What is a supergrid?

By H.H.

ENERGY distribution has come a long way since the early 20th century, when cities pumped pressurised fluids to homes and businesses to power pneumatic machines. Today, energy flows around entire countries in the form of electricity. The grids which carry it, made from thousands of kilometres of copper cable, are fundamental to modern life. But there is a new shift afoot. As countries try to add more renewable energy to the mix, a transmission system known as the supergrid is taking shape. What is a supergrid?

Renewable energy sources—solar, wind and hydroelectricity—are different from fossil fuels. Gas, coal and oil can be piped or trucked to convenient locations for burning. Typically, power plants are close enough to population centres that the resultant electricity is easy to distribute, but far enough away that most people don’t have to see or smell them. Renewables come with no such flexibility. Wind turbines must be built where there is wind, solar panels where there is sun. The largest pools of renewable energy tend to be the farthest from human population centres; long, high-capacity electricity cables are needed to transmit their power. Traditional electric grids use alternating current (AC). These require huge amounts of power to push energy across long distances. Even when demand for renewable electricity is relatively close by, it can overwhelm the AC grid as it travels between source and destination. An entirely separate network of high-capacity cables can take the pressure off the AC grid.

Cables built for these purposes use direct current at very high voltages (HVDC), to minimise transmission losses. They are the beginning of the supergrid. The prefix “super-” conveys three of the word’s meanings. One is literal: HVDC lines function as arteries that move large amounts of electricity above and separate from the existing AC grid. The second is superlative: the supergrid has greater geographical extent than the normal grid. The ex-chairman of China’s state grid, Liu Zhenya, has used the label to describe ambitions to build a grid that allows electricity to flow around the whole planet. The third sense, of quality, is more an aspiration than definition: that the supergrid will be better than what we have now, a vision of a perfectly functioning zero-carbon global electrical transmission system.

China is well on its way to building a “regional” supergrid. If a global supergrid can be built, one which can flexibly carry energy around the planet, it will allow growing cities all over the world to tap much more renewable energy than they do currently. It might allow large nuclear plants to be built far from human populations, to provide a steady, reliable supply of energy to go with the large, fluctuating supply from renewables. Most importantly, access to the densest pools of wind and solar energy will make the capital costs of windmills, dams and solar farms easier to bear, bringing down the cost of electricity for everyone. That would be super.