Towards the increased utilisation of geothermal energy in a district heating network through the use of a heat storage

Geothermal energy is a renewable energy source which can provide base-load power supply both for electricity and direct uses, such as space heating. In this paper, district heating systems that are fed by geothermal energy, the so-called geothermal district heating systems, are studied. It is proposed to apply a hot water storage tank in these systems to store hot water in times of low-load and release it to the system during peak load periods in order to minimise the use of peak-up boilers. In this paper, two different models are presented and the results are shown for three different cases of heat demand coverage by geothermal energy. First, a model for the sizing of these systems is developed. The main findings highlight the importance of the insulation both for the storage tank and the pipelines of the network. Secondly, a model that studies the daily and the annual operation of the installation is developed followed by an integrated economic and environmental analysis of the proposed solution. The results indicate that the proposed solution is financially beneficial compared to the traditional case without use of the storage tank as all the financial indices and cash flows are improved. More specifically, the levelised cost of heating decreases by 4.3–14.9% leading to an increased potential income of £87,000–241,000 per year, while the NPV, the IRR and the BCR all increase. Furthermore, the emissions decrease by up to 54.2% and the load factor increases by up to 3.86%. Therefore, the proposed solution is proved to be beneficial from an economic, environmental and energetic point of view as more geothermal energy is utilised in a more economical way with subsequent environmental benefits. © 2015 Elsevier Ltd. All rights reserved.