Optimal heat storage in district energy plants with heat pumps and electrolysers

District energy (DE) plants are transitioning away from being providers of heat and electricity through the cogeneration of heat and power (CHP) to being heat providers consuming electricity for heat pumps (HPs) and electric boilers. Concurrently, hydrogen production for electrofuels may be combined with DEs to exploit thermal losses from electrolysers and electrofuel synthesis. Where CHP units favour high electricity prices and electric boilers or HPs favour low – thus providing incentive for operation at both high and low electricity prices - future DEs with HPs and electrolysers both call for low electricity prices, increasing the need for thermal storage. Costly hydrogen storage could also enable flexible operation. In this article, energyPRO is applied to investigate optimal system compositions with a focus on storage capacities. Results show that added flexibility in the shape of more thermal storage is valuable. Storage costs are more than compensated by the improved performance on the electricity market. Added electrolyser capacity and HP capacity also improve flexibility, but only added HP capacity pays off in business-economic terms. All the modelled ways of increasing flexibility enable the units to perform better on the electricity market – and thus give value to the overall energy system.