Storing Wind for a Rainy Day: What Kind of Electricity Does Denmark Export?

On windy days, Denmark tends to export electricity to its neighbours, and to import power on calm days. Storing electricity in this way thus allows the country to deal with the intermittency of wind generation. We show that this kind of behaviour is theoretically optimal when a region with wind and thermal generation can trade with one based on hydro power. However, annual trends in Denmark's trade follow its output of thermal generation, Nordic production of hydro power, and the amount of water available to Scandinavian generators, not wind generation. We estimate the cost of volatility in Denmark's wind output to equal between 4% and 8% of its market value.