A Study Into The Feasibility of Local Renewable Energy Systems With Storage, Using Security and Sustainability Metrics for Optimisation and Evaluation

The aim of this thesis was to develop tools for evaluating the potential sustainability and security of renewable energy systems in the UK, with a long-term view of maximising the potential renewable energy penetration of wind and solar by deployment of electrical energy storage. Using computer modelled renewable energy systems, a number of system variables are considered such as system size, energy sources (solar and/or wind), type of demand load, and capacity and type of storage technology. The results allow for a broad comparison of different types of renewable energy systems, and their optimisation. The optimisation methodology is also critically evaluated with consideration of its robustness and applicability, using two alternative metrics to measure system energy security and two different measurements of energy return on investment (EROI) to measure sustainability. When comparing renewable energy systems, results found that large systems that predominately got their power from wind sources were the most sustainable and secure, using optimisation methods that penalised both their overproduction and underproduction. Nearly all systems benefit from the use of electrical energy storage, without impacting too much on sustainability levels, but larger wind systems used less storage, suffering lower energy security as a result. System performance can best be improved by developing solar power technologies with lower embodied energy costs, followed by a reduction in embodied energy of storage technology. The former will enable more effective use of storage methods, while the latter allows for larger storage capacities with less environmental impact. Sustainability and energy security were given equal priority in the optimisation, however it was found that more sustainable generation technologies were preferable to more secure technologies, as there is more scope to improve energy return on investment than security. Therefore there is a limit, generally around 45-85\% (depending on size of system and choice of technology) to the proportion of time that renewable energy systems using variable energy sources can be autonomous, meaning that energy backup from the grid and/or dispatchable sources is still required