Selco systems typically include a small panel connected to a battery that stores enough power to run one or more lights, phone chargers and, with higher wattage options, some small appliances. Since its inception in 1995, Selco India has sold 318,400 solar home systems, and has provided power systems to almost 10,000 schools, hospitals and other institutions, almost all in Karnataka.

“Solar home systems have been around for a long time by now, and they are a successful model,” said Robert Stoner, the director of the Tata Center for Technology and Design at M.I.T., which works directly with Selco and others, including the Indian government, on renewable technology development. “Their challenge is that they cost a lot — far more than the average person has, even a relatively well-off person.”

So if it is difficult to persuade a middle-class family in an industrialized country to invest in solar, how do you persuade a family that lives on a couple dollars a day?

Mr. Prasad is a consummate salesman who talks a mile a minute, wears his hair in a side-part and keeps three pens in his breast pocket. On his home turf in the villages of the Chikkamagaluru district in Karnataka, his salesmanship is put to the test. If he can manage to interest people in what is often an unfamiliar technology, he then pitches his potential customers on the more mysterious, but crucial idea of financing.

For two decades, Selco has worked to persuade a network of banks to provide financing options to poor people who were typically seen as too risky. As Mohan Hegde, the company’s operations manager, noted, “The idea behind Selco is to take a poor man to the bank and see if what he can afford to pay per month is acceptable to the lenders.”

The sales presentation, once it includes assurance of financing from a bank, is much more palatable to potential customers: Pay the bank monthly installments of roughly the same price you’d spend on kerosene, and in a few short years, you’ll own the system and your basic energy needs will be fulfilled by the sun free.

“When we say free, their ears prick up,” Mr. Prasad said.

Without financing, decentralized renewable energy could never compete in India with kerosene, which is cheap because the government subsidizes its sale at a cost of more than $5 billion a year. Use of kerosene contributes to carbon emissions, but also to more personal and immediate hazards like skin irritation, respiratory problems and a significant fire risk. Ultimately, it provides only dim, flickering lighting.