Reversible solid oxide cells in microgrids and peer-to-peer energy markets

The drive to decarbonise energy systems is leading to increased deployment of renewable generation; such generation is typically intermittent, leading to difficulties in matching supply and demand. Whilst battery storage and related technologies can address intermittency on a short timescale, longer timescales will likely require storage of energy as hydrogen (or perhaps other fuels). Reversible solid oxide cells (rSOCs) embody both electrolyser and fuel cell in one device; that is, they can convert both power to gas, and gas to power - when combined with hydrogen storage, an energy store is the result. They also boast superior efficiency to the rival alkaline and PEM technologies, whilst the high-grade heat given off during fuel cell operation provides an interesting opportunity to supply heat demand.
This project aims to assess the possible application of rSOCs as electrical energy storage for the residential sector. Simulation models are developed to investigate the techno-economic benefits of the technology, principally as a store for solar power. In the first two results chapters, these models are combined with global optimisation in order to investigate the optimal sizing of the energy storage system, and the choice of energy storage technology (rSOC versus battery). Findings indicate challenging economics for electrical energy storage with the rSOC. Battery storage and / or oversizing of generation is often a more cost-efficient way to address the intermittency of generation, with the rSOC an optimal selection only when a high degree of self-sufficiency is required of the system, leading to a need for seasonal energy storage; even in this case, the financial metrics (payback period, net present value) for the rSOC are not entirely encouraging.
A secondary theme of the work is peer-to-peer (P2P) trading, whereby electricity (and perhaps heat) can be traded between customers, rather than with the utility company only. P2P is introduced to the modelling in the last two results chapters, using an agent-based approach to model the P2P market. Electrification of transport and heat will introduce large loads to the electricity network in the future, but these loads are expected to have a degree of flexibility; P2P provides the incentive to synchronise these flexible loads with local generation, as far as possible. As such, P2P may be seen as competing with energy storage as a solution to intermittency, or as synergetic. The third results chapter demonstrates the efficacy of P2P in conjunction with solar PV and energy storage using electric vehicle batteries (‘V2H’). Financial savings are demonstrated across technology penetration scenarios, and for all classes of participant in the market. In the fourth results chapter, the rSOC returns, participating in a simulated P2P market alongside EV chargers, PV and heat pumps. For this work, a novel P2P model is constructed on the basis of continuous double auction, along with strategies for bidding with flexible devices or energy storage. It is demonstrated that the P2P electricity trading gains significant profits for the rSOC owners, as well as bringing environmental and technical benefits. In future work, it is hoped to recombine results of the P2P market with the earlier work on optimal technology choice and sizing.