  In this paper aspects related to handling of intraday imbalances for hydro
and wind power are addressed. The definition of imbalance cost is established
and used to describe the potential benefits of shifting from plant-specific
schedules to a common load requirement for wind and hydropower units in the
same price area. The Nordpool intraday pay-as-bid market has been the basis for
evaluation of imbalances, and some main characteristics for this market has
been described. We consider how internal handling of complementary imbalances
within the same river system with high inflow uncertainty and constrained
reservoirs can reduce volatility in short-term marginal cost and risk compared
to trading in the intraday market. We have also shown the the imbalance cost
for a power producer with both wind and hydropower assets can be reduced by
internal balancing in combination with sales and purchase in a pay-as-bid
intraday market
