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Small Backup System


r1biker

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Hi

Im busy helping a retired couple decide on a backup system that they need.

Since they are retired , they have a limited budget.

Usage a day is 9 units, which includes the geyser and stove. but they dont want that on solar.

So I can work on 4-5 units as average usage.

What they want to run of the system is 2 brand new fridge freezers and sometimes the tv, air cooler, alarm plug, gate motor plug and lights.

They are already using minimal stuff and do not waste electricity.

I personally would recommend a 5kw system, but they cant afford it.

And a battery back up system without solar wont work, as the power sometimes goes off for extended periods, this week it was 38 hours.

So a 24V system is what they can afford and solar panels is a must.

I was thinking a 3.5kw inverter, 3.8kw 150ah battery and 6 solar panels?

A 100ah battery seems a bit small I think.

Any suggestions would be appreciated.

 

Edited by r1biker
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48 minutes ago, r1biker said:

Hi

Im busy helping a retired couple decide on a backup system that they need.

Since they are retired , they have a limited budget.

Usage a day is 9 units, which includes the geyser and stove. but they dont want that on solar.

So I can work on 4-5 units as average usage.

What they want to run of the system is 2 brand new fridge freezers and sometimes the tv, air cooler, alarm plug, gate motor plug and lights.

They are already using minimal stuff and do not waste electricity.

I personally would recommend a 5kw system, but they cant afford it.

And a battery back up system wont work, as the power sometimes goes off for extended periods, this week it was 38 hours.

So a 24V system is what they can afford and solar panels is a must.

I was thinking a 3.5kw inverter, 3.8kw 150ah battery and 6 solar panels?

A 100ah battery seems a bit small I think.

Any suggestions would be appreciated.

 

It will have to be a battery system. The 6 panels can even be as small as 330W each and that will on most days provide enough power to charge the battery and also make hay when the sun is shining. 

Even during 38h outings the day time will be able to power things like the fridge. Just ensure that if the battery is lead acid not to cycle it through the night when there is grid power. Keep battery power for LS and no grid power. Also some battery power can be save at after sun periods by not keeping the fridges running during normal LS and only power during power failures. 

6x330W panels can during a full sun day provide over 8kwh. Enough to power some loads as well as charging the battery. 

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21 hours ago, r1biker said:

Ok, next question.

Which brand of inverter and battery will be the most reliable without breaking the bank?

In the 24v range its slim pickings.

 

Victron(not cheap) Synapse, Axpert(Mecer), Growatt to name a few.

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I am house renovating and last year I simply wasn't ready with a proper place to mount a system.  Then in January, with the storm of load-sh!tting events, I went into overdrive getting an education and attempted shopping spree.  I spend 2 weeks nearly solid, trying to source equipment.  I'm a electronic engineer, so I understand tech, but I was new to this market and had to pick up the ropes.  THREE times I placed orders with different suppliers and each order failed.  Normally the final purchase price was still pending due to some sort of variable delivery charge, so the order needed to be accepted (by the supplier) and a formal invoice to be sent.  I am still waiting for answers from some of these.  Luckily I never made any payments.

My initial gut told me to go for a 3KVA 24V system.  Every time an order failed, I revisited sites and pricing and reconsidered my options.  A friend said I should rather go for a 48V system.  So at one stage I wanted to place an order for a Kodak 5.48 with ONE Pylontech at Powerforum shop.  I was told the supplier is not willing to sell one battery.  I would at least need to submit a power budget.  Time was ticking.  No example of a power budget was provided.  Communications where slow, taking 2 days turn-a-round.  I moved on and scrapped my 48V idea.

I ended up ordering a clone on Takealot.  A MCE 2.5KW VM II with a 3KW 60-400V MPPT.  I paid R 6200.  A very good price considering the high voltage MPPT.  I then decided on a Hubble AM4 battery.  It is rated at 110Ah with a max discharge of 100A.  Rated at 1C.  Well, at 1C and 110Ah it should actually have a max discharge current of 110A, should it not?  But let's not split hairs.  I order the battery from Liteglo, paid 20K.  I should add that the MCE inverter's status on Takealot altered between sold-out and available multiple times over a period of about 2+ weeks(!)

I intend getting panels later.  Yes, I am concerned of a possible total meltdown of Eskom.  Then I would sit with my finger you-know-where.  Funds are not the problem, but again, my renovation is lagging and I am not really ready for roof dances.  More importantly, I simply do not have the energy to go through another similar purchasing exercise, hitting my head against closed doors.  So I want to take a breather for 3 months and wait for stocks to replenish before I venture into this market again.  I do have a 5KVA gennie to fall back on, in a worst case scenario.  However, the inverter self-consumption (inefficiency) is a problem.  Thus I am a big fan of running as much as possible from 12VDC.

Today, it is NOT about what you WANT but what you can get.  That is my experience.  I could not even get a fuse holder(!)  I looked EVERYWHERE, including Auto electricians.  Later I did manage to order one from Communica.

You need to see what is in STOCK and realise, that even if you phone to confirm, next day the stock might be zero.  I would recommend suppliers that are not dedicated solar system sellers as I think they are more likely to have stock.  I think a solar seller is everyone's obvious first stop.  Also watch out for scheisters out to scam you, as I expect more and more of them will be crawling out of the woodwork in these times.  I see on Gumtree there are some guys asking an absolute fortune for total junk.

When deciding on batteries, make sure that they can handle your required discharge rate, for whatever max power that might be required.  For a 2.5KW inverter you want at least 100A.  And then we haven't even factored in the 10% inverter losses.  Those Mecer Second Life 200A batteries that @Red Falconmentioned, I think, are 0.5C or 100A peak.  If those can be sourced for a good price, do consider them.  Just know that they will not give the full rating of your RCT, Kodak 3.24 or whatever 3KW inverter you decide on.

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Ive decided on building a 24v 200ah lithium battery. I have done it before and I know what I get.

Im looking at different 3.5kva high voltage inverters. There is 3 that looks ok.

Also getting 4 550w solar panels.

This should be a good basis with upgrade possibilities, not that I think they will.

 

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