Diane Cardwell / New York Times News Service

HOLMDEL, N.J. — Jay Nuzzi, a New Jersey state trooper, had put off installing solar panels on his home here for years, deterred by the $70,000 it could cost. Then on a trip to Home Depot, he stumbled across a booth for Roof Diagnostics, which offered him a solar system at a price he couldn’t refuse: free.

Nuzzi had to sign a 20-year contract to buy electricity generated by the roof panels, which he would not own. But the rates were well below what he was paying to the local utility. “It’s no cost to the homeowner — how do you turn it down?” Nuzzi said on a recent overcast morning as a crew attached 41 shiny black modules to his roof. “It was a no-brainer.”

Similar deals are being struck with tens of thousands of homeowners and businesses across the country. Installers, often working through big-box chains like Home Depot or Lowe’s, are taking advantage of hefty tax breaks, creative financing techniques and a glut of cheap, Chinese-made panels to make solar power accessible to the mass market for the first time. The number of residential and commercial installations more than doubled over the last two years to 213,957, according to Greentech Media, a research firm.

Major players in the installation business, like SolarCity, Sunrun and Sungevity, are thriving even as the other side of the industry — solar module makers — has been squeezed to the breaking point by fierce competition from Chinese manufacturers. In a case to be decided later this month, a coalition of solar manufacturers has asked the United States government to impose steep duties on the imports, arguing that the Chinese companies are violating international trade rules.

“You hear a lot of the gloom and doom about the industry and, you know, ‘The manufacturers are losing jobs, they’re shutting down,’ but if you look at where the actual money is in these systems and where the jobs are, it’s really in the installation,” said Lynn Jurich, Sunrun’s president.

Big corporations like Google, U.S. Bancorp, Morgan Stanley and Bank of America Merrill Lynch see the potential for steady profits in rooftop solar projects and have been supplying the capital to help cover the upfront costs, which typically run $30,000 or more for a single-family home. The investors say they believe the returns, generally 7 to 13 percent, are relatively safe because the solar providers generally sign up only homeowners and businesses with solid credit. In addition, installers say that people tend to pay their electric bills even when facing other financial problems.

“We have customers that are foreclosed,” said Lyndon Rive, chief executive of SolarCity, one of the largest installers. “They’re still paying their electric bill so they still pay us.”

The company has raised more than $1.4 billion to finance its projects and is so confident in its future that it is planning an initial public offering of its stock. The company has declined to comment on the stock offering.

Industry executives even predict that solar leases could one day be bundled and sold as securities like mortgages and other loans.

Some analysts caution that despite all the activity, the sector still faces hurdles, like the high costs of bringing in new customers and getting financing. “It’s not clear to me that anyone yet has cracked the code of scaling the business massively,” said Dickon Pinner, co-author of a recent McKinsey report on the industry.

Solar customers can finance their systems in a variety of ways. Businesses often purchase them outright so that they can reap the savings and take advantage of tax incentives and depreciation.

But homeowners are increasingly choosing to avoid the upfront costs. In California, the country’s largest market, more than 70 percent of residential customers putting in solar this year have opted to sign a lease or power purchase agreement with someone else owning the systems, according to PV Solar Report.

The structure of the deals varies by company and state, but the overall approach is generally the same: Customers agree to pay a fixed monthly charge or rate for all the solar power produced, and the companies that finance the systems pay for the installation and take the value of any tax breaks or renewable energy credits for which the customer would ordinarily be eligible. Some companies concentrate on financing and use local contractors for sales and installation, while others do everything themselves.

A concern is the trade case, brought by a group of manufacturers who say they cannot compete against Chinese companies able to cut their prices below their costs because of unfair subsidies from their government. The Chinese companies aim to monopolize the market and then raise prices, U.S. manufacturers say.

The Commerce Department has already imposed modest tariffs on Chinese-made silicon cells based on a preliminary finding of improper subsidies. On May 17, the department is scheduled to announce its determination of whether the Chinese companies engaged in dumping, or selling products below fair value, which could lead to steeper duties.

Those on the installation side of the business say that cheap imports benefit consumers, and they have urged the government not to penalize the Chinese manufacturers.