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Analysis: Storage pilot project proves smooth delivery - at a cost

CHINA: A combined total of 450MW of wind, 100MW of solar and 20MW of storage facilities are in operation on an elevated terrain of around 100 square kilometres in Zhangjiakou, Hebei province, a little more than three hours drive north of Beijing.

Three tiers… Project adds storage to wind and solar capacity
Three tiers… Project adds storage to wind and solar capacity

Launched in 2009, the first two phases of the wind-solar-storage-transmission (WSST) demonstration project were completed by the end of 2014.

The development aims to find a solution to the grid-connecting problems of renewable energies, which are typically intermittent and fluctuating in generation. Wind and solar power offer complementary production times, and storage batteries are expected to help them become grid friendly.

"Experimental operations in the past few years have been fruitful," said Liang Lixin, deputy director for the general management of the State WSST Power Station.

Thanks largely to the storage facility, the wind and solar-generated power is fed into the grid smoothly and steadily.

To avoid accidental disconnection, the project tackled the issues of low and high-voltage ride-through of double-fed or direct-drive wind turbines early on, and the integrated WSST system is now capable of black starting (or independent restoration). Wind curtailment as a result of grid technology has been reduced to the minimum.

Stable supply

The WSST project has a panoramic monitoring and comprehensive control system to forecast and manage the generation of wind and solar power and ensure that the clean electricity is fed into the grid and transmitted to consumers. "Our wind and solar electricity are as stable as fossil-fuelled power," Liang said.

The state-level demonstration project owns the full intellectual property rights and has contributed to a host of national technical standards, having published 103 papers, developed seven copyrighted softwares and awarded 108 patents over the past six years.

The practices of the WSST project have been copied by several renewable projects in northern China, in Gansu and Qinghai provinces, as well as in Inner Mongolia. But the costly storage hampers the spread of the project findings, which partly explains the delay in installing another 50MW storage capacity planned for the second phase. It is not known when this work will be done.

The storage capacity is used to help the wind and solar facilities remain connected, feeding their variable power into the grid smoothly. The assembled batteries in operation are not adequate to perform peak load shifting. This would require much more storage capacity and, from an economic point of view, is implausible.

Large-scale storage could in theory halt curtailment, but China does not have a policy to recognise the extra storage cost, and there is little hope that renewable power produced with storage equipment would receive higher feed-in tariff rates. It is not even clear whether it is the responsibility of an energy developer or the grid operator to build the storage facility.

Total grid-connected wind installations in Zhangjiakou reached 6.6GW at the end of 2014. However, the local load demand was only around 1.5-1.6GW in 2013. Suffering the same proportion of curtailment as other wind or solar facilities in the region, the WSST project is running at a loss. To solve this problem, China would have to build high-grade power lines to transmit the region's surplus electricity to other places, reform the grid-feeding policy and change the distribution of development.

Research focus

As a state-level large-scale experiment, the WSST project was launched by the State Grid Corporation, with several government departments as early sponsors. Jibei Grid, a Hebei-based subsidiary of the State Grid, currently oversees the project.

Profit is not the major concern of a project like this. "We take it as a social responsibility to explore ways of making renewables grid-friendly," Liang said.

The project has installed different wind turbines, ranging from 1.5MW to 5MW in capacity, supplied by manufacturers including XJ Wind Power, Goldwind, United Power and Dongfang Electric. A 5MW XEMC turbine was installed last year and connected to the grid in August. Wind capacity of 50MW planned for the second phase is reserved for large turbines.

Both wind and solar resources at the site are very good. The annual average wind speed is 6.3 metres per second at a height of only 10 metres.

The site is next to Chongli County, where most of the skiing events of the 2022 Winter Olympics are expected to take place. If the government achieves its wish of powering the sports facilities with 100% renewables, with wind likely to contribute most of this, the WSST project will have a role to play.

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