Flat Panel or Evacuated Tubes

Here are 2 links for direct solar PV heating..i am considering going this route as i have excess energy from solar panels and need to dump it somewhere.

http://www.nu-inc.co.za/nuthermo/titanium-elements/
http://energimart.co.za/

I am not bothered about efficiency argument...as PV panels are not that expensive and I have lots of roof space available. The difference is that solar panels last many years..but solar water heating starts packing up after a few years (i have had pumps and valves get silted). Also PV panels still output some energy under cloudy conditions.
 
thehuman said:
Evt tubes is between 90% and 70% efficient .
You will need 3 x more roof space / pv pannels to generate same amount of heat .
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More like 6x the roof space.

treeman said:
Here are 2 links for direct solar PV heating..i am considering going this route as i have excess energy from solar panels and need to dump it somewhere.

http://www.nu-inc.co.za/nuthermo/titanium-elements/
http://energimart.co.za/

I am not bothered about efficiency argument...as PV panels are not that expensive and I have lots of roof space available. The difference is that solar panels last many years..but solar water heating starts packing up after a few years (i have had pumps and valves get silted). Also PV panels still output some energy under cloudy conditions.
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The figures from nu-inc seem very suspicious, there is either something very wrong with their panel setup, or they are cooking the numbers. 750W of heating capacity will give you about enough hot water for a single person in Gauteng, most of the year, there will be about 1-2 Months where it will not be sufficient.

Evacuated tubes are much more efficient than PV panels, especially under cloudy conditions.

If you spend the same amount of time and energy researching evacuated tube heating solutions, you will find more reliable solutions for much lower cost. Combine an indirect system with a pump like the Laing D5, and you have a system that will run reliably for more than 10 years.
 
P924 said:
More like 6x the roof space.


Evacuated tubes are much more efficient than PV panels, especially under cloudy conditions.
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Under cloud, evac tube does nothing.
 
SoftDux-Rudi said:
But the heatpump doesn't work so well in winter, especially in Gauteng.
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So, then you save less for about 2 months a year. Efficiency drops to about the same as resistive heating when the ambient temperature is around 0*°C, but since the heat pump is maybe 1200W (input), it will likely not be enough, then you will need to supplement it with resistive heating. A controller can automate that for you.
 
P924 said:
Are you suggesting that PV performs any better?
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Nope, have no experience of PV under cloud so can't comment. But my tubes really do fokol when it's cloudy ;)
 
Just spec your vtubes correctly for summer. My brother-in-law has vacuum tubes, and in summer he has to clamber onto the roof and turn half of them 180-deg to stop the water from boiling. His system has twice blown from over-heating. Pressure-relief just didn't kick in as it should have.
 
Arthur said:
Just spec your vtubes correctly for summer. My brother-in-law has vacuum tubes, and in summer he has to clamber onto the roof and turn half of them 180-deg to stop the water from boiling. His system has twice blown from over-heating.
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My system boils in summer. It just blows steam out the overflow ;) No harm done.
 
Sinbad said:
My system boils in summer. It just blows steam out the overflow ;) No harm done.
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My solar pump had a different sort of pressure relief...
IMG_20150503_150925321_HDR.jpg

Got a nice big metal 220VAC one now. Those plastic ones are gabbidge.
 
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