3.3 SOLAR THERMAL SYSTEMS APPLICATIONS

3.3.1 Domestic hot water production

Passive and active solar hot water heaters can provide households with a large proportion of their hot water needs while cutting back on home energy costs. The amount of hot water that solar energy will provide depends on the type and size of the system, the climate, and the quality of the site in terms of solar access. There are several different kinds of solar hot water system, ranging from low cost, simple thermosiphonic "batch" systems, where the water circulates naturally and the storage tank doubles as the collector, to more efficient, complex and costly forced circulation systems that use pumps and sensors/controllers to move the hot water from flat-plate or evacuated tube collectors to a separate storage tank, as shown in figure 3.6.

Figure 3.6 A solar collector heating an antifreeze solution for domestic water

 

 

The economics will depend on both the system chosen and the geographical location. Solar water heating can be more economical over a lifetime of several decades than electricity, fuel oil or propane gas. Savings are greatest in sunbelt areas, where an investment of several thousand dollars in a solar system can earn a return in excess of 10% per year - higher than returns on savings accounts or government bonds.

Looking at the lifetime savings is important, because the initial installation cost of a solar system can be three to six times greater than any electric or propane heating system. It is the daily energy savings through the use of the sun's free rays that make a solar thermal system a good investment. The initial cost of a residential system can range from 1200€ (or less) to 3000€, with the fraction of solar energy provided ranging between 50 and 85%, resulting in a cost of delivered energy that ranges between 3 and 7 c€ per kWh at a good site.