Reversible high-temperature heat pumps for peak load coverage in geothermal heating plants: A techno-economic analysis

High-temperature heat pumps (HTHP) are a promising technology to cover the peak demand in geothermal heating plants (GHP) during winter, but are often not economical due to few operational hours. Reversible HTHPs (RHP), which can also operate as an ORC for power generation, could tackle this issue. Therefore, this work investigates the use of RHPs for peak load coverage in GHPs by means of annual plant simulations. The subsequent techno-economic analysis compares the RHP to conventional peak load technologies such as HTHPs and gas boilers. By introducing a physical model for the air-cooled condenser (ACC), part load effects during ORC operation and the impact of different ACC sizes are investigated. The results show that the ACC size can be reduced by 50 % of its initial value without relevant reductions in annual net electricity generation. With a 50 % reduced ACC size, the RHP becomes competitive, yielding a levelised cost of heat (LCOH) of 145.4 €/MWh, and replaces the HTHP (LCOH of 150.4 €/MWh) as the second-best peak load system after the gas boiler (LCOH of 99.9 €/MWh) for 2024 energy prices. Finally, a sensitivity analysis is conducted to investigate the impact of fluctuating energy prices, different ACC sizes and varying electricity price ratios (i.e. the ratio of sales and purchase price). The results indicate that RHPs and HTHPs are most competitive for higher gas prices and the RHP system is well suited to lower the investment risk, as it shows a high resilience towards fluctuating electricity prices. • Realistic operating conditions through load profiles derived from an existing plant. • Realistic capacity limitations through part-load models for the major components. • Comparisons of different peak-load technologies for geothermal heating plants. • Gas boiler favourable for low gas prices, HTHP or RHP best for larger gas prices. • RHP shows higher resilience towards fluctuating electricity prices than the HTHP.