Are Carnot Batteries an Alternative to Converting Coal Power Plants? : An open-sourced technoeconomic optimization approach for testing a new niche for Carnot Batteries.

Abstract: As Europe transitions away from coal-fired power plants, there is an opportunity to reshape the electrical infrastructure. Many of the current plans are to make a switch to natural gas, another fossil fuel. Refurbishing existing power plants has several advantages. Components can be put to a new purpose. Employees of the plant can remain in their capacity. The locations are connected to the electricity and the district-heating grid. Whilst natural gas can have relatively low emissions and address peak loads, it is a fossil fuel with high marginal costs and its sourcing can be problematized. There is an alternative to consider: Thermal Energy Storage system. The literature regarding the retrofit of operating power plants with thermal energy storage is improving the key performance indicators of an existing power plant. This paper determines the technoeconomic feasibility of replacing the boiler as the source of heat. A thermal energy storage system is more profitable in energy markets where the price varies in a forecastable way. To determine the technoeconomic feasibility a bi-level optimization is carried out. The first step is a deterministic analysis of dispatch and then genetic optimization for the sizing. The optimization relies on open-source software for replicability and further development. The economic aspects are Net Present Value, capital expenses, Power Purchase Agreement price, and Levelized Costs of Storage. Technical aspects are round trip efficiency, Capacity Factor, Utilization Factor, and carbon dioxide emissions from the grid or fuels. For the electricity markets analyzed in detail here, it is possible to find a solution with a high but competitive Levelized Costs of Storage of 300 €/MWh. It is possible for a district heating grid connected to Combined Heat and Power plants to achieve competitive Levelized Costs of Heating of circa 50€/MWh. Technical parameters have highlighted the importance of round-trip efficiency. The results show that even with optimistic assumptions regarding capital costs, operational costs, and electricity market variations, price arbitrage is not an economically feasible business model for repurposing coal-fired power plants. It is possible to find insights regarding the relative sizing of Carnot Battery components and the properties of the electricity market. Round trip efficiency and utilization factors are important technical indicators of the economic success of a given configuration. Conversely providing heat to a district heating grid can be a viable market for Carnot batteries.