Urban Off Grid in NZ

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. :s
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.

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-systems/#tab-b95c5d84815e7497255

$12k + Installation, 2.7 kW panels, 19.2 kWh Lead gel storage, 4/5 kW inverter/charger
https://gridfree.store/collections/...s/products/freedom-kit?variant=11999574655023

$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.
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.

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, ifyou 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 wanta chance for a10+ year lifespanand have a chance to get your $ back

Good luck on your journey.

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.

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.

OffGridInTheCity said:

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, ifyou 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 wanta chance for a10+ year lifespanand have a chance to get your $ back

Good luck on your journey.

Click to expand...

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

ajw22 said:

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.

Click to expand...

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 isexported 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-solar-power/residential/solar-investment/
https://www.mysolarquotes.co.nz/about-solar-power/residential/solar-power-buy-back-rates-nz/

Redpacket said:

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.

Click to expand...

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 15c above ambient. It has not gotten over 20c for the last two months.
Unfortunately this is not a 100% as I discovered.
No one didn't blow up, thanks for your concern
If the other cells were charged up with enough energy, they can now discharge into thefaulty 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. 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
http://solarpower.cer.auckland.ac.nz/

Getting close to activating the battery bank.

Some Progress since last update.

-Switchboard upgrade
A good excuse to upgrade from the old one.
To reduce the maximum peak power required from the inverter I have left the high peak drain kitchen devices on mains/utility power. Cooktop/oven/toaster/microwave/kettle.
Otherwise I would have to allow for a max draw of 10kW during cooking times.
They do not run for long so should be minimal cost.



-Inverter/Charger installed.
New 5kW SRNE inverter installed with cutover switch.
In case of failure or maintenance I can switch the power over to utility and isolate the inverter/battery.Like now while the system is being built.



-Battery bank enclosure built.
It is a metal filing cabinet. To be moved to a safer location once first pack is in and running.
Put in 8 drawers. They can be pulled out while live. Cables routed through a drag chain.
Built with fire resistance in mind.
Just using old cables I had lying around for the first set.
Each cell pack will be a 15s40p.
Fully populated it will be a 15s320p.
Running at 3.5 - 4.0v should give me about 28kWh usable storage.
Tested a few 40p packs to get an idea of actual capacity.
Low density for ease of maintenance. I will be able to see down the side of each cell properly with a thermal camera.
Unfortunately testing has shown I might need to switch to 14s.
Due to the charge controller not getting the voltage ranges I want.
Maximum low cut off voltage of 50v, works out to 3.3v at 15s. Too low for my liking.
Max charge is 58.4v, 3.89v at 15s. Less than my target but workable.



-Solar panels installed.
It was a complete package with warranty. 5.2 kW of panels, SolaX Power X1-5.0-T-N inverter.
They could have supplied an inverter with battery capability but it would have voided their warranty connecting my own battery.
Our longest day was in 21 Dec, so all downhill from here in terms of daylight hours.
Highest production day so far was yesterday, 27th dec. 38kWh. There were a few passing clouds so I think maximum potential is 40kWh.
I am thinking about an automatic tilting/tracker for the panels to capture that early morning sun. Might need it to get all that sun in winter. Will wait and see.



-Cell recovery, ongoing
My recycling supplier had a batch of similar packs. This first bank will be made from entirely from ICR18650-26J , ICR18650-26F.
Ex convict gps tracker battery packs.

-Pack building, ongoing.
I have now settled on a design. Not the ones shown below.
Initially I wanted to use glass fuses.
After making 3 packs I decided to go with bare wire instead for efficiency of assembly.
Testing showed they blew at about 10A
Pack build revisions from left to right.


-System Diagram

Very cool and sounds like you're having fun - I sure did.

>After making 3 packs I decided to go with bare wire instead for efficiency of assembly.
Me too - I use 30awg for fusing. My packs are 260ah so that will melt a 30awg wire in an instant if a cell goes bad

>5.2 kW of panels .... 27th dec. 38kWh.
My highest was 83.7kwh on 12.85PV array on 6/25 (I'm opposite). By ratio to your 5.2PV array I would have gotten 33.9kwh (less than you). My panels are 25deg (roof) and 17deg (yard array) - not optimal but what I was constrained to do.

This Dec (horrible/worst month of year for solar and cloudy) I'm down to 19kwh/day! My plan is to have 45panels in storage to deploy in the back yard in a total emergency.... and just wire into existing strings as the charge controllers will not even be strained... but even so that's only 38kwh/day for a 25.7kw PV array and I could use 50kwh or 60kwh. Its a large gap for a generator solution.

By extrapolation, with 5.2kw/38kwh summer you'll be down to 9kwh winter. If your daily consumption is 26kwh then that's a 17kwh difference. Not that different from my own situation. Tracking and optimal tilt and all that is perhaps a 20%? gain - so 20% on 9kwh = 1.8kwh. That still leave a 15kwh gap. Its just a gap due to lack of sun!

Unfortunately, running a generator for 17-20kwh/day is just A LOT of generator time/fuel... I don't have anywhere near the kind of wind that would be needed for wind power. And capturing rain gutter water is about 1watt - useless. I'm still trying to process things in my head to see where I go. Unfortunately I have real numbers now over 2 years of operation and it is what it is but I'd truly like to power my whole house - even in the winter. Will be interested to see where you wind up as you progress.

Thanks for sharing

Offgridinthecity. From what I’ve seen, there is very few people that use 50+kWh a day that are fully offgrid. As you have realized it takes alot or panels to have enough power in the winter with a 50kwh a day load. Most people that successfully take their house completely offgrid have a much lower daily kWh used. They typically do this by using wood for heat and living in areas that don’t need much (if any) aircon. The op having a much lower 26kwh daily load could successfully be 100% offgrid but I’d assume he would need roughly a 15kw array to make it thru the winter.

It has come to my attention that I do not want to invest the amount of money needed to be completely offgrid. Would never see an ROI. I went grid tied with battery instead. I supply on average 85% of all my loads year round. The power goes out very rarely where I live. I instead have a critical loads panel - offgrid inverter. That I will use in the rare power outage situation. The critical loads will give me what’s needed, lights freezers and heat from wood boiler. With my 5.6kw array and a 12.4kwh battery I can power those critical loads 24/7 during the winter.

>Most people that successfully take their house completely offgrid have a much lower daily kWh used
Yes - agreed 100%. But its a fun goal to have... and its made me appreciate the 'amount of sheer power' we all take for granted. My hats off to power companies for sure.

>...and heat from wood boiler.
Yes - its heat 'in the winter' that is THE issue for me. And that answer's my question as to how you'll address 'the gap'.

I live in a moderate climate (low of 30F/-1C) and I looked into wood solutions (heat or power) but they won't work for my house/situation/city-permits etc. So heat pump technology is the best I can do. The 50kwh would keep my house in the 60F/16C range... but in an emergency... some heat is better than none so maybe 40-50F/5-10C for house at large and just a room at comfortable temps. Also manage the heat-pump water heater / dryer and just use once a week (on sunny day) or something like that.

Thanks for the conversion from your freedom units to queens units

I too have decided to go grid tied. I should still be able to achieve a $0 power bill with feed in/buy back to the utility.
May need to install a few more panels to do that. Will see in a year.
Temperatures are pretty mild this end of NZ. Averages 19.8 °C | 67.6 °F - 10.6 °C | 51.1 °F.
Unfortunately most houses pre 2000 are poorly insulated, if any.


Looks like my sunshine hours haven't peak yet.

Based on that, my potential production in winter will be 50% of my max. Of course taking into clouds into account , OffGridInTheCity's estimate should be close.

nz_lifer said:

-Pack building, ongoing.
I have now settled on a design. Not the ones shown below.
Initially I wanted to use glass fuses.
After making 3 packs I decided to go with bare wire instead for efficiency of assembly.
Testing showed they blew at about 10A
Pack build revisions from left to right.
View attachment 23053View attachment 23054

Click to expand...

I think you should spread the different types of cells over all 14 (15?) parallel packs, not bunch the same types into one pack.

Main reason being that different cells will likely degrade differently over time. Say the green ones age badly and lose capacity a bit quicker than the other packs. Greens will be forced to discharge deeper and deeper to keep up with the other packs, resulting in even quicker degradation.

Another reason is that different types of cells will likely have slightly different charge/discharge curves. So during charging/discharging, you will probably have packs at varying voltages levels. While not a big issue, as they should all converge as they reach their full/empty voltage, it would look weird and could potentially mask other problems.

ajw22 said:

I think you should spread the different types of cells over all 14 (15?) parallel packs, not bunch the same types into one pack.

Main reason being that different cells will likely degrade differently over time. Say the green ones age badly and lose capacity a bit quicker than the other packs. Greens will be forced to discharge deeper and deeper to keep up with the other packs, resulting in even quicker degradation.

Another reason is that different types of cells will likely have slightly different charge/discharge curves. So during charging/discharging, you will probably have packs at varying voltages levels. While not a big issue, as they should all converge as they reach their full/empty voltage, it would look weird and could potentially mask other problems.

Click to expand...

Thanks for the tip.

Those packs are destined for another project where they will be run in parallel.
Which is why I wasn't too concerned that I had grouped them together like that for this initial test.
The house pack will be all one type of cell.
3 started, 117 to go.