If there is a solar energy home application that is the logical place to start, it almost always is the making of domestic solar hot water. The objective reason for this is that this application is almost always the most financially rewarding and the easiest house solar installation that can be undertaken.

Usually, the cost of making domestic hot water by conventional methods amounts to between twenty-five percent and one-third of total house energy costs, and a solar hot water system can save between two-thirds and over seventy-five percent of this energy cost.

Another major reason to start with this project in converting a conventional energy home to solar is the numerous possibilities of quality do-it-yourself (DIY) solar water tools, either from scratch or buying easy to install products available on the internet that are simple to implement and much less expensive than a full contractor installation. Additionally, if complete or partial solar water house heating is a possibe project, this kind of system can be very economically and effectively combined.

Usually solar water systems have solar thermal panels, a fluid system to transport the heat collected from the heat collector to storage or its point of usage; and a method for transfering the liquid between the collector and storage or the place of usage.

An active system uses electric pumps and controllers to transfer the water, and a passive system uses only thermosyphon and gravity to naturally move the water as it is heated. However, some passive systems have an integral collector-storage system (ICS or "batch system") may be employed if circumstances are appropriate. These systems have one or more dark storage containers inside a glazed insulated box where cold water is preheated in the solar collector containers before moving into a conventional water heater.

If a completely green active system is wanted, there are also some excellent, cheap DIY solar power electricity kits which make it feasible to produce sustainable onsite electricity with which to transport the water and to operate its control electronics. Regardless of whether an active or passive system is employed, both usually have a backup heat source integrated to heat the water as required to maintain appropriate temperatures.

There are two reasons that flat-plate collectors are mostly used in home solar applications: they attain adequately high temperatures (below 200 degrees Fahrenheit), and they are much less costly than the next panel alternative. A flat-plate collector usually consists of (1) a dark metal or plastic panel to absorb the solar heat, (2) a transparent glass or plastic cover which allows the solar heat to transmit to the absorber but reduces heat loss, and (3) some kind of insulated box with which to surround the heat absorber. The heat transfer liquid moves through pipes that are normally attached to the heat absorber. The usual installation affixes flat-plate solar collectors with a fixed orientation to the sun. And, the greatest solar capture efficiency is effected if the collector faces toward the sun and slopes at an angle to the horizon equal to the latitude plus about 10 degrees.

This solar application like all others delivers the double benefit of greater energy independence and a contribution to a cleaner environment.