Solar array not delivering expected power

[jehsom]

Hi all,

I am trying to figure out why my solar setup doesn't deliver much power.

I have 2 x 200w solar panels on my Northwood Arctic Fox 25W trailer.

I have never gotten more than about 160-180w total from the charge controller, and I'm not sure why. Even when the house batteries were low and the sun was overhead, and the panels were windexed clean.

My Solar Mate SP100-40 MPPT charge controller only shows output power not input, so I can't tell how much power they are actually sending into the MPPT.

I noticed that if I covered EITHER ONE of the panels with a blanket, the MPPT output would go to zero, even though the other panel was receiving sun. Is this expected behavior? Because the panels are facing different directions, and if it can only output 2x whatever the less active panel is sending, then that would make sense.

Trying to make sense of all this. Thanks for any help!

[hamm2018]

Originally Posted by jehsom

Hi all,
I noticed that if I covered EITHER ONE of the panels with a blanket, the MPPT output would go to zero, even though the other panel was receiving sun. Is this expected behavior? Because the panels are facing different directions, and if it can only output 2x whatever the less active panel is sending, then that would make sense.

Trying to make sense of all this. Thanks for any help!

I would think you have the panels wired in series, as it is taking out the system.
Wired in parallel, would still allow output.

[SafariBen]

I'm not familiar with the panels or controller. If the panels were parallel, the output should drop in half if one is covered. With an MPPT, I'd expect they're in series, but the panels should have bypass diodes so one would still produce with the other covered. Possibly one panel is not high enough voltage to meet the minimum for the MPPT, or they do not have bypass diodes.


The panels should be pointed the same direction. The amperage of the series panels will be limited to the less exposed panel, but that's not the big factor here.


The other half of the equation is the batteries have to be able to take the charge, so you won't get 200W into one nearly full battery no matter how many KW of solar you have. Have you tried putting some load on the system to see if the output goes up?

[atreis]

A handful of random thoughts that might be relevant depending on the specifics:

Some inexpensive older panels don't have bypass diodes, which allows one panel to continue to supply power even if the other is covered. Most modern panels have them.

If you're using flexible panels mounted directly to the surface of the roof without an air gap beneath them, they can overheat and the amount of power they produce drops significantly. Over time, it also causes the panels to degrade faster.

The angle of incidence that the sun is hitting the panels at matters A LOT. Panels ratings are for ideal conditions, with the sunlight hitting the panels directly. https://www.teachengineering.org/con...2_tedl_dwc.pdf There's also a nice graph here: https://www.quora.com/What-is-the-re...ogarithmic-etc

Resistance in the wiring between the panel and the solar charge controller could be causing significant losses if the wiring is undersized. Wiring panels in series, like yours appear to be, helps to reduce losses, but if the wire wasn't properly sized you could still have significant losses.

[d23haynes57]

Originally Posted by jehsom

Hi all,

I am trying to figure out why my solar setup doesn't deliver much power.

I have 2 x 200w solar panels on my Northwood Arctic Fox 25W trailer.

I have never gotten more than about 160-180w total from the charge controller, and I'm not sure why. Even when the house batteries were low and the sun was overhead, and the panels were windexed clean.

My Solar Mate SP100-40 MPPT charge controller only shows output power not input, so I can't tell how much power they are actually sending into the MPPT.

I noticed that if I covered EITHER ONE of the panels with a blanket, the MPPT output would go to zero, even though the other panel was receiving sun. Is this expected behavior? Because the panels are facing different directions, and if it can only output 2x whatever the less active panel is sending, then that would make sense.

Trying to make sense of all this. Thanks for any help!

Do you have battery monitoring, voltage and current in-out of the bank? Ideally the best 400 watt panels will do is ~20 A/H. That is a 5 hour rate for a 100 A/H battery

[rarebear.nm]

Low sun angles can reduce panel output by about 30%. So depending on your latitude and if you referring to winter time usage I think that your numbers are about right.


There is so much we don't know about your setup: Latitude, panel mounting, flat or curved roof, bypass diodes, type of cells (poly or mono), gauge of wires in the roof down haul and wires from controller to batteries. All of these play into the total output.


I typically figure installing about 30% more panel wattage than rechagring calculations indicate as being needed. For example a new install I'm designing now I want about 600 watts usable, so I'll install 800 watts on the roof.

[shoreco]

Normal output is about 50% of the total wattage....then you need to consider having the panels wired in series or parallel....

Good info here about the two set ups...


https://www.renogy.com/blog/solar-pa...s-vs-parallel/

[rarebear.nm]

Originally Posted by shoreco

Normal output is about 50% of the total wattage....then you need to consider having the panels wired in series or parallel....

Good info here about the two set ups...


https://www.renogy.com/blog/solar-pa...s-vs-parallel/

I've never published numbers like "Normal output is about 50% of the total wattage." What are your sources for this low value? In some environments I can understand a 50% value but not in general.


The big factors in difference between rated and realized value is the weather and solar angle.

[shoreco]

Originally Posted by rarebear.nm

I've never published numbers like "Normal output is about 50% of the total wattage." What are your sources for this low value? In some environments I can understand a 50% value but not in general.


The big factors in difference between rated and realized value is the weather and solar angle.

I guess I should have added Im.from NY....and my.50% values are true experience....my panels are flat.on the roof....

..

[Stircrazy1]

Originally Posted by jehsom

Hi all,

I am trying to figure out why my solar setup doesn't deliver much power.

I have 2 x 200w solar panels on my Northwood Arctic Fox 25W trailer.

I have never gotten more than about 160-180w total from the charge controller, and I'm not sure why. Even when the house batteries were low and the sun was overhead, and the panels were windexed clean.

if I remember right the panels on the artic fox are on the sides in the middle so one angle to the left and one angles to the right so that means while one will be outputting good, the ac and the angle will be effectively reducing the output of the other. the best thing some one could do is get the rack added to the back and relocate the solar panels there so they are both flat to the ground not angles and remove the ac obstruction between them that shadows the panels in the morning and evening. also wiring them in series once they are moved and adding a MPPT charger will do wonders also. a MPPT might even improve them as they are right now to an acceptable level.

[Stircrazy1]

Originally Posted by shoreco

Normal output is about 50% of the total wattage....then you need to consider having the panels wired in series or parallel....

Good info here about the two set ups...


https://www.renogy.com/blog/solar-pa...s-vs-parallel/

that's not normal at all, the rated output is what you should see in ideal conditions, if they are flat and not on an angle then you will loose about 10% then as you travel away from the "perfect solar location" you will lose power. I think where I live up north we are rated for 75 to 80% of the output you would get at the equator and - 10% should be 65% roughly but in actual practice for the real 4 hours a day when I am running my 325 watt system give me 306 watts on a 325 watt panel so that is 94% of the rated output being up north in canada on a flat mounted setup with a MPPT controler. on the other hand my 480 watt setup ( three 160watt 12V panels in parralell) in my 5th wheel on a PWM setup only gives me 59%. that one is getting upgraded to 24V panels and a MPPT charge controler. so the charge controler makes a huge difference as well as the charging voltage.

my camper will be charging with 0.5amp at 7am where my 5th wheel doesn't even start charging till 9 am.

[hclarkx]

The issue has been pretty well covered. Some thoughts though ..

Covering one panel probably drops the voltage below that needed for the MPPT controller to develope power. I.e., about 16 volts, sometimes higher.

As noted above, having different angles is costing you power though if the difference in angle is around 20 degrees or less, it's probably not worth correcting.

If the panel full sun open circuit voltages total less than about 30 volts, you are going to lose some potential production early and late in the day and this will be compounded by the less than ideal angle matching.

MPPT controllers lose about 4% of the solar energy flowing through them, so this isn't much of a factor.

If you have lead-acid batteries, you will see available power only until the state of charge gets up to around 70-80% then the solar controller output will drop regardless of sun conditions. With LFP batteries one can see charging right up to sunset (or until the battery is full).

New York isn't an ideal location for solar. If you want to play a bit, bring up the NREL PVWatts solar calculator and input your data to get a look at the power you should be able to produce. The program does not allow panels at different angles so results will be a bit optimistic. PVWatts also does not know your shade situation so may be optimistic in that regard as well. But, it will take into account atmospheric conditions which vary based on weather. Look at the hourly data to see maximum power (on days when PVWatts is assuming full sun).

[hclarkx]

The issue has been pretty well covered. Some thoughts though ..

Covering one panel probably drops the voltage below that needed for the MPPT controller to develope power. I.e., about 16 volts, sometimes higher.

As noted above, having different angles is costing you power though if the difference in angle is around 20 degrees or less, it's probably not worth correcting.

If the panel full sun open circuit voltages total less than about 30 volts, you are going to lose some potential production early and late in the day and this will be compounded by the less than ideal angle matching.

MPPT controllers lose about 4% of the solar energy flowing through them, so this isn't much of a factor.

If you have lead-acid batteries, you will see available power only until the state of charge gets up to around 70-80% then the solar controller output will drop regardless of sun conditions. With LFP batteries one can see charging right up to sunset (or until the battery is full).

New York isn't an ideal location for solar. If you want to play a bit, bring up the NREL PVWatts solar calculator and input your data to get a look at the power you should be able to produce. The program does not allow panels at different angles so results will be a bit optimistic. PVWatts also does not know your shade situation so may be optimistic in that regard as well. But, it will take into account location and atmospheric conditions which vary based on weather. Look at the hourly data to see maximum power (on days when PVWatts is assuming full sun).

[Marine359]

You can figure out quickly what the panels are doing with a clamp multimeter. When they’re in full sun, disconnect the panels from the gland and put the negative probe into one of the mc4 connectors, and positive probe into the other. The multimeter should display Voc (open circuit voltage). Vmp (maximum power point voltage) is usually a couple of volts less than Voc. The charge controller uses Vmp to convert to output charge amperage. Reconnect the panels to gland and clamp around one of the cables before it enters the gland. If your panels are wired in parallel, they will be connected to a parallel harness, and Vmp will be equal to the Vmp of a single panel. In series, no harness is needed, and Vmp will be the sum of the voltage of both panel. The Imp (maximum power point current) you measure should come close to the wattage rating of the array divided by Vmp. If these numbers are close the the manufacturer’s ratings for the panels, the panels are good. If not, test each panel individually to find which one is faulty. If one of the panels is bad, the manufacturer will replace it under warranty if you show them photos of your multimeter tests. If both panels test to spec, as mentioned by others, likely culprit is a full battery. If battery is full, charge controller will reduce current so as to not overcharge the battery. You should also check to ensure your charge controller is programmed for the type of battery you have. If it’s not, output current from the charge controller may be wrong for your battery.