# Low amps produced by 100 watt panel? Why?

Registered Users Posts: 8
I'm a newbie so appreciate your thoughts.  What could I check on why I would only be getting 2-4 amps from my new 100 watt panel in direct sun?  From what I read, shouldn't I be getting about 6-7 amps?  I am running 10 amp wiring about 50 ft. from the panel to the charge controller and the temp is about 20 outside.
Thanks
«13

• Solar Expert Posts: 3,738 ✭✭✭✭
Joesv57 said:
What could I check on why I would only be getting 2-4 amps from my new 100 watt panel in direct sun?  From what I read, shouldn't I be getting about 6-7 amps?  I am running 10 amp wiring about 50 ft. from the panel to the charge controller and the temp is about 20 outside.
What is "10 amp" wire?  50 ft of it might have too much resistance and be limiting your current.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Registered Users Posts: 8
Sorry I meant 10 gauge wire.
Nominally, a 100 Watt panel would probably have:

100 Watts / 17.5 volt Vmp = 5.7 Amps Imp

Short the panel and measure your Isc in noon-time sun (use a 10 Amp DMM, or use a DC Current Clamp type meter).

And running 50 feet (one way run) at 4 amps on 10 AWG, the voltage drop would be:

http://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=3.277&voltage=17.5&phase=ac&noofconductor=1&distance=50&distanceunit=feet&amperes=4&x=51&y=5

Voltage drop: 0.40
Voltage drop percentage: 2.29%
Voltage at the end: 17.1

So, for a 6 amp run, significant voltage drop, but not enough to cause the 2 amp full noon time draw... Of course, this also depends your "loads"... A panel will only output as much as the charge controller will accept.

If the Isc is less than 50% of rated output on an average sunny day at noon time--Then the panel may be bad.

One repairable possible problem in the panel... If there is a shorted bypass diode or a bad blocking diode in the panel's Junction Box, you may be able to replace the bad diode.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 175 ✭✭✭
Another thought would be the state of charge of your battery(s), if they are around 90% I would not expect full output from the panel.
• Registered Users Posts: 8
Thanks for the ideas folks.  I have 2 100 watt panels (both new from Renogy) and they both are measuring about 3.2-3.6 amps and about 7-7.5 in parallel so looks like its not the panels.  This is in the midwest at 10 am, full sun.  Battery is at 60% soc.  I welcoome any other thoughts.
Thanks again.
• Solar Expert Posts: 3,436 ✭✭✭✭
Try measuring voltage before the connection to the charge controller?  If the voltage is where it should be, then your problems may lie elsewhere from the panels.
First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
• Registered Users Posts: 28 ✭✭
pwm controller?
small hobby/learning system in Toronto, Canada:
3x100w parallel via 30A PWM to old 12v car battery to 200w inverter for shed LED lights
(1x100w may-sept)
• Registered Users Posts: 8
Yes PWM controller from Renogy.  I called tech support today and they said that getting 3-3.4 max. amps in full sunlight is what they would call acceptable.  Doing my math the doesn't come close to even 80-90 watts.  Even reducing the wattage with my 50' of wire by 2-3% (thanks BB) this is rather disappointing.  When measuring the panel output only (unhooked from the wiring and controller) in bright sun today  I was getting 21 volts (good) but only about 2 amps so doesn't seem to be anything other than the panel not putting out what they claim.
• Registered Users Posts: 28 ✭✭
edited January 2016 #10
ah ha, good write-up here:

http://www.solar-electric.com/mppt-solar-charge-controllers.html/

The best I've ever gotten is 4.5A from my 100watt panel using my pwm charge controller at peak of summer 1pm...
The most I've seen in last few months this winter on very rare sunny afternoons is 3.5A, but I'm in Toronto, Canada...

small hobby/learning system in Toronto, Canada:
3x100w parallel via 30A PWM to old 12v car battery to 200w inverter for shed LED lights
(1x100w may-sept)
• Solar Expert Posts: 766 ✭✭✭✭

Welcome to the inefficiencies of PWM charge controllers.

I started with a PWM but quickly realized the benefit of MPPT. Come to the MPPT side, we have a lot more power. We have so much power we are tired of having so much power. Not struggling to charge the batteries take a lot of the excitement out of it. You might as well be on grid power.

Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

• Registered Users Posts: 8
Thanks guys. Mike49 sounds like I'm in the same ball park as you.
LOL Oil Pan so it sounds like MPPT might be worth the investment rather than returning my panels.  If you have any recommendations from Amazon I would appreciate it.  I'm still learning here and appreciate the input!
• Registered Users Posts: 28 ✭✭
edited January 2016 #13
I recently got a 2nd identical 100watt panel and put it in parallel with my 1st one.
Getting at best 7A total currently on rare sunny afternoon with my pwm controller. Pathetic, yes.
But my battery is getting charged fully now after every 2 days of totally no sun, so I'm happy.

I'm holding off on getting an mppt controller since my canadian dollar is in the dumps 70cents to the USD, so ordering an mppt from overseas is super expensive for me whereas getting another 100watt panel locally wasn't too bad.
When I eventually do get an mppt, I'll have so much power I won't know what to do with it just like Oil Pan 4

There are alot of fake mppt controllers out there, beware.
The lowest priced real one I've found so far are "Tracer" mppt controllers and I'll likely be getting one of those if my dollar is ever worth more than 70 cents again
small hobby/learning system in Toronto, Canada:
3x100w parallel via 30A PWM to old 12v car battery to 200w inverter for shed LED lights
(1x100w may-sept)
• Solar Expert Posts: 766 ✭✭✭✭
edited January 2016 #14

Yes there are a lot of fake MPPT controllers out there.

I can say for sure genasun and Morningstar are MPPT. My genasun for example runs at about 97.5% efficiency according to my fluke325 clamp meter.

The genasun 10 amp was about \$180 and the Morningstar 15 amp was about \$220. Worth it.

I run them in portable and vehicle applications, so I don't have the option to put up more panels.

If it says MPPT and then does not say Outback, Genasun, Morningstar, Midnight, Solar Converter inc., Blue Sky, Renogy then it might not be a real MPPT.

Here is our vehicle mounted solar panel wiki. Its geared towards vehicles but talks about charge controllers a little.

http://ecomodder.com/wiki/index.php/Solar_12v_assist

Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

• Solar Expert Posts: 5,183 ✭✭✭✭
edited January 2016 #15
May the MPPT be with you!

Have you looked at the MidNite KID?  or if you insist on PWM the BRAT?   Both 30A models... and shown on this page just 1 or 2 pages down  http://www.midnitesolar.com/
Look for pricing here http://www.solar-electric.com/inverters-controllers-accessories/chco/misoclchco.html

KID #51B  4s 140W to 24V 900Ah C&D AGM
CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM
Cotek ST1500W 24V Inverter,OmniCharge 3024,
2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
• Solar Expert Posts: 5,328 ✭✭✭✭✭
http://www.renogy-store.com/100W-12V-Monocrystalline-Solar-Panel-p/rng-100d.htm Here's a link to Renolgy 100 watt panels, Their rated output is 18.9 volts at 5.29 amps, I suspect being around 70% of their rated output, you are doing pretty good...
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
• Solar Expert Posts: 5,328 ✭✭✭✭✭
http://www.renogy-store.com/100W-12V-Monocrystalline-Solar-Panel-p/rng-100d.htm Here's a link to Renolgy 100 watt panels, Their rated output is 18.9 volts at 5.29 amps, I suspect being around 70% of their rated output, you are doing pretty good...
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Prosine 1800 and Exeltech 1100, 660 ah 24v ForkLift battery. Off grid for @16 of last 17 years. Assorted other systems, and to many panels in the closet to not do more...lol
• Registered Users Posts: 8
I'm learning guys...thanks a bunch.  SO if I'm pulling 3-6 amps in direct sun wth my 2-100 watt panels now with PWM, what might I expect with a decent MPPT controller?  SInce I don't antcipate expanding to more panels wondering if its worth it for 1 or 2 extra amps but for +3 or so it might be?
• Solar Expert Posts: 3,738 ✭✭✭✭
Joesv57 said:
I'm learning guys...thanks a bunch.  SO if I'm pulling 3-6 amps in direct sun wth my 2-100 watt panels now with PWM, what might I expect with a decent MPPT controller?  SInce I don't antcipate expanding to more panels wondering if its worth it for 1 or 2 extra amps but for +3 or so it might be?
What to expect with MPPT?  Depends on the temperature.   Are you familiar with STC and NOCT?

Standard Temp and Conditions (STC) is how panels are rated.   Rarely do you achieve STC output because in the hot sun the panels heat up and their output is reduced to Normal Operating Cell Temperature (NOCT) output.

In order to benefit from the cold temperatures (which raise Vmp) you will need an MPPT controller.   In hot weather there is much less to gain by switching from PWM to MPPT.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Solar Expert Posts: 3,436 ✭✭✭✭
There is sound logic in trying the Renogy mppt controllers on Amazon. Very reasonable priced, I am considering one for my back up 24 volt array. With this system, Renogy is far more likely to be of assistance if things go sideways.

Are you sure that all connections are sound? Have you checked for wire abrasion that could be shorting out power? Couple ideas...

Joesv57 said:
Thanks guys. Mike49 sounds like I'm in the same ball park as you.
LOL Oil Pan so it sounds like MPPT might be worth the investment rather than returning my panels.  If you have any recommendations from Amazon I would appreciate it.  I'm still learning here and appreciate the input!

First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
Measure the panel voltage at the panels, and the current of each panel (you could have one bad panel/electrical connection and MPPT will not "fix" that).

Personally, there are lots of reasons for getting MPPT charge controllers... But just to get (roughly) 10% typically more output in cooler weather is, many time, not worth the cost--Just get another solar panel instead.

I am not convinced that your panels/electrical connections are "good"... I would suggest getting a "good enough" \$60 DC Current Clamp DMM so you can easily measure their operating current.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 762 ✭✭✭
The Renogy panels I own have always met their specification under full sunlight, BUT do yourself a favor - open the junction box and take a look.

Quick manual manufacturing sometimes leaves loose terminal screws, "frog hairs" from stranded wire jammed into connectors, screws tightened down half-way over insulation etc.

They aren't bad panels, and work to spec, you just need to make sure the person on the line that day whipping these out wasn't distracted.

• Registered Users Posts: 8
Quick update.  Looks like after lower my expectations of what could "really" be achieved with 2- 100 watt panels it is performing as it should, getting between 6 -10 amps in direct sunlight.  I was unaware that they were measuring 100 watts as the output at 18-20 volts from the panel vs. me figuring it at 12 volts at the battery.  So in reality, getting 60 watts from a 100 watt panel is more realistic.
Thanks for the help.  Learning a lot!
• Solar Expert Posts: 762 ✭✭✭
I would try measuring them AGAIN like you did before directly at the panel with no load attached on a different day, and in the middle of the solar insolation period - ie, when the sun is practically directly overhead - or as much as possible in winter.  And no overcast, haze or so forth.

100w / 18v = 5.5A.  Each panel should be capable of near that when measuring directly.  Haze can sometimes be hard to detect sometimes, so that's why I'd recommend testing again on a different day to see if you notice any major difference.  And of course, is your amp meter actually correct?

You mentioned that your batteries were at 60% SOC.  If you were to test the current charging the battery, ordinarily this would be ok at this level, but know that once you reach about 80%, the current will be much lower in absorb as it tapers naturally.  I'm just hoping you havent been underestimating your 60% SOC level - or worst case, a sulfated battery that rapidly rises in voltage, and fooling the controller into showing you the reduced current absorb reached prematurely by a sulfated battery.

Still, I'd just do the direct panel measurement on a different day.

Maybe you DO have faulty panels, or perhaps even a mis-marked or mislabeled one, maybe a return?  What are the dimensions of those panels - with measurements taken by you, not what is on the spec-sheet?  Something just doesn't sound right leading you to frustration.

• Solar Expert Posts: 1,218 ✭✭✭✭
edited January 2016 #25
Mate, solar panels are current generators, and the curretn they produce is dependent on a number of factors.

1. where abouts in their IV curve your controller / battery operates them at.
2. how hot the panels are
3. how low on the horizon the sun is (season, air mass)
4. how much wire you have, and what sort of controller losses

For 1, your PWM controller forces teh panel to work at 12-14V, which is lower than their sweet spot of 18.9V. BTW if they are Vmp 18.9 then that is on the high side for "12v" panels which are nornally 17 to 18. So youll only get your actual battery charging voltage times rated Isc. So assuming you have equinox sun, zero angle of incidence, youd expect something like: 13V *5.3A= 68W.

For 2, its winter in the north and as temperature increases teh Vmp, and ever so slightly decreases teh Isc, your effect is: slight drop in current, and even more loss potential from PWM controller on the votlage.

For 3. Its winter and the sun is low in the sky thus, take off say 5% for the thicker air in the lower part of teh sky. STC assumes an air mass of 1.5 which is roughly what you get when teh sun is 40 degrees from teh dead overhead.

For 4, the rule of thumb is that PWM controllers are 95% or so effcient, although it depends on teh quality. A (cheap) big olde silicon back flow diode will wrack havoc there, but in general terms PWM has high electrical effciency. Your culprit there is primaryly wire loss i think.

First thing to do is get a bog standard 10A multimeter. Go outside at noon on a sunny day, point the panels exactly perpendicular to the sun, measure the open cicruit voltage, and teh short circuit current. Then mesure the voltage at each end of the cable during bulk stage charging, to work out your actual array cable loss. And before and after teh PWM to determine the loss there.

After youve done that, youll understand solar!

1.8kWp CSUN, 10kWh AGM, Midnite Classic 150, Outback VFX3024E,
http://zoneblue.org/cms/page.php?view=off-grid-solar

• Solar Expert Posts: 766 ✭✭✭✭
Joesv57 said:
Quick update.  Looks like after lower my expectations of what could "really" be achieved with 2- 100 watt panels it is performing as it should, getting between 6 -10 amps in direct sunlight.  I was unaware that they were measuring 100 watts as the output at 18-20 volts from the panel vs. me figuring it at 12 volts at the battery.  So in reality, getting 60 watts from a 100 watt panel is more realistic.
Thanks for the help.  Learning a lot!

Yes with a PWM charger you will only be getting your panels working amps through the charger. Typically 60% to 70% of the panels watts. All those watts you thought you were getting in the form of extra volts are just wasted, unless you have a real MPPT charger.

Solar hybrid gasoline generator, 7kw gas, 180 watts of solar, Morningstar 15 amp MPPT, group 31 AGM, 900 watt kisae inverter.

Solar roof top GMC suburban, a normal 3/4 ton suburban with 180 watts of panels on the roof and 10 amp genasun MPPT, 2000w samlex pure sine wave inverter, 12v gast and ARB air compressors.

• Solar Expert Posts: 762 ✭✭✭
I understand what you guys are saying about pwm being 60-70% efficient, but this has always been a rule of thumb "hedge" to account for non-perfect conditions,  not a failure of the pwm CC in itself.

I don't know about you guys, but in bulk, my CC's (Morningstars, Xantrex, what have you) are basically a direct connect to the panels - so yes, gigo for the most part.  If I measure 6A output from my panels directly, I have much less loss through the pwm controller - and get nearly 6A out in bulk.  Not exact, but NOTHING like only 70% efficiency going through it.

This is why I think something is squirrely somewhere in the ops setup.

I'm not trying to start the boring pwm vs mppt war, but pwm controllers are easy targets for the mppt cure-all pill.

• Solar Expert Posts: 762 ✭✭✭
Clarification for lurkers:

Prior to the common use of mppt controllers, a hedge of about 70-75% of rated output of a panel was included in calculations to account for poor / varying conditions.  This is good practice, but it does NOT mean your panel / pwm CC combo is only *capable* of 70% of it's rated output.

When mppt controllers came on the scene, they provide under certain conditions of "up to" 30% more efficiency than pwm.  This is true.  Pay attention to "up to" weasel words.

However, slick mppt marketing and wording would tend to make the newcomer think that a pwm controller itself is producing 30% loss from the panel and is somehow faulty.

Just be careful out there.

• Solar Expert Posts: 3,738 ✭✭✭✭
edited January 2016 #29
oil pan 4 said:

Yes with a PWM charger you will only be getting your panels working amps through the charger. Typically 60% to 70% of the panels watts. All those watts you thought you were getting in the form of extra volts are just wasted, unless you have a real MPPT charger.

Agreed.  All of the panel's amps go into the battery, but not all of the panel's (potential) watts.
I understand what you guys are saying about pwm being 60-70% efficient,
<snip>
If I measure 6A output from my panels directly, I have much less loss through the pwm controller - and get nearly 6A out in bulk.  Not exact, but NOTHING like only 70% efficiency going through it.

PNJ,
to me, low efficiency of a charge controller means heat production... watts must be disappearing in the controller and making heat.  PWM controllers are typically MORE efficient than MPPT controllers.

BUT... When an 18 volt (Vmp) panel is connected to a 12 volt battery, only 12 of the potential 18 volts is being used to charge the battery.  All of the panel's amps are available, but only 12 of the panel's 18 volts.  Since power (watts) is volts x amps, only 12/18 = 66.7% of the POTENTIAL power is harvested.  The "missing" power is not lost to inefficiency of the controller, it is never produced.

During bulk charging the panels themselves will run hotter with a PWM controller than with an MPPT controller.  This is because the sun's energy that is absorbed by the panel, but not exported from the panel (as electrical energy), will create extra heat in the panel.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Solar Expert Posts: 295 ✭✭✭
edited January 2016 #30
vtMaps, brilliant explanation.

Have a question thought. Values are purely for clarifying my point.
In the perfect world I have 3000w panels powering a 3000w inverter. A MPPT in this case is a no-brainer.
But inevitably my system may draw 3000w for a short while, then 1500w, then 2500, 700w etc. during the course of the day. In other words, there are inevitably a surplus of power.

Would a MPPT make a difference still?
• Solar Expert Posts: 3,738 ✭✭✭✭
Would a MPPT make a difference still?
How much more power is transmitted by an MPPT controller than a PWM controller during bulk charge depends on many factors, most especially the string voltage of the panels and the battery voltage.  In cold temperatures string voltage is higher and the gain can be utilized better by an MPPT controller.

Once absorb stage of charging is reached, an MPPT controller works like a PWM controller.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i