# Could I just keep adding panels to compensate for overcast skies?

Registered Users Posts: 4

I am learning the basics from a 75-watt solar panel from Harbor Freight and the charge controller that comes with the kit which looks like this:

http://4.bp.blogspot.com/-qzJvyTbF05c/UsyWxkIJauI/AAAAAAAAAWY/tkvgxh_qa7w/s1600/IMG_0474.JPG

I have other equipment too but for now am just focusing on this old kit.

These 2 pages say...

https://blog.voltaicsystems.com/solar-performance-clouds-rain/

https://cleantechnica.com/2018/02/08/solar-panels-work-cloudy-days-just-less-effectively/

...that on overcast days, solar panels produce about 10-25% as much as on sunny days. I noticed that myself today - that even when it's raining my charge controller still says about 3-4 V. That's about a quarter of what it says on sunny days when it says 14 -15 V.

I tried searching online but couldn't find anything specifically answering this. Is there a way to compensate for cloudy conditions by adding panels until you have enough power? It seems like it should work as long as the panels aren't producing 0% of what they produce on sunny days.

I currently have a 75-watt panel. If I added panels in an array, in a series, would that work? Or would it perhaps need to be in parallel for some reason, instead of series? If I quadrupled my current wattage by adding 225 watts of similar panels (300 W total. 4 * 75 = 300) would that compensate for this 25%-of-normal output I'm experiencing due to cloudiness and allow me to charge up my stuff just as much as on sunny days?

I'm confused about some basics. If I wired the quadrupled array in a series to increase the volts to 14-15 V from 3-4 V then the system voltage would no longer be 12V. It would be a 48V system if I wired four 12V panels in a series. That means the charge controller automatically stops charging (according to the manual) at some cut-off point way above 11.1 V, which is the low-voltage cut-off point for a 12V system. For a 24V system, for example, the manual of one of my other charge controllers (not pictured) says the cut-off point would be 2 times 11.1 V which is 22.2 V. So, doing it that way wouldn't be making it any easier for me to get enough voltage on a cloudy day. Is there any way around that? Like perhaps by setting the charge controller to 12V somehow (if possible) despite it being a 48V system or does it automatically detect that it's a 48V system?

If you wired it in series instead would that work? I assume I need the charge controller to no longer say that only 3-4 V are coming through. Is that right? Does it absolutely have to say about 14-15V for me to go back to being able to charge my phone by plugging it into the USB plug that you see in that picture I linked to above on the Thunderbolt charge controller?

Right now, I only want to power (by usb cords) a phone, hotspot, and a 20,000 mAh power bank. The batteries of these small devices say "3.8 V lithium ion..." Why do I need the charge controller to say 14-15 V? I'm not charging a 12V battery so I was hoping that even with only 4 V coming through on the charge controller, that it'd still be enough to charge my phone. When I plug in when it's saying 4 V, however, it doesn't charge. The phone will only charge when it says about 14-15 V. When it says anything below that, it won't charge my phone.

Thank you for any guidance.

Tagged:

• Solar Expert Posts: 3,815 ✭✭✭✭✭✭
edited December 2020 #2
Welcome to the forum

You panel is likely 18-21V open circuit, the voltage whilst charging would be pulled down to slightly above the battery voltage. The PV input voltage must always be above the battery voltage  in order for current to flow into it, if not it will remain in lmbo until it drops below a given value and determine it is night time.

Whilst it may seem logical to series panels to increase the voltage in overcast conditions, the idea is flawed because the controller would be in an over voltage condition as soon as the sun comes out, most likely damaging it. The same principle in logic would apply to parrallel panels but this would cause a overcurrent condition when the sun comes out which will definitely damage the PWM controller

There are ways around this but would involve additional equipment, with what you have however, a very low end basic system, there is little that can be done, it is what it is.

To move beyond whats on hand unfortunately will involve some expenditure... \$\$\$...everyone starts somewhere, learns from mistakes and eventually ends up with something that works, many here will offer guidance which will save you in the long term.

The Harbor Freight box will have a 12V battery inside which is what is charged by the panel, the state of charge will determine when loads or USB can be used, when that battery drops below a certain value, usually dead, it should disconnect all loads. Any battery voltage  reading on the display less than~11.5V likely means the battery is toast, quality isn't something the manufacturer is attempting to achieve, once it's sold it's done it's job is done, unfortunately it's the unwary who pay the price.

To design something from scratch it's best to start with what it is you're hoping to achieve rather than assuming some off the shelf kit will do exactly that, it likely won't.

Please don't take this as discouragement, solar energy, even in its most basic form follows the same rules as a sophisticated whole house installation, albeit on a smaller scale, nothing really changes, the basics are where to start. Hopefully we can help and guide you on the experience, nfortunately from what I'm reading above you have a long way to go in understanding the fundementals, but to repeat myself we all started somewhere...want to get started?
1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery with Battery Bodyguard BMS
Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah LFP 24V nominal battery with Daly BMS, used for water pumping and day time air conditioning.
5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
• Registered Users Posts: 4
Thanks for the welcome and the advice. This beginner's corner forum looks like a good forum to participate in. I need a lot more knowledge on the fundamentals.

The Harbor Freight stuff was given away to me. I wonder if some of this other equipment I have would help which I recently bought.

I have these 2 other CC's:

Victron SmartSolar Charge Controller with Built-in Bluetooth. MPPT 75/15. 75 Volts, 15 Amps.

I have, in addition to the 75W Harbor Freight panel, a 120W, 24V solar panel made by Newpowa that I ordered from amazon as well as a 20', 10AWG solar extension cable.

I have two 12V, deep-cycle, AGM used batteries which have 85 Ah each which I bought a couple months ago for \$80 from a local battery store and a used flooded lead-acid 12V battery that someone gave away to me. I haven't gotten around to connecting them yet to anything. I should do that soon. The old Thunderbolt CC from Harbor Freight can charge my phone from its USB port without a 12V battery being connected to the system as long as the old CC says there are about 14 or 15 V.

It's my understanding that it's rare for newer CC's to offer battery-less charging but I'm not clear on that. Maybe it's because it's bad for the phone battery if there's not that steady voltage which a battery provides. I think I read that. It's why I only plug in my old phone.

Would this following plan resolve the problem of a parallel array causing an overcurrent condition, which you brought up?

If I bought a second or third 120W Newpowa panel and arranged it in parallel with the other 120W Newpowa panel then I would have 240-360 W total. The short circuit current for the 120W panels is 3.74 A. Multiplying 3.74 by 2-3 panels equals 7.48 A - 11.22 A. Multiplying 11.22 by a safety factor of 1.25 equals 14.03 A. That's less than the rated charge current of those 2 CC's above: 15 A and 30 A.

Or maybe I could keep things simple by buying a 300W, 24V Renogy panel instead which has a short circuit current of 9.78 A. Would that 300W panel be enough power to charge a phone on cloudy days?

I'm very interested in knowing more, when you say there are ways around this issue of heavy cloudiness. By saying that, are you referring to buying a bigger battery bank and more solar panels so that on clear days I can stock up on battery power to be used on cloudy days? Should I give up on the notion of charging anything (for example, just a phone) on heavily overcast, winter days when my Harbor Freight charge controller says only 4.0 V? Or is there another way around it?

• Solar Expert Posts: 9,274 ✭✭✭✭✭
It's rare for ANY charge controller to function without being booted up from a battery first.  Even the 25 year old Trace PWM controllers need a battery to stabilize the solar voltage for their own internal logic.

Adding panels is fine, till the sun pops thru a hole in the clouds,  then you have -0.5 seconds to disconnect the panels before you fry the fuse in the controller.

Panels produce nearly full voltage with very little light.   But with low light, you have very low power, and so your 18v panel may only read 4 volts because the load of the meter sucks the voltage right down.   If you add panels in parallel, you will gain enough micro amps to get the meter to read.   When you get enough brightness, the panel will start working
Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,

• Registered Users Posts: 4
edited December 2020 #5
mike95490 said:
It's rare for ANY charge controller to function without being booted up from a battery first.  Even the 25 year old Trace PWM controllers need a battery to stabilize the solar voltage for their own internal logic.

Adding panels is fine, till the sun pops thru a hole in the clouds,  then you have -0.5 seconds to disconnect the panels before you fry the fuse in the controller.

Panels produce nearly full voltage with very little light.   But with low light, you have very low power, and so your 18v panel may only read 4 volts because the load of the meter sucks the voltage right down.   If you add panels in parallel, you will gain enough micro amps to get the meter to read.   When you get enough brightness, the panel will start working

When you say ... "When you get enough brightness, the panel will start working"

...I'm curious whether that means the parallel wired panels would work in heavy overcast conditions. The CC said about 4 V to 8 V before when my one panel was in very heavy overcast weather. So, can I fix that and power just my phone if I add 2 more panels in parallel? Or if I used 10 panels or any amount of panels?

I guess I don't know eaxctly what you mean by "bright enough." If my CC says about 4 - 8 V now, in heavy overcast, it seems like I don't need it to be bright maybe. It's almost bright enough even in heavy overcast weather. That's the only reason I want to add two more panels in parallel - to power my phone even when it's heavily overcast and not bright at all. What I'm clueless about is whether that's possible. I don't want to have to wait for brightly overcast or partly cloudy days to power just my phone. I should be able to power my phone even in heavy overcast, I think, I hope.

Or what I hypothetically wired 5 or 10 more panels in parallel and used a CC rated for all those amps? Would having any amount of panels - even 1,000 watts - enable me to charge my just my phone even on heavily overcast days or am I way off base and barking up the wrong tree? Thanks for any advice.
• Solar Expert Posts: 5,576 ✭✭✭✭✭
edited December 2020 #6
In the end, I think there is no real path for you, using a charge controller.

As said by others, if you add solar panels, you will exceed the charge controllers ability to work and fry it, if it's not turned off when bright sun hits it.

You could add a battery band just charge from the battery, but I don't think that's what you want to do...

So what you CAN DO, is setup the solar panel, the ones you have or another set, with a voltage regulator to provide a 5 volt (USB range) output. Since solar panels don't HAVE TO make power, the voltage regulator can be designed for the amount of current that will pass through it. In this manner you can use the charge controller built into your Phone to charge it. Better yet, you could charge a battery bank for those days when you have cloudy weather.

Something like this (link below picture);

https://www.amazon.com/jiang-5V-20V-Charger-Regulator-Charging/dp/B01MTJCOL6/ref=sr_1_9

This will limit the output voltage of a 6-20 volt solar panel to a USB range and allow up to 2 amps charging if you have enough incoming current. You could combine this with a USB - Power bank to have extra power to charge your phone when you need to... This one is \$6, and I've picked them up shipped from China on eBay for \$1-2, just takes 6 weeks.

You could, likely just add a power bank to your current PWM charge controller with USB ports and solve your problem;

Ones large enough to charge a cell phone fully are likely 10,000 mah; and can be had for \$10-20. Look around on Facebook market place, search for "power bank" likely you find someone selling reviews and selling the products.

...or here's one;

https://www.amazon.com/EAFU-Portable-High-Speed-Flashlight-Compatible/dp/B07X64THC5/ref=sr_1_5

Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
• Solar Expert Posts: 5,576 ✭✭✭✭✭

So this was my test running a fan from 100% for 24 hours on low from the 10,000 mah battery bank. Drew down to 57%. My cell phone is for size reference, I have charged my phone from the battery bank.

It works fine, I setup a couple 6 volt panels and sent mom a fan and a couple battery banks and 2 weeks later she had a storm and lost electric for 20 hours. We did discover that leaving the battery banks under the solar panels outside to charge wouldn't work when hot! The charging circuitry shuts down charging when the battery reaches a certain temperature. This was in North Florida. Found leaving the battery bank on the ground with a light colored towel over it, with the solar panel in a chair shading the battery bank worked, though they didn't leave it there after the electric came back on. Not sure how long they allowed it to charge.

Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
• Solar Expert Posts: 9,274 ✭✭✭✭✭
Almost anything is possible, within the limits of physics.   to charge the battery, the panels need to collect photons from the sun.  No sun, no photons.    Add enough panels to work on a cloudy day, and you are fine until the sun comes out bright, and all the extra power frys something.
Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
|| Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
|| VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

solar: http://tinyurl.com/LMR-Solar
gen: http://tinyurl.com/LMR-Lister ,

Regarding "bright enough"... Solar cells are current sources. More or less, the current out of solar cell is proportional to the amount of sunlight (photons) hitting the cell(s).

Solar cells are also just "large diodes"--And they have internal losses too (a little bit of leakage current from + to - through the "diode junction"). Each (silicon) cell is rated for Vmp~0.5 volts... You need enough sun to get the cell output to ~0.5 volts--Which is about the amount when the sun rises and casts the first direct light on the panel (you can also have enough light from back scatter from the sky if the panel is otherwise in shade).

Once the cell reaches 0.5 volts (you have ~36 cells in series for a Vmp~18 volts for a typical "12 volt" panel... That current is proportional to the sunlight hitting the cell/panel.

On my grid tied system, I have seen very dark days (a few of them) where I got something like 1% of the array output (35 watts from a 3,500 Watt array+GT inverter)...

Adding more panels in series is not going to help much--When the cell voltage is below 0.5 volts, you are going to get very little current anyway.

The better solution is to have an oversized array (5-10x if you cannot be without cell phone/USB power), and have a few extra battery USB battery packs so that you can carry through the (hopefully rare) 2-3 days of heavy cloud cover. When the sun comes back, you will have plenty of power to recharge the phone and battery banks.

Other thinks to look at too... Cell phones can have highly variable power usage... The smart phones with data usage and screen time/brightness can really suck down the watts. Going into the configuration and setting the power conservation mode can really help reduce the draw. Turning off unneeded apps (putting them to sleep in Android terms)--All that can 1/2 your power usage easily (with reduced email reponsivness, etc.).

I had one older Android phone that would extend battery life by something like 6x in the extreme power save mode.

It all depends on your needs.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Registered Users Posts: 4
edited April 1 #10

Photowhit said:

So this was my test running a fan from 100% for 24 hours on low from the 10,000 mah battery bank. Drew down to 57%. My cell phone is for size reference, I have charged my phone from the battery bank.

It works fine, I setup a couple 6 volt panels and sent mom a fan and a couple battery banks and 2 weeks later she had a storm and lost electric for 20 hours. We did discover that leaving the battery banks under the solar panels outside to charge wouldn't work when hot! The charging circuitry shuts down charging when the battery reaches a certain temperature. This was in North Florida. Found leaving the battery bank on the ground with a light colored towel over it, with the solar panel in a chair shading the battery bank worked, though they didn't leave it there after the electric came back on. Not sure how long they allowed it to charge.

...

Hi,

I bought the Jiang regulator you linked to. It says its input range is 5 V to 20 V. Is that referring to the VOC? Because my 12V panel has a 23.6-V VOC. Does that mean I may fry it if I try to use that panel with this regulator?

If so, then do you think it would solve the problem to instead use a converter with a higher maximum input range? I have these two converters I could use for this purpose.

amazon.com/gp/aw/d/B07JZ2GQJF?psc=1&ref=ppx_pop_mob_b_asin_title

That's the first one. It's made by Drok and has an input voltage range of 6 V to 32 V.

amazon.com/gp/aw/d/B07H6YZ9XS?psc=1&ref=ppx_pop_mob_b_asin_title

That's the second one I have and it's made by Ekylin and has an input range of 8 V to 52 V.

Voc (voltage open circuit--I.e., no loads) and Vmp (voltage maximum power) are rated for "standard temperature and sunlight"--Or around 75F/25C... When panels get hot (under full sun and hot ambient temperatures with no wind), the solar cells get hot and Voc/Vmp falls (by roughly 20%)... Conversely, when solar panels get cold (typically very cold, well below freezing) their Voc and Vmp voltages can rise quite a bit... your 12 volt panel may very from 14.4 volts (Vmp-very-hot something like 40C) to 28-29 volts (Voc-very-cold something like -30C).

So, in general, it is best to have a wide input voltage range for your solar panel loads/voltage converters... If you are running in moderate climate such as a tropical island or non-winter camping--Then you don't have the issues of Voc-very-cold and high Vpanel voltage.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 5,576 ✭✭✭✭✭
tascern said:

Photowhit said:

So this was my test running a fan from 100% for 24 hours on low from the 10,000 mah battery bank. Drew down to 57%. My cell phone is for size reference, I have charged my phone from the battery bank.

It works fine, I setup a couple 6 volt panels and sent mom a fan and a couple battery banks and 2 weeks later she had a storm and lost electric for 20 hours. We did discover that leaving the battery banks under the solar panels outside to charge wouldn't work when hot! The charging circuitry shuts down charging when the battery reaches a certain temperature. This was in North Florida. Found leaving the battery bank on the ground with a light colored towel over it, with the solar panel in a chair shading the battery bank worked, though they didn't leave it there after the electric came back on. Not sure how long they allowed it to charge.

...

Hi,

I bought the Jiang regulator you linked to. It says its input range is 5 V to 20 V. Is that referring to the VOC? Because my 12V panel has a 23.6-V VOC. Does that mean I may fry it if I try to use that panel with this regulator?

If so, then do you think it would solve the problem to instead use a converter with a higher maximum input range? I have these two converters I could use for this purpose.

amazon.com/gp/aw/d/B07JZ2GQJF?psc=1&ref=ppx_pop_mob_b_asin_title

That's the first one. It's made by Drok and has an input voltage range of 6 V to 32 V.

amazon.com/gp/aw/d/B07H6YZ9XS?psc=1&ref=ppx_pop_mob_b_asin_title

That's the second one I have and it's made by Ekylin and has an input range of 8 V to 52 V.
I suspect you would be fine, but don't know. For \$5 I'd give it a go, as to the others working, likely they would beat least as good if not better, though some phones/devices are very picky about voltage regulation Apple/Nokia.
Home system 4000 watt (Evergreen) array standing, with 2 Midnite Classic Lites,  Midnite E-panel, Magnum MS4024, Prosine 1800(now backup) and Exeltech 1100(former backup...lol), 660 ah 24v Forklift battery(now 10 years old). Off grid for 20 years (if I include 8 months on a bicycle).
- Assorted other systems, pieces and to many panels in the closet to not do more projects.
• Registered Users Posts: 0
I'm new to solar related stuffs. I have a similar question!
Can I run electronic devices directly from a solar panel without needing an inverter and battery?

Solar Panels are like very "poor" batteries... For example, a "12 volt" solar panel will output from 14 volts (very hot day 35C+, full sun) to nearly 28 volts at -40C... For a panel rated Vmp (voltage maximum power) around 18 volts (36 cell panel).

And the output current will range from zero amps (dark to first light from sun falling on panel) to full Imp (current maximum power) at high noon on a clear day with panel pointing at sun (more or less, the available output of a solar panel is proportional to the amount of sun hitting the panel).

So, your device needs to accept a wide range of input voltages and be able to operation at less than full current (sun rise, sun set)... And typically the solar panel is "over sized" to support energy needs on partially cloudy days, closer to sun rise/sun set, etc...

Batteries are used to "buffer" the solar panel output voltage, and "charge" when the sun is high in the sky, and provide power when the sun is down.

AC inverters are power converters--They take (for example) 12 VDC and convert to 230 VAC @ 50 Hz--or whatever... There are also DC to DC converters that can increase or decrease solar panel voltages, or even "stabilize" solar panel voltage. While your can run these types of devices directly from solar power--These devices are not common as it is not often people have loads that can randomly start and stop during the day depending on sun/clouds, and not run at night.

But it is done... There are solar battery chargers (from very small for AAA NiMH batteries) to very large battery banks that can run a home. There are solar->Grid Tied inverters that can feed energy back into a utility AC power grid (very common use for solar power)... And water pumping based on solar panels=>VFD (variable frequency drive--or a type of AC inverter)=>3 phase pump (basically pump water into cistern or field of crops while the sun is up). And, of course, many satellites are solar powered.

You need to figure out what load(s) you want to run just during the day, and how to restart them when the sun "fails" (rebooting computers is not actually an easy thing to do with unreliable input power).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset