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This paper describes a new underwater pumped storage hydropower concept (U.PSH) that can store electric energy by using the high water pressure on the seabed or in deep lakes to accomplish the energy transition from fossil to renewable sources. Conventional PSH basically consists of two storage reservoirs (upper and lower lake) at different topographical heights. It needs special topographic conditions, which are only limitedly available in mountain regions. Furthermore, due to the lack of acceptance and the environmental impact, new conventional PSH projects are very unlikely to be built in larger numbers in Europe in the near future. The presented solution solves these issues by placing the storage system on the seabed, thus having other geographical requirements. It operates as follows: in contrast to well-known conventional PSH plants, which use two separated water reservoirs of different heights, the U.PSH concept uses the static pressure of the water column in deep waters by installing a hollow concrete sphere in deep water. Storage of electricity is achieved by using a reversible pump in the hollow sphere. Upon opening a valve, water flows into the sphere, driving a turbine/generator, thereby discharging the storage device. In order to re-charge, the water is pumped out of the sphere against the pressure of the surrounding water. The power and energy, respectively, are proportional to the surrounding water pressure at the seabed. The amount of energy stored depends on the water depth and the volume of the spheres. The spheres need a cable connection to the shore or to a close-by floating transformer station (e.g., an offshore wind plant). No other connections such as pipes are needed. The functional principle of this energy storage technology, its state of the art, its storage capacity and the shape and size of the required spheres are discussed in this paper. [ABSTRACT FROM AUTHOR]

Abstract: This paper analyses the hybrid solar and hydro (SHE) system as a unique technological concept of the sustainable energy system that can provide continuous electric power and energy supply to its consumers and the possibilities of its implementation in Europe and areas with similar climate. The sustainability of such system is based on solar photovoltaic (PV) and hydroelectric (HE) energy as renewable energy sources (RES). For the purpose of connecting all relevant values into one integral SHE system, a mathematical model was developed for selecting the optimal size of the PV power plant as the key element for estimating the technological feasibility of the overall solution. Sensitivity analysis (parameter analysis) was made for the model, where local climate parameters were varied: solar radiation, air temperature, reservoir volume, total head, precipitation, evaporation and natural water inflow. It has been established that, apart from total head (which is to be expected), solar radiation, hydro accumulation size and natural water inflow have the biggest effect on the calculated power of the PV power plant. The obtained results clearly show a wide range of implementation of the new energy source (SHE system), i.e. from relatively cold climates to those abundant in solar energy, but also with relatively small quantity of water, because it only recirculates within the system. All this points to the necessity for further development of hybrid systems (RES+HE systems) and to the fact that they could play an important role in achieving climate objectives. [Copyright &y& Elsevier]

As the share of variable renewable energies in the power system increases, so does the need for flexibility options. These include, inter alia, energy storage, network optimization and expansion, and demand side management. In this paper, a broad sensitivity analysis is carried out to assess the potential role of innovative electrical energy storage technologies in comparison to well-established ones. The innovative technologies considered include compressed heat energy storage, adiabatic compressed air energy storage, power-to-heat-to-power storage, and reversible solid oxide fuel cells storage. To this aim, the cost-optimizing energy system model REMix has been applied to analyze the impact of main techno-economic parameters of electrical energy storages on their role in the future European power supply system. Two main studies have been calculated. The first one deals with a cost sensitivity analysis on a generic storage technology. Among the main findings is that – beside cost – the ratio between photovoltaics and wind power potentials in a particular region have a relevant impact on the capacity as well as on the energy to power ratio of the installed storages. In addition, a strong competition has been observed between energy storages and gas turbines. The second scenario evaluates the competition between well-established and innovative energy storage technologies. The results show that while some of the regions – namely southern Europe, alpine regions and Scandinavia – mainly rely on pumped hydro storage, in most of Central European regions and United Kingdom the cost optimal solution consists of a mix of pumped hydro storage (totaling 64.2 TWh/y of discharged energy in Europe), hydrogen underground storage (45.1 TWh/y) and batteries (27.1 TWh/y), with an additional small share of power-to-heat-to-power storages (0.1 TWh/y). In line with earlier studies, hydrogen storage is found mostly in regions with high wind power supply, while the distribution of batteries is more spread overall in Europe. The model results underline the high sensitivity of the economic efficiency of storage facilities to the investment costs and their components. [ABSTRACT FROM AUTHOR]