(42b) Baseload POWER from Wind Farms Using Magnesium Hydride Slurry for Hydrogen Storage

Renewable energy farms, such as wind and solar farms, have the potential to supply all the energy that is needed by the United States. The issue is to use the energy when it is available or to store it until it is needed. The intermittency of wind and solar makes it difficult to power more than 50% of the electric grid.

We are all quite familiar with stored energy. Our economy relies on the energy stored in fossil fuels. The use of stored energy allows us to use energy when we need it to produce light, heat, and motion.

Hydrogen provides an alternative to fossil fuels for energy storage. Electricity, from wind or solar farms, can be stored by electrolyzing water to produce hydrogen and oxygen. This hydrogen can be stored until it is needed and then burned with air in a gas turbine to turn a generator and produce electricity again. The byproducts of these reactions, besides electricity, are water and some nitrogen oxides. Alternatively, the hydrogen can be used in a fuel cell to produce electricity directly with byproducts of only water.

Safe Hydrogen, LLC has been developing a hydrogen storage medium using magnesium hydride in a slurry with light mineral oil. This slurry is an inexpensive large-scale storage medium for hydrogen. Once stored in the metal hydride, the slurry can be stored very safely at ambient temperature and pressure. It can be pumped between tanks like a liquid fuel and transported and stored inexpensively using the existing liquid fuels infrastructure. When charging or discharging, the slurry is pumped into a reactor where conditions are provided to enable rapid hydrogen absorption or desorption. The slurry can be cycled repeatedly. Safe Hydrogen has demonstrated 50 cycles with the slurry to show that the slurry can be cycled enough times to be economical. At the conclusion of the cycling test, the performance of the metal hydride was the same as at the beginning of the test. Others have demonstrated cycling of dry magnesium hydride up to 1,000 times.

In this paper, we present the results of a study evaluating the cost of electricity using magnesium hydride slurry for hydrogen storage to make a wind farm, producing intermittent energy, into a dispatchable or baseload electrical energy system. For the study, we use 10 min. wind data, from the National Renewable Energy Laboratory, and hourly load data, recorded by ISO New England, to model the performance of dispatchable and baseload wind systems. The computer model calculation uses an entire year of data to determine the amount of wind power sold directly, the amount of energy stored and recovered, and the amount of electrical power sold to make up for when the wind is not blowing sufficiently. Costs for all the major components of the systems are used to estimate the capital cost of the systems. Maintenance and operating costs estimates are included. Costs for the hydrogen storage system are scaled from our experimental systems. The hydrogen storage system includes electrolysis machines, magnesium hydride slurry, reactors for hydriding and dehydriding the slurry, compressors, and gas turbine generators. The capital cost for the storage is approximately $10 per KWh stored. We conclude that a renewable energy farm system using a wind farm and storage system can operate as a baseload power plant for an electricity cost of $88/MWh providing a return of 10% to its investors. When the system is operated to provide dispatchable electricity, a 10% internal rate of return (IRR) can be achieved with $110/MWh.

The paper discusses the results of the study for a range of contract prices. The higher prices might be found on an island system. The lower prices are typical of large metropolitan areas.

The analysis assumes an investment tax credit of 30% and the sale of electrical energy, above that contracted, up to the full capacity of the grid connection (250MW) when the price of electrical energy is higher than the contract price with the utility. The contract power production is assumed to be 150 MW. The wind farm is scaled to provide the energy required to supply the needs of the baseload or dispatchable systems.

The storage system is sized to meet the demand of the system throughout the year. This requires about 21 days of storage for the dispatchable case and 30 days of storage for the baseload case. The data used for this analysis showed more wind energy in the winter than in the summer. This required storage to carry some of the winter wind energy to the summer demand. If the renewable energy system were made up of wind farms and solar farms (which supply more energy in the summer than in the winter), then the storage system could be smaller and the costs would be reduced.

Other storage technologies like Lithium Ion batteries, flywheels, and flow batteries technically can be used as storage media. Unfortunately, these technologies have extremely high capital costs per KWh stored. Their use would require a cost to consumers in the range of $2000-$5000 per MWh. These technologies have markets in frequency and voltage control, short time shifting to reduce peak power, and to defer building of additional transmission and distribution capacity.