Solar water heating: can someone recommend a good resource for high water demand projects?
I’m reviewing a document that quasi-recommends solar water heating (SWH) for projects with large water supplies such as dorms, dining facilities, laundry facilities, etc. I’ve not worked on any projects where SWH is used, so I’m a little behind the learning curve on this one and most of the material I’m able to find talks about SWH in residential applications.
I was surprised to see it recommended for projects with significant water demands, b/c it seems like it’s not a technology that is able to reliably meet the heating requirements where the requirements are fairly small, which makes me question the ability to meet the requirements where demand is high. Does anyone have any insights that might help me better understand SWH in this application or might be able to recommend a good resource for large facilities?
Thanks!
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Jennifer,
Solar hot water systems are hard to justify for single-family homes, because the hardware costs so much that the payback periods are quite long.
However, on larger commercial projects, there is some economy of scale. The per-collector installation cost is less for a 20-collector job than a 2-collector job.
The only way to determine whether a solar hot water system makes sense on a commercial project is to run the numbers. Estimate the installation cost, estimate the annual usable hot water production, and calculate the projected annual savings.
There are many pitfalls to these calculations, however. Here are two: solar thermal contractors are notorious for exaggerating annual production figures; and not every gallon of solar-heated water will be used (because on sunny summer days, it's possible that the system will produce more hot water than needed).
Any solar hot water system needs a backup system to produce hot water during long stretches of cloudy weather.
For more information, see:
Solar Thermal is Dead and
Solar Hot Water.