A UK project is working through the commercial and technical aspects of a direct current (DC) microgrid architecture that integrates electric vehicle charging, storage and solar generation while supporting the wider network.

 

Benefits of DC microgrids have been covered extensively, albeit more recently since the late 1800s, when direct current delivered power for electric lighting in the first grids.

Solar PV panels, batteries and rapid chargers all produce, charge/discharge and consume power in its DC form, so it makes sense to operate them together within a DC microgrid. The system architecture is simplified for a start. There is no need to convert power to alternating current (AC), so inverters are not required and energy wastage from conversion is eliminated. DC microgrids are both more energy efficient and cost-effective.

 

Edison would be proud

The work by the Smart Hubs project consortium in the UK is an attempt to demonstrate the commercial benefits of DC microgrids and their optimal technical design. Flexi-Solar, which designs makes and installs solar PV carport structures for customers, including Bentley, is leading the project, which is supported by the government through Innovate UK.

Smart Hubs will integrate low carbon DC technologies, including solar PV, battery storage and vehicle-to-grid (V2G) chargers, managing supply and demand of power within a DC network, while minimising any impact on the ageing AC local distribution infrastructure. The microgrid can be called on to support the local distribution network at times of congestion and also help balance the wider grid.

For example, energy stored in the batteries of plugged in parked EVs and a bulk battery system can be used by the grid during peak times. EV owners are able to charge their cars while parked under the solar carport canopy. When not in use, the cars can remain connected, allowing the power grid to use a proportion of the stored capacity in the vehicle batteries during times of higher demand.

Other partners in the consortium are Turbo Power Systems, a specialist in power control and electronics, Powerstar, an energy storage system provider and aggregator Flexitricity, which extracts commercial value from generation and load assets through adjusting energy demand and output in return for payments from grid balancing services and energy trading.

The Smart Hubs project will be installed by mid-2020 and will develop the infrastructure in time for when EV volumes will require public charging infrastructure from 2023 onwards.

Powerstar has developed its own energy management system which will be used to optimise the use of the various components include solar PV, battery and chargers and also integrate with the main grid. Turbo Power Systems has developed power electronics, which interface the DC microgrid with the AC grid and can reduce imbalances that can occur on the network, further upstream. The company’s technology will also be used to maintain optimal voltage for charging, regardless of any vehicle that’s plugged in. In a separate project, Turbo Power Systems’ power electronics technology has been used and verified by wires utility UK Power Networks.

 

Charged up with sun power. Flexi-Solar engineers solar carports that incorporate EV charging. Images courtesy of Flexi-Solar

Locations and suitable host sites

The Smart Hubs demonstrator will start with one location, likely to be in Oxfordshire, which will be publicised in the coming weeks, but later the project will roll-out DC microgrids to as many as six locations.

Since the project was first announced earlier in 2018, Flexi-Solar has been in discussions with potential hosts.

“We’ve seen lots of interest from local authorities, as well as commercial businesses. In terms of sites suited to hosting and benefitting from this type of DC microgrid, an ideal fit would be leisure centres or gyms. You have carparks to build a solar carport over, a heavy baseload, and frequent usage, with cars parked up for 1-2 hours, which is enough time for an electric car to top up,” says Adam Goves, business development director at Flexi-Solar.

Flexi-Solar was established in 2009, initially designing and building solar carports. With an eye on the future the company began taking an integrated systems approach early on, designing systems that bring together solar PV generation, battery storage and EV charging.

 

Building off the solar carport approach

Securing funding from Innovate UK in 2017 has helped accelerate commercial deployment of its technology and, to date, Flexi-Solar has completed solar PV carport projects both in the UK, as well as Latin America, Africa and the Middle East. A well designed solar carport can achieve returns in the region of 10%. Demand for integrated structures to facilitate EV charging has increased. More recently Flexi-Solar has begun to attract the attention of big players in the oil and gas and energy sectors.

Smart Hubs takes this integration a step further. DC microgrids are an elegant approach needed to fully exploit the compatibilities between distributed clean generation and loads. It’s not hard to see a whole DC ecosystem blossoming from the core infrastructure, such as energy efficient LED lighting for illuminating carports at night, to payment machines and digital advertising.

 

Proving a business model for DC microgrids

But through Smart Hubs the consortium has to prove that a DC microgrid architecture supporting low carbon technologies can work commercially and balance the needs of a diverse range of stakeholders. It needs to generate revenues and returns for investors and operators, provide a cheap source of power for EV owners, which span private individuals as well as fleet operators. It also must ensure EV charging does not adversely impact the local distribution network, managed by utilities, and can also benefit the wider grid, where transmission system operators increasingly rely on flexible loads to manage supply and demand.

“Do I see an opportunity to export what we are doing in the area of DC microgrids? Absolutely.” Having worked in the solar industry, for Goves a positive benefit of the EV transition is that it is consumer, not subsidy, driven.

“The UK’s skillset in engineering and design came to the fore in the solar PV boom and that’s now being deployed in terms of working through solutions that bring together various technologies, including solar PV, energy storage and EV charging, and optimising their integration. But we need to successfully deploy these systems here first, before pursuing all other opportunities. The pipeline is significant though.”