A Hybrid Energy Storage System Based on Metal Hydrides for Solar Thermal Power and Energy Systems

Author(s):  
Shahin Shafiee ◽  
Mary Helen McCay

Thermal storage in an important operational aspect of a solar thermal system which enables it to deliver power or energy when there is no sunlight available. Current thermal storage systems in solar thermal systems work based on transferring the generated heat from sunlight to a thermal mass material in an insulated reservoir and then withdraw it during dark hours. Some common thermal mass materials are stone, concrete, water, pressurized steam, phase changing materials, and molten salts. In the current paper, a hybrid thermal energy storage system which is based on two metal hydrides is proposed for a solar thermal system. The two hydrides which are considered for this system are magnesium hydride and lanthanum nickel. Although metal hydride Energy Storage Systems (ESS) suffer from slow response time which restricts them as a practical option for frequency regulation, off peak shaving and power supply stabilization; they can still demonstrate significant flexibility and good energy capacity. These specifications make them good candidates for thermal energy storage which are applicable to any capacity of a solar thermal system just by changing the size of the ESS unit.

Author(s):  
Cary E. Laird ◽  
Andrew G. Alleyne

Abstract The practice of hybridizing energy storage systems is vital to high ramp rate power applications, in which energy storage systems are constrained by strict power and energy requirements. Hybrid energy storage is typically studied in the electrical and thermal domains separately, but due to the inherent link between electrical and thermal energy domains, it is necessary to examine hybrid energy storage in both domains simultaneously. In this paper, a combined electro-thermal energy storage system is modeled and simulated. Equivalent circuit and lumped-parameter models are used to facilitate control design. PI controllers are designed for both the electrical and thermal domains to demonstrate the ability to perform multi-domain energy management.


2021 ◽  
Author(s):  
Farzin Masoumi Rad

For a hypothetical solar community located in Toronto, Ontario, the viability of two separate combined heating and cooling systems were investigated. Four TRNSYS integrated models were developed for different cases. First, an existing heating only solar community was modeled and compared with published performance data as the base case with suggested improvements. The base case community was then used to develop a hypothetical solar community, located in Toronto, requiring both heating and cooling. In this second model an absorption chiller was added – Solar Thermal Chiller (STC) system. The chiller received its source heat from the solar thermal system with the supplemental heat from a natural gas boiler. The STC system was designed with two borehole thermal energy storage units (BTES). One was high-temperature BTES for the solar thermal energy storage, and another was medium-temperature BTES for the chillers’ heat rejection. The twenty year simulation results showed that by the fifth year in the heating season, the community operated with 100% solar fraction (SF). In the cooling season, the chiller received 18% of its required energy from the same number of solar collectors as the heating-only community system. The third model was based on the central heat pump system with borehole thermal storage for the heating and cooling, using a PV system as the heat pump power source - Heat Pump Photovoltaics (HPPV) system. The simulation results showed that the system operated favorably from the first year and did not have any significant performance degradation in 20 years. On average, the heat pumps performed with the seasonal COP of 3.3 in the heating mode and 5.9 in the cooling mode. The fourth system, Solar Thermal-Heat Pump Photovoltaics (ST-HPPV), a solar thermal system with borehole thermal energy storage as a supplemental heat source to the HPPV, was investigated. The simulation results showed that this system would be beneficial for a community with the annual heating and cooling difference of more than 75%. By adding a solar thermal system to the HPPV system, the heat pumps’ performance improved by 26% in the heating mode, and exhibited a negligible drop in the cooling mode.


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