Solar geyser performance

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ritz_sa

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I had a solar geyser installed last winter - 20 evac tubes for a 200ltr geyser. The performance has not been great thus far - while it does work and can increase the geyser temp by 20-25 degrees in a day, it does mean that you still need to use A LOT of electricity. I spent some time monitoring the temperature of the water on the roof and in the geyser (via the Geyserwise controller). In winter, the system loses15-20 degrees by the time it gets pumped to the roof (eg. geyser temp is 55 degrees, but when the pump runs and rotates water between the roof and geyser, the water sent to the roof is around 35-40 degrees only). Thus the water just pumped to the roof needs to be heated from a lower temperature and takes a lot longer - creating a huge inefficiency. The installer did insulate the pipes going from the geyser to the roof and back again - I initially thought that was not done but checked the ceiling myself.

Also, on cooler days when we use warm water for washing hands, dishes etc, the tubes have a minimal effect on the overall heating (maybe 10-15 degrees increase).

Is this normal performance? I'm curious about anyone else's experience/performance with evacuated tubes...
 
My flat plate collecter solar system was just replaced by insurance with a 300l evac tube system. Geyserwise says it raised from 53 to 69 in the letter part of the afternoon. I have turned off the geyser circuit breaker and will monitor over the next few days. Seems much more efficient than the old system but then that was 15+ years old.
 
ritz_sa said:
I had a solar geyser installed last winter - 20 evac tubes for a 200ltr geyser. The performance has not been great thus far - while it does work and can increase the geyser temp by 20-25 degrees in a day, it does mean that you still need to use A LOT of electricity. I spent some time monitoring the temperature of the water on the roof and in the geyser (via the Geyserwise controller). In winter, the system loses15-20 degrees by the time it gets pumped to the roof (eg. geyser temp is 55 degrees, but when the pump runs and rotates water between the roof and geyser, the water sent to the roof is around 35-40 degrees only). Thus the water just pumped to the roof needs to be heated from a lower temperature and takes a lot longer - creating a huge inefficiency. The installer did insulate the pipes going from the geyser to the roof and back again - I initially thought that was not done but checked the ceiling myself.

Also, on cooler days when we use warm water for washing hands, dishes etc, the tubes have a minimal effect on the overall heating (maybe 10-15 degrees increase).

Is this normal performance? I'm curious about anyone else's experience/performance with evacuated tubes...
Click to expand...

Definitely not normal. For starters, the water shouldn't even circulate if the sensor in the collector isn't at least 7 degrees warmer than the geyser sensor so I'm not sure how you get the 40 degree measurement of water sent to the roof. The only temp sensors are meant to be in the geyser and at the exit of the solar collector.
 
We have 1 solar geyser with a flat panel. The geyser and panel are both on the roof.
The geyser don't really consume much electricity for the better part of the year. In summer the tems go over 80c.
Our flat panel faces north.
In winter we heat it with solar electricity to 55c and the flat panel will still add another 10-15c ontop of that between 12pm -5pm
 
Sounds like a bad install in summer my geysers can hit 80 plus in winter hits about 50
 
During the day with my system, the water on the roof is always hotter than the geyser.
For instance, if the geyser is 50, the pump will switch on when the roof is 57. It wil drop slowly to about 54 and the pump stops again.
 
ritz_sa said:
I had a solar geyser installed last winter - 20 evac tubes for a 200ltr geyser. The performance has not been great thus far - while it does work and can increase the geyser temp by 20-25 degrees in a day, it does mean that you still need to use A LOT of electricity. I spent some time monitoring the temperature of the water on the roof and in the geyser (via the Geyserwise controller). In winter, the system loses15-20 degrees by the time it gets pumped to the roof (eg. geyser temp is 55 degrees, but when the pump runs and rotates water between the roof and geyser, the water sent to the roof is around 35-40 degrees only). Thus the water just pumped to the roof needs to be heated from a lower temperature and takes a lot longer - creating a huge inefficiency. The installer did insulate the pipes going from the geyser to the roof and back again - I initially thought that was not done but checked the ceiling myself.

Also, on cooler days when we use warm water for washing hands, dishes etc, the tubes have a minimal effect on the overall heating (maybe 10-15 degrees increase).

Is this normal performance? I'm curious about anyone else's experience/performance with evacuated tubes...
Click to expand...
Something's wrong.
Do you have lagging on the pipes? My system has even had the TP valve kick in from too much sun. What geyser tank are you using?
 
This might be a silly question but your evac tubes are actually in the sun? I have seen some ppl have solar panels installed in the shade by dodgy installers...
 
its hard to tell from your post without knowing how much water you are using. I have a similar system and it will tank the day to heat the tank from 35C to 55+C in April without hot water being used. In summer it can hit 80C.
 
Tim_vb said:
its hard to tell from your post without knowing how much water you are using. I have a similar system and it will tank the day to heat the tank from 35C to 55+C in April without hot water being used. In summer it can hit 80C.
Click to expand...
Mine never gets that hot.
From middle 70s it starts dumpling water through some safety valve.
Maybe it's set too sensitive, don't know.
Then again, it's not often, only the couple of really hot January days.
 
I got a SWH, 300L, many moons ago with evacuated tubes.
With 6 people in the house it is not enough to satisfy the demand, you need 100L per person per day. When there are less people around I don't have to supplement the SWH.
I have had instances when the geyserwise went into error mode because the temperature in the geyser went too high, these evacuated tubes are lethal.
One issue I had was losing a lot of temperature overnight because there was not a non-return valve in the system so it was back cycling and cooling down the water. I think this principle applies when you put the geyserwise into 'holiday mode' so it can cool down your geyser at night.
The way you are measuring your temps may be misleading. When the water in the collector is 7 degrees higher than your geyser the water will be moved from the collector into the TOP of the geyser where the hot water is, at the same time the cold water from the BOTTOM (also where the cold water comes in when you use the hot water) is pumped up to the collector to be heated. Washing dishes etc will draw cold water into the geyser which now needs to be heated.
Some members of my household used to open the hot tap to wash their hands and then close it before the hot water even got to the sink, the problem with this is that cold water is drawn into the geyser and the hot water in the pipes will now get cold.
I installed a heat pump to supplement my SWH and it made a huge difference in electricity consumption.
In October I installed solar in my house and I use the excess solar to heat the geysers now and the SWH just does its thing and helps.
 
Speedster said:
Definitely not normal. For starters, the water shouldn't even circulate if the sensor in the collector isn't at least 7 degrees warmer than the geyser sensor so I'm not sure how you get the 40 degree measurement of water sent to the roof. The only temp sensors are meant to be in the geyser and at the exit of the solar collector.
Click to expand...
Yip, mine is set to circulate when there is a 7 degree difference between the collector and geyser. The problem though, is once it circulates, the temperature of the water going into the collector is 15-20 degrees cooler than what the geyser temp is.

Also, the evac tubes are in the sun (good sun from 8am to 5pm) and north facing.
 
ritz_sa said:
Yip, mine is set to circulate when there is a 7 degree difference between the collector and geyser. The problem though, is once it circulates, the temperature of the water going into the collector is 15-20 degrees cooler than what the geyser temp is.

Also, the evac tubes are in the sun (good sun from 8am to 5pm) and north facing.
Click to expand...
That makes no sense. If the collector is cooler than the geyser it shouldn't be circulating.
 
Also, the temp sensor is definitely in the collector - because I can see the temp drop when the water is circulated, and also how it gradually heats up in the collector before the next cycle
 
Speedster said:
That makes no sense. If the collector is cooler than the geyser it shouldn't be circulating.
Click to expand...
I'm referring to the collector temp after the cycle runs eg. geyser is 50 deg, then collector heats to 57 deg, then cycle runs...and now the temp in the collector is only 30-35 deg
 
ritz_sa said:
I'm referring to the collector temp after the cycle runs eg. geyser is 50 deg, then collector heats to 57 deg, then cycle runs...and now the temp in the collector is only 30-35 deg
Click to expand...
Is your geyser vertical or horizontal? Water temp can differ significantly between top and bottom of geyser. Pump should take water from the cold (bottom) part of the geyser.
 
Surprised that others have geysers going to 70+deg...wonder if that's via the evac tubes only
 
ritz_sa said:
Surprised that others have geysers going to 70+deg...wonder if that's via the evac tubes only
Click to expand...
Yip my thermostat is set to 55 and only gets energized at 4pm as a backup for very cloudy days - also in summer you use less hot water (who want a nice long hot shower? and the water is so hot you use less hot water)

In retrospect a heat pump would be far better for consistent temps and frees up roof area for solar
 
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