By Irina Slav
China’s renewable power generation capacity—including hydro—reached over 38 percent of total newly installed capacity at the end of last year. The country is clearly the world leader in wind and solar power additions as it seeks to move away from coal as quickly as possible. But it has yet to solve its problem with what the industry calls curtailment, or the waste of renewable power due to grid limitations. China is solving this problem with supergrids.
China has 22 ultrahigh-voltage power transmission projects in operation: an emerging supergrid that could, among other things, reduce the waste of renewable energy by linking the regions that produce it to the regions with the highest rates of electricity consumption, writes Peter Fairley for Spectrum, the Institute of Electrical and Electronic Engineers’ magazine.
The ultrahigh-voltage grid is unique in that it combines DC with AC lines, with the DC lines transporting the electricity over great distances at reduced rates of waste and the AC parts of the grid distributing the electricity to regional grids and individual consumers. The grid is unique, Fairley says, but it’s not without its problems.
For one thing, there is worry among some engineers that the nature of the supergrid increases the risk of cascade blackouts. For example, Fairley explains, if the DC line of the 8-GW ultrahigh-voltage line that carries electricity produced by the wind and solar farms in northwestern China’s Gansu region to the east failed, the blackout would spread across the regional AC grids causing a lot more problems than if the country’s grid continued to be fragmentary.
In a bid to reduce this risk, the State Grid Corp. of China is running a lot of these lines below capacity. The 8-GW Gansu-Hunan has been running at about a quarter of its capacity for this reason since launch, and that’s accounted for a lot of the renewable power curtailment in the area. What’s more, there are many solar and wind projects that have yet to be approved for joining the grid and start generating electricity.
Even with the challenges, however, the ultrahigh-voltage lines have been instrumental in advancing China’s renewable energy plans, Fairley notes. In 2017, these lines alone moved 161.5 TWh of solar, wind, and hydropower. There are still power shortages in China’s biggest electricity-consuming urban and industrial centers, but the central authorities seem to be set on the ultrahigh-voltage line course and rely on the further development of the supergrid to eliminate these.
In this, they are encountering obstacles, however, and these are slowing down the progress on the ambitious world-first project. Local authorities are unhappy with the fact the ultrahigh-voltage line grid requires centralized management. Engineers, Fairley says, are criticizing what they see as a monopolization of the engineering and production of grid components and the construction of new lines.
Besides opposition and misgivings, there are also practical challenges, such as the amount of reserve power that needs to be kept available in case of loss of the main source of power. With lower-voltage grids, this usually comes in at about 1-2 GW. With pines carrying 8-12 GW of electricity, the emergency reserve of power will need to be a lot higher.
Last year, China generated 1.87 trillion kWh of electricity form renewable sources. Even with new project limits, the utilization rate of existing facilities are rising, and this amount will continue up. The course for transmitting and distributing this power seems set despite the obstacles and the challenges. At some point, the unacceptably high curtailment rates will no doubt start going down.