Merit Study of Battery or Hydrogen Energy Storage for Large Scale, Combined Wind and Solar Electricity Generation

Ashley K. Moore, Wright State University


In the past several years, the energy sector has experienced a rapid increase in renewable energy installations due to declining capital costs for wind turbines, solar panels, and batteries. Wind and solar electricity generation are intermittent in nature which must be considered in an economic analysis if a fair comparison is to be made between electricity supplied from renewables and electricity purchased from the grid. Energy storage reduces curtailment of wind and solar and minimizes electricity purchases from the grid by storing excess electricity and deploying the energy at times when demand exceeds the renewable energy supply. The objective of this work is to study the generation of electric power with wind turbines and solar panels coupled to either battery energy storage or hydrogen energy storage. So that logical conclusions can be drawn on the economic effectiveness of battery and hydrogen energy storage, four scenarios are analyzed: 1) purchasing all required electricity from the grid, 2) generating electricity with a combined wind and solar farm without energy storage, 3) generating electricity with a combined wind and solar farm with battery energy storage, and 4) generating electricity with a combined wind and solar farm with hydrogen energy storage. All four of these scenarios purchase electricity from the grid to meet demand that is not met by the renewable energy power plant. All scenarios are compared based on the lowest net present cost of supplying the specified electrical loads to serve 25,000 homes in Rio Vista, California over 25 years of operation. The detailed economics and electric power production of both wind and solar combined with energy storage for any size of wind facility, solar facility, battery facility, and hydrogen facility are analyzed with a MATLAB computer program developed for this work. The program contains technical and economic models of each of these systems working in different combinations. Current equipment capital costs and operation and maintenance costs based on industry reports or general literature are utilized in the economic model. Electricity production and storage are modeled and compared to the specified load on an hour-by-hour basis. The program contains models of electricity production with solar panels given the amount of radiant energy incident on the panels in Rio Vista, California. Electricity production with wind turbines is modeled based on the local wind resource. The models of energy storage in lithium-ion batteries and chemical energy storage using hydrogen are included in the program. The hydrogen energy storage model includes hydrogen that is generated and consumed via reversible solid oxide electrolyzer/fuel cells and stored as compressed hydrogen in tanks buried in the ground. The results from these models provide the least cost equipment configurations for each renewable energy power plant, given the local resources, local load demand, and equipment costs. The results from wind and solar with and without energy storage are compared to purchasing all load electrical power from the grid at prevailing prices. The economic results of wind and solar with both types of energy storage are calculated and compared to wind and solar alone to determine if energy storage is economically justified. In addition, the least cost equipment configurations show where adding energy storage justifies the installation of additional wind or solar capacity. While economic optimization is the primary focus of this work the performance of wind/solar/energy storage scenarios are also compared. The net present cost results show that electricity generated by wind and solar without energy storage, wind and solar combined with battery energy storage, and wind and solar combined with hydrogen energy storage all result in significant cost savings versus purchasing all the electricity from the grid to serve the load. However, a strong economic case cannot be made to justify adding battery energy storage or hydrogen energy storage in combination with wind and solar versus wind and solar alone. The resulting optimum cost equipment configurations show that battery energy storage justifies more solar capacity than wind and solar alone, illustrating that battery energy storage is a good partner for solar in this location. At current equipment and electricity prices, the addition of a hydrogen energy storage system did not change the least cost sized capacities of wind and solar equipment compared to the least net present cost capacities of wind and solar alone. In the optimum cost configuration, battery or hydrogen energy storge in combination with wind and solar serves more load than wind and solar alone, for similar net present costs.