Stories from Physics for 11-14 14-16
As discussed above, the use of solar panel technology requires systems that can store energy and release it when solar power output falls. A potential solution to this problem is to use a body of water, such as a lake, to store solar energy. However, convection currents set up in the water result in efficient energy loss from the water and, during a day, the temperature of a pond may vary by only a few degrees. If convection currents could be inhibited, the transfer of energy from the pond would be reduced leading to a significant water temperature rise and more effective solar energy storage. One way to do this is to dissolve salt into a pond. Due to the difference in densities of high and low salinity water, saltwater will form a natural concertation gradient, a halocline, with concentration increasing with depth. In a solar pond, a halocline is created. When solar radiation warms the dense highsalinity water near the pond’s floor, convection is limited as the high-salinity water does not mix readily with the low salinity water in the layer above. Using this technique, researchers have managed to create ponds that can reach up to 90°C simply from solar heating. From the 1950s, researchers in Beit Ha’aravah in Israel have used a 210,000 m 2 solar pond to generate a maximum of 5 MW of power at an efficiency of around 1%.