The price of electricity in Sark has been capped at 54p per kilowatt hour (p/KWh) for two years from 1 January.
Electricity price control commissioner Dr Anthony White has imposed a price control order (PCO), which prevents Sark Electricity from charging more.
The current price of electricity in Sark is 66p/KWh, more than four times the average price in England.
The PCO follows a year-long dispute over cost, which almost led to supply being cut off in November 2018.
An agreement between Sark Electricity and the island's government, Chief Pleas, was reached to buy out the company and appeared to resolve the crisis.
However, there has been little movement in the last year, with disagreements over the valuation of Sark Electricity causing the process to stall.
Dr White said the new price was "fair and reasonable", allowing the company to provide a "reasonable return" to investors.
He added the imposition of a PCO followed a "lengthy process" of consultation and investigation.
Sark Electricity's owner David Gordon-Brown has previously blamed the price on legal costs related to disputing the imposition of a PCO.
Mr Gordon-Brown has also said the efforts to impose PCO was being used to bankrupt the company.
In September, he announced the price would rise to 85p/KWh, leading to the cost being described as among the "most expensive" in the world.