Microinverters vs Victron MPPT controllers

davelondon

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I'm planning a big expedition vehicle electrical system, centered around 57kWh of LiFePO4 in a 48v configuration, 2 x 10kW Victron Quattro inverters, and 8 x 500W solar panels. Here's a rough electrical layout:

Victron (4).png

I was planning on running 2 x Victron 250/60 48v MPPT controllers, but a friend has suggested adding an Enphase micro-inverter to each panel, and running the 240V AC output to my Victron inverters to charge my batteries. This seems to have a few benefits:

1) Panels are all completely independent, so no problems with shading
2) No MPPT controllers taking up space inside my truck
3) No high voltage DC to worry about (is ~200V DC more dangerous than ~200V AC?)

However, there are some disadvantages:

1) Costs more (~$150 per panel)
2) Electronics on the outside of the truck is not ideal (although nicely hidden under the panels)

Can anyone suggest any more pros and cons?

What would the overall efficiency be? I'm worried that with the microinverters I'm doing two separate voltage conversion steps (from the panels to 240V in the micro-inverters, and back to 48V in my Victron inverter). With the Victron MPPT controllers we're just doing one voltage conversion from the panels straight to 48V.

Would my Victron Quattro inverters be able to understand that this is solar power and display it as such on the display? Or would it look like I'm plugged into shore power?
 

davelondon

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Right so my assumption above of two voltage conversion steps when using micro inverters is based on the solar panels being used only to recharge the batteries... in actual fact the Victron inverter will just use the 240v provided by the solar to directly power the 240v loads... and this will mean just one voltage conversion step when using micro inverters, as opposed to two when using the Victron MPPT controllers. hmmm
 

the_colorist

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Hey Dave. Installer here. Not sure why anyone else hasn't responded to you and I'm just now seeing this. A few points that may help:

1. There are still 2 conversions happening however the conversion from PV to 240V AC should take place at close to 98% eff so I don't typically worry about it. Overall though I would either use micros (Enphase is too expensive though IMHO) or a string inverter such as a Fronius Primo, SMA Sunny Boy, or Solaredge W/ optimizers. Solaredge with optimizers is essentially the same as micros when it comes to per-panel monitoring. String/microinverters could actually come out cheaper than the MPPT's depending on the model chosen. I can even get you pricing on that if you would like to PM me.

If you are charging at around 3500W (assuming 500W load), the Quattro(s) might be operating in the 89-90% eff range. So total PV -> Battery could be around 87% Eff at its peak. It fluctuates depending on how many amps the Quattro is charging at.

PV -> Loads would be around 98% eff.

Battery -> Loads would be the inverse of charging. It all depends on the load. Here is a chart from Victron. Sadly they don't have one for that particular Quattro but I know it will be worse than what is shown here due to the size of the transformer etc.

1614126957657.png

2. I know you are only asking about the micros but if I may, I see you are using REC BMS Q with slaves? I was wondering if you had a particular reason for that? In this type of application that configuration is usually a massive expensive when a standard REC BMS SI (Victron model) plus Active Balancers will do fine.

Many times on large installations paralleling at the cell level makes the most sense or at least for us it does. Not always but most of the time. Orion has a document on it if you aren't already aware of the concept.

Strings, Parallel Cells, and Parallel Strings - Orion BMS

1614127175107.png
3. I see you are connecting your alternator to your Lynx. Are you intending to charge your LiFePO4 bank off of the alternator directly? Beware that could be fairly dangerous with no BMS control. Many have ruined their LFP banks using an alternator made for lead to charge them without any intermediary control. Sadly I don't have a perfect solution for it yet either. Victron doesn't have a VE.Direct or VE.CAN DC-DC converter yet. I have been contemplating the use of an MPPT between the alternator and the battery bank but there are some caveats to that...

Hopefully that helps.
 

davelondon

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Hi @the_colorist, thanks very much for your input, and yes I was surprised I hadn't got a response yet too!

1) The price of the Enphase (~£100 per panel) isn't a big consideration for my build, so specs like the size, efficiency, and reliability are more important. I'm always looking for the most redundant system, where a single point of failure won't completely bring down the electrical system, which is why the Enphase system of having each panel completely independent appeals to me. Also, space is limited, so having all the electronics self-contained underneath the solar panels is a huge win. I don't have any extra space on the roof, so if I used a string inverter it would have to be in the body of the vehicle.

However, it seems that Enphase units wouldn't support my 500W panels? I'm looking here at the Rated Output Power, and the max is 349VA? Could I use two micro inverters per panel?

2) I've been talking to REC about two options: either using a single BMS and a single battery bank connected in 4P16S configuration, compared to a master BMS with four slaves and four independent battery banks each connected in 1P16S. Again my choice comes down to reliability, and especially the consequences of a cell failure. I'm going to have 64 cells, so the chance of one cell failing at some point it pretty high. In the layout with 4 independent batteries I'll just need to disconnect that battery bank to do the repairs. I'll be taking spare cells, but in order to replace a cell, I believe I'll need to manually top-balance the new cell, as well as the pack without the cell before replacing the cell. Additionally the repaired pack will probably need to be at the same charge state as the other three when it's added back into the system? Obviously I'll need power to do this, so won't be possible to do if the entire battery system was down.

3) I'm going to use the Balmar 48V alternator and their MC-620 external regulator? I was under the impression that with this solution you could just connect the alternator to the battery and the regulator would manage things? Or perhaps I'm misunderstanding...
 
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the_colorist

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1. I completely get where you are coming from. As long as your 500W panels do not exceed the input specs (VOC/ISC) the Enphase will work fine but you'll lose quite a bit of output power which IMHO is not ideal for your application. My recommendation would be Deye. I'm assuming you are needing 230V/50hz? If so, their new G3 series would be a great fit. 10-year warranty to boot. Wifi built-in to each micro for monitoring on their central platform.

Attached are the datasheets. Using more/multiple of the smaller 600W-input models such as the SUN1000G3-EU-230 would provide more redundancy but cost more overall if that matters as the cost per unit doesn't shift that much between the larger models.

If you'd like a quote/pricing on the units feel free to PM me.

2. Glad to hear you are talking with REC. I just wanted to make sure someone wasn't just telling you that was the only option so they had a larger sale/commission. Sounds like a plan though. IMHO with proper capacity/IR testing before deployment the chance of cell failure is extremely low and I see that reflected in the larger commercial/EV industry BUT I'm not ruling out the possibility for sure.

3. The regulator would to some degree but it would be better to have charge coordination and BMS control. You might consider the Wakespeed controller. They have native REC integration. You would need to speak with REC though to confirm integration of the Wakespeed controller and the Victron GX on the same CAN bus.

 

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Rocketman

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On the BMS, look at Batrium too. After looking at both, I choose a Batrium bms. The big reason is I found the software much easier to understand and work with, plus it has more relay connections. (It also has a CAN-Buss connection to the Victron GX).
 

the_colorist

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Batrium makes great hardware and the MM8 is ideal for multiple banks. The downside with Batrium (last I spoke with them) is no current control at the top of the charge cycle. They let the inverter handle it. This can be a little harder on the cells (faster degradation possibly) in the long run depending on what you use as your charging target and how much current you are pushing through them.
 

davelondon

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One more question... Is the Quattro / Cerbo clever enough to know that the 240V coming from the microinverters is actually solar? e.g. On the display will it show as solar and not shore power?
 

the_colorist

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You'll be running power back through the Quattro via the AC-Output (yes, the AC-Out) so you'll see that as the Quattro charging. Input from shore power will be shown separately. The only thing you won't be able to see is how much power is direct-to-load from the micros vs how much is charging. To see those values, you can add a Victron single-phase current sensor on the total output from the micros. Part #CSE000100000

With the current sensor installed, you should see something like this however this does show additional grid input.

1614543811470.png

Here is a good place to start for information:

AC-coupling and the Factor 1.0 rule
 

the_colorist

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Another note is that you will need to configure your micro's for grid-zero/zero-export or every time shore power is connected they will attempt to back-feed assuming there is excess power. Will require an additional current sensor on the AC-Input line of the Quattro.
 
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