They are not system losses, it is clipping. The inverter can only produce 3.6kW AC. If it has 4kW of DC coming from the PV there will be 400W left over that could go to the battery if it wasn't full. But it is full so it's clipped.
Solar Panels being clipped /limited on Inverter Input
- Thread starter JonesyJT
- Start date
wattmatters
Solar Wizard
The graph says 4.03 kW are being generated by the PV array.
No monitoring system can show you production which is not generated.
If the battery was full and PV was being clipped, it would be clipped to 3.6 kW. But it's not, so where is the spare 400 W going?
To suggest that the 400 W just disappears into thin air breaks the first law of thermodynamics.
But that's exactly what MPPT does. It samples output and applies the required resistance to extract most power from PV. Presumably it does this by checking the voltage from each string and making some assumptions. So it's possible for it to only use 3.6kW but know that 4.03kW are potentially available without having to use the full 4.03kW.
wattmatters
Solar Wizard
Nonsense.
Go read up on MPPT before you dismiss what I am saying. There are apparently multiple strategies used to optimise power output but they all require the system to know what the panels are doing without applying full load.
Maximum power point tracking - Wikipedia
I'm referring to the quote that referenced my system, you didnt expand the picture I was referring to.
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wattmatters
Solar Wizard
This is not about MPPT algorithms. That's a complete red herring.
This is about the DC power output from the PV array, as measured by the inverter. If 4 kW is being generated by the PV array, then it has to go somewhere.
wattmatters
Solar Wizard
Ah, you were talking about this one below from an earlier post, where there is a missing 177 W:
Rather the one skylink posted in this post below:
Solar Panels being clipped /limited on Inverter Input
What's the mystery? The Inverter is putting out 3.6KW as rated. In the third picture the house is getting 2.7KW and the Battery is being charged at 840W. The Inverter is using 3.8KW to do this and about 200W is being lost in the conversion. Any extra power the panels could produce during the...
diysolarforum.com
Where there is a missing 400 W (in the first image).
My point was that it's possible for the inverter to know that the PV is currently capable of generating 4kW without actually using it as this is exactly what MPPT does. It doesn't have to go somewhere if it isn't actually being generated.
wattmatters
Solar Wizard
Your chart however does show it being generated. So where is it going?
Bud Martin
Solar Wizard
- Joined
- Aug 27, 2020
- Messages
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To get Watt reading there must be current flow through a load some where, you can have Voltage present at the power source but if no current flow then there will be no Power, to have a measured power of 4KW, that means there is current flow some where.
My point is that the inverter has an MPPT of 7kW and it can tell what the potential output of the PV is without using the full load. It's not a massive stretch to assume that they could display that potential power output on the screen even if it is only using half of it. The alternative is that this unit is soaking up 400W which I doubt.
Sorry but there is no input to a MPPT that tells it potential power from the panels. It uses what it finds up to the limit of its charge current output if any load exists. Panels do not generate power without a load. If you are getting a reading for power than the equation of W=VA must balance.
As I said earlier, just by looking at the voltage you can calculate what the potential output of the PV is. You don't need to be drawing 4kW to measure 4kW.
Still incorrect. In your quote "the controller measures incremental current and voltage changes" You can not measure current without a load. Without a load the panels output Voc. Panel voltage under a load changes and therefore the MPPT can use this to calculate the point where voltage and current create the most wattage.
Okay, you are correct then. The inverter is just losing >400W. Happy?
You've completely ignored the bit that says "The current from the array can be expressed as a function of the voltage". A lot of clever people here all willing to accept that the inverter is soaking up >400W continuously. Quite impressive for a unit without a fan.
Let me try once more. W=VA
The statement that "current from the array" can off course be explained as a function of the voltage. See the equation above.
I really wish people would stop using the word "clip" to suggest that power from panels is being removed somehow. Potentail power from panels is only relevant if you load them. Rated power for panels depends on STC (standard test conditions of solar irradiance) and is a variable if STC does not happen.
For instance if your MPPT charger has a maximum charge current of 10a at 14.5v. That equals 145w. It will only load the panels till it achieves this (plus internal power conversion loss). The panels may be capable (potential) in full sun to provide 1000w. They however only see a 145w draw. The MPPT loads the panels but it does not care that there is 1000w-145w=855w potential not being used. Nor does it read out to the user "hey buddy you have 855w available." it does not know that since it does not need more than 145w. In order to know that it takes more than a voltage amount since voltage without amperage does not equal watts.
If your unit is accurately measuring 400w more than it is delivering to a load than it is losing it internally.
I'm emailing Sunsynk right now to let them know that their inverter efficiency is actually only 87% and not the 98% they claim. They will need to update their spec sheets.
I doubt you will get them to do that based on your testing of your unit. I expect their testing for their product of 98% efficiency was accurate (whatever the basic test conditions were).
They might (if they have good customer service) ask you to send your unit in for testing/repair.
