Modelling of firm offer from combined wind and hydro generations

Abstract—This paper analyses the impact of a firm combined offer by wind and small hydro generators located in the river chain, with a view to address the intermittency of wind generators. Both generations are dispatchable and cleared against their offer prices. They offer a firm, hourly-schedule (WH schedule) for 24 hours ahead of real-time operation to an auction based locational marginal price (LMP) market with other generators offering to meet the system loads. The model network consists of other generators and loads at different buses. The scheduled power is taken off at a predetermined bus, as a load at the bus. This schedule must be met by the wind and hydro combined generations. If necessary, a notional thermal generation is available at a considerable higher price to meet the schedule, at the off-take point. The objective is to minimise the total supply cost for 24 hours and examine LMPs and constraint-on costs while respecting the given WH schedule, nodal power balance constraint, generation limits, branch flow and other limits. Discussion is based on New Zealand (NZ) Electricity Market rules, where generators are self- committed into the market. Three scenarios are studied, and the results presented. Index Terms—Constraint-on payment, Dual Problem, Electricity market, Firm offer, Hydro generation, Optimization