Scientists at the Risø National Laboratory for Sustainable Energy in Denmark have developed an inexpensive way to integrate solar cells, LEDs, and ultrathin lithium batteries to create a lamp that can produce reading-quality light. The lamp's polymer solar cells and circuitry are printed onto large flexible plastic films, and the LEDs, flat batteries, and diodes are mounted using silver epoxy. After being encapsulated in a second sheet of film, the sheets are rolled up and snapped together at the corners with metal fasteners.

Large modules of organic photovoltaics, however, capture just 1 to 2 percent of the photon energy that hits them. But the scientist said even that measly return adds value in the price-sensitive context of rural lighting. In rural areas of Africa, Asia, and Latin America, the average household spends $40-$80 per year for kerosene lamps, and even the cheapest solar-LED lighting devices on the market today cost about a year's worth of kerosene. The total cost of the Denmark scientists' solar-LED lamps is only about $27, and they think they can manufacture an improved version for about $10.

Last summer, the scientists field-tested 196 prototypes with the help of children who attended a Danish-run summer school in Zambia. The results showed that some of the lamps had problems due to excessive flexing and light quality degrading after 10 to 20 minutes, which the scientists are fixing by repositioning the solar cells and adding circuitry to deliver power to the LEDs at a constant current. The researchers plan to test improved versions of the lamps in Mali and Malawi.