Solar charging not getting maximum power

[Solar Hobby]

My first post.
There are 2 panels connected in series.
Pmax: 280w
Voc: 43.99v
Isc: 8.23a
Vm: 36.57v

Charging at maximum, it should charge at the speed of 280w*2 = 560w

Am I wrong? I was only able to charge at the speed of 360w

 

[MichaelK]

Couple of issues.

First, I like to de-rate panel specs to 85-90% for real-world production. Remember, panels are tested/rated in an artificial sunlight chamber held at 25 degrees C.

Second issue is the state of charge of the battery. As your battery reaches full charge, the charge controller will be tapering off the amount of current. For a true test of output, you need to put a load on your system that is as big, or slightly bigger than the rated output of your panels. Only under load at ~noon will you see full output.

So, wait till noon tomorrow, and switch on a toaster and go look at what the output is. Then you'll have the true output. I'll guestimate and say the most you are likely to see in the real-world is 475-500W.

 

[400bird]

If you are in the northern hemisphere, it's winter now and panel output is lower.
If you angle them perfectly, you might get 80% of name plate rating.

The rating is in lab conditions, not real world numbers.

 

[Solar Hobby]

You guys are genius. Adjusting the angle works. Was Abe to achieve 80%. Thank you everyone for your help!

 

[Tomthumb62]

You guys are genius. Adjusting the angle works. Was Abe to achieve 80%. Thank you everyone for your help!

Also, due to the winter conditions of the Norther Hemisphere, the length of usable daylight is much lower than in summer. We're just less than a week away from the winter solstice, the shortest day of the year.

Glad that the angle is helping more production, that's good! But still, production will be quite low in winter, unless you have a much bigger solar panel array to compensate (which will be way more panels than necessary in summer, lol!)

 

[Solar Hobby]

Also, due to the winter conditions of the Norther Hemisphere, the length of usable daylight is much lower than in summer. We're just less than a week away from the winter solstice, the shortest day of the year.

Glad that the angle is helping more production, that's good! But still, production will be quite low in winter, unless you have a much bigger solar panel array to compensate (which will be way more panels than necessary in summer, lol!)

How do you mean by have a much bigger solar panel array? Isn't over sizing the panel array dangerous and can render the mppt charger unless?

 

[Tomthumb62]

How do you mean by have a much bigger solar panel array? Isn't over sizing the panel array dangerous and can render the mppt charger unless?

Well of course you don’t put more volts into your MPPT than its rated for (if you live in a region that gets cold, you’ll want to be sure to stay well below the max PV volts input.)

So you’ll likely have more than one MPPT.

If you need 10 panels to get through summer and 25 panels to get through winter, your setup might look like this:

12 panels on one MPPT, 12 on another and that lonely last panel on a cheap PWM controller.

In summer, you’ll simply produce more solar than you’ll need. But in winter you’ll get by.

Some people who live off grid size their systems this way. Others go with a smaller system and run a generator for 2-4 hours a day.

Edit to say: again don’t go over your MPPT’s max volts input. So you’ll not be able to do 12s in this case. Perhaps 6s2p or more likely 4s3p or even 3s4p. The last two scenarios will require fuses or a fused combiner box since it’s more than 2p. You do NOT want to skip out on these fuses - skip them and if one panel shorts out, it could lead to a fire. Fuses will prevent that from happening.

 

[Solar Hobby]

Well of course you don’t put more volts into your MPPT than its rated for (if you live in a region that gets cold, you’ll want to be sure to stay well below the max PV volts input.)

So you’ll likely have more than one MPPT.

If you need 10 panels to get through summer and 25 panels to get through winter, your setup might look like this:

12 panels on one MPPT, 12 on another and that lonely last panel on a cheap PWM controller.

In summer, you’ll simply produce more solar than you’ll need. But in winter you’ll get by.

Some people who live off grid size their systems this way. Others go with a smaller system and run a generator for 2-4 hours a day.

Edit to say: again don’t go over your MPPT’s max volts input. So you’ll not be able to do 12s in this case. Perhaps 6s2p or more likely 4s3p or even 3s4p. The last two scenarios will require fuses or a fused combiner box since it’s more than 2p. You do NOT want to skip out on these fuses - skip them and if one panel shorts out, it could lead to a fire. Fuses will prevent that from happening.

Should I be concerned? It charges 550w out of the possible 560w panel rating for about 30 seconds. This is a simple 2 panels in series. Should I be using a fuse?

 

[Tomthumb62]

Should I be concerned? It charges 550w out of the possible 560w panel rating for about 30 seconds. This is a simple 2 panels in series. Should I be using a fuse?

Two panels in series doesn’t need fusing. As long as your total volts input doesn’t get close to the max PV volts input of your MPPT, you’re okay.

What is the make and model of your MPPT? And what is the Voc listed on the back of your panels? Finally, what is the coldest temperature recorded in the last 35 years in your location?

 

[Solar Hobby]

Two panels in series doesn’t need fusing. As long as your total volts input doesn’t get close to the max PV volts input of your MPPT, you’re okay.

What is the make and model of your MPPT? And what is the Voc listed on the back of your panels? Finally, what is the coldest temperature recorded in the last 35 years in your location?

Thank you for your inputs.

There isn't much information available for the MPPT. I have a portable power station Pecron E2000LFP.
From the website: 2*GX16MF: Voc 32V~95V / 600W Max / 15A Max (1200W solar panels input: 2~3 hours can be juiced up.)
Power station: PECRON E2000LFP Expandable Portable Power Station

Solar panel: Voc: 43.99

The lowest temperature recorded there during that period was 28 degrees Fahrenheit (-2 Celsius) on January 4, 1949.
Today's low: 55 degrees Fahrenheit.

When charging, the unit display watts. It doesn't display current. Not sure if the voltage is specificly for charging, as it does not display it as a primary source of information. It seems to be between 26 to 27 volts. The unit is a 24 volts system.

Per the 2 MPPTs, I have 2 panels in series per each of the MPPTs. There is a 3rd charging port. Not sure if it is MPPT. I am not using it, since it limits 100 watts.

There are also 2 fuses on the unit. There's no information available either. I don't think it is for the AC. When I was testing for an overload, the unit display the message, and shut down the AC. DC and everything else run normally. I just hit the AC button again to reset it. What do you think the 2 fuses are for?

 

[Tomthumb62]

From the website: 2*GX16MF: Voc 32V~95V

Solar panel: Voc: 43.99

43.99v times two = 87.98V

That’s awfully close to your max input of 95V.

At 28F, you’ll be at approximately 112% of your Voc, so that would be 87.98 x 1.12 = 98.5V. Which is over your max input of 95V and you’ll fry your MPPT. You’ll see the magic smoke escape, but you’ll only see it once and then you’re buying a new MPPT.

So with your panels you can put them in 2P. What is the Isc rating on the label on the back of the panels. That will determine what size wire you’ll need, since going in parallel will keep the voltage at 43.99v but double the amps.

 

[Solar Hobby]

43.99v times two = 87.98V

That’s awfully close to your max input of 95V.

At 28F, you’ll be at approximately 112% of your Voc, so that would be 87.98 x 1.12 = 98.5V. Which is over your max input of 95V and you’ll fry your MPPT. You’ll see the magic smoke escape, but you’ll only see it once and then you’re buying a new MPPT.

So with your panels you can put them in 2P. What is the Isc rating on the label on the back of the panels. That will determine what size wire you’ll need, since going in parallel will keep the voltage at 43.99v but double the amps.

Wow!

I am curious how do you get 112% from 28F?

Panel Isc: 8.23A
In parallel, would you recommend fuse?

 

[Solar Hobby]

Wow!

I am curious how do you get 112% from 28F?

Panel Isc: 8.23A
In parallel, would you recommend fuse?

Also, today's low is 55F. This is far from 28F. Can you elaborate on that?

 

[Tomthumb62]

Wow!

I am curious how do you get 112% from 28F?

Panel Isc: 8.23A
In parallel, would you recommend fuse?

PV array temperature correction table (NEC 2017)

There are calculators like this one made by @upnorthandpersonal which help you calculate PV array voltage and power for low temperatures based on the specific specifications of your panels. These are great tools and will give more precise...

diysolarforum.com

No fuse needed for 2P or less.

 

[Tomthumb62]

Also, today's low is 55F. This is far from 28F. Can you elaborate on that?

You’re safe today, but if it were closer to freezing, poof. Voltage goes up In the cold.

There’s a reason why there is such a thing like fans or liquid cooling in high end desktop computers. The electrons flow better at cooler temps. Which in the case of your specific MPPT, is not well suited with your specific panels in any type of series orientation.

Some MPPT will go poof if you simply get too close but don’t actually go over the PV input limit. In these cases, they provably were fibbing a bit on that limit to make their model look better than it is. Good rule of thumb is find out how cold you can go and then still keep a 10% buffer at minimum.

It’s possible in theory that your MPPT input limit is actually 100V and they’re trying to protect you by saying 95V, but I doubt it and there’s no real way of knowing unless you actually tested it.

 

[Tomthumb62]

When charging, the unit display watts. It doesn't display current. Not sure if the voltage is specificly for charging, as it does not display it as a primary source of information. It seems to be between 26 to 27 volts. The unit is a 24 volts system.

Measure voltage at the input terminals of your MPPT with a multimeter. It will read about 80-88 V. That’s the magic beauty of a MPPT - it converts those “extra” volts into more amps. Since you’re on a 24v system, charging needs to be about 26-28V for a 24v lifepo4 battery. So your MPPT is charging correctly at 26-27v.

 

[Solar Hobby]

Once again, thank you for your help!

Since Voc is so close to the max of the MPPT, maybe I’ll place a small hand towel over the panel corner if it doesn’t reduce the output by a lot. I couldn’t test it today, since it is cloudy today.

 

[Tomthumb62]

maybe I’ll place a small hand towel over the panel corner if it doesn’t reduce the output by a lot.

That won’t work. It will kill production of both panels.

If it’s not likely to get cold overnight in the next week or two, then you likely can get by to just fix this soon. If it’s going to get cold or could get cold, then you want to unplug your panels from the MPPT asap and rewire into parallel.

What AWG is your wiring from panels to MPPT?

 

[Solar Hobby]

That won’t work. It will kill production of both panels.

If it’s not likely to get cold overnight in the next week or two, then you likely can get by to just fix this soon. If it’s going to get cold or could get cold, then you want to unplug your panels from the MPPT asap and rewire into parallel.

What AWG is your wiring from panels to MPPT?

The extension cable is 12 AWG.

https://www.amazon.com/dp/B07XLHRC44?ref=ppx_yo2ov_dt_b_product_details&th=1