AC to DC

2015 12 Macro level top HR

Illustration: Stephan Timmers / Total Shot

Laura Ramirez Elizondo and Pavol Bauer believe it is time for a complete overhaul of our electricity grid. Laura and Pavol are running the Direct Current.

Although the large coal-and gas-fired power stations in the Netherlands are currently indispensable, they will have a minimal role to play in 20 years’ time. Researchers in the DC Systems, Energy Conversion & Storage research group (faculty of Electrical Engineering, Mathematics and Computer Science (EEMCS)) believe our electricity supply is going to change radically in the years to come.

A poster hung at the entrance to the research department depicts a cartoon that is a fairly good representation of the researchers’ vision of the future. We see industry, a power plant, an urban area, wind turbines at sea and solar energy parks. There are just a few high-voltage cables connecting the wind parks to land and providing the factories with electricity from the power plants. There are almost no high-voltage cables in or going into the city. The city dwellers are self-sufficient and connected to a DC grid. All the roofs and lots of the walls are covered in solar panels, with here and there a wind turbine on a roof or between the houses.

According to Dr Laura Ramirez Elizondo and Prof. Pavol Bauer, the leaders of the Direct Current (DC) Distribution Smart Grids (DCSMART) project, residential areas will generate their own electricity, which they will exchange with each other through low-voltage DC grids.
What will be the future role of energy companies? “Their role will change enormously,” says Ramirez. “The direct link between energy companies and the consumer will be very different. I think that energy companies will largely take on a service provider role. They can help manage the grids and connect households to these grids.”

The researchers are focusing primarily on what needs to happen to make the transition to a sustainable low-voltage DC grid possible, where DC stands for direct current.

The century of direct current
According to the scientists, alternating current has run its course and the 21st century will be the century of direct current. This would turn the dream of Thomas Edison, who pioneered the world’s first electricity supply, into reality. Starting in 1882, he supplied a few dozen customers in Manhattan with 110 volt direct current. The problem with direct current was that it was difficult to transport over large distances as it could not be transformed into higher voltages. However, this is now possible thanks to power electronics. A competitive battle developed between Edison (direct current) and the American business man George Westinghouse, a strong supporter of alternating current. This battle would go into the history books as the ‘war of the currents’ and was settled to the advantage of alternating current. Even so, it seems that Edison will posthumously get his way, because we are all going to generate our own electricity.

“Alternating current is a relic of the past,” explains Ramirez. “Decentralised generation technologies such as solar panels produce direct current and storage technologies such as batteries and electric cars use direct current. This is all low-voltage and we can generate and use the electricity at the same place. If low-voltage grids work using direct current, we do not need to convert the output of the technologies into alternating current.”

Laura Ramirez Elizondo

Dr Laura Ramirez Elizondo. Photo: Marcel Krijger

This also means that we no longer need adapters. All our equipment, from laptops to toasters and televisions, work using direct current. Transformers currently convert the alternating current that comes out of the socket into direct current for this equipment, even though solar panels also produce direct current. It really makes no sense to convert electricity from DC to AC and back to DC again.

However, this is not the only motive for the researchers. Ramirez: “I think we can make the world more sustainable using lowvoltage smart DC grids, as these grids make the transition to fully sustainable electricity using wind and sun easier. Furthermore, they require less thick cables and remove the need for large adapters. This reduces the amount of material required. Plus, in areas in the world in which the money is not available for the construction of traditional high-voltage infrastructure such aS many places in Africa – DC can still make electricity grids possible.”

Algorithms

A switch to direct current still presents some big challenges. To give an example, direct current grids need to be made more resistant to problems such as short-circuits. This is one of the areas that is being worked on within the European project. The researchers are also working on algorithms to balance supply and demand in DC grids. The electricity produced from solar panels and wind turbines can vary greatly, and a solution needs to be found for this.

The new focus on low-voltage means that some changes have also been made to the EEMCS high-voltage laboratory. Solar panels, electric cars and home batteries were added to the current high-voltage equipment. For one project, the Delft researchers simulated a Dutch household. The aim was to evaluate the effectiveness of home batteries for smart energy management.

When can we expect the transition to take place? Bauer: “It will probably take about ten years before we see the first development projects in which whole residential areas are connected to smart DC grids. It helps that electric cars are becoming so popular, because charging a car requires a lot of power. Our present electricity grid will no longer be able to cope with all the electric cars after a while. Distributed DC grids can therefore be created in their place. It would not surprise me if DC grids are created especially for electric cars.”

The team is also working on a demonstration project in Haarlemmermeer, where a few horticultural companies are switching to a DC grid. The companies will use combined heat and power with a gas turbine to produce their own heat for the greenhouses and to generate their own electricity. “Our input in this project is the intelligence,” explains Ramirez. “We want to set the turbines so that they produce the right amount of residual heat for the greenhouses while also generating as much electricity as possible. We also need to maintain the stability of the DC grid using control algorithms.”
The researchers also plan to work on a residential area with DC grids, for which they will apply for an EU Marie Curie subsidy. If they are successful, they can work on concepts for smart DC grids at the local area level. “We will then look into lots more applications, including ships and aeroplanes that work on direct current,” says Bauer. “Over 30 European research partners have joined us to work on this project.”
The DCSMART project has been accepted in the ERANET (European Research Area Network) research programme and was awarded a two million euro subsidy earlier this year. In addition to TU Delft, TU Eindhoven, Direct Current, Fraunhofer-Gesellschaft in Germany and Centre Suisse d’Électronique et Microtechnique are also involved in the project.

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