Jump to content

Should I go for Evacuated tube or PV? 


Slaaiblaar
 Share

Recommended Posts

Currently busy building new offgrid house. I have north facing roof on large garage with roof pitch of 22deg.

The house roof is facing either east or west. 

I need 2 x 200l geysers, if installed on house roof they will either be east or west facing meaning either morning or afternoon sun wil heat geyser. 

Current PV system is 10kv Victron inverter with 12x 455 panels, I have lot's of space left for more panels on garage. 

Normal geyser R6000, solar geyser R16000, take the difference x2 and I have R20000 of PV panels and MPPT that I can add to current system. 

Should I go for Evacuated tube or PV? 

Edited by Slaaiblaar
Link to comment
Share on other sites

My sums showed that it was far cheaper to add PV panels to a system than installing a proper solar evacuated tube system.  Your PV system probably already have spare capacity so you don't need to add as many panels if you would require for only water heating. But then I have grid for backup.

200l storage for me was not enough to last through the night with 5 people using the geyser. Presume your bathrooms will be split over the two geysers.

Is a 200l geyser now R6,000?  Paid R3,000 for a 150l last year.

Edited by Pietpower
Link to comment
Share on other sites

10 minutes ago, Pietpower said:

My sums showed that it was far cheaper to add PV panels to a system than installing a proper solar evacuated tube system.  Your PV system probably already have spare capacity so you don't need to add as many panels if you would require for only water heating. But then I have grid for backup.

200l storage for me was not enough to last through the night with 5 people using the geyser. Presume your bathrooms will be split over the two geysers.

Is a 200l geyser now R6,000?  Paid R3,000 for a 150l last year.

Thanks, yes 2 geysers, one feeding left side and other right side of house. Household of 2.

Link to comment
Share on other sites

45 minutes ago, Slaaiblaar said:

Thanks, yes 2 geysers, one feeding left side and other right side of house. Household of 2.

IMO the best is to use PV for heating and then feed your geyser output through a forced exhaust gas geyser as a backup for rainy days. It must be a forced exhaust geyser, not a normal gas geyser because with forced exhaust you can set your desired temperature. They basically take the the input and output temperature of the water and adjust the gas flow to the needed amount. That way you use a lot less gas and you won't have temperature issues.

Link to comment
Share on other sites

Gas backup makes sense if you are going off-grid.

Here is another idea:
Instead of R6k 200l geyser then install 2x 150l geysers in series for a few dollars more. Use a cheap flat plate collector to heat the first geyser and PV to heat the second one electrically during the day.

Link to comment
Share on other sites

On 2021/06/24 at 6:43 AM, Slaaiblaar said:

Should I go for Evacuated tube or PV?

My preference lean towards EV tubes but for reasons of practicality. If you have a PV system when dealing with faults or insurance claims you could end up without hot water as well as no power while the insurance are dragging their feet with approving the claims. 

Than a EV tube geyser can be fixed by just about any plumber and no need for inverter experts that might not be available when you need them.

Link to comment
Share on other sites

14 hours ago, Slaaiblaar said:

No, borehole and spring water from reservoir

Ok, then you are looking at gravity fed from a Jo-jo tank? that would be low pressure, unless you're  wasting energy running a pump to pressurised the household water.... so the low pressure evacuated glass tubes setup cost a whole lot less than you seem to indicated and that would be the suggested route with maybe a low-ish (1kW) power electric element in the cylinder as add-on, to help out when the water's a tad on the chilly end... but basically the evacuated tube setup works pretty well and when the sun doesn't shine the solar panels generating electron flow wouldn''t do too much either to help heat up the water... just my thoughts on the matter, the evacuated tube low pressure setup is probably half of what you're stating... looking at this one for R 7k7... so around 1k7R X 2 more than the normal one, you're looking at, that's R 3400.00 more for the two solar HWC vs the convential...

Link to comment
Share on other sites

The household water will be pressured as it a double story on top of a mountain with roof height at close to 10m. 

Main concern with evacuated tube is the roof only have east and west facin at 23 deg. The garage have 107m sq of North facing surface where solar panels are mounted. 

Evacuated tube direct couple system was my first choice but will not get enough sun being east or west facing at 23 degrees 

Link to comment
Share on other sites

7 minutes ago, Slaaiblaar said:

will not get enough sun

If its a pressurised system, then you could, I'd imagine mount the tube system elsewhere, even ground mounted, assuming you have space and have a spot, not too far away that gets sun all day... maybe... I have my solar panels ground mounted, roof mounting would have limted the production... my neighbour who put up panels a week or two after me, has been cutting down more and more trees around his house, since his roof mounting move was a stupid move, in my eyes, he has plenty of space (11 Ha in total) and could have put the panels where he could still have the shade from the trees  without it impacting his solar panels.... c'est la vie...

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...