Over the last few years, the interest of the general public in the energy transition and the integration of renewables has risen appreciably, with photovoltaic (PV) panels being an increasingly common sight in cities and the countryside alike. However, the hurried launch of the transition was undertaken without a full understanding of its impact on public and private electricity grids.

With the demand for electricity in the UK projected by some models to rise five to sixfold by 2050, and with housing projects waiting approximately four years to be assured of a connection to the grid, the need to rethink and modernise our electricity infrastructure has never been more urgent. A similar trend is afoot in Europe, with both French and Dutch authorities sounding the alarm on increasing grid stress in their countries, while Spain experienced a major blackout in May.

Might an alternative framework to complement the public AC (alternating currrent) grid be the solution?

Growing pains for the public grid
The phaseout of fossil fuels impacts more than just electricity generation. It also creates a new paradigm for sectors such as heating and transport, hitherto directly reliant on fossil fuels rather than electricity. The growing adoption of heat pumps and electric vehicles has thus driven a sharp rise in electricity consumption, pushing existing infrastructure towards unprecedented levels of peak demand. For an AC grid, which must strive to match demand and supply at all times, such spikes in demand risk destabilising the network.

The same holds true for the supply side: production from PV panels and wind farms is intermittent, and seldom correlated to peaks in demand. Therefore, this power from PV panels cannot always be readily reinjected into the AC network, for fear of destabilising it.

Despite the technology serving us well for over a century, today’s challenges highlight the growing strain on main grids. Private installations – such as tertiary and residential buildings – could help ease this pressure by dynamically adjusting their electricity consumption, rather than defaulting to abrupt on/off switching. Furthermore, they could more effectively manage the injection of their distributed energy resources – solar panels and storage batteries – to the main grid.

Such fine-grained control and bidirectional energy management are readily enabled by direct current (DC) architectures deployed behind the meter.

DC for a sustainable electrical system
To address these issues, the Current/OS Foundation brings together over 90 partners in 25 countries, including electricity stakeholders, certification companies, trade groups and universities, to promote a unified standard for DC distribution. We believe that the technical properties of DC are perfectly suited to relieving the pressure on the public grid and complementing ongoing investment in public infrastructure.

Chief among these technical properties is the dynamic adjustment, by the appliances themselves, of electricity consumption in DC. Rather than putting stress on the power source, devices can automatically adjust power consumption among themselves, slowing down or speeding up consumption according to the power available, and prioritising certain end uses if need be.

In such a scenario, a hybrid DC microgrid becomes plausible. Electricity is produced locally, primarily through solar panels, and consumed within the building or the neighbourhood. Hence, the generation and consumption of electricity is fully localised, only drawing from the public grid to cover shortfalls. Any excess electricity generated is stored in battery systems, or reinjected into the public grid as required. In our various projects, we have consistently found that DC microgrids reduce the peaks and troughs of power demand by a factor of two to five, significantly alleviating the stress on the public grid.

By fully relying on renewable sources such as PV panels, such grids are quicker to set up, require 30–50% less copper, and are also more cost-effective to expand when needed, reducing the grid connection waiting times for new construction projects. Since power generation and consumption occurs independently of the public grid, conversion losses between AC and DC are avoided, generating further savings of 10–15%. Total savings rise to about 20% when the flexibility of DC motors is factored in.

Switching to local installations also translates to improved protection against blackouts. By delinking their production and consumption from the public grid, DC microgrids would remain operational during a blackout, keeping urban lighting, train stations, or any similar infrastructure operational during a blackout. Such independence is of particular importance in the worst case scenario – DC microgrids would not be affected by a total European blackout, providing an invaluable asset for a black start to get infrastructure up and running again.

By delinking their production and consumption from the public grid, DC microgrids would remain operational during a blackout, keeping urban lighting, train stations, or any similar infrastructure operational during a blackout.

Already undergoing deployment
Several projects are already demonstrating the real-world benefits of DC. Consider the N470 highway in the Netherlands, with solar panels embedded in its noise barriers. Coupled with a 1 MWh battery storage system, this forms a DC microgrid which powers the road’s lighting and traffic signals sustainably. Compared to similar AC systems, the highway achieved energy savings of 10%, requiring 40–60% fewer convertors and 35% less copper for electric cables.

The WAVE office building in Lille, France, by VINCI Energies provides another example of how the public grid and a DC microgrid may work together seamlessly. With part of the offices powered in DC drawn from solar panels, the WAVE building uses DC at the local level in conjunction with the public grid. This has reduced energy consumption by 20%, with no need for converters for IT equipment, given they operate natively in DC.

A similar setup at the Rosie Hospital in Cambridge, UK, led by Arriba Technologies, connects a 750 kW facility in DC to an 80 kW solar array, forming a DC microgrid that already meets up to 90% of the hospital’s HVAC needs. Having replicated similar setups across five separate hospital buildings in south-east Britain, Arriba has observed electrical efficiency savings of around 7% by pushing solar power directly into high amperage DC-HVAC systems without unnecessary excursions through the 50 Hz AC network.  

Locations abroad, situated at lower latitudes, may see even higher returns, owing to both the higher number of sunny hours per year, and the higher usage of air conditioning and refrigeration in such locations.

The views and opinions expressed in this article are strictly those of the author only and are not necessarily given or endorsed by or on behalf of the Energy Institute.

• Further reading: ‘How a new generation of power electronics will sit at the heart of the energy transition’. Power grids and electrical consumer needs are changing radically. Dr Katie Hore, Innovation Director at power electronics R&D consortium REWIRE, explains how UK researchers are developing a new generation of semiconductors that will be key to boosting device performance in the energy transition, with higher voltages and improved energy efficiency.
• Find out how the NeuConnect electricity interconnector is forging a new energy link between Germany and the UK, potentiallly providing a model for clean energy distribution.