Centre for Sustainable Technologies, University of Ulster

The increasing deployment of renewable energy illustrates the conflict between its availability and the demands of society. Energy storage is proven to be able to reduce both the peaks (and troughs) in demands, leading to higher efficiency supply-side operations. Storage can allow alternative energy formats to reduce operating costs through energy which is supplied at some earlier time, and delivered when required. Energy storage examples include pumped storage, hydrogen storage, compressed air storage, electrical storage, mechanical storage, demand side management and thermal storage. However, mechanisms which match renewable energy supply to energy demand are required, and these need to be in keeping with the socio-economic conditions encountered.

Growth of the energy market

The current annual UK£21 billion global energy storage market is set to grow by 55% to UK£33 billion by 2012. Venture capital expenditure supporting energy storage projects increased by 74% to UK£360 million in 2007 with bulk energy storage for energy utilities having the largest potential. The unpredictable (non-dispatchable) nature of wind power, for example, currently limits share of supply to the electricity network. Storing excess energy for later release enables a smoother, more predictable and, therefore, a more lucrative electricity supply. This will in turn reduce the short cycling and standby of fossil fuel electricity generation plant, thus reducing maintenance and running costs, decreasing the reliance on imported fossil fuels and increasing carbon reduction.

Parallel to this, energy policy and related drivers are necessitating greater energy efficiency in buildings, together with diversification from traditional forms of energy supply by using, for example, on-site renewable electricity generation. Costly electricity infrastructure enhancement may limit the ability to spill locally derived non-dispatchable renewable electricity onto overburdened distribution networks. As a consequence, energy storage must match the wide spectrum of non-dispatchable renewable energy supplies with user demand patterns if carbon, strategic energy and cost savings are to be fully realised.

While the development of large-scale energy storage will find opportunities, substantial civil engineering works will encounter environmental and cost barriers in their implementation. Therefore, to what extent can the built environment, an entity that uses over 40% of primary energy and which has considerable inherent response times and storage capability, provide local energy storage and virtual bulk thermal and electrical energy storage for non-dispatchable small and large scale renewable energy?

Credible energy storage

To establish the credibility of built environment energy storage, we need to be able to predict built environment energy use, the impacts of renewable energy and energy efficiency policies and aspirations going forward. Furthermore, what energy storage mechanisms are compatible with the built environment? What techno-socio-economic instruments are necessary to evaluate and influence legislation, policy, business opportunities, public interpretation and public education as to the role of energy storage within the built environment?

Examples of the University of Ulster’s approach to this issue include the development of effective thermal energy storage systems utilising phase change between solid and liquid to store and release thermal energy at nearly constant temperature is of interest. However, many Phase Change Materials (PCMs) have unacceptably low thermal conductivity, leading to slow charging and discharging rates, hence requiring heat transfer enhancement techniques.

The University of Ulster has studied heat transfer enhancement techniques and include finned tubes of different configurations; e.g. circular fins, longitudinal fins and multitubes for both charging and discharging of materials such as Erythritol. Micro-encapsulation of PCM has been evaluated in both higher and lower temperature applications with regard to integrated collector storage water heating systems and chilled beam ceiling applications and the impact of PCM wall systems as passive systems in controlling the response to solar gain as been modelled. Retrofitting advanced high temperature heat pumps, developed at the University of Ulster, in domestic housing stock has given a unique insight into the rate of heat supply and building dynamics and provides further opportunities to combine demand side management with energy storage.

Thus, the Centre for Sustainable Technologies at the University of Ulster is able to bring forward a timely series of innovations capable of meeting a sustainable energy agenda.

W: www.cst.ulster.ac.uk