Solar questions

swakop_toe said:
Yes, the directly attached tubes setup.
But even the circulation setup I have heard is prone to boil.
It is because the vacuum tubes was developed for northern hemisphere applications, our southern hemisphere conditions sun time is "too much".

Solar Water Heaters Overheat

» Solar Water Heaters Overheat | Skypower
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That's rubbish. I've got tubes and never had the water boil
 
Snyper564 said:
Hey guys, I am in the process of considering going solar. I think I would likely go grid tied. Before I go into too much detail there is something I just wanted to check. We use about R1500 worth of electricity a month. We have two geysers (150l). I see retrofitting these with tubes is about R15-R20K each.

Would it be a better idea instead of doing this just adding to the PV panels? R30k worth of panels? which is the better option? Ill pose more queries over time but I think this is the starting point.
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I lean towards oversizing your PV capacity as the cheaper option on this. As @Sinbad says, solar geysers are definitely more efficient, but I do believe upsizing PV is cheaper. Here's my thinking.

As you mentioned, retrofitting your geysers will cost R30k, so that is our target cost. To heat 300l of water you will need 15kwh daily. 15kwh with 7 hours of sun is 2.15kw of panels. From sustainable's home page, a 335W Canadian solar panel is R2228 meaning the required 7 panels are R15 596. This leaves R15k which you can use to add even more PV, upsize the inverter or simply save.
 
Speedster said:
I lean towards oversizing your PV capacity as the cheaper option on this. As @Sinbad says, solar geysers are definitely more efficient, but I do believe upsizing PV is cheaper. Here's my thinking.

As you mentioned, retrofitting your geysers will cost R30k, so that is our target cost. To heat 300l of water you will need 15kwh daily. 15kwh with 7 hours of sun is 2.15kw of panels. From sustainable's home page, a 335W Canadian solar panel is R2228 meaning the required 7 panels are R15 596. This leaves R15k which you can use to add even more PV, upsize the inverter or simply save.
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You haven't factored in the cost of mounting, mppt and inverter capacity.
Also, in winter, your numbers generated will be down a fair whack, and your input water colder. Also roof space may be at a premium, you're using 14 sqm compared to 2 for a vacuum tube collector.
 
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Sinbad said:
You haven't factored in the cost of mounting, mppt and inverter capacity.
Also, in winter, your numbers generated will be down a fair whack, and your input water colder. Also roof space may be at a premium, you're using 14 sqm compared to 2 for a vacuum tube collector.
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You raise valid points. My assumption is that he already has a MTTP controller and doesn't need more inverter capacity as the geyser will typically run during a "quieter" time of the day (early afternoon). The roof space is a valid concern, although the difference is slightly smaller than you've suggested. For 150l they'll typically put up a 2m squared flat plate or about 15 tubes, which is 2.5m squared. He'll need two of those for between 4 and 5 squares, leaving a difference of say 10 squares.
 
Speedster said:
You raise valid points. My assumption is that he already has a MTTP controller and doesn't need more inverter capacity as the geyser will typically run during a "quieter" time of the day (early afternoon). The roof space is a valid concern, although the difference is slightly smaller than you've suggested. For 150l they'll typically put up a 2m squared flat plate or about 15 tubes, which is 2.5m squared. He'll need two of those for between 4 and 5 squares, leaving a difference of say 10 squares.
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But does his existing MPPT have enough capacity for the extra 2.2kw? Generally they're sized for the existing installation. I know that I can't even add 2 panels to mine. Also, to run a 3kw element to put 15kwh into the geyser, that's 5 hours of operation. So he'll need battery capacity as well - and that 5 hours could well run into the evening when other appliances, lights etc will be used.
 
Sinbad said:
But does his existing MPPT have enough capacity for the extra 2.2kw? Generally they're sized for the existing installation. I know that I can't even add 2 panels to mine.
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That would depend on his installation spec. If not, he can upsize. He has R15k available for upsizing the MPPT and/or inverter as necessary. If that doesn't cover the additional cost, then going solar geyser is the better option.
 
Speedster said:
That would depend on his installation spec. If not, he can upsize. He has R15k available for upsizing the MPPT and/or inverter as necessary. If that doesn't cover the additional cost, then going solar geyser is the better option.
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Add R600 per panel mounting... suddenly, not so much available.

Here's the ex-vat costing from mine over a year ago (ie, before the rand turned to ****)

1595827986174.png

To add another 10 panels and an extra 5KVA inverter in parallel to my existing system:
1595828204053.png
 
Sinbad said:
Add R600 per panel mounting... suddenly, not so much available.

Here's the ex-vat costing from mine over a year ago (ie, before the rand turned to ****)

View attachment 881565

To add another 10 panels and an extra 5KVA inverter in parallel to my existing system:
View attachment 881567
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Why the extra inverter though? I get that adding extra hardware is expensive. However if you upsize your spec from the get go the pricing is far more friendly.
 
Speedster said:
Why the extra inverter though?
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Well, remember we were theorising that he might need more inverter capacity...

I would have liked it as there's less worry about tripping it during load shedding... but not for 70 grand.
 
I run two websites as a community service that cover a lot of these issues:
PowerSaving.co.za and OffGridDIY.co.za

Plenty of info and discussion there.

Just a quick word on heating water. I've noticed there is a trend towards suggesting using electricity from PV panels, instead of conventional solar water heating systems, such as flat plate collectors or vacuum tubes.

The easy way to make that decision is just look at the efficiencies of the different technologies. Even the best PV panels these days have energy conversion efficiencies somewhere around 17% (and that is excluding losses from cables, mppt's etc) , whereas a flat plat plate solar water heating panel has an energy conversion efficiency of about 65%, and vacuum tubes are even higher. So you need a lot more surface area collecting solar energy using PV panels to get the same amount of net energy available for heating water. The price of solar panels is not low enough to make this a cost effective option IMO.
 
alanB said:
I run two websites as a community service that cover a lot of these issues:
PowerSaving.co.za and OffGridDIY.co.za

Plenty of info and discussion there.

Just a quick word on heating water. I've noticed there is a trend towards suggesting using electricity from PV panels, instead of conventional solar water heating systems, such as flat plate collectors or vacuum tubes.

The easy way to make that decision is just look at the efficiencies of the different technologies. Even the best PV panels these days have energy conversion efficiencies somewhere around 17% (and that is excluding losses from cables, mppt's etc) , whereas a flat plat plate solar water heating panel has an energy conversion efficiency of about 65%, and vacuum tubes are even higher. So you need a lot more surface area collecting solar energy using PV panels to get the same amount of net energy available for heating water. The price of solar panels is not low enough to make this a cost effective option IMO.
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You don't think you could add 15kwh per day to a setup for under R30k?
 
Best decision I made was converting to pumped evacuated solar (2 x 150l geyster). A few lessons:
- The pumps dont last forever, so ensure they put handvalves in so you can isolate and remove the pump without having to turn off the house water
- Avoid the pumps with "speed-control", the simple on-off pump i have has worked for 7 years (touch wood) and had to replace an "intelligent" one, twice with a on/off version.
- ensure they install non-return valves on the outlet of the pump, to the tubes to prevent thermosiphon effect.

Mine is controlled with 2 geyserwise controllers (one which i had to replace because the capacitors leaked) but otherwise the system has been working for 7/8 years without too many issues.
 
Sinbad said:
Add R600 per panel mounting... suddenly, not so much available.

Here's the ex-vat costing from mine over a year ago (ie, before the rand turned to ****)

View attachment 881565

To add another 10 panels and an extra 5KVA inverter in parallel to my existing system:
View attachment 881567
Click to expand...

Thanks for sharing, prices have definitely gone up, especially on Victron kit.
 
Speedster said:
You don't think you could add 15kwh per day to a setup for under R30k?
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This was what I was trying to get at. I havent done anything yet so I can add R30k towards PV side as opposed to the solar geyser but only if it makes sense.
 
Snyper564 said:
This was what I was trying to get at. I havent done anything yet so I can add R30k towards PV side as opposed to the solar geyser but only if it makes sense.
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I think it is worth at least getting quotes on the options. Also, you probably don't need to add the full 6kw for two geyser elements to your inverter capacity. You could run them one at a time, and probably at the time when your usage is lowest.
 
Speedster said:
I think it is worth at least getting quotes on the options. Also, you probably don't need to add the full 6kw for two geyser elements to your inverter capacity. You could run them one at a time, and probably at the time when your usage is lowest.
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Just need those recommended installers in Pretoria area now, thanks :)
 
Snyper564 said:
Just need those recommended installers in Pretoria area now, thanks :)
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My manager used Johan from Farmer City Solar for his initial install of a Goodwe 5kVa inverter and PV panels...

farmercitysolar.co.za

Home - Farmer City Solar

WE'VE BEEN CATERING FOR YOUR CLEAN ENERGY NEEDS FOR MORE THAN 16 YEARS Read More →
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Hi all

Quick query to those that have solar. I plan to install the below 50W panel to run my UPS(Ratel 860p)

What size wiring would be sufficient and should I include a fuse? If so, what rating should the fuse be

Thanks
 

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