Local CHP Plants between the Natural Gas and Electricity Systems

Local combined heat and power (CHP) plants in Denmark constitute an important part of the national energy conversion capacity. In particular they supply a large share of the district heating networks with heat. At the same time they are important consumers as seen from the gas network system, and they contribute significantly to the electricity production.

CHP is, together with the wind power, the almost exclusive distributed generation in Denmark. This paper deals with the CHP as intermediary between the natural gas system and the electricity system. In particular, the relationship between the peak hour characteristics of the electricity and gas systems will be investigated.

The point is here that the two systems will tend to have peak demand during the same hours. This is the typical situation, since load is high during the same hours of the day and of the year. Moreover, the random variations in the load will be correlated between the systems, because both demands in part depend on the climate.

The analysis in the paper is based on a numerical model which simulates the operation of a CHP plant with heat storage. The conditions for the operation of the plant are assumed to be consistent with the conditions that are expected to be in force in Denmark during 2005, where a large part of the local CHP plants will change from being paid for electricity production according to a feed-in tariff, to a situation where the electricity is to be sold on market conditions.

The results will highlight the CHP plant as the link between three energy supply systems, viz., district heating, gas and electricity.