Abstract
Compressed Air Energy Storage is recognized as a promising technology for applying energy storage to grids which are more and more challenged by the increasing contribution of renewable such as solar or wind energy. The paper proposes a medium-size ground-based CAES system, based on pressurized vessels and on a multiple-stage arrangement of compression and expansion machinery; the system includes recovery of heat from the intercoolers, and its storage as sensible heat in two separate (hot/cold) water reservoirs, and regenerative reheat of the expansions. The CAES plant parameters were adapted to the requirements of existing equipment (compressors, expanders and heat exchangers). A complete exergy analysis of the plant was performed. Most component cost data were procured from the market, asking specific quotations to the industrial providers. It is thus possible to calculate the final cost of the electricity unit (kWh) produced under peak-load mode, and to identify the relative contribution between the two relevant groups of capital and component inefficiencies costs.
Highlights
Compressed Air Energy Storage (CAES) and Pumped Hydro Energy Storage, air and water being the most inexpensive fluids, are likely to be the most reliable and technologically sound options for massive energy storage [1,2], even if other alternatives are proposed [3].Pumped Hydro Energy Storage systems require two reservoirs at different elevation and a pump/turbine for storing/recovering energy in form of water head
The analyses considered in this work involves a slow evolution of steady-state operating conditions; for the analysis of most components, it is sufficient to consider the steady-state form of the exergy rate balance
Intercooler 3 has the largest heat duty (1800 kW, Table 2) and it is not surprising that it gives the largest contribution to exergy destruction among all similar components (29%); the second largest contribution (21%) is produced by IC1, even if its heat duty is not among the largest (1414 kW, Table 2); this can be explained by the distribution of pressure rise among the seven compression phases
Summary
Compressed Air Energy Storage (CAES) and Pumped Hydro Energy Storage, air and water being the most inexpensive fluids, are likely to be the most reliable and technologically sound options for massive energy storage [1,2], even if other alternatives are proposed [3]. Existing CAES plants are all gas fuelled, compressed air being heated in a combustion chamber ahead of the turbine during the expansion phase These systems combine energy storage within a power plant. All components of a CAES plants are commercially available: compressors, heat exchangers, large volume vessels for high pressure (in case of artificial storage), radial expanders, insulated water reservoirs. The proposed ACAES system (Figure 1, from an idea by ―ENEL Ingegneria e Innovazione‖ similar to the scheme proposed in [4]), is designed as a typical backup unit for wind energy plants It is based on a seven-stage intercooled compression train. Before re-use, water is cooled down to the temperature of the environment by an external cooler
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