Countries in Western Europe and the US are now rapidly decommissioning their coal-fired power plants. Policies mandating the adoption of renewable energies and reduction of carbon emissions are the driving force behind the coal phase-out in Europe. Meanwhile, closures of coal-fired power plants in the US are mostly attributed to cost considerations. As shutdown plans are being carried out with much enthusiasm, there has been little effort going into the formulation of follow-up strategies for the numerous idled generation facilities. Consequently, what to do with a decommissioned power plant has become a dilemma for governments worldwide.
Siemens Gamesa, a major winder energy developer, is proposing to reuse abandoned coal-fired power plants by converting them into energy storage facilities that adopt its electric thermal energy storage (ETES) technology. Based on the information provided by the company, this solution appears to be well suited for this new era of green energies.
Energy storage complements renewable generation by resolving issues such as intermittency and load balancing. Track records have provided many cases where the integration of energy storage systems with photovoltaic arrays or wind farms have not only addressed the problem of grid instability but also encouraged the use of renewable energies for various applications.
Lithium-ion batteries currently represent the mainstream technology in the market for utility-grade energy storage systems, but they still have shortcomings that make them unsuitable for long-term operation and scaling up. Hence, many companies in this market are now working on alternative technologies including ETES.
Siemens Gamesa began developing a thermal energy storage system 10 years ago, when it had yet acquired Gamesa and was still known as Siemens Wind Power. ETES, which is the latest culmination of the company’s R&D efforts, uses volcanic rocks to recover and store heat that can be converted back to electricity for end-use customers. How it works is as follow: During the charging phase, the volcanic rocks in the energy storage module are heated up to a temperature of 800 degrees Celsius through convection or conduction. During the discharging phase, cold air enters the module and becomes hot air as it comes in contact with volcanic rocks. The hot air is then directed out of the module and to the boiler. It is thus the energy that heats up the boiler and produces the steam for turning the turbines of the generator.
Siemens Gamesa finally put its concept into practice in 2019, when it installed a 30-megawatt/130-megawatt-hour demonstration system at the harbor of the German city of Hamburg. After observing the operation of this system, which has been supplying electricity to the local grid for more than six months, Siemens Gamesa now plans to develop ETES modules with gigawatt-hour capacity. The target customers for this type of products are wind farm operators that are looking to reduce their curtailment rates and exploit arbitrage opportunities (i.e., selling stored power back to the grid when there is high demand). At the same time, ETES modules are very useful for owners of decommissioned coal-fired power plants because they work with turbines and other existing plant equipment. The technology can effectively capture the residual value of older power generation assets.
The competition in the market for long-term and large-scale energy storage is intensifying as system developers introduce rival technologies. Siemens Gamesa believes its technology is ahead of its competitors’ because of several key advantages, such as being highly compatible with conventional thermal power plants. The number of defunct coal-fired power plants in Europe and North America is already quite large and will grow even larger in the future. Hence, repurposing these abandoned generation facilities into energy storage hubs presents a wealth of business opportunities and helps push our society into the era of green energies.
ETES also adds new values to a coal-fired power plant
Siemens Gamesa has pointed out that even though coal-fired plants are a major source of air pollution and carbon emissions, they still contain advanced power generation equipment. Steam turbines, for example, have reached a high level of technological maturity and efficiency. Furthermore, owners of soon-to-be decommissioned power plants would prefer to continue operating their facilities for another 30 years. Shutting down a plant too early would be an enormous waste because of the high upfront costs related to construction and equipment acquisition. Siemens Gamesa thus contends that ETES can give a second life to legacy generation assets in the era of green technologies.
Under Siemens Gamesa’s solution, transforming a coal-fired power plant into an energy storage plant only requires installing ETES modules in the section of the plant site that was previously designated as the coal depot. Most of the existing plant infrastructure and equipment (e.g., boilers, steam turbines, electrical equipment, tubing, and wiring) would remain the same as before. There is also no need to invest in interconnection since the plant is already hooked up to the grid. The management of the whole facility would be very familiar to an electric company because ETES modules would be treated in the same way as equipment used in coal-fired generation.
Besides modifying existing coal-fired power plants, Siemens Gamesa also plans to build ETES facilities at industrial sites. This technology can play a supporting role in the operation of factories, especially those that need both steam energy and power. While the scheme to repurpose older power plants appears to be well thought out, there is still the issue of attaining an optimal energy conversion efficiency rate. If a thermal generation system is modified into a thermal energy storage system, energy loss will occur during charging (turning electricity into heat) and discharging (turning heat into electricity). This drawback can make thermal energy storage less cost effective than electrochemical energy storage (or batteries). Thus, Siemens Gamesa and other system developers will have to overcome the fundamental challenge of energy loss in order to expand their market share.
(News source: TechNews. Photo credit: Pixabay.)