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Still haven't been able to make up my mind. And must say from everything I have read the jury is still out.

Has anybody measured how effective the PV geyser is in Cape Town closer to the ocean ? I get a bit of salt spray/wind

and thinking the PV might just need cleaning more often and being in Cape Town they might limit me when going

PV for the house. Must also add, I have very little north roof space.

But then again I don't like the failure rate of evacuated tubes. Pump, Plumping, etc is all a failure point that I don't

have today.

Would be interesting to get the views of people that has either in Cape Town. Also if you guys know of a company

in Cape Town that installs both I would like to have them come out and give advice.

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Hi do not live in the Cape. I did install two evac tubes banks to feed my normal  two 159l geysers 5yrs ago.

My experience is that I had to replace both 220vac pumps after a short period of time. I replaced them with 12vdc pumps.  I also lost my control units from lightning. Replaced them with Geyserwise units. Also replaced one Geyserwise recently that failed. The setup is useless in Winter also depending on your hot water usage if you use a lot of hot water in the morning it is not that cost effective because of heat loss at night. My evec. tubes are not the best however had no problems with them. I always had the electric element to help. Replaced the original elements with smaller ones.

I now have the one of the setups with the evac. tubes heating my geyser and the geyser feeding a gas geyser with the electric element as backup. The house is also runs off a 8kw Sunsynk Inverter with 6Kw pv and 6 ×48v 100ahr li -fe batteries.

 

Edited by Peter Topp
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I replaced a flat panel with evac tubes. Tubes are much better,  in Winter I get 45C from cold. I use geyserwize.

The dc pumps are the way to go but you must buy decent quality. The installers go cheap because the client always goes for lowest price! We are to blame.

I have solar as well, so what the sun does not heat the PV/Inverter does.

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1 hour ago, Chris Louw said:

12volt pumps we use does not last long. Replace 1 and repaired 1 in 4 years. Also replaced flat plate collecter with burst pipe with EV tubes. To much maintenance, if I have to do it over it will be PV panels

Do you mean a dedicated PV solar geyser? (like the Geyserwise Dual)

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No I will just add panels to my existing solar setup. During Winter I have enough power to heat the geyser. Summer time we run a pool and will need an extra 750 Watt for a few hours a day. The geyser was done a few years before the solar. The EV system has too much maintenance. The water pump failed this week. It also melted the insulation tube covering the copperpipe on the roof. The pipe was at 144° C when the pump failure was discovered. 

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The complication of adding a large load like your geyser element to your inverter is how to schedule/control/connect the load so that it uses PV power when it's available. The fancy inverters have an output for non essential loads which helps a lot.

Thus far I haven't got a warm feeling about how most users are controlling when their inverter heats the geyser. I gave up on this challenge and went with the Geyserwise Dual with it's 3 or 4 dedicated PV panels. This simplifies this control issue big time!  

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Either way if the element runs at night, you will be using good amount of power. 
Scheduling can be done in many different ways, but my opinion is that delaying re-heating the water is counter productive.

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10 hours ago, Richard Mackay said:

The complication of adding a large load like your geyser element to your inverter is how to schedule/control/connect the load so that it uses PV power when it's available. The fancy inverters have an output for non essential loads which helps a lot.

Thus far I haven't got a warm feeling about how most users are controlling when their inverter heats the geyser. I gave up on this challenge and went with the Geyserwise Dual with it's 3 or 4 dedicated PV panels. This simplifies this control issue big time!  

Although the geyser is connected through Geyserwise and I have the simpel old Axpert inverter, the supply to the geyser is also controlled by the Dry Contact of the inverter. It will switch off when the battery go below 50v. This with 2kW element works good and inverter and batteries are well protected. 

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9 hours ago, Brani said:

delaying re-heating the water is counter productive

only if you're on the grid, if you are battery bound... you're better of waiting for daylight and spare energy...

As for running pumps, I wonder whether it would not be worthwhile to instead run gravity fed, reduce the pressure to the Solar HWC/EV tubes and do the same with the cold water for showering purposes...

Pro's :
1: lower water consumption

2: no pump & its apparent problems
Con's: I can't think of any, but I'm sure there must be...

Not having municipal services/water here, everything is gravity fed to the house, from a Jojo tank about 6m above the ground, there is enough pressure out of this setup to shower etc... pumps? we don't need no stinking pumps!

 

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When I built my new house, I contemplated installing 2 x 200l Solar geysers with Evac Tubes. The quote I received was R46000 for both. I went with the second option which was to install 2 x 200l electric geysers which costed R11000 and I used the R35000 on upgrading my main solar PV system which supplies the entire home with power. 
 

I changed the 4kw element in each geyser to a 2kw. Both geysers are powered by the Sunsynk 8kw and are on timers to come on at 9am and switch off at 4pm. And when it’s cloudy then the batteries and Eskom supplement the load. We never run out of hot water especially in the morning. 

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49 minutes ago, Chris Louw said:

Although the geyser is connected through Geyserwise and I have the simpel old Axpert inverter, the supply to the geyser is also controlled by the Dry Contact of the inverter. It will switch off when the battery go below 50v. This with 2kW element works good and inverter and batteries are well protected. 

Okay. But my point is how difficult it is to determine the PV power that is available. You have reduced your element kW to cater for this I presume. As a control guy I would like to know when the 3kW load can be switched on when there's enough PV power available..

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1 hour ago, Richard Mackay said:

Okay. But my point is how difficult it is to determine the PV power that is available. You have reduced your element kW to cater for this I presume. As a control guy I would like to know when the 3kW load can be switched on when there's enough PV power available..

I just use a bang-bang controller.  If PV voltage is above 'x', turn on the geyser for 10 seconds. Check PV output and battery draw, then leave it on/turn it off based on time of day and geyser temp.

This is the logic I use:

https://github.com/justinschoeman/ModbusThermostat/blob/master/SunsynkController/config.h

Has worked perfectly for me for the past 6 months.

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1 hour ago, Richard Mackay said:

Okay. But my point is how difficult it is to determine the PV power that is available. You have reduced your element kW to cater for this I presume. As a control guy I would like to know when the 3kW load can be switched on when there's enough PV power available..

With the dry contact set to 51v on and 50v off the geyser will only run in this range. If any other large load example the oven is on then the oven will receive priority, the geyser will switch off.

If there is not enough solar power the battery voltage will dip below 50v and the geyser switches off automatically and will not drain the batteries. 

We're running off grid, this voltage range works well with our batteries and system. 

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20 hours ago, Chris Louw said:

12volt pumps we use does not last long. Replace 1 and repaired 1 in 4 years. Also replaced flat plate collecter with burst pipe with EV tubes. To much maintenance, if I have to do it over it will be PV panels

This should last you a while: (mine has been running flawlessly for 7 years...)

https://www.sustainable.co.za/laing-ecocirc-d5-38-700b-circulation-pump.html

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1 hour ago, JustinSchoeman said:

I just use a bang-bang controller.  If PV voltage is above 'x', turn on the geyser for 10 seconds. Check PV output and battery draw, then leave it on/turn it off based on time of day and geyser temp.

This is the logic I use:

https://github.com/justinschoeman/ModbusThermostat/blob/master/SunsynkController/config.h

Has worked perfectly for me for the past 6 months.

Thinking about this (and a possible refinement) I would be inclined to do some proportional control: Instead of the on/off control if a PWM controller could be used to power the geyser element. 

PS: Are there any variables that you are reading from the inverter? If so which ones (and how many are available?)

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You can read *everything* from the inverter...

I read and use, time, inverter output power, load output power, battery state of charge, battery current, pv voltage and pv power, and then have a big look up table to determine target temperature based on all of those.

I did contemplate using proportional control (Google PV diverters).  It would make life a bit easier, but I don't like the idea of putting such a large non-linear load on the inverter.

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4 hours ago, JustinSchoeman said:

You can read *everything* from the inverter...

I read and use, time, inverter output power, load output power, battery state of charge, battery current, pv voltage and pv power, and then have a big look up table to determine target temperature based on all of those.

Do you have a list (or point me to one) of these inverter variables?

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On 2021/03/12 at 7:43 AM, rterblanche said:

PV geyser is in Cape Town

I have 2 Geyser Wise units. One old dual HWC and one new single HWC kit. Both work well in Summer in Cape Town. With less sun in winter, the main dual unit still heats the HWC to desired temp(has ac backup). My panels  are all north facing. I have the PTC dc/ac elements in both of the  2 x 150lt HWC's. It heats up very fast. My main system has 4 x 325W in series/parallel and the secondary 3 panels (275W) all in series.

I have had my share of evacuated tube troubles (pumps and non returns ) which the PV system does not have.

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10 minutes ago, flamegrilled said:

I have 2 Geyser Wise units. One old dual HWC and one new single HWC kit. Both work well in Summer in Cape Town. With less sun in winter, the main dual unit still heats the HWC to desired temp(has ac backup). My panels  are all north facing. I have the PTC dc/ac elements in both of the  2 x 150lt HWC's. It heats up very fast. My main system has 4 x 325W in series/parallel and the secondary 3 panels (275W) all in series.

I have had my share of evacuated tube troubles (pumps and non returns ) which the PV system does not have.

I know one don't ask something like this but can you maybe give me an idea of cost and who did the install ? And what size DC element do you have in your geyser ? 

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23 hours ago, Richard Mackay said:

Okay. But my point is how difficult it is to determine the PV power that is available. You have reduced your element kW to cater for this I presume. As a control guy I would like to know when the 3kW load can be switched on when there's enough PV power available..

I have built a simple pyranometer - a cheap 5W panel (from Micro Robotics) with a 5W load resistor.  The resistor needs to be sized to keep the panel in the linear part of its operating characteristics.  After calibration it gives an almost perfect indication of the PV that my system can extract. For the last few percent of accuracy I had to add temperature coefficient correction, as my main panels have a different temperature coefficient from the small one.

20 hours ago, Richard Mackay said:

Thinking about this (and a possible refinement) I would be inclined to do some proportional control: Instead of the on/off control if a PWM controller could be used to power the geyser element. 

I have done this for both my geysers, using a micro controller (the same one that reads the pyranometer - it also reads information from the BMS and inverters) and triac control switch.  A suitable SSR could also be used.

The microcontroller is programmed to:

  • Divert any spare PV to the geysers.
  • Never run both geysers in proportional mode at the same time. (In order to minimise waveform distortions)
  • Instantly reduce power to geysers if the system approaches overload conditions.

I have bee using this for about 9 months now and it works really well.

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