Solar Pump temperature timer settings

[AchmatK]

I had a solar panel which was retrofitted to my existing 150l geyser.

The unit consists of the following:

20 evacuted alluminium tubes 58mm diametre and 1.8m long
Hi Temp solar controller with 3 temp probes.
AC 220v circulation pump.
Cu Solar Convertion Jet Kit system.

The distance between the panel and the geyser is about 1.5m. I was lucky in that the geyser in the roof is very close to where the panels were placed.

I want to set the pump to get optimal use out of it without having the pump swich on too many times.

The default setting for the pump is as follows:

Pump switch on at 8deg and off at 4deg.
If the temp in the geyser is 45 and the temp in the solar reserviour is 53, then the pump will start to pump this water into the geyser. As soon as the difference between the solar reserviour and the geyser reaches 4 the pump will stop and the process would restart ie wait for the difference to be 8, pump into geyser until difference is 4 and stop.

I just need to know if this is the most effecient settings. The best I've seen only on solar so far is 67 degrees. Its not a particularly sunny day in Strand but the temp in the solar reserviour is 57 and in the geyser its 50 as of 14:14.

I've had the system installed in May this year and haven't really bean able to see the saving as it was the start of winter and with summer coming I just want to tweak the sytem to get the most out of it.

The complete system cost me R10 800.00 including installation and after the rebate is taken out.

 

[upup]

Sounds ok to me. Do you still wait for that rebate thing.

 

[AchmatK]

Sounds ok to me. Do you still wait for that rebate thing.

They did the rebate on their side and was included on there invoice.

Total invoice amount = R13 677.66
Less Rebate = - R2 793.00
Total amount paid to supplier = R10 884.66

Most installers will have you claim directly with eskom for the rebate so you would have to pay them the full amount first, then apply to eskom for the rebate and then wait a few months for eskom to refund you with the rebate.

 

[hislordship]

Hello Signates.
Up here in JHB I have the Sunflower Solar 150L system (approx R16000 and you get R7300 rebate).
I've found no difference in the amount of hot water between 10C to 5C differential and 15C to 10C differential.
I've now set it to the 15C 10C differential because this way the pump runs the least amount of time.

My logic is that the greater the temperature difference between the panel and the incoming water, the quicker it exchanges heat - therefore less pump running time (seems true in practice).
Also, I don't know if you've noticed that when you use the geyser at night, the bottom tank temp drops and of course the pump switches on when the differential is reached, so it stirs up the whole geyser and you end up with luke warm water.
Managed to minimise this by running the higher on/off temperatures.
(The default settings were the 10C 5C settings by the way).

Honest opinion, I'm not that impressed with solar. I think it's the wrong way to go - we should rather look at heat pumps which are 75% free energy all the time (day or night!) plus only 800w load on Eskom instead of 2/3/4KW! Imagine we change all geysers to those - bye bye load shedding and capacity problems :-D

 

[AchmatK]

Hello Signates.
Honest opinion, I'm not that impressed with solar. I think it's the wrong way to go - we should rather look at heat pumps which are 75% free energy all the time (day or night!) plus only 800w load on Eskom instead of 2/3/4KW! Imagine we change all geysers to those - bye bye load shedding and capacity problems :-D

I have to agree with you on the heat pumps. A pity I only found out about them after I had my solar system installed. I will investigate more into heat pumps later when I eventually go off grid completely at a later stage.

One small step at a time.

 

[hislordship]

I have to agree with you on the heat pumps. A pity I only found out about them after I had my solar system installed. I will investigate more into heat pumps later when I eventually go off grid completely at a later stage.

One small step at a time.

I'm looking for the R744 refrigerant option to become available. The other refrigerants do work, but they have serious global warming potential many times that of R744 (R744 is actually CO2, apparently much better at achieving higher temperatures).
Can you believe they are still selling units that use R22!
(Have a look at www.r744.com)