There are good reasons to have a bit of both.
I have no doubt … I just like the KIS principal at certain times.
We are a bunch of ‘what box’ thinkers here and it can get very ‘complicated’ very fast when solutions are found to fit needs, that sometimes KIS is overlooked … no fun in the boring KIS principal.
I suppose it depends which direction you are walking down the road.
AC-coupling sounds complicated coming from a hybrid inverter background.
But for a man who has experience in hooking up PV inverters, (which is as simple as it gets) the hybrid world is the complicated one.
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Now THAT hits the nail on the head!
For me, hybrid is as simple as it gets.
Where I think it gets complicated with PV inverters, is the moment you add batteries to the mix.
It then gets even more ‘complicated’ when Eskom goes on ‘lunch’ daytime, the user then one day asks how to keep using the panels and not only the batteries, seeing as the panels are sitting there doing nothing on a sunny Eskom’less day.
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For the battery capacity, 12kWh should be enough for 3.6kWp of panels, which is the limiting factor, not the inverter. I’ll probably almost never reach full rated power so thought 10 should be enough, but better to err on the safe side I suppose.
I could relatively easily transfer the panels to a backup inverter on a sunny day if Eskom goes AWOL with a DC disconnect and transfer switches. What makes this setup more complicated though is if I want to use the battery for self-consumption at night and then charge up with available PV during the day.
Probably best to ditch the Solis and get a hybrid when the time comes, but I just liked the idea of grid-tie/mini-grid.
True, and you are unlikely to get that so 10kWh of battery is plenty.
I am sorry, I have been under the impression your PV inverter is in addition to a Victron Multi that you have already? Is that not the case?
No I have the Solis already. I considered adding a Multi upstream of the Solis for backup and not having to switch DC if Eskom goes down. I assume you can tell the Multi to not charge batteries from the grid, which would improve self-consumption.
I’ll probably just get a hybrid when the time comes though.
OK, then you have to excuse my metering replies which assumed you had certain facilities available to you that you only get with Victron VRM.
Yes, you can practically tell the Multi to stand on its head if you want.
You have a few options.
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You can put the Solis on the Output of the Multi. If the grid fails, the Multi can use frequency shifting to limit the PV-inverter. So it operates like an off-grid site. The Multi will also see the power from the Solis flowing backwards through it and will charge the battery with that power.
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Put the solis on the grid-side of the Multi. If the grid fails, the Solis shuts down. If you then install an external meter (a Carlo Gavazzi), the GX device can use that information to instruct the Multi to import that power. So again, any surplus from the Solis is used to charge batteries.
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You can install the Solis’ own limiter back to back with the grid meter for the Multi. But then there are some caveats. You have to configure the Multi to import a little power. As an example, say you configure the Multi to import 200W. When you do that, the Solis will increase production to get the grid consumption down to zero… but the Multi will increase its power import (and charge batteries, feed loads) in an attempt to get the grid consumption UP to 200W. By setting them up in opposition like this, the Multi still imports the excess made by the Solis. But… but but but… this isn’t always stable. I would not recommend it. If you do this… configure the Multi to import a nice healthy amount of extra power so they have a large enough amount to fight over.
When using a Fronius in the system, the same offset method is used (the Multi attempts to pull power up while the Fronius is instructed to push it down). The difference is that you know when the sun sets… and then you can remove the offset. Which means you’re not importing lots of power at night…
And of course such a combo is not supported, so if something doesn’t work right, Victron support will tell you to install a supported PV inverter 
I have a question.
You can use Fronius/ABB pure grid tied inverters, all is already integrated with the Venus.
You can use Solis pure grid tied inverter, and make it work.
You can connect them all before, after the Multi, dependent on what you want to do.
So my question: How is that better/easier/simpler than just getting a MPPT?
MPPT vs PV inverter?
OK. let me say that I never took a binary view on this, I said there were good reasons to have a bit of both. Of course an MPPT cannot function (make AC) in isolation of a hybrid inverter, ( a PV inverter can), but to be fair I’ll consider there is a hybrid inverter in both instances.
To try and answer your question I think we have to look at what an conventional DC standalone MPPTs can do and what they can’t.
- It can change your PV voltage to suit your battery and charge them.
- It has a single tracker.
- If a Victron product then comparably priced to a high end PV inverter.
- It can’t create extra AC power, that is still limited by the hybrid inverter output.
- It can’t efficiently be used in a situation where your PV is a distance from your battery without using a lot of copper, (the new HV range excluded, mainly on price).
- It can do black starts.
- Doesn’t have system limitations as to how many units can be used (within reason).
- Can produce power when the grid is lost.
What a downstream PV inverter can do and what it can’t.
- A PV inverter can also change your PV voltage into AC and in turn use the bi-directionality of your hybrid to charge batteries. (Not as efficient, but if using the AC for consumption then it is more efficient, so a tie there). - Tie
- Generally, a PV inverter has two trackers. - Win
- Same price if high end, a Solis is probably cheaper at equivalent kW. - slight win
- It can create more AC power, available power is now the threshold of the hybrid inverter + the PV inverter. - Win
- Due to the higher PV voltages used, copper losses are not an issue when the PV arrays are a distance away. - Win
- It cannot do black starts. - Lose
- If on the hybrid’s output it does have limitations as to capacity due to battery size and hybrid inverter capacity. - Lose
- If on the hybrid’s output it can also produce power when the grid is down. - Tie
So to conclude, everyone’s system is different, but there can be a place for both, and in certain applications a bit of both is better than just one or the other.
Well, technically a PV-inverter is also an MPPT. The difference is how it gets the power to where it needs to go.
If you use most of your power immediately, during the day, and many many of us do exactly that (to spare the batteries a bit), a PV-inverter is the way to go. You get 95% of the power from the PV modules directly to your loads.
If you use “an MPPT” (aka a solar charger), it’s like 93% efficiency or so to the DC bus, and then on average 88% from there to the AC side (using an old-school low frequency inverter). So that’s 0.93*0.88 = 82% efficiency. Vs 95%.
But the PV-inverter is more expensive to buy. And is a little more complex to set up. And in off-grid setups where a large chunk of energy is stored for use at night… you may prefer a solar charger over a PV-inverter. Because using a PV-inverter where the bulk of energy is stored for later use is even worse… somewhere around 70% efficient round trip.
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Now we are cooking wit gas … or is that solar panels rather? 
Methinks it would be a huge benefit to also point out the caveats. Those teeny little pesky caveats that trips you up after all was paid and installed, weeks/months later.
What triggered that question was two posts:
In bold is heavily reliant on what the Solis array voltages are, one or two built-in MPPT’s?
And the pesky point of self-consumption using solar to re-charge daytime.
Now I KNOW we don’t think in boxes here, we don’t have boxes, but the teeny pesky details are what always gets in the way … and the costs.
I think my Solis takes anywhere between 50V and 500V and makes AC.
Most PV inverters don’t go this low, but do go higher.
NOW we are getting to the core methinks.
Cause the above is spot on … if we did not have a worsening grid ito pure PV inverters.
… and we want to use batteries at night, recharged daytime only.
With the above comments, the “round trip efficiency” is mitigated, even nullified, by the convenience of a KIS system with no Eskom impact and the additional “savings” of using more stored energy after having had to spend a ton on batteries.
Victron MPPT’s are max 250v or the new 450v one … so that caveat needs to be carefully considered swapping the array manually from say a Solis to a MPPT … but why then have both is what I’m wondering, my needs would never even consider that.
I would start with a Solis, get all else installed, then sell the Solis and a get a MPPT having installed the array so that it is “plug and play” with the new MPPT.
Unfair assumption: I want to use the grid at night,
a) Because I want full batteries for power cuts.
b) Because I believe its cheaper.
You’ll get a nice PV inverter for the price of that 450V.
I’m the same. I would technically be much better off with a PV-inverter. Odds are that for the next batch of panels I add, I will likely use a PV-inverter.
Unfair, why? You have lead acids, makes perfect sense where you are coming from. I was there too.
With lithium, your perspective will change.
Another perspective to consider … Evening load shedding: T&C’s apply with summer and winter adjustments.
Batteries are used from say 10 pm at night till the sun takes over and we are not bothered if there is LS event at night.
I simply limit the inverter to a wattage that shaves off not only the base loads at night but also so that it can carry the critical loads during evening LS events, cause the SOC will be there to do so, without going below 30% SOC.
The ONLY trick I have to watch for, is tomorrow’s weather and IF there is LS planned. Those days, few and far in between, I set to Keep Charged. And IF I missed it, bleh, just use less critical loads.
The peaks at night, that is Eskom’s loads. Cents on the rand, not worth putting that on batteries ever.
And that is on a 150ah bank, not even the 280ah one.
I think once we have a final cost on the new 280ah cells coming in, that it is time to recalculate the kw/h from batts vs Eskom, and keeping in mind that Eskom charges differ between us all.
In the non-pejorative sense. You didn’t do anything wrong… it’s just not an assumption you can make for everyone. Unwarranted might be a better word, but English isn’t my first language.
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