ABB, the large power and automation company, has developed technology that could provide an efficient way to transmit power from widely distributed solar panels, wind turbines, and other sources of renewable energy. The new technology is a fast and efficient circuit breaker for high-voltage direct-current (DC) power lines, a device that has eluded technologists for 100 years. The breaker makes it possible to join high-voltage DC transmission lines to form a resilient power grid.
If renewable energy is ever to account for a large part of the total energy supply, countries will need to install new, large-scale transmission grids, both to get power to cities from remote areas such as deserts that often have the best renewable resources, and to combine power from widely distributed wind turbines and solar panels, which can help average out fluctuations in their output. In Europe, there’s been talk for years of a supergrid that would pull together power from hydroelectric dams in Scandinavia with wind farms in Germany and large solar farms in Spain and even North Africa (see “A Supergrid for Europe”).
But such a supergrid has faced serious technical hurdles. The transmission lines that make up conventional power grids use alternating current (AC), which loses large amounts of power over long distances unless complicated and expensive measures are taken. DC is more efficient over long distances, and it offers the additional benefit of working well underground and underwater, reducing or eliminating the need for the unsightly transmission towers that can make it difficult to site new transmission lines.
DC lines have long been used to transmit power across the North Sea, and from large hydroelectric dams to cities. But until ABB’s advance, it wasn’t safe to connect DC lines into a large-scale grid.
ABB’s circuit breaker changes that. Within five milliseconds it can stop the flow of a huge amount of power—equal to the entire output of a nuclear power plant, ABB says. The breakers could be used to nearly instantaneously reroute power in a DC grid around a problem, allowing the grid to keep functioning. “Ordinarily, if something goes wrong anywhere, all the power goes off,” says Claes Rytoft, ABB’s chief technology officer. “The breaker can cut out the faulty line and keep the rest healthy.”
Researchers have been trying to develop high-voltage DC circuit breakers for a century (see “Edison’s Revenge: The Rise of DC Power”). Mechanical switches alone didn’t work—they shut off power too slowly. Power electronics made of transistors that can switch on and off large amounts of power offered a possible solution, but they proved far too inefficient. ABB’s solution combines power electronics with a mechanical switch to create a hybrid system that’s both fast and efficient. The new circuit breaker could also be far less expensive than systems that use only transistors.
“The cost of the power electronics breaker was humongous,” says Ram Adapa, a power delivery technical leader at the Electric Power Research Institute. “The hybrid breaker should be less costly.”
With the major hurdle to DC grids out of the way, ABB is now developing algorithms to control them. The system will still need to work in concert with AC lines for distributing the power in local communities, since there is no inexpensive DC equivalent of the transformers needed to step down power to the relatively low voltages used in homes and businesses. One of the first markets for the new technology could be Germany, which has decided to turn off its nuclear power plants and rely heavily on renewable energy (see “The Great German Energy Experiment”).
The degree to which high-voltage DC grids can help renewables may depend on the economics of installing underground cables versus overhead lines. Obtaining rights-of-way is one of the biggest obstacles to installing new transmission lines in many countries, and underground installations don’t require obtaining new rights-of-way, since they can be easily installed along existing roadways. ABB says that when the entire system cost is taken into account, underground installations are only slightly more expensive than overhead ones. But Adapa is skeptical, saying that underground installations could cost five times as much.