grid stability the government is set to lift its limit on wind generation to allow a further
7000 MW onto the network
Spain's transmission system operator, Red Eléctrica de España (REE), has produced a grid code for all intermittent generation sources, though mainly with wind in mind. "There is already broad consensus, apart from one or two details currently under discussion," says Alberto Ceña, technical chief of national wind association Asociación Eólica Empresarial (AEE), which has been closely involved in formulating the Procedimiento Operativo (PO) 12.3. Publication of the code is expected shortly.
Under the new rules, all wind turbines must stay online during large spontaneous drops in voltage and contribute to system recovery. Ceña has received assurances from wind turbine manufacturers that their products will be meeting the requirements from March 2006. A second requirement, however, is subject to controversy. The procedures for when the transmission system operator (TSO) may and may not curtail production and constrain wind turbines off the system "still need a lot of ironing out," says Ceña.
A functioning grid code is vital for the future development of Spanish wind power. Once rules are in place to ensure security of supply with large volumes of wind power on the system, the government says it will raise the long-standing cap on installed wind capacity from 13,000 MW to 20,000 MW. Spain has 9000 MW online today and thousands of megawatt authorised. Finalising the rules has become a matter of urgency.
AEE has worked closely with the TSO on a thorough grid and wind integration study since July 2004, including formulating the main technical criteria for the technology's interface with the grid. PO12.3 is partly based on rules produced by German TSO E.ON Netz. "But the Spanish rules are more demanding," says Ceña.
No easy ride
In Spain, wind plant are required to react faster in times of trouble. They must cease to draw reactive power from the wires within 100 milliseconds of a drop in voltage (E. ON Netz makes no such demand, says Ceña), yet be able to inject reactive power within 150 milliseconds of grid recovery. AEE is contesting REE's requirements, which it says were not part of the draft grid code issued over a year ago. Ceña considers them "excessive" and "unnecessary." He says the demand for reactive power should not start before 400 milliseconds into recovery.
Not all the Spanish rules are tougher than in Germany. In Spain, wind turbines may trip off the system if voltage drops to 20% of what it should be. In Germany they must stay connected down to a 15% threshold, says Ceña.
PO12.3 applies to all operators connected to the main transmission grid, though REE is considering including wind plant connected at the level of the distribution networks. Existing wind power stations will require retrofitting. "When PO12.3 comes into force, half of the 20 GW targeted for 2011 will be installed. New turbines will not be able to connect if existing ones are not modified," says Ceña.
New projects must use turbines individually equipped with fault ride-through capability. "Spanish turbine manufacturers have long since developed ride-through technology and just need a framework for selling it," says Antoni Martínez of Ecotècnia, a wind turbine supplier. A financial incentive to meet the code is part of the revised wind market framework for wind power introduced in March -- wind plant complying with it will receive 5% more for their output.
"What remains to be done is to verify that new turbines actually provide the ride-through capability they claim," says Ceña. Manufacturers active in Spain have carried out simulations on ride-through technology. "But field verification for each turbine model will be required as part of a verification procedure established by the sector and the TSO," says Ceña. He believes manufacturer field tests could be complete by the spring.
"If everything works, manufacturers could start selling turbines with ride-through capability before that date, based on indemnity contracts with customers," says Ceña. Such warranties will be a stopgap until the lengthy process of standard certification is complete. Meanwhile, manufacturer Vestas is so confident of its technology, it has already committed ride-through capability in a 50 MW contract with Spanish developer Wigep (Windpower Monthly, July 2005).
Sanctions for non-compliance with PO12.3 are not yet defined, but it is not expected that licenses will be granted for new projects not meeting the grid code. Existing plant will lose the 5% incentive. "But anyway, nobody wants to risk losing production and earnings by tripping offline if they can help it," says Ceña.