Photovoltaic solar cells have long been seen as the most efficient source of inexpensive lighting in rural villages that lack electricity.
Now a scientist at Denmark's Risø National Laboratory for Sustainable Energy has built a lamp made of a flexible plastic sheet on which are embedded a photovoltaic (PV) solar cell, an LED light source, a lithium battery, a diode and copper circuitry.
The rectangular plastic sheet is about the size of an overhead-projector transparency (yes, they still exist). Snapping together the fasteners on two corners of the sheet results in a funnel-shaped structure that produces directional light.
The solar PV cell charges the lithium battery during the day so the battery can power the LED bulbs at night. The cell is made of organic polymers and carbon nanostructures. It is inexpensive to produce but converts only 1% to 2% of the energy falling on it to electricity.
Sure, the light is dim, but the price ($27 for now) is about half what a villager would pay for a year's worth of kerosene to fuel an existing lamp. Each plastic sheet/lamp would last for a year. After all, you can flex a plastic sheet only so many times before it cracks.
Frederik Krebs, the lamp's inventor, hopes to start selling them this year. The market consists of 1.5 billion people in villages in Asia, Africa and Latin America that don't have electricity. Many of these places are so inaccessible they may never be on the grid.
If you were wondering whether an ordinary battery-powered lamp might not cost less, the answer is no. The batteries would run out after about 20 hours, which means each customer would have to buy hundreds of batteries to keep the lamp lit for a few hours every night of the year.