Large scale SWH cost effectiveness
Monetary savings from installing a solar water heater depends on a variety of factors, including climate, the amount of hot water used at your location, the cost of conventional fuels, and system performance. Using these parameters for a large solar hot water system that could be applied to a cluster of buildings, the cost effectiveness can be illustrated with regional coloring presented on the maps of the United States shown in Figures 4.7 to 4.10. The information presented in these figures are for solar hot water systems that are replacing electrical or gas heating of hot water. An average efficiency of 40% for the solar system is assumed and a life of 40 yrs is used in the analysis. Two solar system costs are used: $50 per sq ft of collector, and $75 per sq ft (~377 €/m2 and 565 €/m2).
This course is focused on large centralized solar thermal systems with short and medium-term storages connected to heating networks and they provide much lower specific system costs than decentralized small-scale solar systems. As can be seen in Figure 4.11, the cost/benefit-ratio (investment cost/ energy savings per year) for large solar systems with collector areas > 1,076 sq ft (100 m2) is about half that of small, decentralized systems, and can even be reduced by more than 20% when using large scale systems combined with seasonal storages.
A general rule of thumb for federal facilities is that a renewable energy installation should pay for itself within about 10–15 yrs. System life spans can be as much as 30 yrs, which means a facility can look forward to as much as 20 yrs of “free energy.”
Appendix A (Not in Course) provides includes descriptions of a number of case studies, which illustrate the application of solar hot water collector systems that supply buildings with hot water and heat.
There are very few large solar collector systems in the United States. In Europe the use of such systems is more commonplace. Table 4.5 lists the selected systems size, cost, and performance values.
