The capacity of renewable energy for electricity generation has been rising substantially and is expected to reach a record high of 9,200 megawatts by year-end, according to the Department of Alternative Energy Development and Efficiency.
Director-general Thammayos Srichuay said major renewable power sources had a combined capacity of about 7,300 MW and another 2,000 MW would come online soon.
As of May, domestic hydropower plants provided about 3,000 MW, followed by biomass (2,500), solar farms (1,300), biogas (326) and wind farms (225).
Mini hydropower plants provide 142 MW, while waste-to-energy plants contribute 75 MW.
Mr Thammayos said the additional 2,000 MW would comprise 1,300 from solar farms and 700 from biomass, biogas and waste-to-energy plants.
However, the capacity to generate power from renewable sources is expected to be limited from next year due to the country's limited transmission lines. Thailand is expected to have extra capacity of only 800 MW from 2016-18.
Under the Renewable Energy Development Plan, Thailand will be able to generate power from renewable sources of 19,600 MW by 2036 when total capacity from all sources is due to rise to 50,000 MW.
"We hope that the production costs and development costs of power generated from renewable sources drop over the coming years so that it can compete well with power generated from fossil resources," said Mr Thammayos.
The Electricity Generating Authority of Thailand (Egat) plans to allocate a budget of 300 billion baht over the next five years to develop more high-voltage transmission lines in the South and Northeast.
Lines will be extended to Phuket and from Surat Thani to Songkhla. Two lines will be developed in the Northeast.
All line extension projects are due to start operations from 2019-23.
Egat governor Soonchai Kumnoonsate said renewable energy plants had the disadvantage of producing unstable power and their capacities were quite low compared with plants that generate power from fossil resources.