Erasmus Wambua no longer has an excuse for not doing his homework.
In the past, the 18-year-old would have to find light elsewhere when his family's off-grid home in the village of Ndela, 80 kilometers (50 miles) east of then Kenyan capital, ran out of paraffin. That's changed since his mother, Rebecca, signed up with M-Kopa, a Nairobi-based provider of solar-lighting systems.
The 35-year-old mother says she was paying 100 shillings ($1) a day for kerosine. Her daily expense has since plunged to 42 shillings a day, she said. The laptop-sized solar panel and battery generates about 8 watts of energy, enough to run two LED light bulbs.
M-Kopa is using technology to make solar panels affordable in a country where two out of three people have no access to the grid. So far, about 230,000 people have signed up with the company.
"The number goes up so quickly," says Julian Mitchell, director of calls and credit operations at M-Kopa. "On a typical day, we're selling something like 500 units."
Customers agree to pay for the solar panel with regular instalments. M-Kopa then monitors payments that are made using a mobile-phone money-transfer service. If payments are missed, the panel is deactivated via the SIM card. Once the panel is paid for, clients keep it.
As Rebecca spoke, Erasmus returned in the dusk from fetching the family's four cows, went inside their small home and switched on the light.
"It's helping us," Rebecca says. "When it's the night, my children are able to read, to do their homework."