Integration success leads to easy curtailment

SPAIN: Spain has been hailed a world leader in integrating wind within the national grid. The country has achieved total wind capacity of almost 23GW.

On top of the world… Spain has been a pioneer when it comes to integrating wind (pic:REE)
On top of the world… Spain has been a pioneer when it comes to integrating wind (pic:REE)

Wind was Spain's top electricity generator for the first half of 2013. Yet, government policies since November 2011 - when the conservative People's Party took power - have frozen the wind market and, according to wind association AEE, the integration work is now at risk.

Under the recent chairmanship of former energy minister Jose Folgado, grid operator Red Electrica de Espana (REE) curtailed around 850GWh of wind in the first four months of 2013, for grid security. According to AEE, this cost wind-power producers EUR 83 million, or 10% of potential turnover. Windpower Monthly requests to REE to discuss integration issues were denied, a lack of dialogue characteristic of the government's energy policy. Under a series of privately drafted decrees since 2011, the government has frozen the wind market.

A July 2013 decree, which ended price subsidies to renewable-power sales, also requires wind operators to compensate combined-cycle-gas and large hydro generators for providing back-up power for when wind falls below programmed output. The government is drafting the details, to be rubber-stamped by the end of the year. But wind already pays EUR 0.7 for every megawatt hour delivered that deviates from programmed production. "Now we will have to pay twice," says Albert Cena, technical director at AEE.

"Spain has been one of the leading countries in integrating wind into the grid and market, so (Spanish producers) should benefit from it," says Justin Wilkes, policy director at the European Wind Energy Association. But now the government reforms are threatening that achievement, he adds.

Mass curtailment

The starkest event so far involved the Easter weekend wind curtailments in March/April, when reduced demand combined with constant wind after high rainfall. Hydro reserves were offloaded before reaching bursting point, generating 31.6% of the electricity mix. Inflexible power from six nuclear reactors and combined heat and power (CHP) covered more than 30% and nearly 15% of daily consumption. To absorb all this while maintaining some rapid-response combined-cycle gas on standby, 150GWh of wind power was thrown offline, equivalent to around 30% of that day's total electricity consumption. In all, between 28 and 31 March, 637GWh of wind was curtailed.

Under the curtailment threat, AEE claims wind to be a victim of its own integration success. Wind operators met the demands of a 2007 grid code by providing the grid operator with centralised, real-time monitoring and emergency override control of plant operations. By 2012, Spain's entire 22GW of installed wind capacity was connected to REE's Renewable Energy Control Centre (Cecre) in Madrid, an unmatched feat, according to Cena.

With Cecre, it is easier to curtail wind production than other technologies, argues AEE. Cena points out that no other renewables or CHP technology was curtailed at Easter. "The regulation says it is too difficult for those technologies to offer centralised control," he complains. "Well, it was difficult for wind to do so. But we did it. The irony is, we're being penalised for it."

Victim of success

AEE recognises, however, that the control centre gives wind production more room for manoeuvre. Previously, the grid operator could order wind farms to stay offline hours ahead of its electricity schedule. During low demand periods, allowing all predicted wind power online could sometimes push flexible rapid-response gas offline, which would present a supply threat if wind finally fell short of expectations, as gas would be unable to bridge the gap. With the control centre, REE can now allow much larger amounts of wind to operate closer to the critical moment, temporarily reducing production if necessary rather than shutting down entire plants.

Being singled out for easy curtailment is only half of AEE's gripe. The other is that Spain - unlike Denmark and Germany — does not compensate generators for curtailed wind, despite wind having to pay for backup power from other technologies that enable nuclear, CHP, hydro and rapid-response gas to stay online. Cena says AEE is happy to help out the system, providing responsibilities and remuneration are spread evenly.

AEE admits that it is, of course, the centralised control that has enabled wind capacity and penetration to snowball over the years, a growth that is demanded by the EU's binding renewables objectives to 2020, by which date Spain is committed to reaching at least 35GW.

REE has always said the EU target is a big challenge. Spain is almost an electricity island, able to import and export just 1.5% of its peak electricity generation, mainly through France. "The European average is 10% and Denmark, with the biggest wind-power penetration rate, has interconnection capacity equivalent to 50% of its generation capacity," points out Peter Sennekamp, EWEA media officer. Unlike Denmark, REE must balance variable demand and variable wind almost entirely internally. A 2GW connection with France, scheduled for completion in 2016, will only ease the load slightly.

Improved predictions

Huge as EU targets may be, the challenge poses an opportunity for grid integration leadership, former REE chairman Luis Atienza said while at the helm 2004-2011. On his watch, each wind producer met an obligation to programme generation a day ahead of delivery by incorporating a combination of advanced wind-prediction technologies and using agents to aggregate and broker power sales on the wholesale electricity market. Combined with wind-power prediction tool Sipreolico, AEE believes prediction has reduced wind delivery deviations from day-ahead predictions to less than 10% now, from an average of 16% in 2006.

Also, since 2012 all but 3GW of national wind capacity is able to continue operating through short sporadic voltage dips, so-called low-voltage ride-through (LVRT) capability. In 2007 there were more than 85 cases of wind plant curtailments due to lack of LVRT capability, in 2011 there were none.

In all, more than 15GW of wind power was installed on Atienza's watch. Wind produced 29.9TWh over the first six months of this year, meeting 22.6% of demand overall, up from 17.8% over the same period the year before. Spot wind penetration reached a record 63% of demand on 24 September 2012. While this is a far cry from 2002 when REE calculated Spanish wind could not surpass 12% of spot penetration, a pull-back on continued integration may mean that these statistics will not be surpassed or even matched in the foreseeable future.


For many, the idea of variable wind providing extra power when the grid demands it may seem counterintuitive. But that is exactly what Spanish utility Iberdrola has been doing since 2011 at wind plants totalling 480MW, comprising 250 turbines across the southern provinces of Granada, Malaga and Cadiz.

Aided by turbine supplier, Gamesa, the turbine blades are pitched out of the wind to keep production slightly below full potential. If system operator Red Electrica de Espana (REE) needs extra power, blades pitch in, enabling optimum output.

Iberdrola's EUR 8.15 million Syserwind project is one of six projects in the EUR 56.5 million EU-funded Twenties programme, aimed at demonstrating how wind can add to grid stability while helping the EU achieve its 20% renewables target by 2020. Syserwind has been an outstanding success, according to Roberto Veguillas, project co-ordinator at Iberdrola.

For the small, inevitable variations from REE's hourly programming of power supply against demand, the operator uses large conventional generators - especially flexible gas power — to respond in seconds, stepping output up or down in what is known as primary regulation.

For more pronounced variations, when spot power demand exceeds expected demand, small generators step in, charging a bonus for raising or lowering output within a 15-minute response time. Coal, gas and large hydro participate in this secondary regulation, from which wind is excluded.

Voluntary reserve

Power offered as reserve from Syserwind could not participate in that market and was not paid for. Yet, Veguillas says Syserwind has performed real-life secondary regulation five times, voluntarily providing reserve power - unremunerated by the electricity system — with a response time faster than required.

While Iberdrola had hoped Syserwind might convince the government to let wind participate in secondary regulation, the recent government measures against wind make that unlikely.

Meanwhile, Madrid's Comillas University, a Syserwind partner, is studying the cost impact of both keeping wind output below optimum and managing secondary regulation. It will also assess the costs of wear and tear on turbines.

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