Chapter 3 Dead Battery? Wind Power, The Spot Market, and Hydro Power Interaction in the Nordic Electricity Market Abstract It is well established within both the economics and power system engineering literature that hydro power can act as a complement to large amounts of intermittent energy. In particular hydro power can act as a ”battery” where large amounts of wind power are installed. This paper attempts to extend that literature by describing the effects of cross-border wind and hydro power interaction in a day-ahead ”spot” market. I use simple econometric distributed lag models with data from Denmark 35