The fuel tariff on electric bills from January-April will fall by 10 satang a kilowatt-hour or 2.5%, says the Energy Regulatory Commission (ERC).
The ERC on Thursday approved the lower tariff for the period in response to the decline in global oil prices.
The fuel tariff rate is reviewed every four months.
Commissioner Viraphol Jirapraditkul said the new rate would be 59 satang per kWh, down from 69 satang now, while the average power bill including base factors would stand at 3.86 baht per kWh in each of next year's first four months, down from 3.96 baht.
The average natural gas price is also expected to drop by 2.5% during that period to 286 baht per million British thermal units, with the price of bunker oil falling by 21% to 22 baht a litre.
The price of diesel is tipped to fall by 9.4% to 24.50 baht a litre as imported coal prices shed 6.88% to 3,383 baht a tonne.
Natural gas accounts for 68% of Thailand's power generation, with coal contributing 19%, imported power from Laos and Malaysia 7% and renewable energy 5%.
The ERC forecasts demand in the first four months of 2015 at 59.4 billion kWh, up by 1.6% from the final four months of this year due to the hot season.