Chepnyaliliet school, with its rough concrete walls and tin roof at the end of a dusty lane lined with cacti and wild roses, seems an unlikely place find early adopters of technology. But that is exactly what Rhoda Sigei is. The determined nursery teacher was the first person in Bomet county, a verdant patch of Kenya's Great Rift valley, to buy into the potential of using solar lamps. When the headteacher brought some samples to the school, Sigei knew she had to have one, so she asked for an advance on her tiny salary. "It was a struggle to get the first one, but I didn't stop there. I bought three," she says.

She quickly realised the £5 orang plastic lamps, branded as d.lights, would pay for themselves because she and her husband, who farms a small plot, would no longer have to pay £8 a month in fuel for their paraffin lamp.

That is a substantial saving when you earn just 3,000 Kenyan shillings (£21) per month. A reliable light in the evenings has enabled Sigei to help her 12-year-old daughter, who is struggling at school, and let her 14-year-old son indulge his interest in science.

It has also allowed Sigei to study for a diploma that could result in her being promoted to a full teaching job that would treble her earnings.

The d.lights are part of a range of durable and affordable solar lamps made by Sunny Money, a subsidiary of the UK charity Solar Aid.

Rhoda Sigei, a nursery teacher in Bomet county, is now studying for a diploma that could see her promoted. Photograph: Nichole Sobecki

By investing in Sunny Money, Solar Aid has helped the firm expand to more remote areas such as Bomet, where shareholder-led ventures might fear to tread. Being a philanthropic rather than purely commercial investor gives it extra time to develop new markets.

Chepnyaliliet, an hour's drive over rutted tracks from the nearest paved road, is dark after nightfall, like much of Kenya. The single power line that has run since 2011 to Sigei's school is not connected to any of the nearby homes. Fewer than 20% of homes in east Africa's largest economy have access to electricity and there is nothing to suggest hamlets such as this, where many of Kenya's 43 million people live, will be connected to the national grid anytime soon.

Sunny Money works by approaching schools and persuading headteachers like Chepnyaliliet's Richard Bii that their products can transform their pupils' performance.

Milton Cheriot is a prime example. The scruffy 13-year-old spends his spare time falling out of trees, testified by the scars on his smiling face. His name is stitched into his jumper so his mother can make sure her six children put on the right clothes. Now he consistently has light in the evening, Milton can concentrate on his homework.

"In the old days we would have a lamp maybe three days a week. Now it's every day. And it doesn't produce smoke."

Nights spent straining his eyes to a flickering paraffin flame often led to headaches, itchy eyes and allergies, he says.

Milton says he reads for three hours every evening. It's paid off – he scored 86 out of 100 in general science, a mark that propelled him to second spot in his school's rankings.

"As soon as people saw someone they knew having one of these then everyone wanted to have one," says Bii. Mr B, as everyone calls him, estimates that after one year of sales, nearly half of the 517 pupils at his school now have the lights at home.

The 53-year-old expects to post a big improvement in his pupils' results this year.

The money saved on paraffin has changed what families such as the Sigeis can afford to eat.

"Instead of just eating ugali (maize porridge) every day I can mix using rice or chapatis.

"I'm now balancing the diet for them," says Sigei.

The UK Department for International Development has promised to help fund the project. Justine Greening, international development secretary, said: "Building a team of entrepreneurs to distribute over 80,000 affordable solar lights in Kenya, Zambia and Malawi means Solar Aid will provide light after sundown to thousands of families for the first time, while creating new jobs and helping people to save money. Increasing the market for solar lanterns will also benefit communities by improving access to clean energy and increasing the amount of time children can spend studying.

"By matching Solar Aid's project pound for pound we are enabling more people in Africa to earn a decent income and helping to end aid dependency through job creation."

Meanwhile, Sigei has her eyes on a new range of bigger, brighter lights known as Firefly and the Sun King, which come with a separate solar panel and a USB port that can be used to charge a mobile phone. The Sun King costs £25, but she has already started saving for one and expects to have enough for an upgrade early in the new year.

The willowy mother, typical of the tall, thin Kalenjin tribes of the Rift, would like her son, Hasbon, to have more choices than his father. The growing population of Bomet county means future generations will have smaller parcels of land to farm.

"I want him to do something different. Nowadays farming has become too difficult and the plots are so small.

"I would like him to be a doctor," says Sigei.