The Gates Foundation, UNICEF, and other organizations spend millions every year to vaccinate people against diptheria, tetanus, pertussis, haemophilus influenza B, hepatitis A and B, polio, and other diseases. Nearly all of those vaccines must be refrigerated, but not frozen, while they are stored or they can go bad. In many countries, though, refrigerators are at the mercy of intermittent power supplies. And even in developed countries, about 13 percent of vaccines are accidentally exposed to freezing temperatures—the number in developing countries is double that.
This solar-powered refrigerator with a clever freeze-proofing mechanism addresses both the power and the temperature problems. U.K.-based True Energy’s refrigerator can run all day after an average of 4 hours of charging in the sun. It can also charge at an available outlet, and use its batteries as backup if the power cuts out.
The device exploits the physical properties of water to keep its contents at a constant 4 degrees Celsius—just above freezing. Water is most dense at that temperature, decreasing in density as it either warms or cools from that point. In the True Energy design, a water bag surrounds the cavity where vaccines are stored, and it’s connected to a water reservoir above it. As the reservoir cools, the 4-degree water falls because of its density, occupying the water bag. The reservoir on top can even ice over, but the bag will keep a cold-but-not-freezing 4 degrees C around the vaccines. If the ice builds up too thick, the cooling unit switches off.
The refrigerators have a high price tag at $2000. But Stewart Jones, who heads True Energy, says that competition and doing future manufacturing in India could eventually cut the price by half.
A planar antenna is often found in mobile hardware such as cellphones and GPS devices, like the one seen here. It is essentially a metal plate mounted on a larger metallic base, forming a thin, rectangular unit that is a lightweight spacesaver. Suresh Kumar saw that it could be more: Subbing in photovoltaic cells for the metal that is usually used in the antenna can turn it into a power generator.
When it is fitted with solar PV cells replacing the upper metal plate, the antenna can still transmit and receive radio waves as well as ordinary versions. Kumar led a team at Pavendar Bharathidasan College of Engineering and Technology in Tamilnadu, India, to test how well they could generate power.
The researchers tested their antennas as vehicle-mounted power generators for GPS units and for satellite radio receivers that can operate off the grid. Off-grid communications are especially important in rural areas of developing countries, where outlets and up-to-date information are both scarce. Other applications for the antennas, Kumar and his team say, could be environmental monitors and on solar-powered autonomous aircraft, where weight and space matter.