by Tim Storer
Wind power comes with the disadvantage of intermittent gaps in energy production and instances of excess supply. This variability puts strain on the electric grid and is the primary barrier to large-scale wind power integration. In order to combat this issue, various forms of energy storage have been considered to bridge the gap between supply and demand of wind power. Gao et al. 2014 conduct a brief literature review on all existing energy storage systems (ESS) for wind power. Each method comes with drawbacks associated with scale, cost, or safety, but hydrogen-oxygen storage was seen here as the best future option. By improving storage technologies, wind energy will become more viable in the market and help to reduce the share of energy coming from fossil fuels that contribute to climate change. In addition to the literature review, this study examined a possible hydrogen-oxygen ESS in Jiangsu Province, China and saw that such an operation could be profitable in the current market.
While there are some operational forms of ESS, there is a variety of issues preventing ESS –and subsequently, wind power– from becoming widespread energy sources. For example, battery power is too costly and difficult to build at a large scale, systems that involve pumping water upward for energy storage have geographical limitations, and magnetic energy storage has low storage time. In the case of hydrogen generation from electrolysis, the costs are simply too high to be competitive in the energy market with capital costs of 1000-2500$/kW (when they need to be near 400 $/kW).
Hydrogen-oxygen combined storage consists of electrolyzers that break water down into hydrogen and oxygen. The hydrogen and oxygen are combusted to form super-heated steam that powers turbines. The system is closed, and uses water as a recycled fuel. Gao and colleagues examined three variants of hydrogen-oxygen ESS: simple integrated ESS, integrated ESS with a feed water heater, and an integrated ESS with both a feed water heater and a steam reheater. In simple terms, these systems each contain an additional measure to capture heat from the steam turbines and use that heat elsewhere in the process, thus improving efficiency. All of these integrated systems contain a complex web of mechanisms that can be adjusted alongside price fluctuations in the power market to minimize costs. The former two had roughly equivalent efficiencies of 49%, but the latter system had efficiency of up to 54.6%, thus demonstrating the benefits of feed water heaters and steam reheaters.
While the 54.6% efficiency of the fully integrated system is marginally below that of some other ESS technologies, hydrogen-oxygen systems come with certain advantages. They can be implemented on a large scale, are fully eco-friendly, not limited by geographical and material restraints, and can be adjusted rapidly based on demand changes. The system was analyzed under two extreme scenarios: an “intermittent operation mode” simulating an extremely variable wind supply, and “continuous operation mode” simulating a perfectly steady supply. Because of how effectively the system dealt with times of low wind, it was actually more profitable under the intermittent scenario with annual income of $13 million per year. Real wind conditions lie somewhere between these extremes, and efficiencies of approximately 50% and prices of 0.03–0.05$/kWh were estimated.
Dan Gao, Dongfang Jiang, Pei Liu, Zheng Li, Sangao Hu, Hong Xu, 2014. An integrated energy storage system based on hydrogen storage: Process configuration and case studies with wind power. Energy, Vol. 66: 332–341.