Is a solar hot water heater worth the upfront cost? What is the average time to pay it off?
Your cost return is going to depend on local sun conditions, local energy costs, initial system cost and cost of maintenance. I have generally heard that it may be as quick as 8 years or as much as 20 years or longer to pay itself off. Of course the higher energy costs rise the sooner the payback time would be.
The department of energy site listed below discusses the costs and payback terms. One thing they point out is that if the solar system heats provides less than 40% of the overall heating of your house then it’s probably not going to be cost effective.
Checkout the other site listed below for a comparison of life-cycle costs for different water heater options, including solar with electric backup heat. According to this site, indirect gas hot water heaters are the lowest cost option over a 13 year period and are less than half the cost of the solar with electric backup option.
Renewable Energy – Solar Thermal (Hot Water)