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Urban Off Grid in NZ
#1
I would like to share my experience converting my house to Off grid solar.
More a train of thought than a curated and polished presentation.  Confused
My weakness is sometimes going too deep on a particular subject and losing the big picture.
eg, Yes we can gain 0.5% more efficiency if we dope these wires with carbon nanotubes.  Dodgy

Project time frame is about 2 years. Cell harvesting started this month.
This will be done in stages. DIY as much as possible.
Professional when required for compliance or insurance purposes.
Or when I have had enough and just want to throw money at it.

My background is hobby electronics engineering. Technical problem solver.  Cool

Lets begin. . . .

My household annual power bill is about nz$2,200
Over 10 Years $22k.

Can I get a system that will do the job for that price?
Some rough number crunching.

Average daily use 26 kWh. 10 Daytime, 16 nighttime. Typical upban wastefulness, please don't judge.  Blush
Assuming all the daytime usage can be serviced by direct solar, we will need to capture and store 16kWh.
Based on mid winter worst case scenario, 5 hours full sun. 5 hours to generate 26 kWh.
Rounding down, a 5kW panel setup should do the trick.
Peak power usage, without changing a thing, 5kW. Electric heating/cooling - cooking.

A quick search of local off the shelf systems that meet these requirements.
5kw panels, 16kWh storage, 5kW peak power.
So far these calculations have not taken into account the more detailed stuff like losses, partial battery use.
It is just a very rough yes/no preliminary exercise.

Prices are just a quick google search. Not a fine cross referenced price/quality checked assessment.

$25k + Installation , 3.42 kW panels, 14.4 kWh lithium storage, 4/8 kW inverter. Generator.
https://powerstation.nz/off-grid-solar-s...15e7497255

$12k  + Installation, 2.7 kW panels, 19.2 kWh Lead gel storage, 4/5 kW inverter/charger
https://gridfree.store/collections/compl...9574655023

$14k + Installation, 5.21 kW panels, 14.4 kWh lithium storage, 5/7 kW inverter/charger
From parts, http://sunnytech.co.nz/shop/


The crystal ball says YES.  Big Grin
Now for the WAF, "Hey honey, can I take the house off grid? It will take 10 years to pay itself back", "Sure, go ahead."  Heart

GO, GO , GO. Quick before she changes her mind.  Arrow Arrow Arrow

I leave you with some project pictures to be explained in detail at a later time. Smile

                                                
ajw22 likes this post
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#2
Welcome to the forum - this is a fantastic place to get DIY info.  

Your PV and battery kwh don't seem that far off; however, if you want 16kwh from your battery bank, I'd suggest thinking in terms of 70-50% depth of discharge - e.g. a 23-32wh battery bank to get 16kwh each cycle.    Lead-acid is famous for 50% DOD but this also applies to Lithium-ion if you want a chance for a 10+ year lifespan and have a chance to get your $ back Smile

Good luck on your journey.
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#3
I think you've missed one major issue in your preliminary calculations that skew the numbers by several factors: rainy/cloudy/foggy days with near zero solar power generation. Possibly several days in a row.
Probably the most convenient and cost effective approach is to keep a minimum grid connection, just to power a backup trickle charger as required. Or just go hybrid like so many others on the forum.
Redpacket likes this post
Modular PowerShelf using 3D printed packs.  60kWh and growing.
https://secondlifestorage.com/showthread.php?tid=6458
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#4
In your pics above, do leave some space, shorts between batteries will be spectacular.....
+ 1 to comments about the weather.
Bad days can be helped significantly by having say 50% more solar panels, helps my system a lot - they're not an expensive part of the system.
You might like to get big prismatic cells.
Running off solar, DIY & electronics fan :-)
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#5
(08-27-2020, 11:30 PM)OffGridInTheCity Wrote: Welcome to the forum - this is a fantastic place to get DIY info.  

Your PV and battery kwh don't seem that far off; however, if you want 16kwh from your battery bank, I'd suggest thinking in terms of 70-50% depth of discharge - e.g. a 23-32wh battery bank to get 16kwh each cycle.    Lead-acid is famous for 50% DOD but this also applies to Lithium-ion if you want a chance for a 10+ year lifespan and have a chance to get your $ back Smile

Good luck on your journey.

Thanks OffGridInTheCity, My initial go grid cutoff target is 20kWh.
Soft launch target is a 1kWh pack. Lighting will be switched over first.
I did find your project after going through the forums. 
There is a lot of forum to go through Smile



(08-28-2020, 12:08 AM)ajw22 Wrote: I think you've missed one major issue in your preliminary calculations that skew the numbers by several factors: rainy/cloudy/foggy days with near zero solar power generation. Possibly several days in a row.
Probably the most convenient and cost effective approach is to keep a minimum grid connection, just to power a backup trickle charger as required. Or just go hybrid like so many others on the forum.
Thanks ajw22, I was planning to have a backup generator as well.
But keeping a minimal connection had not crossed my mind as I really wanted to cut the cord.
But for $10 per month, it is worth having. Vs generator and associated maintenance.

Looking further into it, if enough is excess power is exported it might cost nothing annually.
Will have to relook into the cost of getting set up to sell back to generator.
I think I glanced somewhere it would be about 2k to setup.

Some links for my own info for later reference.
https://www.mysolarquotes.co.nz/about-so...nvestment/
https://www.mysolarquotes.co.nz/about-so...-rates-nz/




(08-28-2020, 12:27 AM)Redpacket Wrote: In your pics above, do leave some space, shorts between batteries will be spectacular.....
+ 1 to comments about the weather.
Bad days can be helped significantly by having say 50% more solar panels, helps my system a lot - they're not an expensive part of the system.
You might like to get big prismatic cells.
Thanks Redpacket, that set of images seemed to be missing this picture.


That setup is my initial sorting/charging station.
It monitors the temperature of each cell and cuts off the charge if any go over temp.
Set quite low 15°c above ambient. It has not gotten over 20°c for the last two months.
Unfortunately this is not a 100% as I discovered.
No one didn't blow up, thanks for your concern Smile 
If the other cells were charged up with enough energy, they can now discharge into the faulty cell.
With the temperaturemerature threshold set so low this has not happened.

The shelving was custom built to handle a potential unscheduled energy releases.
Thick tiles directing the blast/flame from any flammable surfaces.
I am of the "get it going good enough" school. Function over form. Wink  Don't laugh too hard at the mess.

I will make the system look pretty where it counts.  Angel

Looks like I am in a good spot for solar capture Smile
http://solarpower.cer.auckland.ac.nz/

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