Integration of pit thermal energy storages into district heating networks – a techno-economic case study
Ioannis Sifnaios, Jianhua Fan, Adam R. Jensen
Abstract
• Case study of the economic impact of short-term pit thermal energy storage. • Optimization of storage volume and charge/discharge capacity. • Adding a short-term pit storage decreased the levelized cost of heat by 14% • Reducing the charge temperature of the storage resulted in overall cost reductions. In recent years, many district heating (DH) providers have started transitioning from fossil-fueled generation to electricity-based alternatives such as heat pumps and electric boilers. Consequently, DH plants are switching from being predominantly electricity producers to electricity consumers, making DH prices more exposed to variations in electricity prices. One way the impact of electricity price volatility may be mitigated is by deploying short-term operated pit thermal energy storage (PTES). While previous studies have investigated PTES systems for seasonal heat storage systems charged with thermal generation units such as solar thermal, the objective of this study is to investigate their impact on DH grids relying on electricity-based generation capacity. To address this, the present study used the district heating grid of a Danish city as a case study and modeled the system in TRNSYS using operation data from 2021. Results showed that adding a PTES to an electricity-based reference system decreased the levelized cost of heat (LCOH) by 14 % with a relative payback period of one year. Also, reducing the PTES charging temperature from 90 °C to 80 °C had a positive impact on LCOH (3 % reduction). Last, increasing the control strategy optimization horizon from one week to three was shown to reduce the LCOH by a further 4 %. Overall, integrating PTES in the DH system was found profitable and beneficial to the system in all investigated cases.