A Hybrid PV-Battery Unit Optimised for LV Grids Using GaN Transistors

Under their "Gone Green" deployment scenario, National Grid forecast that energy generated from photovoltaics (PV) in the UK is expected to rise from 2 GW to 15 GW over the next 20 years. This is being driven by the UK's legal obligations
around the installation of renewables and cutting greenhouse gases, the rising cost of energy and concerns around the security of supply - the so-called energy "trilemma". Power Electronic converters are a key enabling technology for PV and a range of other low-carbon technologies (LCTs). However the use of LCTs has resulted in problems for the Distribution Network Operators (DNOs) in terms of supply voltage distortion and over-voltages, which threatens to limit or delay the uptake of these technologies. The aim of this project is to mitigate this threat by exploiting the benefits of new Gallium
Nitride (GaN) power module, which will initially be developed for use in a hybrid PV-battery unit for residential applications, but will have much broader application in LV grid-connected equipment (e.g. electric vehicle, charging & micro-CHP). It is anticipated that the deployment of these units would lead to an increase in the maximum allowable installed capacity on the network and will be much smaller, lighter and have lower cost than existing Silicon based units.

This project is serving to bridge the difficult gaps between the disparate elements of a complex supply chain running all the way from a semiconductor device manufacturer to a power distribution company. The project seeks to investigate the techno-economic viability of a hybrid PV-battery energy storage unit using new GaN transistors, which will provide advantages for both the energy consumer and the DNO. This unit would form a key component of the so-called smart grid and contribute toward improving the efficiency, capacity and flexibility of the local distribution network. The economic
benefits of such a smartgrid have been recently documented in a report by Ernst and Young (April 2012) for SmartGrid GB, a cross-industry stakeholder group, which informs both DECC and Ofgem. In this report the forecast savings to the UK are around £19 billion if a smartgrid solution was employed over conventional investment. In addition an average of 8000-9000 jobs will be generated up to 2030, and exports of £5 billion are possible by deploying smartgrid technology. The combined value to secondary industries such as electric vehicles, distributed generation, electro-heat and renewables is significant. For example the gross value added for electric vehicles alone could be £17-52 billion between 2030-2050. This project directly feeds into this aim, by assessing the feasibility of a new GaN power electronic module, hybrid PV-battery converter and control, which significantly contribute to such a system becoming a reality.

At a Social level as well as the creation of jobs through the design, manufacture, installation and sales of this equipment and its associated supply chain, the use of this technology will result in a more robust electricity supply through the use of energy storage and improved power quality. In addition, as well as reducing consumer's electricity bills through increased use of distributed generation, the cost of the inverter equipment is likely to be lower due to smaller size and weight and ease of installation. The outcomes of this project should therefore help toward alleviating so-called fuel poverty, by reducing the cost of electricity.

At an environmental level this project is a key enabler towards the introduction of local, renewable power generation as well as increasing the efficiency of the local residential power network. As such, by reducing the consumption of energy through grid-connected fossil-fuel power stations it would play a key role in future plans for the reduction of greenhouse emissions.