Hydrogen and Thermal Storage System

University of Nottingham Key Contacts:  David Grant,  Gavin Walker and Alastair Stuart

To deliver compact thermally-driven air conditioning through a totally new innovative route. In this novel air conditioning (A/C) system two metal hydride slurries will be continuously cycled and assessed for its potential as a new solar cooling technology. In order to establish whether this approach has practical and economic viability a prototype system will be constructed and evaluated against recognised performance indicators.

In theory two thermochemically coupled metal hydrides can be used to transform sustainable thermal energy sources into sources of cooling. This has been attempted using a batch process involving two large hydride beds but with limited success. It is possible that by suspending the metal hydrides in an inert liquid and circulating them between the heat source and sink that a continuous operation can be achieved. This is advantageous as it would reduce the size of the system, reduce the mass of metal hydride by several orders of magnitude, improve heat transfer and lead to higher operational efficiencies.

University of Nottingham Key Contacts: Gavin Walker, David Grant, Mark Sumner, Jon Mckechnie

Whilst the background situation in India and UK are very different they have common requirements in terms of community energy management including generation, loads and storage, with the UK moving from centralised generation and control to local generation and control and India trying to get more users on-grid but with a short-term need to manage off-grid at a local community. Whilst reforms to the central distribution system may be slow, significant changes for end users can be achieved using "microgrids" (e.g. communities with microgeneration) which, when coupled to appropriate energy storage technologies, have the capability to operate off-grid. Research into design operation and management of microgrids can have a significant impact, particularly for rural communities, in the short to medium term.

Energy storage is required at different time scales for microgrids in order to ensure the quality of supply (small energy stores that can respond quickly in order to even out fluctuations in the power supply), daily mismatch (medium size stores to provide energy at times of low or no wind/solar generation during a day) and seasonal storage (large stores to meet the seasonal shortfall in microgeneration, for example during the winter or monsoon period). This distributed energy storage for a community's microgrid also provides an opportunity for load shedding from the national grid. Therefore, energy storage for microgrids is not only essential for grid remote locations, but has an important role to play for grid connected microgrids, helping to reduce the dependency of the community on the main grid and providing distributed energy storage at times of over capacity on the main grid.

The aim of the project is to optimise a microgrid in order to maximise the efficiency of the microgrid whilst maintaining the quality and security of supply requires the integration of electricity generation, storage, and transmission/distribution components. The optimal selection and configuration of these components depends on a number of key factors such as demand profile, microgeneration profile, main grid dependency (ranging from no dependency, e.g. grid remote, to a high dependency, e.g. microgeneration capacity is only a fraction of the local power demand). The energy management system needs to balance a community's energy demand through direct microgeneration, stored energy and, when available, centrally generated electricity. The microgrid can be AC or DC, which will affect the power conversion efficiency for the microgeneration and appliances which make-up the demand on the microgrid. Another important factor is the two-way interface between the microgrid and main grid. It quickly becomes evident that one microgrid solution will not be effective for all the potential deployment scenarios and a flexible systems approach is needed to establish the best technologies and best energy management strategies to provide power for the local community but also to help make the main grid more robust.

Collaborators: University of Nottingham, Luxfer, ITM Power and Arcola Energy

University of Nottingham Contacts: David Grant, Gavin Walker and Alastair Stuart

The technology for the generation and use of hydrogen as a fuel is established however at present the best way to store the hydrogen is to pressurise the gas to 350 bar or higher (i.e. 350 times atmospheric pressure). This has cost and safety
considerations. Handling high pressure hydrogen requires thick and heavy metal cylinders or bulky composite cylinders. Electrolysers driven by electricity from renewables or from the grid can readily generate hydrogen but this is at low

pressures. Thus mechanical gas compressors are needed to compress the gas to above 350 bar. Such mechanical compressors are expensive and require maintenance, the storing of large quantities of hydrogen at high pressure requires blast zones. Being able to store the majority of gas at low pressure utilising metal hydride (MH) solid state stores is not only safer but it requires much less volume. Fuel cells (which convert hydrogen and oxygen to water and electricity) operate at these low pressures too, so for certain stationary applications, storing hydrogen by a low pressure MH store makes sense. This project will build a prototype to prove the viability of the technology and explore the market potential for MH stores.

This project will use an innovative metal hydride that has been developed and tested via EPSRC funded research and this combined with our latest heat management modelling will deliver the next generation metal hydride stores with reduced

materials cost, reduced complexity of balance of plant and higher efficiency. These stores will be based on a lightweight aluminium pressure vessel with a passive internal thermal management design. This will deliver a prototype "off the shelf" hydrogen store that can store at a pressure of a few bar the equivalent mass of gas to a 350 bar pressure cylinder for stationary applications yet in a smaller volumetric footprint. The metal hydride has over 2 wt% working capacity operating between 1 and 30 bar, ideal for storing gas from electrolysers and delivering to fuel cells. This is a working capacity double that of AB5 and 30% that of commercially available AB2 hydrides, but at lower raw material cost than either competitor alloy.

This Engineering and Physical Sciences Research Council (EPSRC) funded project aims to produce a highly efficient, innovative, and cost-effective dual-use hydrogen storage technology that can be used in a range of industrial cooling processes, including delivering hydrogen to a fuel cell and generating direct cooling for refrigeration.

The EPSRC funded Ocean-REFuel programme brings together a multidisciplinary team to establish fundamental scientific and engineering understanding for the conversion of ocean renewable energy such as offshore wind, to liquid and gaseous fuels. Led by the University of Strathclyde, the initiative draws on the expertise of the Universities of Nottingham, Cardiff, Imperial, and Newcastle.

This multi-disciplinary EPSRC programme seeks to decarbonise marine transport through innovation in ammonia thermal propulsion. As part of this, the storage of fuel mixed with hydrogen will be explored. Led by the University of Nottingham, key partners include the Universities of Cardiff, Birmingham, Brighton and the Science and Technology Facilities Council (STFC).

This Business, Energy, and Industrial Strategy (BEIS) funded project is exploring high temperature hydrogen stores that can use a cheap metal hydride with an energy density superior to that of compressed gas and liquid hydrogen. The initiative is a collaboration with independent research and technology organisation TWI, and Chesterfield Special Cylinders

These are many and varied. One example is the CitiBus project, where hydrogen stores feed fuel cells and electric machines. This work is undertaken in partnership with the Power Electronics and Machine Centre at the University of Nottingham and is funded by Local Enterprise Partnership (D2N2), the Energy Research Accelerator, and the Propulsion Futures Beacon.