POTENTIAL ANALYSIS OF AN ENERGY STORAGE UNIT BASED ON METAL HYDRIDES

Abstract

Electrical power generation is changing rapidly to adjust to the new requiems of the energy market that demands the reductions of green gas emissions. However, most renewable energy sources are intermittent, which presents a great challenge for the stability and reliability of the grid. Great efforts have been done in searching for viable solutions, including electrical energy storage. In this thesis, a new electrical storage system based on metal hydrides is proposed in. Storage systems based on metal hydrides are known for their low-risk, reversibility, highdensity hydrogen storage. The novel design consists of an adiabatic reactor with two different metal hydrides, that balance the heat of an exothermal reaction with the heat consumption in an endothermal reaction during the absorption and desorption of hydrogen. During charging the hydrogen is pumped from one reactor to the other allowing the system to store electrical energy. During discharging the system is coupled with an expander that reduces the pressure of hydrogen from one reactor to the other, allowing the system to output the electrical energy stored. A mathematical model was set up, to understand the mass and heat transferred in the reactors. From the model important information was obtained, first how fast the system can be charge and discharge. Second, the quantity of material required. Using the results from the model an analytical calculation of the potential of the system was done. Five parameters were evaluated energy and power density, specific energy and power and finally the overall efficiency of the system. The system shows great potential, especially per unit of volume. The power density is between the following interval (400 – 500 W/l) which could be compared to NiCd batteries, and some hydrogen fuel cells. In addition, the energy density is between the following interval (400 – 500 Wh/l) comparable with technologies like Lead-acid batteries, Li-ion batteries, NaS batteries, and some fuel cells. It must be considered that the calculation of the performance variables just considers, the volume and mass of the reactor, not the volume and mass of the entire storage system. The efficiency (20 - 50 %), shows that there are still opportunities for improvement of the storage system.