Measurement question ...

[offgriddle]

A wattmeter reads how many watts are flowing through the meter on the way to a load, therefore, a wattmeter cannot necessarily give an accurate, maximum, reading of how many watts a panel array is producing, UNLESS, the load is asking for 100% or more of what the panel array is capable of producing.

If my above brilliant statement is correct, how then does a person know exactly what their maximum PV wattage production capability is if they do not have a proper and known load to test with?

Thanking you in advance.

OG.

 

[svetz]

Ensure the load is more than the panels can produce, then measure what they're outputting.
Go grid-tied, those inverters act as current sources so they'll jack up voltage to ensure they're pushing 100% power.

 

[DThames]

" maximum PV wattage production capability ", you have to trust the specifications of the panels or test them. What they can actually produce is very much temperature dependent. Actually getting the rated power doesn't happen very often, if ever.

One of the panel ratings is voltage at max power. Under ideal sun conditions, load the panel down to that voltage and read the watts. A good MPPT controller does that dynamically under different solar conditions. They will "milk" the panel for the best watts under the current conditions, varying the load to maintain peak power.

What is the context of the question?

 

[offgriddle]

Ensure the load is more than the panels can produce, then measure what they're outputting.
Go grid-tied, those inverters act as current sources so they'll jack up voltage to ensure they're pushing 100% power.

Understood but the greedy grid is not even near me and it's not going to be anytime soon.

Here's some testing data as taken at the panel rack:

Our test load consisted of a new Bluetti EB240 that was discharged to about 40% when we used it's built in wattmeter to test the output of each panel individually and then in parallel.

The Bluetti's specs. state a maximum input of 500 watts.

Each of the three panels at test time were producing 110 watts @ 21 VDC.

When all three panels were connected using the factory three way, parallel Y connectors. they cumulatively produced only 185 watts at 21 VDC according to the Bluetti's wattmeter readout. RED FLAG, shouldn't that have been about 330 watts?

The 42 volt, 5 amp DC output shore power charger supplied with the Bluetti charges at 215 watts according to the Bluetti's readout.

Is there a problem with the new Bluettti's built in MPPT charge controller that prevents it from taking in the rated maximum of 500?

 

[offgriddle]

" maximum PV wattage production capability ", you have to trust the specifications of the panels or test them. What they can actually produce is very much temperature dependent. Actually getting the rated power doesn't happen very often, if ever.

One of the panel ratings is voltage at max power. Under ideal sun conditions, load the panel down to that voltage and read the watts. A good MPPT controller does that dynamically under different solar conditions. They will "milk" the panel for the best watts under the current conditions, varying the load to maintain peak power.

What is the context of the question?

Understoood that panel output is subject to a variety of variables.

Here's some testing data as taken at the panel rack:

Our test load consisted of a new Bluetti EB240 that was discharged to about 40% when we used it's built in wattmeter to test the output of each panel individually and then in parallel.

The Bluetti's specs. state a maximum input of 500 watts.

Each of the three panels at test time were producing 110 watts @ 21 VDC.

When all three panels were connected using the factory three way, parallel Y connectors. they cumulatively produced only 185 watts at 21 VDC according to the Bluetti's wattmeter readout. RED FLAG, shouldn't that have been about 330 watts?

The 42 volt, 5 amp DC output shore power charger supplied with the Bluetti charges at 215 watts according to the Bluetti's readout.

Is there a problem with the new Bluettti's built in MPPT charge controller that prevents it from taking in the rated maximum of 500?

 

[Deleted member 165]

Make sure your batteries are low enough that the SCC is throwing full power at them. Viola!

 

[offgriddle]

Make sure your batteries are low enough that the SCC is throwing full power at them. Viola!

I know what you mean, but shouldn't a 2.4k watt lithium ion call for a hefty amount of wattage when it's only about 40% full?

 

[Ampster]

how then does a person know exactly what their maximum PV wattage production capability is if they do not have a proper and known load to test with?

If you have a hybrid inverter connect it to the grid athe grid will present the load. If entirely off the grid keep plugging in high Wattage devices until your inverter starts pulling from the batteries.

 

[offgriddle]

If you have a hybrid inverter connect it to the grid athe grid will present the load. If entirely off the grid keep plugging in high Wattage devices until your inverter starts pulling from the batteries.

No grid here at all but thank you I do understand what you are saying.

 

[Ampster]

shouldn't a 2.4k watt lithium ion call for a hefty amount of wattage when it's only about 40% full?

The charge controller will limit the Amperage. That is a user setting up to the max of the controller.

 

[Deleted member 165]

I know what you mean, but shouldn't a 2.4k watt lithium ion call for a hefty amount of wattage when it's only about 40% full?

One would assume, yes.

 

[offgriddle]

The charge controller will limit the Amperage. That is a user setting up to the max of the controller.

The Bluetti can handle a maximum charging input of ten amps and I believe it's factory set in this model but I would have to confirm that. But one nagging question is, why don't three PV panels each producing a confirmed 110 watts individually = 330 watts when connected in parallel?

 

[Deleted member 165]

Measured at 110 each?

 

[offgriddle]

Measured at 110 each?

Yes, we brought the 40% charged Bluetti out to the panels and plugged each panel individually into the Bluetti MPPT cannon plg input and at that time each panel was producing 110 watts according to the wattmeter readout on the Bluetti, but when all three panels were combined in parallel, the watt meter only read 185 watts! I did not "ohm out" the three way connectors to see if there was a short or open or high resistance to DC in either of them, my assumption is they are okay being new and all ..

 

[DASH]

I assume all three panels were in full sunshine, no shading. Have You tried using two panels? Are all the panels the same (specs, manufacturer etc). You might want to try reconnecting them differently, to see if You get the same results.

 

[RCinFLA]

If panels are not closely matched, which can also be caused by one panel being hotter temperature-wise then others, then the Vmp found by controller will be a compromise between the parallel panels resulting in lower summed power output. This is why panels facing different directions should not be feeding in parallel the same MPPT controller input even when matched panels used.

When you disconnect a panel it will dissipate the normal output electrical power more in heating, within panel, then a panel outputting electrical power. Or another way to think of it is a panel is 20% efficient so heating will go up by absorbing about that much more heating power. The light energy must go somewhere.

The process of leaving a panel disconnected can heat it up a bit more creating more mismatch to cooler panels. It doesn't damage them in any significant way and when they all get back to same temp everything should be fine. However in your measurement the illumination conditions may have changed so you cannot say I will just wait until they all stablize to same temp before reading power.

Do not try to interpret this by looking up temp coefficient of panel and saying it is insignificant difference in produced power. That only works for individual panels. When put in parallel a small difference in matching can make a big difference in total output., It is like putting two diodes in parallel, each diode will unlikely pass half the current unless closely matched and at the nearly exact same temps.

 

[svetz]

... one nagging question is, why don't three PV panels each producing a confirmed 110 watts individually = 330 watts when connected in parallel?

Yet another reason to like Enphase microinverters, no mysteries like this.

The only things that come to mind is environmental change (e.g., a cloud... but not likely as you would have noticed), the connector/cable is bad/corroded, the panel voltages are different enough after aging that the most powerful is suppressing the weaker via MPPT maximizing for it at the detriment of the other two (although the Bluetti said 21V for each, so that doesn't seem likely), or a combination of things.

Assuming it's not a bluetti thing (e.g., it's purposely dialing back the wattage) I guess I'd have to go with the most likely... ghostwriter66's #1 pick, the connector/cable.

What sort of power do you get from them if they are in series or the power from two in parallel (using panels A+B, B+C, and A+C)?

 

[DThames]

Power distribution between the source and the load is not something obvious. The source's internal resistance, the wiring/connector resistance, and the internal resistance of the charger(load) create a series circuit. Your panel will only produce the watts that the load is demanding. If you want to really test the panels, build a load bank (parallel resistors or incandescent lights) and adjust the load (more resisters or more lights) to load the panels to the max power voltage rating. Then read the watts. You have very little control over the load that the charge controller produces, so no way for a real test. A real guess, maybe, not a test of the panels.

(edited)

 

[svetz]

Couple of more ideas...

• Could your Y connector have a faulty blocking diode?
• While testing charging, put a big load (heat gun?) on the bluetti DC or AC output (depends on the manufacturer/model, but some will both run the load and charge from solar, so if with no load it's trimmed back the input wattage perhaps that will convince it to stop that).

Let us know what you find. Really curious about this now.

 

[offgriddle]

I have resistance and continuity tested the "Y" cables that connect three, new, Rich Solar, 160 watt panels in parallel and they are fine. YET, when the three panels are each producing 110 watts, the aggregate wattage is a measly 185 watts instead of 330 watts? Why oh why Will, (dropping to knees and shaking fist theatrically at the sky then crumbling into the fetal position whilst sobbing)?