Solar PV energy stored in innovative batteries
The Project Helios demonstration comprises a 3.8 kWp solar photovoltaic power generation system integrated with a 3 kWh OXIS lithium-sulfur battery. It has 16 PV panels connected in series to produce 600 Vdc, which is fed to an SMA Sunny Boy Inverter to generate a 240 V, 50 Hz mains-type AC output.
The inverter includes maximum power point tracking (MPPT) to ensure that the PV panels operate at maximum efficiency under all sunlight and temperature conditions.
The mains output from the Sunny Boy inverter is used to power the charger for a Meridian Navya driverless vehicle at the centre, which is powered by OXIS Li-S batteries. It is also connected to an SMA Sunny Island battery inverter, which in turn charges the OXIS Li-S battery, storing the unused excess energy generated during daylight for use after dark.
Off-grid and grid-connected capability
The Sunny Island and Sunny Boy inverters are currently configured in off-grid mode. But when power is not available from either the PV panels or the battery, the system will switch to mains operation, and take energy from the grid to ensure the loads remain powered.
This off-grid configuration allows the loads connected to the system to be managed, to evaluate the performance of the OXIS battery under controlled conditions.
The system can easily be reconfigured for grid-connected operation, where the battery is used to increase self-consumption.
Stacked units for higher capacity
The single 48 V, 3 kWh Li-S battery in this demonstration can be expanded to a total of four batteries, stacked and connected in parallel, to provide a total storage capacity of 12 kWh, suitable for most domestic installations in Europe.
For larger systems, where a more complex arrangement is needed, the 19-inch rack-mount battery is recommended. This will be available later this year.
Lithium-sulfur battery technology
Each Li-S cell comprises layers of a lithium metal anode, a sulfur-based cathode including carbon and a polymer binder, and a non-flammable electrolyte. This innovative technology is inherently safe, cost-effective because of the low material costs, and lightweight while offering high energy density.
OXIS has signed an agreement with GP Batteries in Singapore, a major manufacturer of primary and rechargeable batteries, and the largest consumer battery manufacturer in China. The partners will work together to augment the commercial production of Li-S battery systems for use in commercial applications.
Global demand for energy storage
‘The significance of this technology is at this stage understated,’ says Huw Hampson-Jones, CEO of OXIS Energy. ‘In the continent of Africa, for example, this is a breakthrough as profound as the introduction of the mobile phone, and allows for the rapid commercialisation of their economies using solar energy storage systems.’
‘For Europe, this technology brings a safe and cheap source of electricity for its citizens, in a manner that allows its economies to lessen their dependency on oil and gas,’ he continues.
Energy storage solution for emerging markets
‘The realisation of the OXIS storage solution is perfectly timed, as we continue to move into emerging markets that have a high demand for safe, reliable, and cost-effective energy storage solutions,’ adds Stuart Macfarlane, Head of Asia Pacific and Storage for PROINSO. ‘Importantly, the technology is robust and easily scalable, which is crucial for use across a wide range of applications and in frequently hostile environments.’
‘PROINSO is constantly looking for that next innovation which will enable us to continue to deliver technically sophisticated solutions that showcase the best the industry can offer,’ he continues. ‘Working with companies like OXIS in the development of new technologies is the foundation of this ongoing process.’
Macfarlane adds that PROINSO is particularly targeting the huge market for small-scale solar energy storage systems in South Africa, India, and South East Asia.
Collaboration of energy storage with solar PV
OXIS Energy, founded in 2005 and based at the Culham Science Centre in Oxfordshire, has been at the forefront of developing lithium-sulfur battery technology. The company has invested heavily in design and development, and is now ready to move to the production of Li-S cells for a series of applications. OXIS has been granted 64 patents, with another 59 patents pending, in 21 patent families.
PROINSO is a global leader in the photovoltaic industry, with extensive experience of systems integration in grid-tied, off-grid, storage and diesel hybrid solutions across residential, commercial, industrial and utility applications.
Electric vehicle applications, and beyond
The Meridian Navya currently running on the Culham site is a driverless shuttle designed for transportation in areas such as theme parks, university campuses, and pedestrianised town centres. The vehicle uses laser rangefinders to measure the distance to nearby buildings and other fixed points with great accuracy, to ensure that the vehicle always knows its exact location. This laser system is complemented by motion sensors, and GPS and video cameras can also be used.
OXIS is also leading the UK’s Revolutionary Electric Vehicle Battery (REVB) consortium, which is working to improve the cell technology in preparation for mass adoption in EVs. The REVB programme – which is co-funded by Innovate UK, formerly the Technology Strategy Board – aims to increase cell energy density to beyond 400 Wh/kg. The REVB programme – which will run until the end of 2016 – also involves Imperial College London, Cranfield University, and Lotus Engineering.
In addition, OXIS is leading a new project – just awarded €7 million in European Union funding – for technology and materials development for the Li-S batteries, working with Spanish automaker SEAT and German battery manufacturer Varta.
Furthermore, OXIS is developing an 'ultralight' version of its Li-S technology for military applications such as soldier-worn portable power and unmanned aerial vehicles (UAVs), which demand higher specific energy density (i.e. more energy for less weight) while accepting fewer charge-discharge cycles during its lifetime.
And earlier this year a consortium including OXIS was awarded funding from Innovate UK for the research and development of the next generation of lithium batteries for marine autonomous systems (i.e. unmanned underwater vehicles, UUVs), involving the National Oceanography Centre at the University of Southampton. The OXIS Li-S cells are ideally suited for use in subsea applications because of their high specific energy, mass density, and safety.