Executive Summary: For a just energy transition, the AC grid is necessary, but with help from all sides. At the demand side, if we can scale-up, DC grids embedded locally, like a laptop, many problems can be solved. We can look up to LV DC distribution to solve the remaining issues.

Key: AC – alternating current; DC – direct current; EHV – extra-high voltage; HV – high voltage; MV – medium voltage; LV – low voltage; SELV – safe extra-low voltage; hvac – heating ventilation and cooling. IEC60038 can be referred to for specific voltage values.

Chapter 1: AC grid’s “happily ever after” has been cut short. Specifically, LV AC grid needs help.

The AC grid (at all voltage levels) evolved gradually to its present unitary state through a few simple, but enshrined, principles. Designing for maximum demand and rotational inertia supporting protection co-ordination are a couple of those principles. Over the decades, this also meant that the AC grid had a large “safety cushion”, primarily through over-designing. As for the rotating machines, complacency had set in that they can’t be replaced. AC grid rightly then became the only transactor of electrons, but wrongly gave hope that all things electric can easily work off it. And that is when the good times ended for the AC grid.

Without looking at the demand side, too much focus and investment was thrown into large and assimilated renewable generation. This has caused long queues for evacuating such renewables, waiting for the AC grid to be reinforced locally. Or, when these renewables have already been linked to the AC grid, and if there’s an excess of electrons to be accommodated in that region, costly curtailments are being paid to the renewable operators to stop them from generating; it can be to avoid system instability or for purely economic reasons. Alternatively, the renewable operators may bid with “negative pricing” (paying the AC grid for taking their electrons) for certain time slots, purely to keep their plants running continuously. The resulting “supply-demand” contracts are complex and eventually don’t help in reducing the tariffs for the actual electricity users (demand side). In parallel, another problem has crept in; with these renewables replacing large generators, the rotating inertia has been reduced significantly, and that’s the cue for system instability risk increasing. Remember the Iberian Peninsula blackout on 28 April 2025 (https://www.entsoe.eu/publications/blackout/28-april-2025-iberian-blackout/). It is fair to say that grid-scale solutions have created other grid-scale problems!

On the demand side, subsidies caused many buildings, residential or commercial or industrial, to install photovoltaic (PV) panels on their roofs, simply connected to the AC grid, in addition to their electrical vehicle (EV) chargers. Whoa, whoa. The whole “neighborhood” now produce electrons when the sun is shining, or are charging their EVs during the night. So, the local AC grid becomes heavily congested, with cables burning off as a result. With LV AC grid not being monitored fully as its MV AC counterpart, such failures can only increase in the future. Other symptoms include slowing down in new supply connections, or in accommodating additional demand requests in the existing connections. The actual electricity users are again in a limbo.

AC grid, therefore, needs help from everywhere, but more so structurally from the demand side. The actual electricity users can step up by reducing their maximum demand on the AC grid, and by managing protection selectivity entirely within their side, with no responsibility transferred to the AC grid. And this is where LV DC enters our context. Any atonement for what has been done to the AC grid in the last few decades will have to involve LV DC at the demand side. Yes, AC now needs DC!

Chapter 2: Unwittingly, we use SELV DC grids already in our laptops. We simply need to scale them up to LV DC level, to reduce maximum demand put on the AC grid.

The wall outlet is the laptop’s “point of connection to the AC”, and the power adapter converts the wall outlet’s LV AC to SELV DC and supplies it to the power rails within the laptop. There is a battery within the laptop, and an embedded controller that decides which SELV DC (from the wall outlet, or from the battery) needs to be fed on to the other power rails, apart from getting the battery charged. In some of the laptops, there could be a provision that could take another power adapter connected to a second wall outlet. Finally, there are additional DC-DC converters powering rails rated for different voltages, suitable for the components connected. Voila, you have an SELV DC grid, managed by an embedded controller.

If we scale up such an SELV DC grid, it could look like a local DC grid, connected to the MV AC or LV AC grid.

Figure 1: A typical DC Microgrid (reference public version of the Current/OS System Reference Document)

Though not all the following values are relevant for a laptop grid, these are the ones that can benefit the actual electricity users using LV DC:

1. Optimise Operational Cost: The controller can choose the electrons from a variety of sources (AC grid or AC supply distribution, battery, local generation or local regeneration) and send them to the loads. This source choice can be based on a priority, or based on tariff, or based on weather forecast, or based on anticipated demand.
2. Flatten Maximum Demand: The controller can simply feed the sudden and momentary fluctuations in demand (say a welding plant, or an AI server) from a battery or a capacitor bank in the local LV DC grid. This would localise the demand fluctuations and would pass only the constant demand on to the AC grid / the AC supply distribution. The release in demand (difference between the maximum demand and the constant demand) of an existing facility can then be used for extra electrification (EV chargers, process electrification), without modifying the maximum demand approved for that facility.
3. Mind-your-own-business though electrically connected: An Inter-Link Converter (ILC), equivalent to the power adapter of the laptop, can act as the point of connection for the local LV DC grid to the AC grid or AC supply distribution. As one can imagine, this ILC needs to be optionally unidirectional, so that the local LV DC grid minds its own business, without supplying fault current to any fault or abnormality in the AC grid or the AC supply distribution. As this does not alter the protection settings of the AC grid or the AC supply distribution, and does not need any reinforcements, there will be immediate planning permission approval from the AC grid operator. This “zero waiting time” improves the Return on Investment.
4. Invest-and-get-return-as-you-go: If such a LV DC grid can be physically embedded next to, and dedicated to, say the heating, ventilation and cooling (hvac), or a welding plant within the larger LV AC distribution of a factory, then the demand fluctuation is contained within that hvac / welding plant. So, we could envisage a locally embedded DC grid for a specific application, like a laptop, or a cooker, or a hvac, or a welding plant. We can already see such a trend in appliances, where batteries get added next to the demand. For example, this trend is already visible in home appliances, such as with induction stoves. Further, if there’s physical space near that application, say the welding plant, to have PVs, they can be directly linked to this locally embedded LV DC grid and these PVs need not be taken all the way to the service entrance. Such an embedded LV DC microgrid allows actual electricity users to modernise their existing facility in steps, without having to invest a lot for a full-fledged upgrade.
5. Sell Flexibility from the service entrance: In addition to the application-specific LV DC grids, the facility owner can add another (larger) LV DC grid at the service entrance (point of connection to the AC grid) integrating the AC grid through bidirectional ILC, the local generation and a larger sized battery. Depending on the contract with the AC grid operator for the AC grid’s stability, the facility owner can sell flexibility services using this bidirectional ILC. These flexibility services are deliberate and expected (as the AC grid operator will send specific requests for flexibility), while the controller can still block any unexpected feed of power from the facility to the AC grid.
6. Bypass the LV AC grid and take power connection directly from MV AC grid: Solid-state transformers, or for the time being conventional transformer plus converters, can tap power from MV AC and provide it at LV DC directly. So, for higher power needs, instead of waiting for an LV AC connection, the facility could opt to get connected to a MV AC grid. This could allow a facility to charge their EVs through a second connection (but from MV AC) with specific curtailments and tariffs contracted for. And such a second connection will not interfere with the first LV AC grid connection.
7. Don’t antagonise the electricity users to go off-grid: By keeping all the electricity users connected to the AC grid, standing charges can be spread in a just way, and that principle is the foundation for a just energy transition.

Chapter 3: LV DC will distribute power to most of the facility in the future.

In chapter 2, we saw that energy management can now be done at the demand side using dedicated local DC grids, even embedded within appliances or loads. We also saw that the local DC grid at the service entrance needs both power management (for flexibility services) and energy management (for resiliency).

How can we distribute power from the service entrance? Power needs to get to the application-specific LV DC grids within a facility, or directly to the other loads spread across the facility (lighting, robot charging, office tables, etc). The answer depends on a few factors as usual, like the constant power demand that gets transferred, or the urge to reduce the required amount of copper or any other material like the conduits. In addition, there’s another factor that can influence this choice, and that is the availability of certified electricians. There are LV DC or SELV DC technologies that can be handled by non-electricians, as the shock-risk or the fire-risk is almost eliminated.

Different contexts may need different approaches, with most approaches pointing towards LV DC power distribution in the future. For example, material efficiency and power quality could force the use of LV DC distribution in a Vertical Farm (Controlled Environment Agriculture); in a vertical farm, instead of using power converters just before the LEDs, LV DC distribution could save copper, improve power quality and even increase the life of the LEDs. In a commercial building, cost can be optimised by using certified electricians only at the service entrance; non-electricians can then do the wiring for use with specific LV or SELV DC technologies, noting that this work can go in parallel with other construction work, thereby saving even more time on the project schedule.

Chapter 4: Schneider Electric are leading this change.

Schneider Electric intend to facilitate LV DC grids in all electricity users’ facilities, solving their energy trilemma (security, affordability, and sustainability). For the sake of the People and the Planet, we will work with our Partners in the New Energy Landscape, by offering our technologies. It is Energy-Tech that will advance industry, drive innovation and connect communities. After all, Schneider’s purpose is to create Impact by empowering all to make the most of our energy and resources, bridging progress and sustainability for all. We are indeed your energy technology partner.