# Design new OFF-GRID domestic system; recommendations?

If you have a low voltage/soc shutdown that is above protection levels then the cold start can Be done with your own batteries
Thanks leon.davibe; I will also test this with Steve later today.

Makes sense too solving the problem of bad weather shortfall has to be solved either by more batteries or more panels
on the 144 days of data i have

Worst day produced
0.997 kwh per 1kwp

Avg
4.46kwh per 1kwp

Best
7.47kwh per 1kwp

So the 13kwp should give you an avg of 58kwh per day
Worst 12.96kwh
Best 97.11kwh

With 25kwh usage
So lets say you have 4 bad days in a row then you would produce
51.84kwh and would need in a perfect world 48.16kwh batteries to pick up the slack so yea the batteries would pull you through

Taking the 60k for 2 extra batteries and spending on 35k on ekstra panels to have 20kwh and the 25k left on another 5kw inverter

So then on my math of worst avg and best

You would get
Worst 19.94kwh
Avg 89.2kwh
Best 149.4kwh

Now naturally the avg and best days would see panel power going to waste, though if you have a pool with a heatpump as dump it would be awesome

But the worst 19.94kwh
Would mean that you are 5kwh short per day so lets take the same 4 bad days in a row

Now you would produce 79.76kwh and only fall short 22kwh that has to come from battery meaning less likely to have generator use on bigger aray with smaller battery vs smaller array and bigger battery
in this area based on the limited data i have (and naturally since not an expert i don't know what i don't know)

If going totally off grid unless a specialist can show me where my math is wrong
Thanks again leon.davibe, I get what you are saying; we will keep on reworking the numbers until everything settles into an optimal answer - I think we are definitely making nice progress along this path now.

Jumping in here as probably one of the few off grid people.

My suggestion for 30kWh usage is:

3 x 8.8kW Sunsynk or the 16kW unit + an 8 if they can be linked.
At least 30kW of panels.

>25kWh of battery + a diesel gennie for the very rare absolutely shitty day.

----

30kW of panels will be ludicrous for most of the year, but panels are the cheapest part of the system, so the cheapest to overspec.
30kWh of battery will give you at least 1 day runtime from empty. Realistically you just need 17hrs of battery in winter, so that could be less, but I wouldn't risk that.

3 x 8KW Sunsynk in master / slave setup = 35k odd x 3 = 105k
30kW of panels = looking about slightly less than R3 a watt now excl, so 30,000 x 3 = 90k odd. I'd go for whatever bifacial perc is best bang /buck. Cursory look at Segen shows 555W TopHiKU6 are the current winners at R2.73/w excl.

Lets call that 200k for panels and inverters.

25kWh of battery is really the minimum you need, although I'd try stretch that to 40kWh if you can afford it. You can add more battery later...
Looking at about R5 / kW for storage, so 25 x 5 = R125k.

Add another 30-50k for CoC, Engineer report, Panel mounting, cabling, breakers etc
You'll need a CoC, and Engineer report for CPT. Other muni's / Eskom not yet, but eventually all will follow CoCT's lead. Call it 50k, but definitely should/can be in the lower range.

Totalling that up, you'd be sitting at about

R375k for something that would keep you offgrid at a minimum. Add another 10k for a diesel gennie for just in case.

= R385k total.

If you want to be really safe, and can afford it, then move to 40kWh of battery @ R5 = R250k...

So you should be budgeting R400 - R510k odd to be offgrid for your needs.

Not cheap, but definitely gives you peace of mind.

I'm sitting at 14kW of panels, and 20kWh of battery, and am comfortably completely offgrid without issues for a good few winters now. No Eskom or CoCT at all.

One note - i'm basing calcs on CPT sun. The further north you are, the better it gets, so you can fiddle with generation a little to lower needs if you're somewhere like Northern Cape or further. Cape Town winters are sucky for PV, which is why I always say to people provision for winter use, panels are cheap...

Does mean that in summer you have so much excess you don't know what to do with it, but maybe feeding back to the grid at some point becomes worthwhile, vs a financial drain.
Thank you very much; this really helps a lot! Our roof space will probably be the limiting factor here; we will be able to squeeze in a maximum of around 16-17 kWp, so we will probably work around this in the way that you mention.

Thanks man, I was gonna tag you but your username is so obscure that I completely forgot how it is spelled
It's a reference to how people used to mispell my name on here, with a bit of afrikaans english thrown in.

"It are an L not an I"

rh1
@AceBar should you not be more worried about your new build collapsing?

@AceBar should you not be more worried about your new build collapsing?
As long as he isn't going more than 2 levels he should be fine

they pulled another survivor out this afternoon

It is eerie knowing all this is playing down 2.5k from me and if it wasn't for social media i would not have known

Did drive past on my way home that day but not like a person would have known

would have just assumed accident