The Energy Regulatory Commission (ERC) plans to open up the long-awaited solar rooftop scheme in March, with a total capacity of 100 megawatts.

This is the second round of the solar rooftop programme for local investors after the first round opened in September 2013 with a total capacity of 200MW, all of which has commenced commercial operation.

Most of the solar rooftops in Thailand have been installed by companies and generate electricity for each customer, but they are not allowed to sell surplus output to the state grid.

Narupat Amornkosit, secretary-general of the ERC, said the commission is close to finalising all the relevant conditions: investment, business model, selling price and property type.

The move comes after a revised national power development plan (PDP) for 2018-37 was passed. Solar power projects planned under the PDP are for 10,000MW.

Currently there is a combined capacity of 2,700MW for both solar rooftops and ground farms.

"The ERC plans to open the solar power scheme at the total capacity of 500MW during 2019-23, and the annual capacity will rise further in five years," Ms Narupat said.

She said the ERC is also studying the conditions to provide licences for waste-to-energy power projects under the new PDP, which set a goal of 400MW in total.

Waste-to-energy power projects are now operating at 236MW of 500MW, and all have been granted licences.

"There is leftover capacity which has yet to be developed, so the ERC will resume granting licences in March, but the capacity will decline to 87MW," Ms Narupat said. "After the process is completed, a new round of waste-to-energy power projects will be launched in April, but we have yet to plan for the new capacity."

These projects will cover two solid-waste yards in Bangkok and include Krabi, Songkhla and Nong Khai.

Separately, the ERC yesterday approved maintaining the fuel tariff (Ft) rate at 3.64 baht per kilowatt-hour (unit) for May-August, the second period of 2019.

Power bills had been stable over the four periods from September 2017 to December 2018 at 3.60 baht per unit, then the ERC increased them for the first period of 2019, January-April, to 3.64 baht.

Ms Narupat said the ERC's decision was aimed at maintaining the cost of living for the period amid volatile global currencies and fuel prices.

But the ERC reported that the base factor for power bills is 3.71 baht per unit for May-August if it does not maintain the Ft rate.

The power rate includes the base factor and the Ft charge. The base factor is calculated based on capital expenditure for power plants and the grid system, while the Ft charge is for the cost of power generation.