Solar geyser heating efficiency

[Snapkop]

I had a 18 vacuum tube panel retrofit to a 200l geyser with a electric pump and geyserwise control panel.

I'm suspecting the installation has not been done properly as the highest temp I've seen in the geyser is high 50c in the last 2 months.

I did a test on a clear perfect 30c day. The temp only rose from 29c to 54c by 4pm with no usage on the geyser.

Others are reporting near boiling temperatures. Your experience?

 

[Keno]

I don't have a vacuum tube ,just a Flat Plate unit with all the extras you describe ,
Mine has hit a temp of 70c in mid Feb here in the Cape. Mine was setup with a 7 degree difference between the solar plate and geyser, ie when the panel is say 67 degrees and the geyser is 60c , the pump will kick in and pump the warmer water over to the geyser.
Note: by law the water temp in the geyser may not exceed 60 degrees because of the danger of children being scalled.(sp)
You can set the temps to suit yourself BTW

 

[Sinbad]

I don't have a vacuum tube ,just a Flat Plate unit with all the extras you describe ,
Mine has hit a temp of 70c in mid Feb here in the Cape. Mine was setup with a 7 degree difference between the solar plate and geyser, ie when the panel is say 67 degrees and the geyser is 60c , the pump will kick in and pump the warmer water over to the geyser.
Note: by law the water temp in the geyser may not exceed 60 degrees because of the danger of children being scalled.(sp)
You can set the temps to suit yourself BTW

Your geyser can go as hot as you like. The law is about tap water temperature. So just install a tempering valve that automatically mixes in some cold water if the outlet temp is too high.

 

[Snapkop]

Yes I also read about tempering valve. As I understand at 80c it will stop heating as the geyser won't be able to handle much more.

Keno, what average temps do you reach? Does my description above sound realistic or too low?

 

[Keno]

Hi Snapkop, I would say, you are on the low side, you should be able to reach 70 degrees, providing your setup is facing the right way.
I set my Geyserwise to come in the mornings for 60 minutes normally with a start up temp of about 35c, the cylinder having cooled overnight from about 55c.
We are only 2 people in the house, so our consumption is on the low side. We have had to make some life style changes, such as, My wife showers in the morning, allowing for enough hot water for the breakfast dishes, I shower at night off the solar system as well as the evening dishes etc,
In the area where I live with average daily temps of about 28c in summer we would average about 60c plus p/day on my system.

 

[Keno]

Thanks for the info Sinbad, learnt something new for today.

 

[Sinbad]

ps I have a 240l vacuum tube geyser (thermosyphon) and it boils in summer. Can pick up 50 degrees in a day, easy. It has 24 tubes, and faces east so is not optimally efficient.

Do you have a temp sensor in your tube collector?

 

[Snapkop]

Yes, the geyserwise has temp sensor in geyser and on tube collector. It runs when there is a 7c difference between the two.

Keno just to confirm. You heat the water for about 60min in the morning so your start temp is not around 30c. Must be higher? Or after the morning usage you used up whatever you heated electrically?

 

[Keno]

Yes, the geyserwise has temp sensor in geyser and on tube collector. It runs when there is a 7c difference between the two.

Keno just to confirm. You heat the water for about 60min in the morning so your start temp is not around 30c. Must be higher? Or after the morning usage you used up whatever you heated electrically?

No, my cylinder temp in the morning is 30c after standing all night, the power then comes on for one hour, pushing the temp to about plus/minus 45c, the next time the power comes on again to the cylinder is the next morning for one hour again. Remember I have used hot water the night before to shower etc thereby dropping the temp in the cylinder by a number of degrees.

My cylinder comes daily at 6.30 to 7.30 and that is my total power consumption for the cylinder/day.

 

[HvRooyen]

Agreed the temperatures are low. I have a similar system to yours: 200l regular geyser inside, with a 200l solar outside. For 6 months of the year the inside geyser is almost never switched on, with water temperatures above 60 degrees. (Edit: I see now you only have one geyser - your temperatures should be way higher) Assuming the panels are installed facing correctly, a few loose ideas:
The fact that the temperature goes up seems to indicate a working pump, but the rise is very slow. The pump may be underpowered, or incorrectly installed. I have also seen galvanic corrosion (copper pipes in contact with iron pump) cause a malfunctioning pump, but that usually happens after a year or so.
Try to feel the exit pipe of the solar geyser (panels) - it should be scalding hot on a very warm day. At least you should be able to narrow down the cause by demonstrating / excluding a significant temperature difference between the outflows of the solar and regular geysers.
I once had someone install a mixing valve (as described above) on the exit pipe of the solar. Reduced the efficiency *a lot*. I was told this needs to be installed by law, but I cannot for the life of me see how it can improve safety *there*. It has since been removed.

 

[thehuman]

We have a 200 litre split system (24 tubes). About a month ago it was 85 on a hot day

 

[Sinbad]

Ja mixing valve doesn't go between the panels and the tank, it goes after the tank before your hot taps.

 

[thehuman]

Mixing valve a must
Imagine being in the shower and somehow loss cold water . Instant burns if tank @ 85 degrees

 

[BigAl-sa]

On my second system (first died when the panel popped after a cold snap), and haven't had a mixing valve - no problems in 20 years. If the cold water stops, the airlock will stop the flow from the geyser before you you realise it.

 

[Snapkop]

Panels def facing north. The 200l geyser feeds another 150l but when I look at the temp I make sure there is no usage so it functions as a stand alone system.

I only have 18tubes should a 24tubes panel been fitted instead?

 

[HvRooyen]

Can't say how many tubes my solar has (not at home) but consider I have 200l outside, 200l inside with 4 persons using hot water (one of which is a teenager...). One holiday the pump did not function so the solar geyser had no way to dump heat - lost 2500l+ in a week due to the solar geyser boiling.

 

[RION@BIDSHIP.CO.ZA]

Hi. I am new to the forum and ha e experienced a similar problem on a recently installed system. I was wondering how you resolved the problem. My system is a kwikhot 16 tube that feeds my current geyser. It has the standard pump and geyserwise max etc. On Friday it was a perfect 26 degree day no clouds and my water heated from 28 degrees at 08h00 to only 46 by 17h00. I was expecting a little more so please let me know how your systems perform. My tubes face north and they have no shade interference.

 

[thehuman]

Hi. I am new to the forum and ha e experienced a similar problem on a recently installed system. I was wondering how you resolved the problem. My system is a kwikhot 16 tube that feeds my current geyser. It has the standard pump and geyserwise max etc. On Friday it was a perfect 26 degree day no clouds and my water heated from 28 degrees at 08h00 to only 46 by 17h00. I was expecting a little more so please let me know how your systems perform. My tubes face north and they have no shade interference.

litres ?
how was it performance in summer
ours a 200l 24 tube split system
reached 60 degrees today
but winter was max 45 to 50 till past few days
summer we get 80+ degrees