Assuming your solar shower has no broken parts and no holes, the question of whether or not it works depends on several factors. They include the amount of hot water the shower container holds, the length of time the water has been in the sun, the amount of sun there is and the ambient temperature. In most cases, showering with a portable solar shower is better than not showering at all, although it's not always comfortable.
Solar Shower Design
Most solar showers have only two parts: a container that holds water and a shower head. Portable units often consist of little more than a plastic bag with a tube. You fill the bag with water, hang it in the sun and shower when the water gets hot. Stationary units, on the other hand, may make use of a solar water-heating panel or a storage tank. One other design consists of a plastic shower stand that connects to a garden hose. The storage container is located at the bottom of the unit, and when the water heats up, pressure from the hose drives it through the shower head.
One determinant of the usefulness of a solar shower is the amount of water it holds. A regular shower uses about 2 1/2 gallons of water per minute, according to the Georgia Water Science Center, so a 5-gallon bag lasts for about 2 minutes, if you let the water run continuously. A standing solar shower, on the other hand, holds about 10 to 15 gallons and should last more than 5 minutes. You'll probably be able to take a full 10-minute shower if you get your water from a flat panel or a tank, but the next person will have to wait for the water to heat up again.
Both the temperature of the water and the ambient temperature determine the feasibility of taking an outdoor shower. You risk hypothermia if you shower in cold weather unless you're standing under a continuous stream of hot water -- ideally with a temperature in excess of 100 degrees Fahrenheit. If you have to keep turning off the shower while you soap to conserve water, the experience can be uncomfortable and even dangerous. If the outdoor temperature is cold enough to be uncomfortable while wearing clothes, you should take symptoms of hypothermia, such as shivering, loss of coordination and confusion, seriously.
Solar Showers Work
A solar panel or tank can heat water to 130 degrees Fahrenheit. That is hot enough for a shower, especially if the shower head is indoors. In fact, the water may even be too hot and thus may need to be mixed with cold water. A small capacity outdoor shower is another matter, but there are ways to mitigate its disadvantages. For instance, if you have to turn the water off while soaping to conserve water, you'll stay warm longer if you construct a stall. It doesn't have to be elaborate -- hanging some plastic from a tree will do in a pinch.
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