Residential hot water is a significant energy consumer for most households. In fact, hot water is sometimes the largest single energy cost. Using solar energy to provide at least some of the hot water in your household can result in significant savings. There are several ways that solar energy can be integrated into a hot water system. Although solar boilers can be used on their own, they are most often used in conjunction with traditional water heaters which are powered by gas or electricity. In this kind of system, the water heated with solar energy can be used on its own (if it is hot enough) or as preheated water for the traditional water heater. Solar boilers can be used in any type of climate but are most practical in areas which don't have freezing weather during the wintertime. Solar hot water systems in colder climates can use indirect heating systems which do not expose the water to the freezing temperatures. Instead, a fluid that resists freezing circulates through the solar panels and is used to heat the water. Southern climates can use direct heating systems where the water itself passes through the solar panels installed on the roof. There are two basic types of solar hot water systems -- active and passive. Passive systems rely on gravity and the natural flow of water from hot to cold. They are simple systems and require very little maintenance. They are durable and long-lasting. You can easely build simple systems yourself all you will need are parts that you can find in any hardware store. Active systems make use of pumps to circulate the water. In some systems, the pumps can be powered with solar energy; otherwise they must be connected to the household electrical supply. In both systems a storage tank is needed to hold the heated water. On hot days with plenty of direct sunlight solar systems can heat water with surprising efficiency. During this kind of weather, there may be no need to use electricity or gas as a backup. When the weather is colder, the solar heaters can preheat the water which passes into the traditional water heater. This preheated water requires much less energy to bring to proper temperatures which can result in significant savings on your energy bills. As with all alternative energy systems there is a lot of room for your own imagination if you like that. If you don't you don't and just use the technology, but for those who like to play around with technology like myself these systems offer a myriad of possibilities to think about. For example, a stirling engine converts changes in temperature into mechanical motion, for example to generate electricity. Mmm, that's a nice thought. A change in temperature is something this system will provide, but it will also heat your water. A double benefit?