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H2020

HP-MOSES Report Summary

Project ID: 774866

Periodic Reporting for period 1 - HP-MOSES (Solar assisted high temperature heat pumps for molten salt energy storage applications.)

Reporting period: 2017-05-01 to 2017-10-31

Summary of the context and overall objectives of the project

The developed project addresses the challenges expressed in the Call - Horizon 2020 dedicated SME Instrument 2016-2017 Topic - SMEInst-09-2016-2017: Stimulating the innovation potential of SMEs for a low carbon and efficient energy system by proposing a new energy storage solution that is expected to contribute in decarbonising and making more flexible and efficient the European energy system. The main objective of the project have been the technical and economic feasibility analysis of an innovative large-scale (50-1000 MW) thermo-electrical molten salt energy storage system based on high-temperature heat pumps (HP-MOSES).
The renewable net generation in EU countries has been progressively growing in recent years. In particular, since 2013 the shares of wind and solar energy have been increasing until reaching the 9.3% and the 3.1% of the total European net generation. These trends of growing shares of variable renewable energy sources in the European electricity grid are expected to continue in future years in order to reach the 20-20-20 climate and energy European targets and the EU transition to a competitive low-carbon economy by 2050. In this scenario, energy storage systems are considered a key technology for enabling the progressively higher degrees of integration of variable renewable sources in the grid. In particular, the main functionalities of transmission grid-bulk storage on a national and European level are: balancing demand and supply (seasonal/weekly fluctuations, large geographical unbalances, strong variability of wind and solar), grid management (voltage and frequency regulation, complement to power plants for peak generation, participate in balancing markets, cross-border trading) and energy efficiency (better efficiency of the global generation mix, with time-shift of off-peak into peak energy).
The proposed storage system can be considered a promising alternative to current technologies for widespread and large-scale electricity storage. Compared to PHS and CAES, HP-MOSES system has the great advantage to be free from geological and geographical constraints (site-independent) with a low environmental impact and present a large scalability. In the European scenario, despite the urgent need, commercial site-independent alternatives with performance and cost comparable to PHS and CAES are not available.
The proposed TEES (Thermo-Electrical Energy Storage) system consists of three main sections: a high-temperature Heat Pump (HP) (charging section), a molten salt Thermal Energy Storage (TES) system (storage section), and a steam Rankine cycle (discharging section). Its working principle is that during periods of excess electricity generation, the high-temperature HP converts surplus electricity into thermal energy (charge phase), which is stored in a molten salt hot tank. During periods of high electricity demand, the stored heat is converted back into electricity in the steam Rankine cycle (discharge phase).The plant acronym is HP-MOSES (Heat Pump Molten Salt Energy Storage system) and its basic concept layout is shown in Figure 1.
While the molten salt thermal storage and the power block (Steam Rankine cycle) are established technologies, the proposed innovation stands in the high temperature (Tmax ≥ 350°C) solar assisted supercritical heat pump. Currently, industrial heat pumps work at maximum temperatures around 120°C, so that reaching such high temperatures keeping a high Coefficient of Performance (COP) has been a technical challenge. Within recent years, various TEES concepts using low-temperature heat pumps were developed with different working fluids and thermodynamic cycle designs for small-scale applications. Although some demonstration projects were planned, none of them has been already realized. Unlike these concepts, the proposed HP-MOSES system is aimed at high-temperature applications for large-scale energy storage, where the involved power is of the order of 50-1000 MW and the stor

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

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 ac

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

The established technologies for bulk energy storage are Pumped Hydro Storage (PHS) and Compressed Air Energy Storage (CAES), both of which exploit geographical storage means and hence constrained in their deployment. According to EASE (European Association for Storage of Energy), there are over 170 GW of PHS capacity in operation worldwide. Europe is the second biggest zone, with 57 GW, accounting for approximately 33% of the market. In general, the future deployment possibilities for PHS are considered to be very limited due to lack of suitable sites. Concerning CAES, only two plants are in operation worldwide with 400 MW of total capacity. The potential sites for future CAES plants are more abundant than PHS ones, but the reliance of CAES technology on fossil fuels is a significant drawback
The HP-MOSES system has the novelty to be a site-independent thermo–electrical energy storage system for large-scale applications. It has no geographical constrains, which means that it can be installed directly within a thermal power plant site, thus creating an integrated power generation/energy storage system. Due to the above features, the key market application has been identified within large-scale power producers: the proposed system would allow plant owners that suffer from an under-utilization of their production capacity, an immediate financial benefit in terms of an increase of the operational utilization factor, fuel savings and thermal efficiency (reduction of off-design working hours). An increase of the average annual thermal efficiency of an existing fossil-fired power plant of about 5% would for instance produce a reduction of about 14% in terms of fuel consumption, with a consequent significant reduction in CO2 emissions.
The feasibility study has demonstrated the strong potential of the proposed technology, which has proven to be competitive with respect to the other existing large-scale storage solutions. The analyzed case studies stressed the need to put efforts in the reduction of HP-MOSES total investment cost in order to reach the target of a cost-effective and commercially viable large-scale site-independent energy storage system. Therefore, the overall risk associated with the studied storage system is mainly strategic rather than technical and economic, in terms of developing a systemic approach to storage, thus bridging technical, regulatory, market and political aspects.

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