The growing use of renewable energy for electricity generation constitutes one of the major global achievements of the first two decades of this new century. In 2000, renewables made up only 5.2% of Germany’s electricity supply, a figure which has swiftly risen to 57% in 2024.

Driven by rapid technological advancements, the cost of newly commissioned photovoltaic (PV) projects fell by 85% between 2010 and 2020 alone, with onshore and offshore wind also registering significant falls (56% and 48%, respectively). In consequence, the installed capacity of renewable energy sources is expected to rise beyond 500 GW in Germany by 2037, according to planning targets.

Ultimately, the total installed power is expected to rise to 800 GW, which represents a factor of 10 in comparison to the traditional capacity to power the grid. The total demand for electricity (in terms of TWh or energy) is set to more than double within this interval: demand for generating capacity is outpacing the demand for energy (in TWh).

Despite PV panels being fairly ubiquitous in urban areas, solar energy’s transformation to household electricity is still quite complicated. Take the case of charging an EV via the grid and a grid-connected battery energy storage system (BESS). Once generated by the solar PV as DC, the electricity is converted to AC to reach the grid. Then it goes to the battery storage system (AC to DC), then back to the AC grid (another reconversion), until it finally reaches the charging station, converted one final time back to DC to charge the vehicle. Converting electricity four times before it is used for its intended purpose leads to significant losses: losing 3% of energy at each stage means a total loss of 12%. Could DC power be harnessed more directly?

DC and AC in the 21st century 
One way would be to envisage low-voltage DC microgrids at building or neighbourhood level, coupling DC systems at the lowest voltage levels without going through the AC grid. This would allow consumers to draw directly from electricity produced locally, without impact on the public grid. This does not entail a complete decoupling with the public grid – the microgrid’s source is meant to be connected to the public grid, allowing either party to draw from the other in case of shortfalls. Therefore, DC microgrids serve as a complement to the AC grid.

One way would be to envisage low-voltage DC microgrids at building or neighbourhood level, coupling DC systems at the lowest voltage levels without going through the AC grid. This would allow consumers to draw directly from electricity produced locally, without impact on the public grid. 
 

At household level, rooftop PV installations tend to be combined with battery storage, both connected directly over DC by the power converter. Thus, a 6 kW PV system directly feeds into the battery, without interfering with the AC grid. Similarly, the battery can provide 6 kW of power to the household. On a sunny day, the EV could now be charged through the wallbox at 12 kW, of which half is supplied by the PV directly, half by the battery. Unfortunately, the wallbox connects over AC, so it takes 6 kW from the power grid and 6 kW from the domestic power converter.

The intake from the grid is entirely unnecessary. A wallbox with a DC connection could directly connect to the domestic DC microgrid (consisting of the PV installation and the battery).

Imagine that the household also uses a heat pump, using 3 kW for the compressor, plus 12 kW for the heating rod. Currently, this adds 15 kW of power to the AC grid connection. Together with the 6 kW of PV, 12 kW for the wallbox and 6 kW for the battery observed earlier, the renewable installations draw 39 kW from the power grid, mostly due to DC-AC conversions. If the PV panel, battery, wallbox and the heat pump were connected over a DC microgrid, the setup draws only 12 kW from the public grid (needed to power either the heating rod or the wall box directly). Hence, a domestic DC grid reduces the load on the AC connection by a factor of three (12 kW versus 39 kW).

The DC microgrid is conected through the public grid via an interlink converter. As seen above, most of the power is exchanged within the DC microgrid, and the converter must only exchange a surplus with, or draw power from, the public grid as applicable.

The same logic applies for larger installations of renewables for industrial use, communal use and at renewable power plants. Connecting renewables to their storage devices (which could also include hydrogen electrolysis and fuel cells) over DC grids relieves power grids of handling and managing power demand at the interconnection. Since DC grids handle the power demand of their devices internally, the AC grid just needs to regulate the interlink converter at the interconnection point.

Ongoing efforts and the way forwards 
We visualise the installation of low-voltage DC microgrids at neighbourhood or local level, readily harnessing the energy generated from neighbourhood PV panels across Germany and Europe. Thus, electricity is both produced and consumed locally, reducing dependence on the public grid. Since their operation is inherently independent of the public grid, DC microgrids would stay operational in the case of a mass grid failure, providing an ideal solution for black start scenarios.

Projects exploring DC grids at various levels are already underway. The Copernicus project ENSURE (New Energy Grid Structures), funded by the German Federal Ministry of Education and Research (BMBF), is testing DC stations, among other things. The German Federal Ministry of Economics and Climate’s (BMWK) HPC-Prime (High Power Charging) project is developing fast-charging columns for DC grids; and the DC-Industry project is working on DC grids for industrial applications.

Given the trajectory of the energy transition, installations currently on AC will eventually be replaced by DC installations when they reach the end of their lifespan, making this transition only a matter of time. Hence, it is important for actors in the electricity sector to develop common standards at this foundational stage, ensuring that end users are not left with a patchwork of equipment which cannot work with each other.

Encouragingly, a long-term, normative approach is already being considered by non-profit foundation Current/OS. In our opinion, such norms would address a critical gap, making DC technology truly plug-and-play, affordable and, ultimately, successful.

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: ‘Relieving Europe’s national grids through local DC microgrids’. Electricity grids are working under considerable stresses due to new patterns of use from the ongoing energy transition. Discover how local distribution systems working on direct current could help.
• ‘Infrastructure electricity: everything just works’. Walt Patterson, Associate Fellow in the Environment and Society Centre at the Royal Institute of International Affairs (Chatham House) in London, sets out how humankind could move to electricity systems that don’t involve combustion, with its various pollutants, at all.