Lead carbon selected for 20MWh ESS in Tibet

A 20MWh lead carbon battery by China Shoto Energy Storage to provide frequency support for a PV installation in Tibet became the world’s highest-altitude large-scale energy storage project in December. It also showcased the news that lead acid batteries, while not the chemistry of choice in the western world, are still the most popular form of large scale energy storage in China based on both functionality and price.

The system, which is connected to the Yangyi power plant’s 30MW PV installation, went live at the behest of the Tibetan government to ensure the quality of supply from intermittent solar generation to the grid with frequency and voltage services.

The project, 4,700 metres above sea level, uses lead carbon rather than AGM or gel-based lead acid batteries because of its robustness in harsh conditions and ability to operate in low temperatures. The altitude means that winters can be severe.

“We chose lead batteries which can operate down to freezing point,” said Shoto Energy Storage’s deputy chief engineer Lucie Yi. “Lithium ion batteries struggle when the weather falls below 10°C.

The project is also the largest grid-tied commercial ESS in China and has an expected lifetime of 10 years. Housed in 16 all-in-one 40 ft ESS containers, the project uses 9,600 of Shoto’s long life lead carbon batteries (LLC-1000) that can reach 4,000 cycles at 70% depth of discharge.

Alistair Davidson, products and sustainability director at the International Lead Association, said lead carbon batteries were a much more economical option than other available technologies.

“The use of carbon and other additives, new grid alloys and active materials have resulted in significant improved shallow cycling performance and energy density of advanced lead batteries,” he said.

“This technology has also demonstrated a marked increase in both cycle life and calendar life, making it an excellent option in renewable and utility energy storage applications such as this. The technology also works well across multiple applications, including at high altitude.”

Lucie Yi said there were four factors that the company took into account before choosing lead carbon for the ESS.

“First is investment costs, which are low, second this battery has a good cycling performance for its life span; third is the lower operating temperature; and fourth is the battery can be recycled easier at its end of life, for lithium ion it is not so easy,” she said.

“The technology uses activated carbon on the negative electrode. The carbon has two roles in this battery; it increases the acceptance of the charge so charging is easier and faster and secondly it enables the battery to have a longer cycle life.

“Because the battery is being charged from solar generation, which is not always stable because sometimes there is not enough sunshine to charge the battery, in a normal AGM or gel lead acid battery you get some aging problems — sulfation —at the negative plate.

“When the crystals of lead sulfate become too big the plate is damaged and the battery’s lifetime is shortened. With this technology, growth of these crystals is stopped or made difficult to form on the plate, making the battery’s lifetime longer.

“In China lots of energy storage projects use lead carbon, especially for commercial use in industrial parks for peak shifting services because it’s cheap; so a lot of projects use these batteries in this type of application.

“The main reason for the project is to improve the quality of supply. Before the output quality of the 30MW PV was not good enough to put on the electricity grid, so the government would ask the PV firm to stop production at certain times during the day, so to avoid that they wanted an energy storage system installed.”

China Shoto Energy Storage is part of the Shuangdeng Group of companies and is a member of the Advanced Lead Acid Battery Consortium.