(Bloomberg) -- South Korean solar-power generators filed a lawsuit Thursday seeking to stop the government from forcing them to curtail output at their plants.

A dozen producers who run small-scale solar farms on the tropical island of Jeju are suing state-owned Korea Electric Power Corp., national grid operator Korea Power Exchange and the Ministry of Trade, Industry and Energy, saying they were forced to cut back operations without clear explanation. 

“My plant is basically being shut off every time the sun is out,” Kim Jaekwon, one of the plaintiffs whose solar farms have total capacity of 4.5 megawatts, said by phone. “It’s the unfairness and unpredictability that we’re raising here because some get more curtailment than others.”

Kepco and KPX declined to comment on the lawsuit, saying they need time to check the official complaint filed by the solar power owners. Curtailment is an unavoidable measure and maintaining a stable power supply is a priority over the need to prevent losses from curtailments, the Ministry of Trade, Industry and Energy said.

Curtailment is becoming a growing issue for the global power industry as countries rush to add renewable energy faster than they phase out fossil fuels or expand related infrastructure, resulting in an overloaded power grid. 

In countries including the US, Germany and China, clean power is prioritized over coal and gas when the grid is overloaded. The situation is different in South Korea — the government often curtails solar and wind first, concerned that a reduction at large-scale power plants poses too much risk to the nation’s electricity supply.

“Insufficient grid capacity, the inflexible operation of fossil fuel power plants and a lack of flexible resources such as battery storage have all contributed to the problem,” said Kim Joojin, executive director of Solutions for Our Climate. “Renewable curtailment is a band-aid fix at best.”

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The solar producers filed the case Thursday to the Gwangju District Court, according to the Korea Photovoltaics Businessman Association. Their move comes after the energy ministry said in March that it would limit solar output in provinces of South Gyeongsang and Jeolla to keep the nation’s electricity supply stable. 

The plaintiffs argue that their plants are running at losses due to frequent curtailment orders, and are struggling to pay off their loans. They also contend that the regulations contradict national and regional climate policies. Jeju has a target of becoming a carbon-free island by 2030, while Korea has pledged to reach net zero emissions by 2050. 

One of the plaintiffs, who owns a 1-megawatt capacity solar farm, received about 60 curtailment orders in the 14 months through early May, causing a financial loss of about 40 million won ($31,000), according to the association. The number of curtailment notices that each plaintiff received varies significantly, reflecting unfairness in the system, the group added.  

“Small solar farm owners are the ones taking the blame and responsibility for overcrowding the grid,” Kwak Youngju, the head of the Korea Photovoltaics Businessman Association. “The government needs to come up with specific guidelines that provide clear criteria for when and why curtailment would occur.” 

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