The Sungrabber is an interesting new commercial solar water heating system that makes use of unglazed plastic collectors (pool heating style collectors).
Their website is: http://www.sungrabber.net
The page below provides a few observations and thoughts on the system.
The diagram just below shows the system.
Two or more plastic mat style unglazed collectors are placed on the roof. Plain water is circulated through the roof collectors and to a heat exchanger inside the Circulation Unit, and then back up to the roof collector. A 2nd pump in a 2nd fluid loop circulates water from the hot water tank through the heat exchanger in the Circulation unit where it picks up heat from the collector water -- in this way, the hot water tank water is warmed by the solar heated water.
The system is a drain back system, meaning that when the circulation pump is not running, water from the collectors drains back down to the drain back tank for freeze protection. This is a well recognized method of freeze protection.
The collectors, plumbing, and drain back tank for the system are all plastic, so the system is nearly all plastic -- which is not necessarily a bad thing.
The performance of an unglazed system is going to depend a lot on climate. Without glazing, the system will produce very little hot water in cold weather. But, for many climates it would probably work well, and the fact that it is not limited to non-freezing climates gives it a much wider range of climates in which it could be applied.
While they state that the 30% federal tax credit is available, I was not able to find either the collectors or system rated by the SRCC -- perhaps they use a collector rated by another company?
You can get an idea how an unglazed collector compares to a glazed collector for your climate by using this calculator ...
For a collector similar to the Sungrabber, use the Fafco unglazed collector,
and for a traditional flat plate glazed collector, use the Heliodyne Gobi.
For typical summer conditions, with ambient temperature of 80F, and a solar storage tank temperature of 110F and full sun:
The unglazed collector efficiency is about 56%, with about 180 BTU per hour for each sqft of collector
The glazed collector efficiency is about 66%, with about 210 BTU per hour for each sqft of collector.
For full winter conditions, with an ambient temperature of 30F, and a solar storage tank temperature of 110F, and full sun:
The unglazed collector efficiency is about 13%, with about 40 BTU per hour for each sqft of collector
The glazed collector efficiency is about 53%, with about 170 BTU per hour for each sqft of collector.
So, the summer performance is quite acceptable, but winter performance takes a serious hit. Note that these numbers are not for the Sungrabber collector itself, but what I think is a similar unglazed, pool heating collector. In spite of the dropoff in winter performance, this system would very likely pay for itself sooner than a traditional $8000 commercially installed glazed collector system.
Consumer Reports (of all places) has done an evaluation of it and reports a 35% annual saving and a 5 to 9 year payback period. They don't provide much detail on how they got these numbers, but the 5 to 9 year payback is pretty respectable -- much better than most commercially installed solar water heating systems.
Another factor would be that the plastic collectors do not have as long a life as the traditional glazed collector, but they would also be much less expensive to replace -- of the order of $5 per sqft vs $30 per sqft for glazed collectors.
One of the sites I looked at stated that the Sungrabber collectors are made by Fafco -- Fafco is a very well known maker of plastic pool heating collectors.
I'm not sure if you can buy the Sungrabber components as a kit and install them yourself -- I have an inquiry in on this, and will update this when I find out. Depending on the price, this might be a good way to go in that your work would be reduced down to just installing the system rather than constructing all the components and then installing them.
But, another way to do a DIY system of this kind would be to take the regular $1K system, and substitute unglazed pool heating collectors for the homemade glazed collector. The rest of the $1K drain back design should be compatible with the unglazed collectors no problems. The performance should be better than the Sungrabber system in that the storage can be optimized for your needs, and the collector at $5 a sqft is cheap enough to get some extra.
Compared to the regular $1K system, the performance would not be as good with the plastic collectors, but you would save yourself all the work of making the collectors. The materials cost would be about the same as for the regular $1K system with the copper/aluminum collector.
An interesting wrinkle on this is that if you pick an unglazed collector that is SRCC certified under OG100 (there are plenty of them), the full system should qualify for the 30% federal tax rebate. So, the $1K system becomes a $0.7K system with a less than 2 year payback.
In Montana with the $500 tax credit on solar water heating systems, the total cost would end up being $200!
It does seem to me that the solar water heating industry in the US has become kind of stagnant, and that this is just the kind of innovation that is needed to get solar water heating systems into the mass market rather than a fringe few as with the current expensive systems. I hope they do well and that others are encouraged to try new designs.
I'd love to hear from anyone who has tried this system, or who has any thoughts on it.
"Another FAFCO Sungrabber Solar Water Heating System Installed" -- hopefully it did not take
all those guys to get those couple little collectors up there :)
Gary September 24, 2011