The company is focused on developing country markets where low incomes plus poor grid access have created pent-up demand for electric lighting and battery chargers. It has not yet made any major sales.

"We're at the tail-end of negotiating big contracts," said Bob Hertzberg, chairman and founder, adding that he expected deals to retail solar chargers alongside simple mobile phones and energy efficient LED (light-emitting diode) light bulbs.

Tuesday's investment valued the company at US$200 million, giving specialist renewable energy fund 4RAE some 15 percent of the company. Morgan Stanley bought a 10 percent stake in June.

G24i's product differs from rigid, silicon-based solar panels and flexible thin-film silicon technologies, using light-absorbing dyes instead to turn sunlight into electricity.

The company is trying to lock up the market in such flexible dye-sensitised solar technologies, having snapped up licences from one originator, EPFL (Ecole Polytechnique Federale de Lausanne) in Switzerland.

The downside is that the technology is not energy-efficient, turning less than 3 percent of light into electricity compared with 15 percent or more by conventional silicon panels. The main plus is that it is flexible and works in low light, including indoors.

One product the company plans to roll out in Rwanda, following a US$200,000 World Bank award, is a 4 watt LED coupled with a 0.5 watt solar charger and battery, which it says it will retail at less than US$50 each.

Poorer communities in Africa will find even that price hard to swallow, Hertzberg told Reuters, so the company is looking at a range of microfinance and other options, including retailing to entrepreneurs who rent pay-as-you-go mobile phones on a call-by-call basis.

In future G24i wants to make smaller, more efficient chargers for more energy-consuming mobile phones.

"Ultimately in a few years you'll be able to buy your mobile phone or BlackBerry fully charged and you'll never have to plug it in," said Hertzberg.