Watami Co., a restaurant chain known best as a hangout for salarymen, is getting into the business of selling power — and it isn’t alone.

The number of companies registered to sell electricity in Japan has more than doubled to 274 from 106 last September, according to the latest Ministry of Economy, Trade and Industry data.

The list includes everything from restaurants like Tokyo-based Watami to homebuilder Misawa Homes Co.

Some of the new entrants are taking advantage of above-market rates made available to producers of clean energy under a government program started two years ago.

The incentives, combined with the government’s promise to open the retail market to more players to spur innovation and competition, promise healthy returns for small-size energy producers previously shut out of the market by Japan’s utilities.

The situation is like “the early days of the Internet when everyone from nonprofit organizations to major companies became a provider,” said Tetsunari Iida, executive director of the Tokyo-based Institute for Sustainable Energy Policies. “There are vague expectations that there will be very big opportunities, though it isn’t clear what they are.”

The rush comes ahead of reforms that promise by 2016 to open up the nation’s electricity market for small and residential users, a market estimated by the government to be worth ¥7.5 trillion. Small users, in this case, are defined as electricity consumers with contracts below 50 kilowatts.

Currently, Japan’s 10 utilities have an effective monopoly over the segment, while the market for larger power users such as factories is already open to competition after the government partially liberalized the power retail market in 2000 and 2005. The new reforms, pushed through following the 2011 Fukushima disaster, will complete the opening of the retail market along with efforts to break up the monopolies.

The change, approved by the Diet in June, will allow new entrants to supply 84 million homes, small stores and offices, offering more options for power users in return.

Electricity prices in Japan, which relies on imports for most of its energy needs, are more than double those of the United States and also above levels in Britain and France, according to a METI white paper published in June based on 2012 figures. Japan has had to rely more on fossil fuel imports since all 48 operable nuclear reactors were shut down for safety checks after the Fukushima nuclear meltdowns.

“There will be a series of companies expected to enter the power retail market as large power companies raise prices and the market opening moves forward,” research company Teikoku Databank Ltd. said in a May 8 report on new entrants.

SoftBank Corp.’s energy unit and automakers Honda Motor Co. and Nissan Motor Co. are among the companies to have already registered as power retailers.

The Watami restaurant chain decided to enter the retail market earlier this year with an eye to eventually supply clean energy to its group facilities, said Kohei Koide, an official developing solar and wind projects for the company’s clean energy unit.

Panasonic Corp. and Epco Co., an energy-management company, set up a venture in January to sell solar power aggregated from residential rooftops. The venture wants to attract customers by offering to buy solar power from their rooftops at an attractive rate and giving energy-saving tips, said Yoshiyuki Furukawa, a Panasonic official in charge of the project.

For power producers, the above-market rates for clean-energy producers introduced in July 2012 lowers the risk of developing renewable projects and means companies have the scope to pursue business opportunities to find suppliers themselves, Iida said.

Some nonutility power companies are offering to buy solar power at a higher rate than that set by the government. They can do that because clean-energy buyers get reimbursed after the avoidable cost is deducted, allowing them to virtually source electricity at a rate cheaper than the wholesale rate.

Panasonic’s venture is offering to buy solar power ¥1 higher than the government-set tariff per kilowatt hour.

“Those who installed panels will be happy if we buy the power at a rate as high as possible,” Furukawa said. “Those without panels will also benefit because we sell the power we buy cheaper.”

So far, the market served by nonutility power companies is only slightly more than 4 percent of all generated power in Japan, according to government figures for the year through March 31. Some municipal governments are among the customers already buying power from the companies, known collectively as power producers and suppliers, or PPS.

While more companies are registering as power retailers, the number actually selling power stands at only 55 for now, according to METI data for April. Some may exit the market as competition intensifies after the market’s opening is complete, Iida said.

For Panasonic, which supplies battery cells to Tesla Motors Inc., the goal isn’t to become a major power supplier, company executives say. Rather, the electronics maker wants to build a customer base ahead of the eventual sale of power storage systems to homes equipped with solar panels, Furukawa said.

Panasonic anticipates that storage system prices will likely fall in the next 10 years at the same time energy prices rise, creating a bigger opportunity for development outside the traditional monopoly power model.

“We anticipate consumption of energy produced at home will significantly expand in 10 years,” Furukawa said.