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Long term performance plots for the
our solar water heating system are provided below.
I'll add a plot at the end of each month as best I can for the first year of
operation. So far, the system has supplied nearly 100% of our hot water needs (2 people).
Other performance test results for the system:
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I will add plots each month for the first year to get a whole years worth of performance.
These plots are for the solar water heating system described here ...
The system started operation on September 10, 2008, and supplied all our hot water for the rest of September.
I don't have a temperature plot for this period.
This plot covers from Oct 10 through Oct 31 of 2008.
Red -- Tank temperature F
Green - Ambient Temperature F
Black - Temperature in the collector cavity F
I monitored top of tank and bottom of tank temperatures, but there was so little difference that I am just showing top of tank temperature.
Our tankless water heater is set to 108F, so whenever the tank temperature is 108F or above, the tankless heater does not come on and all heat is solar.
On 19 of the 22 logged days, the temperature never dropped below 108F, so 100% of hot water for those days was solar.
On the 13th, 15th, and 17th the temperature dropped below 108F to about 103F -- On these days, about (103F-50F)/(108F-50F) = 0.96 or 96% was solar.
So, the solar fraction for October was about: (19/22)(1.0) + (3/22)(0.96) = 99.5%
This October was a bit odd -- there was a several day snow storm with as much as 6 inches of snow on the ground at one point. But, the end of October was unusually warm. It was overall less sunny than October usually is around here.
I will mention again that our hot water needs are modest. There are only 2 of us, and we don't use hot water for laundry at all. Given that the hot water is "free" I have been taking rather long showers :)
There were several multi-day periods with essentially no sun, and the large tank did prove to have enough storage to weather these well.
You can see a few times where the controller shut the pump off because the temperature got up to the 140F top limit that I set for the tank water. On these occasions, the collector temperature goes up to as much as 230F in one case because no water is flowing through the collector to cool it. This is getting fairly close to the upper long term limit for the PEX, but a warm sunny day in late fall is probably about as hot as a collector tilted this steeply will get, because the sun has nearly direct incidence on the collector near midday. So, I think this will be OK.
The heat loss from the storage tank seems high to me, and I do plan to add another layer of insulation on the outside of the tank and to insulate the pipes near the tank.
Gary September 24, 2008, October 9, 2008, Octorber 31, 2008