I have the
growatt 3000 LMV 48es with the following specs:
Max PV Input: 4,000W
Max Charging Current: 80A
Max MPPT Operating Voltage 250VDC
It's my understanding that going over the MPPT Operating Voltage is the biggest factor that break things so i'm designing my 4 solar panel arrays like so
That is either 1) incorrect or, at best 2) misleading.
MPPT charge controllers have a few ratings.
- The maximum input voltage is the one which, if exceeded, will result in damage or malfunction.
- The operating voltage is the range in which the MPPT will perform the MPPT algorithm and maximize production at a given light level.
What you have listed, 250VDC, is the maximum PV array open circuit voltage.
It also happens to be the top of the operating voltage 120VDC to 250VDC.
200V operating volts (well below the 250VDC to be safe)
40Amps ( 4 10 amp arrays in parallel)
I have not seen a solar panel with a data sheet value for "operating volts" - and if there was one, it should be a range, not a single voltage.
What you need to check is the panel's maximum voltage, which is generally stated as the "open circuit voltage" or Voc (or VOC, or "voltage open circuit").
So if your panel has a Voc of 48VDC, then the simple calculation is to string 5 of them and at 1KW/m of solar input, and at room temperature, the panel string will not exceed 240VDC, which is 10V less than the MPPT controller's maximum voltage input.
However, the Voc is NOT the maximum possible open circuit voltage of the panel. At lower temperatures, and/or high solar input, the panel can reach higher voltages. You'll want at least a 10% margin, so if you have 48Voc panels, you'd be safe at 4 per string (under 200VDC Voc), but you'd risk damaging your MPPT controller with 5 panels per string.
The reason I'm trying to be clear about this distinction is that the panels often also have a Vmpp rating - which some think of as their "operating voltage" - a term you are using but not defining, and which isn't a standard term in the solar industry. This voltage is the typical panel voltage when it's operating at its highest efficiency given the standard testing conditions (lighting and temperature, primarily).
If you string the panels so the total Vmpp is 200VDC (about 6 panels) then you're going to fry your controller immediately because the solar panels, with no load (ie, open circuit) will be around 290VDC. (assuming a panel with 48Voc, which has a 37Vmpp - use your own panel values to check)
His will however produce 8000 watts of solar. (over the stated 4000w max)
There have been many people stating to simply not go over the amps and you should be fine. (
as stated in this post)
Is this ok? Will it fry my Growatt? Has anyone over paneled this way on a growatt?
Overpaneling is the practice of putting more panels on one charge controller than it's rated for in terms of wattage. When overpaneled the maximum voltage should NEVER be exceeded under any environmental conditions (light and temperature, primarily), but the maximum wattage can be. So your unit has a maximum charger capacity of 4000W. If you put 5000W of panels on it, but they could never exceed the maximum voltage, then it would be considered overpaneled.
First:
There is no guarantee that the MPPT controller in the inverter will be fine with over paneling. Growatt does not provide documentation or advice regarding this practice, but they do not specifically forbid it in their manuals. You are on your own, and while I haven't heard of anyone having warranty issues with over-paneled Growatt inverters, I suppose they could deny coverage for that reason.
Second:
Many, many, many people and companies overpanel Growatt MPPT controllers. Whether it's because they live in a sun-poor area, or have to mount their panels at suboptimal angles, or they just want to use the inverter at its maximum power all the time, it's a very common and generally safe practice.
Third:
The MPPT algorithm starts at the unloaded voltage with 0A of current. It starts to draw current, which due to the way solar panels work, will naturally cause the voltage to drop. It will increase the current in steps until it finds the maximum power point OR it reaches its own internal maximum power limit. So a 4000W charge controller that's overpaneled to 5000W with 5000W of solar power actual available (cold, sunny day) will stop increasing its current draw once it reaches 4000W of power. If the solar panels increase their power, it will reduce the current, if they reduce in power it will continue to adjust the current until the MPP is found. It continues to adjust the current draw throughout operation to maximum power input and keep under its own power capacity limits.
So, in general, the MPPT algorithm protects the charge controller from damage due to overpaneling. However...
Four:
From an electrical engineering standpoint there is likely to be a limit due to the algorithm itself, and the components chosen for the circuitry. A 4000W charge controller with an operating range of 120A to 250A would expect no more than 35A at the lowest operating voltage and the highest power input, and perhaps they only have a 10% margin so they choose a 40A transistor. The algorithm starts by turning the transistor on, and if a customer decided to overpanel significantly it might instead see 120A. Because they chose a slower processor and can't detect the fault fast enough the transistor, coil, capacitors, and other parts may fail.
They don't tell us what their margin is, or give us any maximum solar input current. Growatt gives a "Maximum solar charge current" but that, non-intuitively, relates to the maximum current it will supply to the battery at the battery voltage (48V), not the current it can accept from the solar array. It's used to help size the batteries (if your batteries can't accept this much current it can damage them).
I believe they know and accept that since you can't perfectly match solar panels to charge controllers then many installations will be slightly over paneled, particularly since most of the time the solar panels will not be pushing their maximum current. Further, other parts of the circuity will prevent or delay high instantaneous currents, and other parts of the circuitry can protect the overall charge controller from this sort of situation. So there is a margin, and the margin is significant.
Five:
Using your charge controller at its maximum ratings wears it down more quickly than using it at a lower power output. If you always run 4000W through the 4000W solar charge controller, it simply won't last as long as one run at 50% of its capacity most of the time, and at capacity only 5% of its time - which is typical for solar equipment. Further, it can handle faults better when it's at a reduced capacity than when it's running at full capacity.
Summary:
Overpaneling
- generally works and is safe as long as the other requirements are met.
- is generally not guaranteed to work by manufacturers beyond small amounts due to typical system sizing mismatches
- will reduce the lifetime of the charge controller
- will probably make the charge controller more susceptible to small faults
