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Inverter Question


Kloon
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So I have been reading up on the different types of inverters and just have a couple of questions.

I will be moving into a new place in 2 months and busy doing some research into going solar and get away as much from Eskom as possible, my first change will be moving over to solar water heating system and moving to gas for the oven/stove. After that I would like to look into a PV setup, since I work from home and have a domestic during the day I will need the majority of my power during the day time so was thinking of a grid-tie solution without feeding back to the grid and battery back ups.

My main question is this, if I get say a 3KW inifisolar plus and just hook up the PV panels with the excess power needed being drawn from the grid, will it be able to handle loads in excess of 5KW?

For example, I brew beer as a hobby and have an electric setup, this setup runs at around 25A at full load, it has 2 5.5KW elements, of which only 1 runs at any given time and then a couple of small pump, but the current can be drawn for long periods of time when I do boils, ie 60min+, it does work in pulses but still.

Assuming the whole DB will be fed through the inverter for ease, if I need excess power of what the PV panels can produce will the inverter be able to handle a load like that? Or is the 3KW rating on the inverter just applicable to the input power from the PV panels?

Maybe I am looking at the wrong inverter, I also looked at the Axepert but they do not seem to be able to provide power via the PV panels and also pull in excess power from the grid to compensate for higher loads, seems like it will just switch to either PV panels or grid, and also requires batteries.

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Kloon another solution is to have separate circuits for all the stuff you want powered by either solar / inverter or Eskom depending on SOC of batteries.

This idea stems from before the time of Axperts and very expensive solar equipment, when one does not want to be bothered with DB boards or feeding back.

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The hassle with the Axpert's are that are not true hybrids. Either the entire load is powered by solar + batteries or the entire load is powered by Eskom. Depending on what your end  goal (and budget) is will determine whether you go for true hybrids or are you willing to settle for an Axpert. I live offgrid so the functionality of a true hybrid is not really necessary. An Axpert in my situation was a no-brainer.

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Okay so the 3KW is for the total load on the inverter even when drawing from solar and eskom at the same time. Budget wise I am trying to keep it as low as possible but do not want to skimp on quality, I also have to keep in mind space for PV panels on the roof, there a pretty big north facing roof but doubt I will be able to accommodate a lot of PV panels and a water heating system.

Also going from the 3KW model to the 5KW model is quite a jump in price, almost double for just 2KW extra. I guess I can just have my brewing stuff on a different circuit that only gets feed by Eskom as TTT suggests, but can I then have the other circuits to run in grid-tie mode?

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Um, but aren't the Infinis grid tie? My understanding is that if you have a 3 kW unit, it can supply 3 kW continuously, and more (perhaps double) for short periods of time, if you have the available solar power. But the output of the infinis goes in parallel with Eskom, right? So if you have 10 kW of load and only 1 kW available from solar, then no problem, Eskom supplies 9 kW. As long as you mostly have enough solar power to cover your day time loads, you should need little energy from Eskom during the day. The 3 kW limit in no way limits your peak load power. What it limits is your maximum power (that you have to pay for) saving.

By contrast, with say a 5 kVA Axpert (4 kW), you can only supply 4 kW, with bursts of up to 8 kW for just seconds (no large transformer to absorb heat). There is no way that you can supply a 10 kW load, except with the Axpert switching through to Eskom, and there would be a limit based on how much current the relays can handle.

Am I wrong here?

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2 minutes ago, Coulomb said:

But the output of the infinis goes in parallel with Eskom, right? So if you have 10 kW of load and only 1 kW available from solar, then no problem, Eskom supplies 9 kW. As long as you mostly have enough solar power to cover your day time loads, you should need little energy from Eskom during the day. The 3 kW limit in no way limits your peak load power.

2

This is exactly what I am trying to find out, I will be running in grid-tie mode to get the boost from Eskom when needed, just wanted to make sure the rating on the inverter is not the total it can handle even when using Eskom.

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I moved from 2 X Axpert to Infini. I run a 5Kw unit. It was very expensive but as I will be saving my batteries it is cheaper in the long run. I get a overload warning when we get around 4.5 KW but its only a warning. My whole house runs on it. I did not split the DB as that makes your COC a nightmare. If you can then I would recommend the Infini as you can run the 5Kw in parallel.

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The rating is the total. You can not run 8kw on a 5kw unit. Only a spike like when a pump starts or something like that. But if you run the inverter that you pull the power from the input side of the inverter and not run the power through the inverter then you can pull as much as you like and the inverter will still push power back. Only thing then is when you do have load-shedding you do not have a auto cut over.

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2 minutes ago, jdp said:

It was very expensive but as I will be saving my batteries it is cheaper in the long run.

How long is the Infini supposed to last? 

I am just now wondering for it all depends on how frequently you need to replace it for none of the inverters last as long as panels do, so when you factor in replacing Infini's, it could skew your savings made on batteries and cheaper inverters?

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I heard a lot of good things about the Fronius inverters. They also use an "open" protocol for communications. Exsolar sells a grid tie limiter that can be used with them if I recall correctly.

C

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installed a few, plastic bodies, have to dismantle the unit to mount on the wall, lug connections no mc4 on the babies i did, but they work well and are not expensive

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My dad has a Fronius installed on the farm, about 200m from where I am now sitting. A 3kva Symo. Lovely lovely little units. Completely waterproof too.
 It was 22k (though that was a year or so ago).

The grid limiter that ExSolar sells is rather costly, as I recall. Even more than a CCGX if I recall.

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17 hours ago, jdp said:

The rating is the total. You can not run 8kw on a 5kw unit. Only a spike like when a pump starts or something like that. But if you run the inverter that you pull the power from the input side of the inverter and not run the power through the inverter then you can pull as much as you like and the inverter will still push power back. Only thing then is when you do have load-shedding you do not have a auto cut over.

Not entirely true.  We've done tests on the 3KW infini and when the mains is available you can draw much more than 3KW. I had a load of just below 6KW for about 15 minutes and MaurioZA (I think) frequently have loads of 266% (8KW) for a few minutes at a time. You should be able to easily draw 10KW + from the output of your infini 5KW (not like you are currently using it without anything connected to the output) for minutes at a time - not for spikes only, as you've mentioned.

Saying that, I don't know if it would be a good idea to draw 5.5KW + from the 3KW infini for extensive periods (more than an hour at a time) as per the OP's posts above.

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So if this is the case why do I get a overload warning when I go over 5Kw if the inverter can handle more ? and by more I mean constant draw not just spikes.

I beeps all the time and the fans come on. I don't think it will last if I run 8kw on 5kw all the time.

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When I say " The rating is the total. You can not run 8kw on a 5kw unit. " I am talking about the normal operating Kw, not the now and then. If the it was not the case then why do we have ratings, then we would just have a inverter and not have to worry about sizing etc.

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When sleeping under a tree with limited technical knowledge you need communication skills!!

Kloon well put, I think you have managed to put words to a technical question that even the technical guys differ in their opinion. Chris previously gave a brilliant description about how the PV panels work " they do not push out the power, the inverter draws out the power needed" if I remember correctly;) so

Here goes my attempt:

Does the 3kw infini sit "in line" (between the load and ESKOM) doing what it does, using PV if available, battery if available but hopefully ESKOM available. Being "in line" does it create a bottle-neck linked to the it's rated output?

OR

Does it sit next to the ESKOM power line looking at the load requested, ready to "help" by providing what it can, and yes maybe even supply the full load but never blocking the ability of ESKOM to supply the full load demanded up to 60 amps!

 

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Hey @Green Bum, thanks. I am not too clued up on the technicalities and what is possible hence I am trying to find out. Ideally if I could get away with a 3KW inverter that would be great, as long as I can have that supplement my full house load in conjunction with Eskom without having to use separate circuits or switches.

Is it even possible to wire the inverter in such a way that it sits next to Eskom providing its power and then only drawing what is needed extra from Eskom?

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5 hours ago, Kloon said:

Hey @Green Bum, thanks. I am not too clued up on the technicalities and what is possible hence I am trying to find out. Ideally if I could get away with a 3KW inverter that would be great, as long as I can have that supplement my full house load in conjunction with Eskom without having to use separate circuits or switches.

Is it even possible to wire the inverter in such a way that it sits next to Eskom providing its power and then only drawing what is needed extra from Eskom?

Yes that is what a GTI does. It makes power all the time, Extra goes to the grid. If you need more it will pull the more from the grid.

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@Kloon I was exactly where you are now. I also did not know what size inverter or even type of system I should get. I was unsure if I should cater for 6KW peak demand. I was conserned that it might not be enough. I saw the prices of 10 KW systems and they were not within my reach. But what would happen if I went smaller, would the smaller inverter work or would I have constant overload/trips?

My Prof at varsity use to say that "If you can not measure something you can not control it." Knowing what your usage is takes a LOT of guess work out of the equation. What I would suggest is move into the new place. Get your solar water system, gas stove in place first. Invest in a energy monitor. Let it run for a couple of months and then use the figures to do proper sizing of your system. At this stage you have so many "unknowns" about what your consumption will look like that its very difficult to know now what size system would be best. 

That said you are already on the right track. Read as much as you can, research all the inverters and types of system, BiDirectional/Hybrid/Grid Tied etc. Look at the different brands and find out where to get what at decent prices. Once you have have the figures about your actual consumption to get the correct sizing is much easier.

About energy monitors. Look at one that you can download the data onto a laptop/pc. When I first bought one (the cheapest I could get at the time) it only gave a small bar graph on a screen and only kept history about total daily/monthly consumption. It could not give me peak usage etc.nor could I download the data onto my laptop.

The second monitor I bought worked a lot better. I could download all the data onto my laptop. See the peak utilization etc. But as I found out this week it does not give me information about the power factor.. but thats another story. So now I have to get a third one.. Maybe save yourself the expense and get a good one from the start.

 

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8 hours ago, jdp said:

Yes that is what a GTI does. It makes power all the time, Extra goes to the grid. If you need more it will pull the more from the grid.

My favourite analogy is to say that it layers the extra power like butter on to bread (Eskom is the bread). When you're very hungry, the bread goes thicker. When you're not very hungry, you butter the bread of the guy down the street :-)

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