Solar Geyser Performance?

linuxgal

Active Member
#1
What kind of performance do you get from your solar geyser? How long does it take you to get hot water in the day?
Our two-month old installation in Benoni is a flat panel mounted on a 45 degree frame and we don't get decent hot water on anything less than scorching days unless the electrical backup is on. Am I expecting too much or is the system faulty, or wrongly installed?
Although we have recalled the installer and he is due to return again next week, he is disappointingly clueless about various technical concepts. Would a geyser expert kindly tell the optimum angle of panel inclination. My research indicates that it should correlate with latitude, (Joburg=26S) but the frame was pre-built at 45 deg.
 

linuxgal

Active Member
#3
Thanks for the link Billy, the article is referring to solar electric panels. I can't find much about solar geyser flat panel angles but evacuated tube mounting angles are recommended to correspond with latitude.
 

upup

Executive Member
#4
is there not a pump to circulate the water from panel to geyser. My family got a heatpump and that make water to 55 degrees.

Your water pump must circulate the water, till its hot inside the geyser.
 

Broadcom

Well-Known Member
#5
With full summer sun, it only takes my homemade black pipe collector two hours to fill the geyser with scalding hot water, no pump, circulates by convection/thermosyphon.
 

linuxgal

Active Member
#6
Robertvv,
No there is no pump. Our geyser works by circulation and doesn't need electricity. If the geyser sits inside the ceiling it would need a pump but ours sits right above the panel.
 

chrisc

Executive Member
#9
Something not right there. Today, hot and sunny from 11h00 and water from my solar panel is now 58 deg. Suggest it might not be circulating the water properly. If the top of the collector is not 300mm below the inlet of the storage tank, thermosyphon action will not take place and a pump is required.

The actual angle isn't critical at all
 
#10
I leave a bucket out in the yard. That's my solar geyser.
We are probably getting a similar performance as your bucket at the moment at 1000 times the cost!
Evacuated tube does apparently give better performance than flat panel but our installer says he doesn't even sell them in Gauteng any more. Needless there is obviously a deeper technical problem with our system.
 

chrisc

Executive Member
#12
I have 2 x 1 sqm panels which are joined together. At the top, a pipe comes off and goes to mt HWC which stores the water. The plumber who put it in told me that it was desirable that the outlet be at least 300mm below the bottom pipe in the HWC

Obviously you don't want it too low since water has trouble enough flowing uphill and the thermosyphon action will become less efficient if the water has to travel a long way uphill.

My HWC is in a separate roof of my house. Have a look at this pic. You can see the insulated pipes from the top of the panel. The bit you can't see over the roof of the front room is a horizontal pipe that goes straight through the wall into the roof where the hwc is located. This panel is 42 deg since it is parallel with the roof, and also faces north.

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McT

The Humble Scot!
#13
It was for this reason that I opted to go with a heat pump. From all accounts I read, it seemed quite probable that I would be tapping into Eskom too often for my liking with a SWH solution. The cost outlay of the SWH on top of the fact that I would still be using Eskom whenever solar wasn't sufficent, pushed me to the heat pump.

The heat pump uses approximately 30% to 40% of a normal electrical geyser. Including installation and the Eskom rebate, I fitted mine for +/- R 15,000. I am happy with its operation so far. We have a small 150L receptacle for the water (smaller than I'd like), but it does the job. I also like the fact that I can programme it to certain temperatures. e.g. during the day when nobody's around, I can keep it down around 30 degrees and bring it up to 50 degrees in the evening when all come home.
 

chrisc

Executive Member
#14
I have a Daikin heat pump and the solar panel. This controlled by a solid state thermocouple into the HWC, currently set at 55 deg. In winter it comes on from 05h30 to 08h30 and 15h30 to 22h30. In summer is is 18h30 to 22h30. However, I agree that a variable temperature control is more desirable. The only device I could see was the "Geyserwise" which I thought was a bit inflexible.

How do you (McT) control the temperature?
 

Broadcom

Well-Known Member
#15
If the top of the collector is not 300mm below the inlet of the storage tank, thermosyphon action will not take place and a pump is required.
Actually, the reason for having it at least 300mm below the tank is so that REVERSE thermosyphon will not take place when the temperature differential is reversed ( i.e. at night hot water flowing into the collector and cooling )

@Linuxgal: Thermosyphon systems are very tricky to plumb. You have to understand the principle, otherwise it won't work. If it has been plumbed correctly, it could be that you have an air lock somewhere in the system preventing the syphon action. There might be a bleed valve or tap at the top of the panel for this.
 

chrisc

Executive Member
#16
Actually, the reason for having it at least 300mm below the tank is so that REVERSE thermosyphon will not take place when the temperature differential is reversed ( i.e. at night hot water flowing into the collector and cooling )

@Linuxgal: Thermosyphon systems are very tricky to plumb. You have to understand the principle, otherwise it won't work. If it has been plumbed correctly, it could be that you have an air lock somewhere in the system preventing the syphon action. There might be a bleed valve or tap at the top of the panel for this.

Yes, just spoke to my plumber about this and he said same thing. So bleed the system, same as you do motor-car brakes. He also calls every 2 years and flushes it out, gets rid of sediment, etc
 
#17
Broadcom,
Thanks, this is the kind of info I need. Will be up on the roof in the morning with tape measure. The installer claims he topped up the glycol and pressure tested the system, so presumably there is no air lock. We have decided to bypass him and get in someone from his HQ.

@Chrisc4290: Cape Town is 33S and therefore your panel inclination is within 9 deg of latitude - more optimal than ours which is 19 deg from latitude.
 

linuxgal

Active Member
#18
Some technical feedback for those who replied to my thread.
According to the technician from the distributor's HQ, the optimum angle for thermosyphon is 29 degrees from the horizontal. Above 50 degrees, thermosyphon will not work.
We had the offending panel moved to our main house roof which is 30 degrees, and the water temperature has improved although it is also getting more sun.
Cynically, it turns out that the flat roof installation with 45 deg frame was pushed on us by the installer to make life easier for him.
 
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