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Newbie Charles

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Hi Charles, welcome to the forum! Your question can be related to 'How long is a piece of string' :)
It will depend on your budget as well as the intended application/requirements. I.e. will the battery bank be cycled daily or is it for standby purposes? Pse share?
There are some experts here who will be able to assist.

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Hi Charles and welcome.

Like @subok01 said, there is a lot of factors to take into account when shopping for batteries and I think the main thing is your budget. You can take a look at previous discussions on the forum and in the meantime post a bit more information. What kind and size inverter you've got, size of PV array, base loads, peak loads, etc. There is a lot of forum members that can give you excellent expert advice but they'll need as much information as possible about your setup.

It's like asking the sales assistant at Tekkie town "I want some shoes" You'll have to be more specific about the colour, type, size, etc, etc.



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What inverter are you eyeing? Since the batteries are probably the most expensive component of your system perhaps decide on the batteries and then choose  a compatible inverter/SCC.

The decisions you need to make are:

  1. Size of the battery bank you need. With this information you can look at what batteries are available to use in the battery bank trying to avoid parallel battery strings. (See SuperDIYs new battery guide in the download section).
  2. Lithium or lead acid? Probably a budget constrained choice.
  3. Where are you planning to house the batteries? This may influence whether you have vented or VRLA  (valve regulated lead acid).

Once you have decided on a battery bank size you can look at inverters and the size of your PV array.

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Hi @Newbie Charles. To calculate your power usage is very difficult. If you want to go off grid, you need batteries that can handle your load for about 12 hours, right through the night. You actually need to measure your usage over a few days to get an average. I think very little of us has the equipment to measure it. For now, the best would be to take Eskom meter reading at 18h00 and then again at 06h00. That would tell us how much kWh you require to get through the night. Just make sure your geyser does not run during that time. From there we can calculate the size of your battery bank.

Then take another reading again at 18h00, that would tell us how much kWh you use during the day time. That would help us to size your solar array size. You need to install sufficient solar capacity for daily usage and to charge your batteries.

I think that would be a good start.

Have you purchased any Inverters or solar panels yet?

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@Newbie Charles welcome. 

Have a question: Why do you want to go off-grid?

To go off-grid is very expensive (Needs and Wants) and you need winter and summer electricity usage plus you have to cater for days where there are no sun. Even more so in areas like the Western Cape.

I ask this question because the point has been made on the forum that to go off-grid where there is Eskom, is not economical, unless you have no Eskom and a generator is your only solution, THEN solar becomes very viable.

Grid tied is another option BUT, to make it work for you, you need to use the power generated during the day, and most of us are at work. So careful consideration must be given with grid tied systems also. 

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11 minutes ago, The Terrible Triplett said:

Have a question: Why do you want to go off-grid?

Good question. I know a common answer, which was my motivation back in 2011 (ish). Eskom asked for (and got) 25% increases 3 years in a row. I decided that that was the last straw, I will not be abused like that, and went on a multi-year reduction plan that was supposed to halve our consumption over the next 5 years. Then the risk of load-shedding finally pushed me into solar in 2013, a little earlier than planned, but there was also clear signs that the currency was about to get worse against the Euro too.

In the following months the recovered productivity (during load-shedding) practically paid for all the equipment, and I also judged the currency situation correctly: It went to almost 17 by 2016, as we well know.

So I think my reasons back then were good.

If I had to do it again today, I'd go purely grid-tied and get a generator for the power outages. Batteries are completely uneconomical. As badly as I still want to tell Eskom to take a hike... I have to be honest.

So what batteries? The cheapest ones (in terms of how much you get out of them for your money). For me, that meant scrounging around for second-hand batteries that come out of various places (so far, a golf cart and a UPS) and to get them cheaply and simply run them to death. If they last a year... that's fine, I paid little enough.

If I replace batteries again, I'm getting a small Lithium Ion bank. But that is for my particular application.

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My opinion as well. I lost one of my energizer sla batteries about 2 weeks ago (it was about 6 months old). I'm not sure what happened to it but i suspect it was faulty from new. I first replaced it with a similar sla 105ah and my system performed better than ever. With the faulty battery i had to push about 2amps into the bank even on float, after the one was replaced float takes about 0.3amps.

Earlier this week i received a great gift. A friend gave me 10 x 102ah silver calciums. I took the best 8 and replaced my bank. Great difference overall. Cannit believe it. So now i'm going to see how far i can get with them before upgrade again.

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1 hour ago, Newbie Charles said:

... my geyser on Eskom. LED lighting in the house. I would need a qualified electrician to set that up.

Geyser: Look at evacuated tubes, they preform quite well under cloudy conditions, solar panels not.
LED Lights: Step 1: All are LED's. Step 2: Install a changeover switch in your DB for Eskom / Inverter power. 

Now do the sums:
100w lights per evening for 6 hours = 600wh - Just the lights: You will need 1 x 250w panel with 4 x 225ah T105RE' batteries plus inverter and odds and ends. Batteries alone about R11k lasting you about 10 years (120 months) for just lights. So for just the batteries, R92.00 per month if they last 10 years.

600wH = 0.6kWh @ your Eskom are cents per evening or at R2.28 per kWh = R41.00 per month.

Now add the cost of the inverter plus panels plus cables plus plus plus ... and you quickly get to R20k plus.

You need to be very sure.
Is this a hobby, want to learn more DIY guy style?
For it is not to save monies.

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Sorry guys, I KNOW we all have solar, but if there is one thing we should also make sure, everyone who wants to go solar, lets make SURE they understand the costs BEFORE they buy and if they buy, make sure they buy the right solution.

I am thinking of the new Infini's you guys are so excited about, coming in as we speak.

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14 hours ago, pilotfish said:

I feel like I was in the middle of this most amazing dream and someone just stuck me with a pin....:blink:

If the pin was from me, I am sorry.

Have read the last few years of so many people who bought solar who after a few months will say they should not have. Or the first battery bank goes and they don't have the funds to replace it. Or wrong inverter, too little batteries or insufficient panels.

Why? Because no-one told me of the expenses, the lifestyle changes etc I would, we would, need to make. And the little hidden costs like fuses and cables ... sorry I lied, they did. I just thought I could do it cheaper. :D

My point is, if you do it to save money, don't. If you do it for fun / hobby / DIY project to keep you out of the Wife's hair, by all means, but with all newbies, we should establish first their actual goal and from there share all our joys and pains.

Sorry if I am a party pooper but we are here to help, and sometimes the help is not what we want to hear.

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No need to apologize you are absolutely correct.

As an electrical contractor I get asked about PV off-grid systems all the time - because I am a lousy salesman I tell my clients that it is a silly idea with a negative ROI despite what various marketing fairy stories might say, and Elon Musk's Power Wall may work in Los Angeles where you will get various government kickbacks and a decent return on power fed back into the grid - but in a country where PV systems are actively discouraged because the municipalities require those wot got to fund those wot not, it makes no financial sense.

However I personally like to have some level of control over my basic survival requirements and I have absolutely no faith in the irrational muppets running this country, to that end I have recently installed a borehole despite the fact that it makes zero financial sense to do so in the suburbs (I am in Joburg - in Cape Town I would be prepared to make my property look like Swiss Cheese in search of water if necessary).

For the same reason I am in the process of installing a PV System at my home;

  • 2x Axpert 5kVA in parallel,
  • 22x 310Wp Yingli (because I cant fit 24),
  • 200Ah battery bank re-tasked from backup inverters required to mitigate the effects of rolling blackouts (we still have regular power failures with a new name).

To be fair I pay trade rates on a lot of the equipment and my labour rate is effectively zero because it will happen during quiet periods in the business so the cost is a bit easier to swallow, but it still costs so while I agree that financially it is not easy to justify I am prepared to take the hit for peace of mind and because I am having a lot of fun doing it! 

When I feel that the government is gaining some level of control over the air that i breathe I will install an oxygen generator :D.

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2 hours ago, pilotfish said:

I tell my clients that it is a silly idea with a negative ROI despite what various marketing fairy stories might say

I agree. I cannot justify any of my installation cost, inverters, batteries, solar panels, or solar tracker. Looking at the figures, I should be on Eskom every day of the week, 24/7. The day it becomes viable, I probably would not have the money to install it. 

I will probably never recover the cost of my installation, unless I live another 25 years and refuse to move to another house.

I just know my electricity bill has come down from R2500-R3000 a month to R200 (R176 to be exact), but if Eskom rates shoots through the roof in the next 3-5 years or Koeberg or Medupi Power station explodes tomorrow, or we start load shedding again, it will not affect me. Life will carry on as normal in my house. 

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Sometimes we buy or install stuff, just because we want it and it is a nice to have. Everything does not have to make economical sense for me to buy it. If that was the case, none of us would have a car, we would all be going to work in a taxis. Me and my wife and say 2 kids want to go to Cape Town for a holiday, we fly down. If I checked the cost of flying down against the cost of driving down in a car, the kids would never see the inside of a plane, but I don't like sitting behind the wheel of a car for 14 hours wife the wife and kids irritate me.

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