Britain’s biggest community solar farm forced to shut over grid overload fears

The north Devon solar farm was ordered to shut weeks before record high temperatures across Europe led to power supply warnings, due to concerns that the large amount of rooftop solar in the area could destabilise the power grid by triggering a “thermal overload”.

The shutdown is expected to cost the cooperative scheme’s nearly 10,000 members about £2m in lost revenue before it is allowed to restart again in September.

In a letter to more than 9,500 people and small business owners who own a stake in the Derril Water solar park, the cooperative’s board said the “unexpected” shutdown order was “enforced on our solar park and other generators in north Devon with no warning”.

The timing of the shutdown at the beginning of its first summer “could not be worse”, according to the board, and would “substantially impact” the scheme’s finances, including payments to members.

It said: “The interruption creates unexpected financial pressure and will impact our ability to pay members at least in the near-term.

“We are not clear on what triggered the shutdown, which came on the Friday before the half-term heatwave with no notice,” the board told the Guardian. “However, it does seem the network operators knew there was a looming problem.”

The National Energy System Operator (Neso) is understood to have ordered National Grid to shut a vital “super grid transformer” over the summer to prevent the rooftop solar in the area from driving the transmission network’s voltage beyond its safety limits.

The surge in rooftop solar power is particularly difficult to manage during the summer when long, sunny days lead to more generation than a local grid might need. Specialist equipment can help to manage potential voltage issues, but these upgrades have not yet taken place in the area near the Derril Water solar park.

The board believes that the problems with the north Devon network have been known since 2023, and new equipment was due to be installed by the end of 2025. However, these measures were delayed and are now due to be completed in September this year.

The project does not expect to receive compensation or insurance to cover the lost summer revenue from the solar park, which was funded by £20m raised from members of the cooperative and a £22m long-term bank loan.

Members originally joined the scheme through Ripple Energy, which offered households the chance to invest in Britain’s first “shared” solar park to earn average savings on their energy bills of at least £200 a year.

Ripple Energy had hoped that Derril Water would begin generating electricity in 2024 and “become a blueprint for consumer-owned solar parks around the world”. However, construction delays and rising costs caused the company to go bust in early 2025, before the park began operations.

Derril Water began generating electricity in September last year under the leadership of its volunteer board, less than six months after Ripple was bought out of administration by the business energy provider 1st Energy.

“Although there has been some justified frustration, the majority of the coop’s 9,500 members who have been in touch understand that the issue does not lie with the solar park, nor its management through the park’s volunteer board of directors,” the board said.

A spokesperson for National Grid confirmed that it had curtailed some generation in the local area to keep the system secure after Neso called for its super-grid transformer to be turned off. “We’re now working with Neso to help provide solutions to these temporary constraints,” the spokesperson added.

Neso declined to comment.