Abstract
Metal hydrides can be utilized for hydrogen storage and for thermal energy storage (TES) applications. By using TES with solar technologies, heat can be stored from sun energy to be used later, which enables continuous power generation. We are developing a TES technology based on a dual-bed metal hydride system, which has a high-temperature (HT) metal hydride operating reversibly at 600–800 °C to generate heat, as well as a low-temperature (LT) hydride near room temperature that is used for hydrogen storage during sun hours until there is the need to produce electricity, such as during night time, a cloudy day or during peak hours. We proceeded from selecting a high-energy density HT-hydride based on performance characterization on gram-sized samples scaled up to kilogram quantities with retained performance. COMSOL Multiphysics was used to make performance predictions for cylindrical hydride beds with varying diameters and thermal conductivities. Based on experimental and modeling results, a ~200-kWh/m3 bench-scale prototype was designed and fabricated, and we demonstrated the ability to meet or exceed all performance targets.
Highlights
To reduce energy consumption and greenhouse gas emissions, we need more efficient ways to utilize energy
The system consists of two connected metal hydride (MH) beds: a high-temperature (HT) bed operating at ≥650 °C and a low temperature (LT)
The hydrogen moves to the LT-reservoir, where it forms a hydride at near ambient temperature and releases ~25–35 kJ/mol H2 of heat to the environment
Summary
To reduce energy consumption and greenhouse gas emissions, we need more efficient ways to utilize energy. We can reach higher energy efficiencies by operating at higher temperatures (the molten salts store latent heat at about 400–550 °C) This technology is simple, straight forward, without moving parts, and we believe that we can lower the cost relative to other technologies to meet the DOE cost target of $15/kWh. Metal hydrides do not freeze at the anticipated temperatures, so they will not need any energy to re-heat, like molten salts, and they are known to achieve a long life cycles, so we expect that they can meet the 30-year lifetime target. The state-of-the-art molten salt NaNO3/KNO3 technology operates at a lower temperature, which reduces the exergetic efficiency and has a low heat of reaction that leads to a low energy storage density
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