Wind-hydro firming with environmental constraints in New Zealand

This paper examines a proposal for firming wind turbine generation by using hydraulic storages associated with a chain of hydro generators on a river. This is the situation in the New Zealand power system where an increasing number of wind turbines could be combined with existing small storage hydro power stations on New Zealand rivers. This paper supposes that wind and small hydro are offered as a firm capacity product into the wholesale electricity market. An algorithm is presented to determine the hydro-wind generator operating strategy for 24 hours ahead of real-time operations in order to minimize cost or maximize the generator´s profit. The algorithm uses i) hydro generation from the small storages in a river chain to mitigate the wind generation variability, ii) variable penalty prices in the objective function to incentivise combined hydro and wind generation to minimize the deviation from a committed schedule and iii) environment constraints on hydrology to examine the effects on cost and profitability with and without a small regulating storage at the end of the river chain. A number of scenarios are studied and their results are presented.