Short Term River Chain Optimisation

Disclaimer

Reasonable care has been taken to ensure that the information in this paper is up to date at the time of issue. Potential users of EMarket should, however, ensure that they evaluate EMarket and this paper through an appropriate evaluation process in consultation with Energy Link. The authors are also reliant on certain information external to EMarket and Energy Link, for which no liability or responsibility can be accepted.

Introduction

This technical bulletin is intended to provide users and interested parties with a detailed explanation of how EMarket’s Short Term River Chain Optimisation (STRCO) module works. EMarket was originally designed to model medium and long-term hydro generation optimisation. This meant that hydro offers were based on medium to long-run marginal costs and did not vary in the short term. The aim of STRCO is to improve the realism of results from EMarket by ensuring that generator behaviour is consistent with the detailed day to day operation of generators in the market. STRCO is not the default for EMarket’s large hydro systems so must be enabled by the user as required.

Other Documents

This bulletin is one of a series of technical bulletins relating to Energy Link’s EMarket model. Taken together, the bulletins replace the old EMarket User Guide. The full series of bulletins covers an overview of the EMarket model, the details of the four major New Zealand hydro systems modelled in EMarket, water values and hydro offers, power flows, dispatch and nodal pricing, short term river chain optimisation and company optimisation.

Overview

Modelling in EMarket is also usually done with steps that aggregate a large number of trading periods together. Whilst changes in load through the day can be modelled, generator offers remain constant. In modelling the market behaviour over the course of a day it is necessary to determine how generators may adjust for intra-day fluctuations in demand and prices.

The benefits of determining short term behaviour extend beyond the ability to model in detail the daily behaviour of the market, since short term fluctuations in offers will have a gross effect on the overall behaviour. An example of this is the meeting of minimum flow requirements on the outflow of a large hydro system. Here the water throughput that is required for the minimum flow at night can be used for generation during the day, accumulating at the lowest reservoir which will empty over the night periods. It is difficult to determine the overall long term effect of minimum flow requirements on energy offered without understanding the short term effects in some detail.

In principle, short term modelling for hydros could include:

• all the hydrological or regulatory constraints on the system;
• the effect of generation on energy price, and price on profit;
• provision of instantaneous reserves.

In EMarket hydro systems can be enabled to optimise using the STRCO module. The optimisation horizon is one week at a resolution of 4 hours.