Solar still technology is well developed. Solar stills today can be manufactured easily and cheaply. Solar stills are one of the cheapest ways to produce fresh water. A solar still that could provide both freshwater and electric would be a boon to the world. Most poor areas need both freshwater and electricity. Also, solar stills are found in most survival kits. The solar stills in these kits could be adapted by adding two porous electrodes so that the still could produce both electric and fresh water, both highly desirable in a survival situation.
Figure 1 shows the use of forward osmosis to produce a solar still and electric. The solar still comprises a tub of water and a transparent covering. The sun shines on the water, cause it to evaporate. The evaporate water collects of the transparent covering and condenses. The condensed water flows down the transparent covering and into a trough. To produce electric, a membrane is placed on top of the water. The membrane has a porous electrode on its bottom and a porous electrode on its top. The membrane and the electrodes become saturated with water. The membrane can be a semipervious membrane or just an ordinary membrane made out of cloth. Salt is placed on the top of the membrane. If the water on the top of the membrane has a higher salt concentration than the water below the membrane, the water beneath the membrane will pass through the membrane to the top of the membrane. The sun will heat the water on top of the membrane, causing it to vaporize. As stated above, this vaporized water will condense on the transparent covering and flow into the trough. If electrodes and are hooked to a load, electric will flow.
The available fresh water on earth is limited. More than two-thirds of the earth’s surface is covered with water, but more than 97% of the available water is either salty or polluted. Less than 1% of fresh water is within reach of human and other organisms. Fresh water demand is increasing day by day due to the increasing population. Polluted water cannot be used directly for drinking purpose as it has harmful microbes and dissolved substance. Many developed and developing countries of the world are facing the problem of supply of drinking water and fresh water. A solar still can be used to produce drinking water from both salty and polluted water. Solar stills are best suited for the production of fresh drinking water at a low cost. They are easy to operate and have a minimal maintenance cost.