Nearby friends of ours installed a rooftop solar water heater in their home about a year ago. Knowing the perils of this under-regulated and non-standardized industry, they really did their homework well. They investigated the different configurations, sizes and collector technologies available and considered these against their needs and the operating environment. They even briefly consulted with us for an additional opinion to ensure they were on the right track. For their use case, the best solution was the very common approach of reusing their existing geyser as a storage vessel below the new collector panels and using a pump for water circulation. This configuration is never ideal as it is not completely passive, but their installation would regardless require a measure of electrical support during the dark heart of winter, so the additional use of one small circulating pump would not significantly add to their electrical bill. One month in and the installation proved to be a huge success! Their household electrical bill had been slashed dramatically and the expected payback period on their investment looked fantastic. One year later they conceded that, while the availability of hot water during winter was not what they had initially hoped for, they had been able to adjust their usage patterns to ensure that the system could cope with their demand. It was less of a huge success, but still a success regardless.
More recently they had an unassociated water leak, so a plumber was called in to look into the problem. This new plumber discovered a simultanously shocking and enlightening fact. That circulating pump was not working at all, and had likely never worked due to a faulty installation. This would have resulted in a crippling performance reduction of the system from day one.
It is now obvious that the huge reduction in electricity consumption resulted mostly from the fancy new solar geyser controller switching the geyser elements off during the daytime, and also from modified water temperature expectations.
Suddenly the return on investment didn't seem as obvious, especially when the impact of modified behavior and expectations is factored in. The family is now enjoying more hot water than they've had in a year but the additional energy savings are not yet proven, especially with winter approaching.
In these difficult financial times the lesson here is this. Before you lay out on the considerable investment for a new solar water system, make sure that you have done everything possible to reduce your consumption by picking those low hanging fruit available through disciplined behavior changes. Then make sure that there are sufficient remaining potential energy savings for the new equipment to offer you at least a 3 year return on your investment. Also make sure your installer is reputable and is competent in system sizing and all things plumbing and electrical. Don't just take his word for it.
(No plumbers were directly harmed in the writing of this article)