High start-up voltage for inverter


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prepared1

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Looking for advice from others: I've seen numerous inverters for sale online, often with either high MPPT start-up voltage, or high operating start-up requirement. For example, a lot of people who like the Delta H6 talk about this issue, and there are some decent videos talking about needing to get 300 or more volts for the MPPT to track properly. There are also some big inverters with multiple MPPT strings that have high start-up numbers. In practice, how big of a deal is this? Panels are getting to be quite a bit more powerful than they were just a few years ago.

Right now, we have well over 20" of snow on the ground, so it would be a very big deal to get them cleaned off, and producing some power. But that isn't typical.

For a unit with multiple MPPT's, would running panels on each MPPT count towards the total required to start tracking? Many of the 3 phase units have independent inverter sections in them. Wondering how that works....or doesn't?

Comments?

Thanks!
 

daromer

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Each MPPT have their own starting voltage so no they dont count. Thats why you need to design the system properly and make sure the input voltage is the most optimal vs start and top voltage. You run multiple mppts since its cheaper overall and you can have panels in different directions. For instance i run 3 you could say. East, South and west due to how my roof is made on my work shop.

3phase systems are 3 inverters you could say yes but there is more logic to it since they need to be shifted in 120 degree in between each other.
 

Roland W

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Looking for advice from others: I've seen numerous inverters for sale online, often with either high MPPT start-up voltage, or high operating start-up requirement. For example, a lot of people who like the Delta H6 talk about this issue, and there are some decent videos talking about needing to get 300 or more volts for the MPPT to track properly. There are also some big inverters with multiple MPPT strings that have high start-up numbers. In practice, how big of a deal is this? Panels are getting to be quite a bit more powerful than they were just a few years ago.

Right now, we have well over 20" of snow on the ground, so it would be a very big deal to get them cleaned off, and producing some power. But that isn't typical.

For a unit with multiple MPPT's, would running panels on each MPPT count towards the total required to start tracking? Many of the 3 phase units have independent inverter sections in them. Wondering how that works....or doesn't?

Comments?

Thanks!

When you are planing your array, just multiply the panels Voc (idle voltage) and try to reach near MPPT max voltage and stay withing max power for that string. The rest will fit automatically. High voltage inverters prefer adjusting voltage down towards output instead of boosting it up.
 
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ajw22

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needing to get 300 or more volts for the MPPT to track properly. There are also some big inverters with multiple MPPT strings that have high start-up numbers. In practice, how big of a deal is this?
As always, it depends. Solar panels are quite capable of putting out high voltages even on cloudy days (though very low current), so the minimum starting voltage should in practice _mostly_ be a non-issue, except in very poorly designed systems that try to operate at the very low voltage end of the inverter.
One potential method of raising the voltage is to use smaller panels, and connect more of them in series.

I'm sure there will be more useful replies if you post exactly which inverter you're thinking of using and with what & how many PV panels.

Each MPPT have their own starting voltage so no they dont count. Thats why you need to design the system properly and make sure the input voltage is the most optimal vs start and top voltage.
Note also that the MPPTs are usually designed to share the workload. So while you can have different voltages on each MPPT channel, the number of panels on each should be more or less balanced. The inverter spec sheet will mention something like "Maximum Current per MPPT Channel"
 

daromer

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No need to spread load. IF thats the case its chinese and underrated. So that youbcan ignore aj22
 

ajw22

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Beg to differ. Not saying that every inverter requires PV panels to be spread between the MPPTs in all cases, but many do.

eg.
Sunny Boy 5.0, from market leading German inverter maker SMA.
max current per MPPT channel is 10A, rated voltage ~480V, so not really possible to safely run at full power of 5kW AC without using both MPPT channels.

I also manage Japanese made solar inverters with 5 MPPT channels, which most certainly require spreading load between multiple MPPT channels.
So during planning, "Maximum Current per MPPT Channel" in the inverter spec sheet demands as much attention as "Max DC voltage".
Also, the internal components will run cooler and last longer when running at lower current and voltages, so it's a good idea to spread the load between the MPPTs in any case.
 

daromer

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Wouldnt call that spreading the load but you are correct that the SMA have weird setup were they state 5kW per MPPT but only 8kW in total as example. I guess thats due to the output from the SMA to save money... Ie they go to same DC bus and the output of that bus is the culprit and therefore you need to spread the load

On the inverter I have the max per MPPT is half the total :)

Interesting design they have that they made them so different in terms of input per channel vs output.
 

ajw22

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I like to think that they've generously oversized their DC/MPPT components, instead of having skimped on smaller AC components. Pota(y)to - Pota(h)to :unsure:

It's certainly a very useful setup for people who do not have the space to put all panels on one south facing roof, and especially for people who want oversized arrays facing East-West. All while adhering to grid limits on how much AC power they're allowed to generate.
 

prepared1

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Thank you all for the info. More info, a novelette....

I've rewired our house into several independent 100 and 200 amp panels, split loads according to priority, and balanced the loads on each leg of the panels. Those panels are wired into a master panel with individual sub-panel breakers, and generator input. We have had a lot of nature related power outages here. The last big one over 2 weeks long. Lots of 2-6 hour outages. So I started with battery backup systems because they interest me, while I finish up the work. Have a 48v Victron off grid inverter, going to buy more. Building 24 and 48 volt battery banks, but have the idea to go higher voltage at some point. We have no interest in grid tied solar. Our number one goal is to avoid losing heat in winter. The amount they pay you here for grid tie is ridiculous, and the bureaucratic headaches double the price of the system.

Have solar hot water panels on site to be erected as soon as the weather warms up. Enough to keep our house from freezing in winter. It is -16F here now as I type this. The solar panels I'm buying are bi-facial, 375w, 49v open circuit. Have a difficult solar site due to tree shading. Very good Eastern exposure, good Southern especially in winter. Zero Western, due to trees, unless roof mounted panels. Historic home, roof mounting not desirable, but have considered a ballasted system. Cannot in any case drill holes in that roof due to cathedral ceilings. Planning to erect multiple, pole mounted, ground mount systems facing E, SE, S, SW. First one will be SE. That one will house 3 large hot water panels, and probably 6 PV. They are 3/8" difference in height, same width.

Been looking really hard at that Tabuchi Enetelus 25kw inverter Battery Hookup is selling for $1000, plus shipping. I researched Tabuchi (Japanese) a lot, and they make very high quality products. The US operation closed down in California so a bunch of those inverters are sitting around. That model has 6 MPPT strings, and (6) 4.1 kwh inverters. MPPT range is 500 watts, system start-up is something like 140. Have to double check that. Massive overkill for my project, but lots of positives. Don't need 3 phase, but I have a 3 phase distribution panel with breakers sitting in storage, a 3 phase disconnect, and I can buy a transformer for $300-$600. The Tabuchi allows you to shut down and work on one string, while still keeping the others online producing power. I'm also very interested in the much cheaper Delta H6. In all cases, my intent is to generate power for our consumption, and gradually feed multiple smaller PV systems into our loads, and batteries. With my recent battery purchases, I'm now at about 60kw. Will buy much more than that. If possible, I will go off-grid, but have a grid connection for back-up.

Also want to mention that I'm seriously considering buying a cheap, small commercial building that has a super good solar site, and an ideal roof structure to put it on. Or, ground mount. 3-phase service runs right past the building, so would hook it up to 480v. The electrical in that building is woefully outdated, and would be torn out immediately after purchase.

The Tabuchi allows for direct wiring to the unit, without combiner boxes. A real downside would be lack or service,lack of warranty. I'd probably buy a spare.

Please, fire away with suggestions.
 

prepared1

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Checked out the stats:

500-800v MPPT range
Min input voltage 140
Starting Voltage 200
6 MPPT, 10A each
1000 volt max input.

Tabuchi calls this a bargain mega-watt system inverter. I saw a block diagram, and it looks like the 6 MPPT all feed into the inverter input in parallel. Not sure if this info will help.
 

daromer

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"MPPT strings, and (6) 4.1 kwh inverters. MPPT range is 500 watts"

Its kW when you talk about the strings power. kWh is amount of energy/power over time :)

MPPT range is not in watts. Its in Volt.

Just a friendly reminder :)
 

prepared1

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So Daromer, would you please comment on the practicality of using a large scale inverter like that, but only use 20-50% of its capacity? Is it a bad idea? One thing I don't know is if you lose the grid connection, can you still use that inverter at all? As I've stated, I don't care to sell back energy, at any point.

Thank you in advance.....
 

Roland W

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So Daromer, would you please comment on the practicality of using a large scale inverter like that, but only use 20-50% of its capacity? Is it a bad idea?

Inverters typically have their peek efficiency at around 75% of max output, but they will not be more then 5% less efficient elsewhere
 

daromer

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As roland said every inverter have its sweat spot. If you also add in the idle-load or more called self-consumption a larger inverter have alot larger self consumption than a small inverter have.

Example my 3phase 10kW use 240W in it self compare to a 5kW single phase use 80W.
 
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