Power transformers as excess heat sources

The future district heating production is highly uncertain. Large-scale heat pumps, biomass CHPs and excess heat from industries and data centres are seen as promising sources for district heating. A large fraction of the excess heat could be used at competitive costs, as investment and operating costs are relatively low.

However, excess heat often remains unused, mostly due to long-term uncertainties. On the contrary, electricity will be an important part of the future energy system. This will unavoidably lead to the use of power transformers. The thermal losses occurring in power transformers can be used for district heating.

The present paper analyses high voltage power transformers in Denmark as sources for district heating. First, we have employed a thermodynamic model of power transformers to determine the amounts of excess heat they produce based on their load. After that, we have applied thermodynamic analysis of a heat exchanger and a heat pump necessary to extract the excess heat and utilise it for district heating.

Finally, we have performed spatial analyses in GIS to link the power transformers with the specific district heating networks. The results show that the average top oil temperature of the transformers is relatively constant at around 30°C over the seasons. From the theoretical maximum excess heat potential for district heating of 0.28 TWh per year, 0.12 TWh or 0.5% of district heat can be supplied to the consumers due to the losses in the networks and large distances between power transformers and district heating areas.

Entire potential for heat recovery can be utilised through heat pumps, working with an average COP of 4. Therefore, excess heat from power transformers does not have a potential to be an important source of district heating on the national scale, but could be an option on a local scale.