'Making the electricity grid more efficient cannot be done without direct current'

"The power grid is the greatest machine mankind has ever created, but keeping it under control is becoming increasingly difficult," states DC specialist Damiën Zuidervliet. As such, it is technology from more than a hundred years ago that is coming under increasing pressure. "It is therefore really time that we dare to slowly let go of the familiar traditional system."

Direct current (DC) is becoming a much more logical choice for the power grid in more and more places than the alternating current (AC) that is now the standard. In a DC-based power grid, electricity can be controlled, throttled and faults can be detected preventively much more easily. Consequently, it is generally much more stable, says Zuidervliet. But what is DC, and why is it still hardly widely used as an alternative? Zuidervliet provides insight into what we can expect in the future.

At one time, alternating current was the right choice, Zuidervliet points out. "Power used to be used for three primary things: lighting, heating and to set machines in motion. The first two can be taken care of just fine with both alternating and direct current. In fact, for the third application, running an engine, alternating current was best. But the main feature that argued for alternating current came from efficient transportation," he explains.

Transport with alternating current

Broadly speaking, the world of electricity consists of three quantities: voltage, current and the resistance of components. Transporting electricity is limited by current and resistance, not voltage. The stronger the current, the greater the resistance and therefore the more loss occurs due to heat generation. In fact, that loss of energy increases quadratically with current strength (P=I²R). But if you are able to make a high voltage with very low current, you can transport that electricity over hundreds of miles without seeing your electricity evaporate.

That's exactly what Tesla did practical research on in the late 19th century. Tesla eventually built a working product that could convert electricity from high currents to high voltages, and vice versa, while retaining the same amount of electrical energy. He accomplished this through the basic principles of alternating current. This product became the famous transformer, which we still fully rely on today within our electrical grid, and which plays a leading role in the grid congestion that exists today.

Alternating current was thus an intermediate step that we needed in the nineteenth century to efficiently transport electricity over long distances. This further required standardizing that alternating current. In Europe, we chose a power grid based on 50 Hertz (Hz), meaning that the voltage jumps up and down 50 times per second. In the US, they chose 60Hz.

New era of power electronics

We are turning the clock forward again some 150 years. The electrical world has changed a great deal in the meantime. "The primary principles of generation and transmission have remained the same, and so we are still stuck with alternating current at 50 Hz," Zuidervliet points out. "But in the last 50 years, with the development of semiconductor technology, a whole new era has nevertheless begun: the era of power electronics. With it, we can also boost direct current to very high voltages, and so we can now transport direct current over long distances." In practice, this is visible in intercontinental connections, such as between the United Kingdom and the Netherlands and between the Netherlands and Norway. Those have been working with direct current for years because it is now more effective over long distances than alternating current.

Efficient transport is therefore no longer a compelling reason to use alternating current. While more and more aspects are being added that make the choice for direct current much more logical. "In recent years, our use and behavior has completely changed," Zuidervliet states. "We've gone from a situation with central power plants, to a complex system where anyone can feed electricity into the grid, either from solar panels, batteries or wind turbines spinning at random speeds. And we have moved from incandescent light bulbs and simple appliances to LED and sophisticated electronics."

Working inefficiently

That's where the first conflict arises, Zuidervliet sees. Our computers, phones, TVs and the like use direct current, and car batteries also store their energy via direct current. But we get the electricity for these devices from the power grid that gives alternating current. "To solve this, manufacturers add adapters to their devices so you can use or charge them from the AC grid. Your TV has these built in, your phone has the adapter in the compact power strip, and an electric car has a large inverter. But this does come with limitations. This is readily apparent with car chargers. For example, charging in the street takes half a day, while the DC fast charger along the highway charges a car in less than an hour."

All those inverters and adapters we use bring with them invisible problems, argues the specialist, which make the grid as it is currently set up less and less efficient. "Not only are we adding more and more conversion steps that cause little bits of contamination in the power quality, the power is coming from all sorts of unknown sources. For example, through solar panels or 'payback' home batteries. Originally, the power grid is a top-down system, from which electricity generated in power plants flows down to end users. Today, no one has insight into where all the power comes from."

Zuidervliet is clearly concerned about how grid use is evolving. "There is also increasing pressure from politics, because after all, we have to keep building, All-Electric of course. To have any chance at all of meeting those deadlines, the safety margins of our energy security are being made paper-thin. So the question is not whether the bomb will pop, but when it will pop."

On top of that, more and more complex infrastructures are being built lately, such as charging plazas and data centers. "These are important but also gigantic electricity-guzzling infrastructures that at their core consist mainly of direct current components. It is important to realize that their consumption can soon reach the residential consumption of half a city. Even these data centers and charging plazas, like your phone and car, need an adapter. So we are being incredibly inefficient."

A controllable power grid

We are forcing electrification far too quickly and in doing so we are causing the problems with imbalance and grid congestion that we are now experiencing, Zuidervliet believes. "In the current AC grid, we can only control electricity to a limited extent. By measuring the voltage and frequency, we can draw a lot of conclusions about the health of the grid, but this only gives a limited picture of the overall health. And in the end, we actually have very little control over where the power ultimately flows."

Resulting in imbalance and congestion. The use of direct current would have a positive effect on this, according to Zuidervliet. "We get more control over Ohm's Law. Because direct current has no frequency, so a direct current network depends on fewer parameters. This allows us to create a much more stable grid. It is much easier to measure and control. We can detect faults much faster, sometimes even preventively. In addition, we can start squeezing the copper line just as if it were a garden hose. This is ideal for restricting the flow in specific directions when it's convenient, without having to completely shut off the flow. That's exactly what you want to be able to do in the modern power grid."

But the benefits don't stop there. Much more energy can also pass through the same cable, and so the infrastructure can even be reduced in volume instead of being weighted down. To build AC, you mainly need a lot of copper, aluminum and iron. "But a lot of copper and iron, trucks full. While the price of copper is going through the roof. For the DC equivalent, a trunk full of material is enough, so to speak. That's not only profit in raw materials, but also profit in space. And in our small country there is considerable scarcity of available space. So you could say that the Netherlands is the ideal country to make DC big."

Only advantages?

Still, direct current is not a magical tool, Zuidervliet emphasizes. "The power grid is the biggest machine mankind has ever made. So that also means that it is immensely complex. It requires a lot of knowledge to fully understand such a complex machine and keep it operational. That's why sometimes it's nice to keep doing things the way they've always been done."

Education and knowledge is an essential aspect of getting the dc chain going. "You have to be a sleeper by nature if you want to give direct current a chance at such an early stage. Fortunately, obstructionism is in my blood, because the technology of direct current makes more sense. Only the logistics around it are not yet prepared for it. But I think that's no different from introducing cars in the age of horses, or computers in the age of paper. Once it has proven itself, it will naturally be normalized by society."

Towards a tipping point

AC distribution is 100 years ahead of direct current, not only in terms of knowledge, but also in the market. AC distribution components are produced in the billions, while for DC components it is a few million. The lack of experts also makes it difficult. This means that DC deployment is still much more expensive at the moment. It is therefore logical, according to Zuidervliet, that it is now mainly used in more complex installations, such as loading docks, data centers or in large industries. This is where more can be invested financially and technically for better systems.

Still, he sees a tipping point emerging in the near future. "The first question I am always asked is: what difference will I notice if I use direct current? When in fact it is best if the user doesn't notice anything at all. Consumers should be able to use their electricity unhindered. You will only notice the difference when neighbors in the street come knocking on your door because there is a fault and your lights are on. In addition, the real benefits of direct current occur higher up in the grid. Balancing and noise filtering are better controlled there. With the massive increase in battery systems, solar systems, complex electrical equipment and perhaps even dischargeable cars, the grid is becoming increasingly unstable. If the policy makers do not dare to take any decisions, we will get to the stage before 2030 where we will have to reckon with bigger blackouts than we are used to now in the Netherlands. These will not be very severe and will also be resolved quickly, but with their short duration they are annoying enough. In other words, energy security is increasingly at risk. Everyone is going to notice that, including ordinary users. That brings us ever closer to the point where we are all willing to pay more for a more effective system."

Unknown and therefore unloved

A residential home works fine on alternating current, so direct current currently remains invisible to the general public. But as a result, its great advantages also remain underexposed, Zuidervliet believes. So he hopes that the great wave of DC for charging stations and data centers will include residential homes. "Let's try to make the whole system as efficient as possible. We can't do that without DC."