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Operating a power system reliant on wind power for 100% of its supply is feasible and would lead to substantial reductions of CO2 emissions, according to Energinet, the system operator for the west of Denmark. Furthermore, the extra costs of the thermal plant used to balance wind generation to ensure security of supply are quite modest, says Energinet in a recent study, System and Market Changes in a Scenario of Increased Wind Power Production.

Energinet's scenario for operating 100% wind does not mean that all thermal plant will be closed. As part of the analysis, the study looks at how the proportions of base load and peaking plant might be optimised. The requirement for base load plant falls from around 4000 MW with an all-thermal system to just over 2000 MW with 100% wind. Peaking plant requirements, on the other hand, rise from about 1600 MW with an all-thermal system to just over 3000 MW with 100% wind on the network.

With a wind penetration today of about 20%, Denmark leads the world in integrating wind into a national power system. In the windy west of the country, wind at times already meets 100% of consumption. But such wind penetration is only feasible, claim some, because western Denmark's power system is linked with that of Norway, Sweden and Germany.

Those links, however, have a limited capacity and would not be able to export more than about 3000 MW. For that reason, the Energinet study makes no explicit assumption about the ability to export surplus wind energy and instead assumes either that output from the wind turbines will need to be curtailed, or that surplus electricity can be sold at a low price (EUR 13/MWh) to electric boilers or heat pumps. In practice, some exports via the external links might be possible.

The study found that it would not be necessary to curtail wind production -- or dispose of a surplus -- until the proportion of wind energy reached 30% of the market share. After that, the volume of surplus rose quite rapidly, reaching 8 TWh (31% of the total supply) when the wind energy share reached 100%.

Under the Energinet scenario, carbon emissions associated with electricity generation fall from 19 million tonnes of CO2 per year with an all-thermal system, to six million tonnes with a 100% wind system. This explodes the fallacy that the need to operate extra reserve plant to keep a wind system stable negates the environmental benefits of wind.

The study estimates the extra costs associated with an all-wind system are EUR 15/MWh if the surplus cannot be sold, or EUR 9/MWh if the surplus can be sold. Since the study's publication, however, gas prices have risen, likely making the extra costs of converting to wind even less.

A separate study from Elkraft, the system operator in eastern Denmark, Long Term Challenges in the Electricity System, looks at the issues surrounding increased wind penetration against a wider backdrop, covering all the Nordic countries. Again, the development of wind energy is forecast to have economic benefits compared with running and all thermal power system.