Thermo-Electric Energy Storage with Solar Heat Integration: Exergy and Exergo-Economic Analysis

Abstract

A Thermo-Electric Energy Storage (TEES) system is proposed to provide peak-load support (1–2 daily hours of operation) for distributed users using small/medium-size photovoltaic systems (4 to 50 kWe). The purpose is to complement the PV with a reliable storage system that cancompensate the produc tivity/load mismatch, aiming at off-grid operation. The proposed TEES applies sensible heat storage, using insulated warm-water reservoirs at 120/160 °C, and cold storage at −10/−20 °C (water and ethylene glycol). The power cycle is a trans-critical CO2 unit including recuperation; in the storage mode, a supercritical heat pump restores heat to the hot reservoir, while a cooling cycle cools the cold reservoir; both the heat pump and cooling cycle operate on photovoltaic (PV) energy, and benefit from solar heat integration at low–medium temperatures (80–120 °C). This allows the achievement of a marginal round-trip efficiency (electric-to-electric) in the range of 50% (not considering solar heat integration).The TEES system is analysed with different resource conditions and parameters settings (hot storage temperature, pressure levels for all cycles, ambient temperature, etc.), making reference to standard days of each month of the year; exergy and exergo-economic analyses are performed to identify the critical items in the complete system and the cost of stored electricity.

LCA and Exergo-Environmental Evaluation of a Combined Heat and Power Double-Flash Geothermal Power Plant

“…where the parameter (Pts/s) is the environmental impact rate, expressed in single score eco-points (here, ILCD 2011 Midpoint) per unit of time (considering 7446 hr/yr [36] and 30 years of lifetime [37]) and (MW) is the exergy content related to each j-stream. With respect to LCA, EEvA applies conservation balances for mass and energy through the whole plant and identifies the exergy destructions and losses.…”

Exergo-economic assessment of OTEC power generation

“…Particularly, through the combination of the exergy an economic models, it is possible to assess the cost effectiveness of each component, allocating to each exergy stream a specific cost [9]. The applied economic model considers the instantaneous cost of each component in €/s.…”

Optimum Choice of Energy System Configuration and Storages for a Proper Match between Energy Conversion and Demands

“…Fiaschi et al [18] propose a solar-integrated thermo-electric energy storage (TEES) system for one to two daily hours of operation to compensate for the mismatch between electricity generation and demand in small-to-medium-size photovoltaic systems (4 to 50 kWe). Given the drawbacks of alternative storage systems in this range of power, such as the limited life cycle of batteries or the low round-trip efficiency of chemical storage, the authors believe that TEES systems may represent an interesting solution to guarantee dispatchability to energy systems based on renewables.…”