Within the last 25 years, the share of renewable energy sources in German electrical energy production has been rising considerably and is expected to increase further in the coming years. The volatility of renewable energy sources results in an increasing mismatch between supply and demand of electrical energy, creating the need for storage capacities. The storage of electrical energy in the form of thermal energy can be realized by Pumped Heat Electricity Storage (PHES) systems, a location-independent alternative to established storage technologies. Detailed analyses, considering the transient operation of PHES systems based on commercially available or state-of-the-art technology, are currently not publicly accessible.
In this work, numerical models that enable a transient simulation of PHES systems are created using the process simulation software EBSILON Professional. For that purpose, numerical models of packed bed sensible heat TES systems as well as latent heat TES systems are developed and validated. While the model of the packed bed sensible heat TES systems is based on modifications of a built-in component, the model of the latent heat TES systems was independently modeled and implemented as supplementary component.
For the analysis of PHES systems, a characteristic operation scenario is deduced from the European market for electrical energy. Based on the day-ahead market for Germany and Austria, which shows a high predictability regarding daily electricity price distributions, the PHES systems accomplish a complete charging, storage and discharging period per day. For a high economic feasibility, an electrical input power in the order of 10 MW is combined with charging and discharging durations of 4 h.
PHES systems based on Joule and Rankine cycles are designed, focusing on commercially available and state-of-the-art technology. Design parameters are optimized in order to reach high round-trip efficiencies. Employing the models developed in this work, the transient operation of the PHES systems is simulated in accordance with the characteristic operation scenario. A detailed exergoeconomic analysis, which combines an exergy and an economic analysis, is conducted for the PHES systems based on Joule cycles. A simplified sensitivity analysis is employed to evaluate the influence of uncertainties in economic input parameters on the results.
Depending on design parameters, the analyzed PHES systems reach round-trip efficiencies between 36 % and 43 %. Having lower efficiencies than established storage technologies, PHES systems have the advantage of being location independent. The exergoeconomic analysis reveals that an economic operation of PHES systems is currently not possible. This, however, is at least partly caused by the conditions at the German market for electrical energy, which are unfavorable for the operation of electrical energy storage systems.
In summary, the PHES systems designed and the numerical models developed in this work enable the exergoeconomic analysis and assessment of these electrical energy storage systems, based on available technology and a realistic operation scenario
