Central monitoring success helps Spain

SPAIN: Ten years ago, the Spanish wind sector, led by newly born industry body AEE and transmission system operator Red Elétrica de España (REE), created joint working groups to tackle the grid challenges posed by increased wind penetration of the power system.

Networking: A new 2GW interconnection between Spain and France will help balance power in the Iberian peninsula
Networking: A new 2GW interconnection between Spain and France will help balance power in the Iberian peninsula

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"The results have been spectacular," says Luis Atienza, pro-renewables chairman of REE since 2004. In 2002, REE said that wind penetration beyond 12% was impossible at any time without destabilising the electricity system. Since then, however, wind-generation peaks have soared — hitting spot penetration of nearly 60% in November 2011 — without causing any system distortions.

In 2006, the national wind objective to 2010 was raised from 9GW to 20.1GW, and met. Last year, a 2020 target of 35.75GW was set and, if financial constraints allow, this is attainable "with continued work on integration", says Atienza.

The challenge of integration is heightened by the status of Spain and Portugal as an electricity island. The Iberian peninsula cannot balance variations in wind by importing or exporting power, as the region's only interconnection with Europe is a weak interconnection with France, able to export 500MW and import 1,300MW. It can carry just 2-3% of the Spanish system's peak load, compared with Denmark's better connection of 18% capacity. System balancing for the Iberian peninsula has to be done mainly internally, and by Spain's much larger and flexible system.

Real-time monitoring

The most important integration achievement in Spain is REE's renewable-energy control centre, Cecre. Previously, REE had to contact wind operators to set limits on power output hours ahead of delivery, in case winds fell short of forecasts, leaving the system low on power. But a 2006 regulation obliged all wind farms over 10MW to operate either directly through Cecre, based in Madrid, or through dispatch offices connected to the centre. Using a broadband internet connection,this enables REE to have real-time monitoring of individual wind farms and emergency override control.

According to AEE, the deviation of wind energy from forecasts is an average of 88MWh for every 1,000MWh produced. Spain has around 36GW of fast-response capability to balance these deviations: 26GW of combined cycle gas along with 10GW of the country's 19GW hydro capacity.

Wind power is occasionally curtailed during the night-time demand trough if winds go so high that absorbing it all would push too much reserve gas power off the system, leaving REE unable to respond to the early-morning upsurge in demand if winds then dropped unexpectedly. But AEE technical director Alberto Ceña believes current electricity system planning will solve this problem, enabling Spain to reach its 35.75GW by 2020 target with negligible curtailment. Apart from an extra 2GW connection with France, Spain and Portugal are also planning to extend combined pump storage hydro capacity, currently at around 3,5GW, to 5GW.

End to voltage-dip curtailments

Spain's wind sector is also a global reference in responding to sporadic voltage dips across the system, caused by incidents such as fallen lines or lightning strikes. In 2004, the government introduced a bonus for wind farms able to continue operating through voltage dips — so-called low-voltage ride-through (LVRT) capability. A blanket LVRT obligation followed in January 2008, with just 2GW of older plant exempted. By 2011, there were no curtailments due to voltage dips.

Meanwhile, utility Iberdrola is leading an €8.15 million project called Syserwind, aimed at demonstrating that REE can call upon wind for extra power if needed, as with conventional power technologies. Throughout 2011, Iberdrola has been demonstrating this at a 480MW wind cluster in Andalusia, as part of a Europe-wide integration research programme called Twenties. Turbine blades are pitched to keep production slightly below full potential; if REE needs extra power, they pitch to enable full power.

Iberdrola hopes wind operators will eventually be invited to operate on the secondary regulation market, where generators are paid extra for offering to lower or raise power in a 15-minute period.

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