A new solar charge is prompting some customers to switch off smaller systems, and installers are saying the rate structure favours larger households while leaving small installations scarcely worth keeping.

At least one Devonshire solar customer has switched off the three-panel system at his workshop after higher monthly facilities charges made it impractical to keep it connected.

Angus Macdonald said the charge to customers with interconnected solar rose from about $52 a month to $148, despite the small amount of electricity he uses at the workshop.

“I disconnected the solar because … I would be paying close to $175 a month by leaving three panels on,” Mr Macdonald said.

He still has a larger solar-and-battery system at his home, but said the change has left smaller installations struggling.

“It’s almost like go big or go home,” he said.

The change was introduced under Belco’s revised electricity tariff structure, which took effect on August 1. It changed the way general facilities charges are allocated among residential customers, including those with distributed generation, such as rooftop solar.

A report prepared for the Regulatory Authority by Ricardo, a consultancy firm, said that solar customers would no longer pay the average general facilities charge across residential tiers. Instead, it recommended that residential DG customers be placed in the highest, or Tier 5, category.

“DG customers would no longer be paying the average GFC tier in the residential class,” the report said. “Instead, they would be classified in GFC tier 5.”

The approved Tier 5 monthly charge is $148.83. Before the restructuring, DG customers paid an average charge equivalent to the former Tier 3 rate of $50.83.

Ricardo’s analysis predicted that more than 90 per cent of residential solar customers would see an increase in their bills under the change, with increases of up to $100 a month in some cases. It also projected that total bills could rise by as much as 150 per cent for some customers.

The consultancy said the approach was to make charges better reflect customers’ use of the electricity system.

“Those less reliant on the grid also pay for the costs they incur on the system,” the report said.

But Robbie Godfrey, chief executive of BE Solar, said the result was a flat charge that treated small and large systems exactly the same.

“It’s a flat rate … whether they’ve got a tiny, tiny system that barely generates power, or whether they’ve got an enormous system that generates a huge amount of power,” Mr Godfrey said.

He added that BE Solar had heard from customers considering disconnecting their systems and that the company had seen a major fall in interest in solar since the tariff change. He added that the company had close to 100 customers for whom the new structure had made their solar investment effectively pointless.

He also cited the example of a charity whose solar system had been funded by a corporate sponsor. According to Be Solar, its average monthly electricity savings fell from $147 to $9 after the tariff change.

The changes have also reignited criticism from solar installers and environmental groups, which warned before the new rates kicked in that the higher charge would make smaller rooftop systems less viable.

In July, the RA said that it recognised that some stakeholders disagreed with the outcome, but said the decision followed a “robust, transparent and evidence-based process” under its statutory mandate.

Belco had supported broader reforms to the facilities charge, but told Ricardo it did not agree with creating a separate customer class for customers with DG, saying that could be seen as rate discrimination. Ricardo nevertheless recommended placing those customers in Tier 5.

The RA was asked by The Royal Gazette whether it knew of customers disconnecting solar systems, whether it would review the impact on smaller installations and why all residential DG customers were assigned the Tier 5 charge. It had not responded by press time.