Tran Nhu Anh Kiet, a grocery manager in Vietnam’s Ninh Thuan province, is compelled to turn off his solar panels for up to 12 days a month during the most profitable peak sunlight hours.

“I’m losing on average 40% of output,” Kiet told.

He installed on the top of his business to sell electricity to the national grid.

Due to infrastructure constraints, authorities in southern Vietnam and the Central Highlands are asking small-scale energy producers like Kiet and industrial solar farms to scale back their activities.

“Before the curtailments, our revenue was 100 million Vietnamese Dong [$4,136], now it is just 60 million Vietnamese Dong [$2,589].”

Following an unprecedented surge in renewable energy investment in recent years, transmission lines connecting solar and wind plants to the national grid are unable to handle supply spikes.

Policymakers have lagged behind, leaving regulatory gaps that prevent some investors from profiting from the influence they wield.

“A [transmission] line takes three years to build, and a wind farm one year to build,” Minh Ha Duong, a clean energy expert, told.

“So lines need to be planned years in advance. This was not possible since in 2018 nobody knew for certain where they would be needed.”

Vietnam provided 20-year contracts to buy electricity from new solar and wind power projects at set rates between 2017 and late 2021, a typical policy used around the world to attract renewable energy investment known as feed-in tariffs (FIT).

The rates were significantly more than what other Southeast Asian countries were offering at the time, at more than $70 per megawatt-hour (MWh).

In Thailand, for example, the rooftop FIT in 2019 was just about $57 per MWh.

“The reason for this policy was to avoid the risk of electricity shortages,” Duong said.

“Because the coal and gas power plants we planned to build were not [concluded] on time.”