming complexities is the result of two years' preparation, ahead of the regulation changes, including 28 meetings with REE, explained Moreno.

The company also finetuned links between its power trading brokerage office, Acciona Green Energy Developments, and its Renewable Energies Control Centre (CECOER).

Reserve power capability had already been demonstrated in real life by utility Iberdrola and turbine manufacturer Gamesa's Syserwind demonstrator in 2010-2013, funded by the EU.

Now that Acciona has provided reserve power to resolve a technical grid restriction, the company is aiming to offer the service for supply-demand balancing  across 1GW — the maximum any company can offer on the adjustment market — of its 4.7GW installed wind capacity total.

Moreno said the company has already demonstrated capability of ramping up an extra 400MW over five minutes.

Profits on the adjustment services market are "not great", explained Moreno, but wind can always offer lower service prices than thermal operators, as no fuel is required to tick over on standby. "And turbines gain longer life by not operating at full loads, so reducing mechanical stress and strain," he added.

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