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Inverter Types


Andrew P
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Hi Guys

 

I am new to the forum and am sorry if this has already been discussed and made clear, but i haven't found anything on the forum or anywhere else that is 100% clear.

 

I understand that we get 3 types of inverters, being:

 

Offgrid: Unable to connect to the utility grid and back feed. No AC to DC charging. Able to charge DC to DC (solar to battery, MPPT included). Mostly for caravans etc, with no utility grid.

Grid Tied: Able to connect to the utility grid and back feed. No AC to DC charging. Mostly for large PV systems without storage/backup.

Hybrid: Able to connect to the utility grid and back feed. Able to charge from AC to DC. Able to charge DC to DC (solar to battery, MPPT included). For PV plus storage/backup systems.

 

Is this correct?

 

Whilst shopping around I noticed large price gaps in the same size inverters for two reasons:

1. Capacitor based vs Transformer based - big price gap.

2. Offgrid and Grid Tied, vs Hybrid - big price gap.

 

I was satisfied with this until recently where I started looking at Hybrid Inverters like Goodwe and Sofar that are in my 'expensive' category but are capacitor based. So they are Hybrid.. yes, but my question is why is an Axpert not considered Hybrid if it seems to do everything?

An Axpert Mark 2 and Growatt SPF TL HVM seem to do everything Hybrid Inverters do but are generally classified as Offgrid Inverters and are half the price. Is it because they cannot operate without batteries? Or can they not back feed into the utility grid?

I am basically trying to understand what really classifies a Hybrid inverter and why they so much more expensive than offgrid inverters that have built in MPPT's and the ability to charge batteries from the grid?

 

 

 

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1 hour ago, Andrew P said:

Hybrid: Able to connect to the utility grid and back feed. Able to charge from AC to DC. Able to charge DC to DC (solar to battery, MPPT included). For PV plus storage/backup systems.

The term Hybrid in the English language means it incorporates features from two (or more) other types, in other words, it sits somewhere in the middle. The question is which types.

Traditionally a hybrid inverter was one that incorporated both battery backup and grid-tied capability. It does not need to also have an MPPT to qualify as hybrid.

Unfortunately the term is used somewhat interchangeably (along with the other term, Bi-Directional) to mean anything the marketing department wants it to mean...

So the best is to ignore it and just make sure you're comparing Apples to apples.

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13 hours ago, Andrew P said:

Offgrid: Unable to connect to the utility grid and back feed. No AC to DC charging. Able to charge DC to DC (solar to battery, MPPT included). Mostly for caravans etc, with no utility grid.

A common inverter-charger used by readers of this forum, the Axperts (with various names) and their clones and work-alikes do (or can, if present) connect to the utility grid, and do provide AC-DC charging. They are classed (at least by the manufacturer, Voltronic Power, and their resellers) as off-grid.

They do not attempt to feed power back into the utility; that's the big distinction from the other two types.

Edited by Coulomb
added "(or can, if present)"
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12 hours ago, Gerlach said:

Something like this @plonkster 😁

Hah! Indeed, I had a teacher in primary school who joked and said I took the entire alphabet for initials (cause my parents gave me three names, like my great grandfather)... so it looks like MLT did the same here 🙂

The term bi-directional means either 1) that it can grid-tie or 2) that it can also charge the batteries, ie it has a charger in the box.

The term hybrid means one of: 1) it is an inverter and a charger, 2) it is an inverter/charger AND a solarcharger, 3) it is both a battery inverter and a grid-tied inverter...

In my opinion only option 3 is correct for the term Hybrid. That means the Goodwe, Infini and Victron are Hybrid inverters, and the Axpert and its many clones are not.

Victron always uses the term "Inverter-Charger" rather than "bi-directional" so that there is no confusion, and to distinguish between the Multi/Quattro (which are inverter-chargers) and the Phoenix (which is an inverter only).

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I think a fairly decent way to describe a hybrid inverter is that it combines a grid tied and off grid inverter in one unit. 

On an off grid inverter like an Axpert, there is no PV to AC inverter function, it's only a DC to DC charger. So the function of the PV is litteraly just to charge batteries. The inverter then uses the DC from the batteries to supply AC loads. 

A hybrid does the above but with the addition of a PV to AC inverter which can supply loads directly from PV but also supplement short fall of PV from either battery or grid or both. Bare in mind that loads not connected to the back up (or off grid) side of the inverter, much like a grid tied system will lose power in the event of grid failure. 

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4 hours ago, Andrew P said:

What happens when a Victron Multiplus 2 system has a full battery, PV Power available that are covering the AC loads and is in float? Does it ever bypass the battery?

Depends how the PV is coupled.

If the PV is DC-coupled, in other words there is a solarcharger (MPPT) that connects the PV modules to the battery, then the battery voltage will rise up to the configured float voltage, and then the MPPT will simply throttle the PV so the batteries are held at that voltage. In practice, the PV power will then equal the AC loads (plus a bit because the efficiency isn't 100%).

If the PV is AC-coupled, in other words through a grid inverter like a Fronius, SMA or similar, then the Multi holds the battery at float voltage, and the loads are powered direcly by the PV-inverter, and whatever remains is fed into the grid (unless you have some sort of limiter set up).

I assume you're speaking of the DC-coupled situation. The batteries aren't explicitly bypassed, but because electricity takes the shortest path, and the impedance into the inverter (which is feeding power to the loads) is lower than the impedance into the battery, there is a sort of natural bypassing happening. Whatever charge arrives from the MPPT takes the shortest route to the inverter and bypasses the battery.

It's a bit like asking what happens if the water tank is full. Well, whatever water comes in just flows off the top of the tank directly to your consumers, and a ball valve ensures that the tank does not overflow. The water entering the tank ends up being exactly the same amount as that going to the consumers, while the tank is essentially floated.

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On 2020/05/15 at 11:01 AM, plonkster said:

cause my parents gave me three names, like my great grandfather

I know people with multiple names have a hard time with call center agents etc.

But lets all take a moment to pay our respects to people like myself with a hyphen in their name...

Sure it looks like 2 names on paper, but its only one.

Even my drivers license has my initials wrong 😕

I tried to get it fixed the last time I went for a renewal, but I guess the person behind the counter thought I was just another idiot that added his middle name to the first name box.

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1 hour ago, PJJ said:

I know people with multiple names have a hard time with call center agents etc.

My father's third name is "le Roux". So he is Mr. A. B. le Roux Venter (not his real name).

So there was this funny case of a newsletter he received which was incorrectly addressed to Mr. le Roux. He asked them to correct it. The next month he received two newsletters, one for Mr. le Roux, and one for Mr. Venter.

He gave up...

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On 2020/05/22 at 10:52 AM, plonkster said:

My father's third name is "le Roux". So he is Mr. A. B. le Roux Venter (not his real name).

So there was this funny case of a newsletter he received which was incorrectly addressed to Mr. le Roux. He asked them to correct it. The next month he received two newsletters, one for Mr. le Roux, and one for Mr. Venter.

He gave up...

Yeah it all fun and games while its still a newsletter.

But once official documents start looking suspect it gets interesting, like when I got my US Visitor VISA I noticed that they had my given name correct with both parts, except they omitted the hyphen, and of course my passport includes the hyphen, I remember shaking like crazy when we got to the customs booth on the US side, luckily it was just a quick thank you sir and I moved on.

But on the SA side I guess my anxiety might have been boiling to the surface, I was "randomly selected" for a search, they even ran a glove through my hair and analyzed it (I am assuming they thought I might have been some kind of drug mule) my hair as well as the sweat under my arms was analyzed in a little machine they had there.

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