Energy authorities have insisted more power purchase agreements (PPAs) made under the state's 5.2-gigawatt renewables scheme will not lead to expensive power bills, as claimed by the People's Party.
People's Party MP Suphachot Chaiyasat expressed concern that new PPAs would cause Thais to pay an additional combined 100 billion baht in power bills over the next 25 years, according to media reports.
He also raised doubts over the process to select power companies participating in the renewables scheme, accusing authorities of favouring certain participants.
Mr Suphachot wants the government to consider pausing the signing of PPAs.
His assertions were denied by the Energy Policy and Planning Office (Eppo).
"Cancelling 67 PPAs that were already signed and signing an additional 16 PPAs is impossible," said Wattanapong Kurovat, secretary-general of Eppo.
He also denied the renewables scheme will increase power prices in the country.
The Electricity Generating Authority of Thailand sells electricity on the state grid at 3.18 baht per kilowatt-hour (unit) to two state power distribution arms: the Metropolitan Electricity Authority and the Provincial Electricity Authority.
This average wholesale price is greater than the price of electricity under the 5.2GW renewables scheme, which is set at 2.7 baht a unit on average, said Mr Wattanapong.
Under the scheme, solar power is priced 2.18 baht a unit; wind power is priced at 3.10 baht a unit; and electricity from solar farms with battery storage systems is sold at 2.83 baht a unit.
These types of clean power have lower prices than electricity on the state grid, meaning Thailand can reduce electricity generation costs by 4.57 billion baht a year, he said.
Mr Wattanapong said the renewables scheme is important to propel investment in clean energy, which is increasingly demanded by both Thai and foreign companies.
Manufacturers wanting to export goods to the EU are required to reduce carbon dioxide emissions to avoid a non-tariff barrier, known as the Carbon Border Adjustment Mechanism.
Energy Minister Pirapan Salirathavibhaga said he is aware of the People's Party's concerns and is delaying the signing of 16 PPAs to look into the alleged irregularities.
The 16 PPAs, mostly wind energy projects, are scheduled to be signed by 2026.