A few questions if someone can help a newby?

I want to install an Axpert 5KVA to manage load shedding with 4 (12v) AGM batteries (180 Ah each)feeding a few dedicated circuits.

The dedicated circuits only carry the essentials of my house (few lights, PC's, Wifi, TV, electric fence, fridge etc). During load shedding the batteries provide the electricity and once mains are restored it charges the batteries. Consumption during peak time in early evening will be about 500 Wh for 2 -3 hours. Other times the base load seldom exceeds 200 Watts per hour on the essential circuits.

If the batteries approach 40% DOD the inverter must shut down further discharge to protect the batteries.

1. I assume it is possible to set up the batteries and inverter in this way?

2. Is 40% DOD a safe level or can 50% be tolerated (keep in mind the batteries are only used a few times a month. Then they should last 5 to 8 years?)

3. The Inverter will also protect against overcharge? 

4. So this gives me theoretical 3456 Wh battery reserve?

5. And thus, to cater for inefficiencies therefor about 3000 Wh?

6. 3000 Wh should run a few lights, 2xPC's , a TV, a fridge and a few small items for 4 hours?

 

Now assume I want to cater for a worst case scenario where there is no mains available for many consecutive days (eg a suburb substation blow-out or a complete Eskom meltdown). 

Then I need panels.

7. I probably need say 6 panels (300 watt each) to assist with the charging of my batteries to keep the essentials going? 

(Despite all the sunshine in Jhb there is still a chance of trouble if we have a few cloudy days but I assume I will see it coming and cut down consumption to virtually only wifi and cell phone charging so I will survive.)

I think I have a vague understanding of the questions (and answers) so far but I am still wracked by uncertainty so if someone can assist and please answer above questions?

Now the final question and  I have no idea -

The panels will (for the most part) be superfluous as the essential circuits only has a base load of at most 300 watts/hour.  So only ONE panel will make a meaningful contribution in the ordinary course. FIVE panels will sit idly producing electricity going nowhere.

This means that  I can only really use ONE panel (for the most part) but I invested in SIX.

8. How do I get the panels (all of them) to supply my DB so as to also contribute to the rest of my ordinary usage? Ie how do I divert the daily solar production into my mains? Can the Axpert be set to do this?  Do I need a manual switch to be wired?  Or is it better to just get a small gennie for an unforeseen crisis? 

A Axpert is a off-grid setup. I think you know that?

We've all started somewhere, your plan is sensible, start at X and end with Y. But if I was you, knowing what I know today, to use the panels all the time - if there are loads - is to go grid tied.

Hybrid grid tied to be exact, so that the panels and batteries are used when Eskom is off.

Solves a lot of daytime power issues AND you have a ROI that makes sense from the very 1st watt in the morning, till the last watt before sunset, off-set against your Eskom bill.

 

3 hours ago, Clivevan said:

Consumption during peak time in early evening will be about 500 Wh for 2 -3 hours.

Your units are wrong; it a very common newby mistake. Instantaneous consumption is measured in watts. So that's 500 W for 2-3 hours, or 0.5 kW, totalling 1 - 1.5 kWh. (Watts times hours equals watt.hours.)

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Other times the base load seldom exceeds 200 Watts per hour on the essential circuits.

Again, you will be seldom exceeding 200 W,

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If the batteries approach 40% DOD the inverter must shut down further discharge to protect the batteries.

1. I assume it is possible to set up the batteries and inverter in this way?

 

Yes, but you'll need a monitoring program like ICC, running on a small computer called a Raspberry Pi, and a battery monitor called a BMV. Or you could just use settings on the inverter, but it's so inaccurate it may switch off at vastly different states of charge. It might be good enough to start with, however.

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2. Is 40% DOD a safe level or can 50% be tolerated (keep in mind the batteries are only used a few times a month. Then they should last 5 to 8 years?)

The quality of lead acid batteries varies widely. I think the consensus is that for 5-8 years, you really have to limit to 20% DOD [ edit: i.e. 80% SOC. ]. It's a continuum;  40% is better than 50%, but 20% is better than 40%. There is not much advantage in less than 20%, however. For your purposes, 40% with the occasional 50% should be fine.

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3. The Inverter will also protect against overcharge? 

Yes.

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4. So this gives me theoretical 3456 Wh battery reserve?

Ignoring efficiency, the Peukert effect (negligible at your proposed loads), and age-related effects, yes. [ Edit: and assuming 48.0 V battery voltage; usually we use 50 V as it's more realistic and a nice round number. ]

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5. And thus, to cater for inefficiencies therefor about 3000 Wh?

Yes.

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6. 3000 Wh should run a few lights, 2xPC's , a TV, a fridge and a few small items for 4 hours?

Yes.

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Now assume I want to cater for a worst case scenario where there is no mains available for many consecutive days (eg a suburb substation blow-out or a complete Eskom meltdown). 

Then I need panels.

7. I probably need say 6 panels (300 watt each) to assist with the charging of my batteries to keep the essentials going? 

That sounds about right.

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(Despite all the sunshine in Jhb there is still a chance of trouble if we have a few cloudy days but I assume I will see it coming and cut down consumption to virtually only wifi and cell phone charging so I will survive.)

 

Good luck with that.

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The panels will (for the most part) be superfluous as the essential circuits only has a base load of at most 300 watts/hour.  So only ONE panel will make a meaningful contribution in the ordinary course. FIVE panels will sit idly producing electricity going nowhere.

 

Not really. When you're using 300 W, you'll need more than one 300 W panel to provide that load. For various reasons, you usually only get 80-85% of the nominal power, and that's under the best conditions (say 10am to 2pm), with no clouds. Plus, while you are recharging your battery from the consumption the night before, you are using 100% of what you have (if the batteries will take it; in your case, you'll have to restrict the maximum charge current to 20 A, 30 A will be a bit too much). But loads will take up most of the rest of it. So you won't really be wasting 5/6 of your investment.

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8. How do I get the panels (all of them) to supply my DB so as to also contribute to the rest of my ordinary usage? Ie how do I divert the daily solar production into my mains? Can the Axpert be set to do this?  Do I need a manual switch to be wired?  Or is it better to just get a small gennie for an unforeseen crisis? 

It's a big step to go from the UPS scenario you started with to "lets just add panels and run a chunk of the house load". For starters, you'll need a much bigger battery. With an off-grid inverter such as the Axpert, you can't just blend excess PV power with the house consumption. So you'll have to split your loads, probably add a manual changeover switch for maintenance, and so on.

A hybrid inverter as @The Terrible Triplett mentioned is a fair bit more expensive than an Axpert. So really you need to decide do you just want to start with a relatively cheap UPS system, or do you want to eventually spend up a fair bit?

An off-grid system can work out quite well; I run one myself and am very happy with it, despite some summer afternoons wasting a lot of potential solar energy. So if you do start off with an Axpert, it won't necessarily be a throw-away item, despite what the Victron camp will tell you. There is no question that the Victron gear isn't higher quality; it is, but of course you pay for that.

So my suggestion for you is to start with an Axpert and the battery you suggested if it's a decent brand, and just run the essential loads during blackouts. Perhaps add some panels when you're ready, and run the essential loads during the day only. Then if you're ready for a bigger system, you need a lot of planning at that point, having gained a lot of experience.

[ Edit: said 80% DOD when I meant 80% SOC or 20% DOD. Sigh. ]

Edited April 17, 20197 yr by Coulomb
"Watts" as a word is not capitalised, except at the beginning of a sentence. Fixed quoting.

Thanks so much (don't know where you guys find the time to be so helpful?)  - bar some terminology I seem to be on the right track. Thank heavens - I am 100% electricity illiterate. I understand basic physics mind you but that finds little application here.

BUT one thing still - you said:

With an off-grid inverter such as the Axpert, you can't just blend excess PV power with the house consumption. So you'll have to split your loads, probably add a manual changeover switch for maintenance, and so on.

1. I assume I CAN use the excess power on the dedicated circuit where the Axpert will first load the batteries and then make the excess available for whatever I use on that circuit?

2. It seems to get the excess power to the rest of the house I need a MANUAL CHANGEOVER switch?

 

6 hours ago, Coulomb said:

A hybrid inverter as @The Terrible Triplett mentioned is a fair bit more expensive than an Axpert.

I smiled. Truth be told, I was thinking Victron yes. And GoodWe (even with some not so positive news on them recently) AND I was thinking Solis with Axpert as the UPS.

Solis is affordable, gives you that ROI on the panels - a lot less "wastage".
And if Eskom is off, the Axpert runs the loads - the dedicated ones.
And don't use Eskom to recharge the batts after a loadshed, wait for the Solis to do that next day.

6 hours ago, Coulomb said:

... you'll need a much bigger battery.

Hybrid and Solis routes, with loads matching the bank, can save a ton of money yes.

6 hours ago, Coulomb said:

... , despite what the Victron camp will tell you.

Ouch. 🙂  We may not like the manufacturer but as a UPS we do support them without any reservations.

6 minutes ago, The Terrible Triplett said:

I smiled. Truth be told, I was thinking Victron yes. And GoodWe (even with some not so positive news on them recently) AND I was thinking Solis with Axpert as the UPS.

Dude, I normally skip any thread that starts with "Axpert" in the first paragraph... cause much as I find time to answer these things I can't answer all of them 🙂 But then I see that you replied and I come here anyway...

8 minutes ago, The Terrible Triplett said:

We may not like the manufacturer

I won't even go that far. The Axpert is actually pretty well made for the money. It's good value for money. But so is a GWM Steed bakkie (seriously, I an buy almost two Steeds for the price of a Hilux). And the Multiplus-II is priced a lot closer to the Axpert now, it's no longer like in the old days where it was close to 3:1.

🙂

2 hours ago, The Terrible Triplett said:

Ouch. 🙂

Sorry, I guess I overstepped the mark. In fact, you guys have been pretty fair.

Also, I didn't consider the Solis with Axpert combination. Probably approvable (if that's a word) in the City of Cape Town, no less.

I worry my final questions fell in between the wiring - can you guys help?

Coulomb said:

With an off-grid inverter such as the Axpert, you can't just blend excess PV power with the house consumption. So you'll have to split your loads, probably add a manual changeover switch for maintenance, and so on.

1. I assume I CAN use the excess power on the dedicated circuit where the Axpert will first load the batteries and then make the excess available for whatever I use on that circuit?

2. It seems to get the excess power to the rest of the house I need a MANUAL CHANGEOVER switch?

11 hours ago, plonkster said:

I won't even go that far.

We don't like the manufacturer. They do not respond to emails. (finish and klaar 😋 )

11 hours ago, plonkster said:

And the Multiplus-II is priced a lot closer to the Axpert now ...

That is true, till you add the MPPT ... and the VenusGX ... and the Carlo ... 🙂 

2 hours ago, The Terrible Triplett said:

That is true, till you add the MPPT ... and the VenusGX ... and the Carlo ... 🙂 

I can't wait for the GX models to land. A Multiplus-II with a built-in venus device. Much stronger CPU too, and will significantly lower the cost. For parallel/2-phase systems you'll buy one GX (with the control unit) and then add additional units without it. Soon...

1 hour ago, plonkster said:

I can't wait for the GX models to land. A Multiplus-II with a built-in venus device. Much stronger CPU too, and will significantly lower the cost. For parallel/2-phase systems you'll buy one GX (with the control unit) and then add additional units without it. Soon...

Remind us when they arrive. I’m tempted.

10 hours ago, Clivevan said:

1. I assume I CAN use the excess power on the dedicated circuit where the Axpert will first load the batteries and then make the excess available for whatever I use on that circuit?

Yes, though I would describe it as the Axpert using PV power first, battery power second. However, if the load on that circuit exceeds what the inverter can supply, then the entire load switches over to AC-in (if available), and PV power only charges the battery (unless full).

Regardless, if there is more PV power available than the load requires and the battery doesn't need charging, or can't be charged at the rate that is presently available, some PV power will be wasted. But this is similar to the situation with a hybrid if you can't export: there is nowhere for the excess PV power to go.

So really, the main place that the Axpert falls behind as far as usage of solar power is concerned is when it is in line mode. In that case, neither battery nor PV power can be blended with AC-in power.

So if you only want to power small loads, well within the capability of your inverter and battery (i.e. you don't need AC-in power), then an off-grid inverter can blend power just as effectively has a hybrid. My understanding is that the Axpert King has an AC-in to DC bus converter, which means that loads up to the rating limit of the inverter can if needed blend all three sources, but I haven't looked into that model thoroughly as yet.

10 hours ago, Clivevan said:

2. It seems to get the excess power to the rest of the house I need a MANUAL CHANGEOVER switch?

Well, no, not a requirement as such, just a major convenience. I advocate an automatic changeover switch, but I don't know the legality of that in South Africa. That means you can switch off the inverter for maintenance and still have computers and other loads running without a glitch.

But as soon as you are talking about the whole house as opposed to essential loads only, you are talking about a larger inverter and battery. This is where the hybrids shine: you don't need a larger hybrid and battery, it can just help out as much as it can, with the AC-in supplying the rest.

22 hours ago, plonkster said:

I can't wait for the GX models to land. A Multiplus-II with a built-in venus device. Much stronger CPU too, and will significantly lower the cost. For parallel/2-phase systems you'll buy one GX (with the control unit) and then add additional units without it. Soon...

Fronius seem to entering the hybrid market with the Primo GEN24 in 2019 as well.

There is very little to go on as yet but I have seem a claim of back-up power without batteries?

Enphase IQ8 microinverters also make this claim.

There are that many advancements in Solar tech it's hard to keep track.

On 2019/04/18 at 9:22 PM, phil.g00 said:

Fronius seem to entering the hybrid market with the Primo GEN24 in 2019 as well.

There is very little to go on as yet but I have seem a claim of back-up power without batteries?

Enphase IQ8 microinverters also make this claim.

There are that many advancements in Solar tech it's hard to keep track.

That would be great!