The goal of the feasibility study of the HP-MOSES storage system was to identify and select the heat pump configuration that would provide the best trade-off between technical performance and economic viability (low system complexity) linked to the boundaries of the specific storage concept.
Using the environment as the low-temperature heat source, a number of heat pump designs have been investigated with regards to the achievable round-trip-efficiency, defined as the ratio between the total electrical energy output and the total electricity input, for different working fluids (CO2, refrigerants, Air and Argon), processes (transcritical/supercritical) and system layouts (regeneration vs. non-regeneration). The selected configuration was the Supercritical-recuperated Air cycle since it represented, for the same round-trip-efficiency, the simplest solution in terms of plant installation complexity. The cycle operative parameters have been then optimized to maximize the round-trip-efficiency.
The main technical and economic features of the optimized HP-MOSES system are summarized and compared to competitive large-scale energy storage technologies in Figure 2.
Once fixed the HP-MOSES configuration, two operational strategies have been defined, the Overnight Storage and the Daytime Storage, that can be respectively adopted depending on which kind of plant the HP-MOSES system is integrated into, as described in Figure 3. Each strategy can provide a combination of the most common energy storage generation/bulk services and a full cost-benefit analysis is required to establish which option is the most suitable for the power system of any European country. The two strategies have been matched to a specific market segment according to the following considerations: the Daytime storage strategy is applied in the first market segment (European countries where VRES>20%) because of the higher share of VRES generating surplus electricity, while the Overnight storage addresses the second segment (VRES>10%) in order to provide support to power system stability.
Germany and Italy have been selected as target markets for each segment since, despite their low VRES share in national generation compared to that of other countries belonging to their segment, they both have the largest VRES installed capacity and the highest number of fossil-fuel power plants. The economic feasibility of the proposed application was evaluated in accordance with the main methods of economic and financial evaluation of investment projects: the recovery period (payback period) and the evaluation of profitability actualized in terms of Net Present Value (NPV) and Internal Rate of Return (IRR). To account for the variations of surplus electricity purchasing price and of the CO2 EUA in ETS, a sensitivity analysis of the HP-MOSES annual revenues for Italy and Germany is performed. In the German case in order to have revenues, the buying and selling price difference must be enough to compensate the energy lost during the thermodynamic cycles of the storage system. Therefore, since the storage system has a round-trip efficiency equal to 0.55 the maximum price at which electricity can be bought is 55% of the selling price. For the Overnight storage, applied to Italy, different scenarios have been investigated varying the discharging hours, which affect the amount of saved coal. Then, fuel savings have been quantified for different coal prices projections.
The case studies demonstrated the strong potential of the proposed technology, which has proven to be competitive with respect to the other existing large-scale storage solutions.
HP-MOSES has ambitious plans to disseminate and exploit the methods developed, ensuring wide-scale replication throughout European countries. The overall goal is to disseminate project results and to increase knowledge about on-going research and activities with commercial potential within the concept of the project.
The planned dissemination activities aim to raise awareness about the activities and the results of the project within the respective industry sectors, the scientific community and the stakeholders (private and public investors and cooperatives of the renewable energy sector).
Another stakeholder group that will be considered and informed at the end of phase 1 will be energy consultants dealing with planning and development of renewable energy systems.
Stakeholders, energy community, policy makers and research community will be informed on the important technological contribution the project will offer to reach H2020 goals towards a low carbon and efficient European energy system.
