Growatt 3000 Spec interpretation

[cwilken]

My Growatt 3000 has a Max PV input voltage of 145vdc. The MPPT volatage range says 60~120.
searching internet i find:
The MPP voltage range denotes the voltage range of an inverter in which the MPP Tracker of an inverter can set the maximum power point in order to operate the PV modules at maximum power. MPP is the abbreviation for Maximum Power Point.
If my input voltage (open circuit) is at close to the max with 142 vdc how does that affect the operation of my MPPT voltage range. What happends if my input is above the 120 specified for MPPT?

 

[wattmatters]

MPP is the abbreviation for Maximum Power Point

Yes.

If my input voltage (open circuit) is at close to the max with 142 vdc how does that affect the operation of my MPPT voltage range.

It's not recommended to be too close to the MPPT's voltage input limit.

Solar PV Voc goes up as temperature falls and Voc is rated at standard temp (25C) and conditions. If your panels experience cold, e.g. freezing then Voc will be up to 10% higher than the rating. If you experience below freezing conditions then leaving about 20% margin is probably wiser.

In any case, if the array's voltage is a bit above the MPPT's operating range (but not exceeding the MPPT voltage limit) it will still work, just less efficiently. Most likely it will just drop the voltage back to be within its preferred range.

 

[cwilken]

Yes.

It's not recommended to be too close to the MPPT's voltage input limit.

Solar PV Voc goes up as temperature falls and Voc is rated at standard temp (25C) and conditions. If your panels experience cold, e.g. freezing then Voc will be up to 10% higher than the rating. If you experience below freezing conditions then leaving about 20% margin is probably wiser.

In any case, if the array's voltage is a bit above the MPPT's operating range (but not exceeding the MPPT voltage limit) it will still work, just less efficiently. Most likely it will just drop the voltage back to be within its preferred range.

Thanks wattmatters... I currently have 2 panels in series for a measured voltage of 82v. Im wondering about putting 3 in series for 123v which slightly exceeds the optimum range. Would I make up for the small inefficiency by the fact that my inverter might have an easier job converting 123v DC to 120AC rather than 82v to 120AC?

 

[wattmatters]

Would I make up for the small inefficiency by the fact that my inverter might have an easier job converting 123v DC to 120AC rather than 82v to 120AC?

It's best to have the panel's operating/max power voltage Vmp (not open circuit voltage) sit within the MPPT's preferred operating range as per the inverter's specifications.

If your measured voltage was open circuit voltage, then Vmp will be somewhat lower. With my panels it's ~20% lower.

Vmp of panels will depend on conditions and should be stated on the panel's spec sheet (Google it). Depending on your cable run between panels and inverter, you can allow for a bit of voltage drop as well.

These inverters with the lower voltage inputs are a bit painful like that and is why 2S or 3S is common. Just be careful to ensure Voc won't go too high and I think you'll be fine with 3S. Voc is typically a fair bit higher than Vmp (with my panels it's ~20% higher).

My inverter has a Voc limit of only 105V and suggested panel Vmp in the 56-72V range (while 60-72V is the preferred MPPT voltage operate range). I have a 2S3P array of 370W panels. These panels each have a Vmp in the 31.5-34.1V range, so 2S means they'll operate (at max power) at around ~62-70V and that's right on spec.

With your Growatt I could run these panels 3S without issue.

 

[cwilken]

Thanks again for the comments. My measured voltages were Vmp through the inverter software. my VOC is 44v each measured and 47.5 according to the Manufacturor spec sheets. If I multiply manufacturers number by 3 I get 142.5 which is extremely close to the max VOC of 145. Los Angeles weather does get down to freezing point for a few weeks in the winter. Thats the only part that makes me hesitate to go 3S.

 

[wattmatters]

My measured voltages were Vmp through the inverter software. my VOC is 44v each measured and 47.5 according to the Manufacturor spec sheets. If I multiply manufacturers number by 3 I get 142.5 which is extremely close to the max VOC of 145. Los Angeles weather does get down to freezing point for a few weeks in the winter. Thats the only part that makes me hesitate to go 3S.

That's a high Voc. What size panels are these?

My 370W Longis have a rated Voc of 41.3V at STC.

 

[cwilken]

I have six JA Solar JAM6(K)-72-355 (355W) solar panels.

 

[wattmatters]

I have six JA Solar JAM6(K)-72-355 (355W) solar panels.

Yeah that's a high Voc. Maybe trade them for something else with a lower Voc so you can go 3S? Else stay at 2S.

 

[iamrich]

I have six JA Solar JAM6(K)-72-355 (355W) solar panels.

I would just run them 2S3P

 

[cwilken]

Yep...that works...I'm mounting them on my shed

 

[wattmatters]

Yep...that works...I'm mounting them on my shed

I can see why you'd prefer 3S2P with that array layout. It's better for panels in the same string to be oriented the same way.

I guess you can have one string with 2 of the panels on the left, another string with 2 panels on the right and one string with one of each. The last string will not perform quite as well as it will operate at the level of the lower performing panel, whichever side of the roof it is. The roof tilt is fairly slight so it won't be bad.

Sometimes with solar we worry too much about perfection in array arrangement.

 

[cwilken]

I can see why you'd prefer 3S2P with that array layout. It's better for panels in the same string to be oriented the same way.

I guess you can have one string with 2 of the panels on the left, another string with 2 panels on the right and one string with one of each. The last string will not perform quite as well as it will operate at the level of the lower performing panel, whichever side of the roof it is. The roof tilt is fairly slight so it won't be bad.

Sometimes with solar we worry too much about perfection in array arrangement.

I have one on each side put together in series which may be wrong. But Im thinking now that if they were 3s2p and it was a freezing cold day their orientation might prevent going over the VOC that I would be so close to because one side would always be a little skewed from direct rays.

 

[wattmatters]

I have one on each side put together in series which may be wrong.

I think with 2S3P you are better to configure the panels as I outlined as it will provide better output overall.
3S2P would be better again but you'd need panels with a lower Voc to be safe.

 

[iamrich]

I have one on each side put together in series which may be wrong. But Im thinking now that if they were 3s2p and it was a freezing cold day their orientation might prevent going over the VOC that I would be so close to because one side would always be a little skewed from direct rays.

I would run four panels on one side (two strings of two) and two panels on the other side (1 string of two). You want all the panels in the same string (2 or 3 regardless) facing the same direction. I would point the 4 in the best of the two directions.

 

[RCinFLA]

The 145v is based on breakdown voltage for controller MOSFET's. Should not exceed this voltage under any panel conditions.

Maximum possible Voc on panels is unloaded or possibly when controller is hunting for MPPT point when panels are cold. You may have to calculate the maximum cold Voc yourself based on lowest temp you expect your panels to see at your location. Panel spec sheet has the temp coefficient per degC to figure cold temp Voc from its listed STP reference temp Voc voltage.

All MPPT controllers hunt for MPPT by varying the load on the panels so the voltage will swing below and above true MPPT voltage while it is searching. Some controllers will just measure Voc at no load and start their wiggle search at 85% Voc which is normally close to MPPT voltage. Some controllers will throw an error message and not go active if Voc is detected to be too high. MOSFET breakdown voltage is lower when they are actively switching so checking Voc first before going active is a good way for controller to achieve more safety margin to danger zone.

 

[wattmatters]

I would run four panels on one side (two strings of two) and two panels on the other side (1 string of two). You want all the panels in the same string (2 or 3 regardless) facing the same direction.

There only looks to be room on that shed for 3 panels on each side.

 

[iamrich]

Yeah it looks like it will be close. Honestly I would probably run this 3S2P and risk it. I just don't think 1 panel per side is going to perform very well. Tough call....

 

[Tecnodave]

Maximum voltage from the panels will happen on that freezing morning at the crack of dawn as soon as the panels are light. The controller will be hit with a voltage that is 15 to 20 volts higher than the rated specs which will immediately destroy the mosfet’s in the input stage of the controller board. This is fatal.

 

[cwilken]

For now I have one panel on each opposite side connected together in a string of 2. These are ballast hung from hinges on the top. I will soon connect each set of three on a side with a bar and make some sort of device that can move 4 feet to lift the far side in the morning and then do the opposite in the afternoon. As it is Im getting 1400-1600 watts from 2000 watts of panels from 10:30 to 1:30 each day and use battery assist in the afternoons as the sun passes over. This is enough to run my 1100 watt AC all day which was my goal. But since Im retired and like making things I will design something to lift ~ 150 pounds on each side as a unit to be all the same angle as the other side. Probably a four foot piece of 1 inch all-thread and a bolt welded on a tube with one of them getting a high torque low speed motor. My neighbor suggested I design it so I can just attach my portable drill and zip it up or down once or twice a day. This way all panels can directly face the sun and give full power 2 or 3 times a day depending on how often I manually move them.

As my electronics improves I will program a device to move them incrementally to face the sun each hour either by time or by sun sensor devices.

 

[iamrich]

As it is Im getting 1400-1600 watts from 2000 watts of panels from 10:30 to 1:30 each day and use battery assist in the afternoons as the sun passes over.

Honestly, I think this is fantastic. 70-80% out of a less than optimal setup? I would take that all day long and be happy. I rarely see more than 1500 watts out of my 2250w setup and it is more than enough to run my AC and keep that batteries charged. I get power from 9am-6pm though.