Annual comparative performance and cost analysis of high temperature, sensible thermal energy storage systems integrated with a concentrated solar power plant

摘要

The present study conducts a comprehensive comparative techno-economic analysis of some near-term sensible thermal energy storage (TES) alternatives to the 'standard' two-tank molten salt system for concentrated solar power (CSP) plants. As such, we conducted detailed, relative annual transient simulations for single-medium thermocline (SMT), dual-media thermocline (DMT), and shell-and-tube (ST) systems. To be consistent with recent literature, the DMT and ST systems use concrete with a porosity of 0.2 (e.g. where concrete occupies 80% of the system) as their low cost filler material. The systems were integrated into a validated 19.9MW(e) Gemasolar CSP model, which has a solar multiple of 2.5. For a relative analysis, the storage capacity of each TES alternative was fixed at 722 MWh(th) (15 h storage) for all TES alternatives. Based on this capacity, a geometric optimization was performed on DMT and ST systems to maximize the discharged power and minimize the pressure drop. Using the optimum designs, it was found that a CSP plant with a two-tank molten salt system enables the highest amount of electricity generation in a year followed by the SMT and DMT systems, which resulted in 7% and 9% less electricity generation, respectively. As the worst performer, a CSP plant integrated with a ST system generates 20% less electricity over a year. This implies that despite having the same theoretical capacity, the real performance is not same for the alternatives. While these losses may seem egregious at first, large TES cost reductions are made possible in these alternatives due to the fact that a single tank or concrete can be used (noting that concrete is <1/20th the price per kg of molten salt). We propose herein that the true techno-economic advantage (or lack thereof) of choosing alternative TES systems should be judged by a 'normalized cost of thermal energy storage (NCOTES)' which normalizes the cost of storage systems with regards to their annual electricity generation capacity. According to our analysis, optimized DMT and ST systems without embedded pipes (e.g. bored or formed concrete) can achieve 55% and 46% reductions relative to the NCOTES of the two tank system, respectively (with 650 K as cut-off discharge temperature), while the SMT system has an 13% lower NCOTES than the two-tank system. With embedded pipes, however, the ST design has a higher NCOTES (+1% to +100%, depending on the discharge cut-off temperature), indicating that embedded piping is the biggest cost driver and that the elimination of piping should be a priority in ST systems. Overall, this study provides a methodology for the relative comparison of various sensible TES alternatives, and it gives insight into the most promising alternatives for moving beyond two-tank molten salt systems. (C) 2017 Elsevier Ltd. All rights reserved.