There is an increasing demand to store energy in order to allow it to be used later, when and wherever needed. New energy storage technologies have the potential to play a transformative role in:
1) Electricity networks. Substantial grid-scale storage would improve the use of existing assets by lowering the peak load and increasing the efficiency of thermal generation by allowing it to be operated at a relatively constant level. It is also needed to accommodate greater use of clean but variable electricity generation technologies such as solar, wind and tidal power, and store nuclear power at times of low demand. Applications range from small scale distributed storage on low-voltage networks to large scale technologies on the transmission network. These energy storage methods also raise various planning, economic, market design and policy issues.
2) Transport. The attractions of hybrid and fully electric vehicles would be enhanced by increased energy density of batteries, to increase range between charges and speed of charging, and use of inherently safe (no fire or toxic risk) material combinations. Synthetic fuels derived from industrial waste using new catalysts may provide a medium to long term alternative to fossil fuels in some areas.
3) Mass-market portable devices. The challenges are to extend battery life, provide environmental compatibility, and introduce transformative designs such as rollable and transparent devices. Integrated energy harvesting from light or kinetic movement may also be combined with storage.
Research in Oxford
Work is underway in Oxford on: new electrode and electrolyte materials and manufacturing technology for batteries for all application domains, real-time management of battery systems, super-capacitors (devices that release stored electrical energy very quickly), thermal storage, production and storage of hydrogen, and conversion of carbon-dioxide to hydrocarbons. Oxford academics also address planning, economic and policy issues related to the integration of energy storage into future systems which, together with analysis of possible technical developments, is a key element of the Oxford Martin Programme on Integrating Renewable Energy (see accompanying case study). Related research is carried out on electricity networks, bioenergy and intermittent renewables such as solar and marine energy.
Electrochemical Storage (Batteries, Supercapacitors)
Material scientists are developing new manufacturing approaches to battery and supercapacitor electrodes aimed at unlocking the full potential of new battery chemistry for faster charge, higher capacity and longer lifetime (technically the emphasis is on graded porosity electrodes to homogenise state of charge and electrode swelling, and large area meso-porous films based on scaleable nanotechnology). Research is also taking place on the materials, chemistry and electrochemistry of new electrodes and electrolytes for Li-ion and Na-ion batteries, the latter for grid storage, and the fundamentals and development of the lithium-air battery, all aimed at low cost and inherently safe energy storage devices. This work is complemented by research in battery and energy storage systems based on reduced order modelling of battery pack performance and novel approaches to battery health management.
Heat produced in solar thermal power plants can be stored, thereby increasing their availability. Oxford scientists are working on the use of phase-change materials as thermal stores for Solar-Stirling generators and also on solar heating applications.
Domestic thermal storage has a great potential to enable cost-effective smart grid activities and has a potentially significant role to play in demand side management. Oxford engineers are developing techniques to determine the ‘state of charge’ of hot water tanks, and also researching refrigerators that can remain without power for up to 12 hours. Research is ongoing to develop smart measurement systems of hot water tanks – enabling both effective sterilisation and demand side management. The use of advanced phase change materials in refrigeration systems ensures safe operating temperatures while allowing a power cycle that is compatible with photovoltaic systems.
Hydrogen is attractive as a storage medium, due to its high energy to weight ratio and because on combustion it produces only water. A major challenge addressed in Oxford centres on new routes to sustainable hydrogen production, from bio-inspired approaches to photo-catalytic decomposition of water. This links to the important area of sustainable ammonia production. Oxford has particular strengths in solid state materials for hydrogen and ammonia storage.
An important alternative is to use hydrogen to produce sustainable hydrocarbons; these fuels have the highest energy densities of any form of storage. This can be achieved using CO2 in the atmosphere itself as the carbon source, to produce hydrocarbon fuels that can be used with existing infrastructure, starting from methanol to ultimately gasoline. With this approach, hydrogen is used in the fuel rather than being used as the fuel.
Regulatory and policy challenges
Grid storage options may determine both the feasibility and the relative cost of low carbon energy systems, as well as the practicalities of “downstream” storage in batteries for electric vehicles. Oxford researchers consider storage as one of four options to provide system flexibility. It competes with flexible generation capacity, demand shifting and enhanced networks (including smart grids and interconnection). Work on the role of storage in low carbon energy systems requires complex economic and policy considerations to design market structures and pricing signals involving all actors in the system. Outcomes will affect everything from investment in storage to the design of vehicles, heating systems and networks and day to day operation of electricity markets. Oxford researchers model the integration of storage and draw on their interdisciplinary strength in assessing policy options and market mechanisms.
Economists at the Oxford Institute for Energy Studies are considering how intelligent planning both for the grid and for market structures could enable pricing signals to balance consumption, generation and storage.