How much panel do I need for 4 12volt 100amp batteries ?

Canadianinjapan

Hello , I have a small off grid solar set up and recently made a few upgrades...I live in Japan and am trying to save a little on electricity by using the system daily...However my 4 new 12 volt batteries at 100 amps are just not getting enough charge during the day...I have six 100 watt panels and one 50 watt panel at 5.6 amps each...SO I was wondering how much panel would I need to use the batteries on a daily basis ? I know that clouds and exposure to sun make a difference in the amount charged...Recently it has been quite sunny...

I am sure you nice folks need more info ... Please let me know what you may need to know...

BB.

Welcome to the forum CanadianinJapan,

Are these 4x 12 volt @ 100 Amp*Hour batteries in parallel for 12 volts @ 400 AH?

Also, are these solar panels all in parallel with Vmp~17.5 volts or so? Is this a PWM charge controller (less expensive than the MPPT type charge controller).

Assuming the answer is yes to both questions... The math would look like this. I suggest 5% to 13% rate of charge with a minimum of 10%+ rate of charge for full time off grid systems used daily. 5% can work for a weekend/seasonal (summer) system.

• 400 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 377 Watt array minimum
  
• 400 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 753 Watt array nominal
  
• 400 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 979 Watt array "cost effective" maximum
  

So, at ~650 Watts, your solar array is not that far from "nominal". The next questions to ask:

• Is the solar array working correctly (bad wiring/bad panel)?
• Is the solar charge controller working correctly? You want it to hold ~14.5 to 14.8 volts (flooded cell batteries) for ~2-4 hours per day
• Are you taking too much energy? It is very easy to have more loads than your solar array can recharge

Regarding loads, lets guess you are in the Tokyo area, fixed array pointing south:
http://solarelectricityhandbook.com/solar-irradiance.html

Tokyo
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 54° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
4.79	4.94	4.75	4.89	4.47	3.78
Jul	Aug	Sep	Oct	Nov	Dec
4.02	4.30	3.43	3.69	4.00	4.57

We are now in April, and the "typical" maximum power available per day would be:

• 650 Watts * 0.52 AC off grid system eff * 4.89 hours of sun per day = 1,653 Watt*Hours of AC power per April day
  

Or, if you are using DC power:

• 650 Watts * 1/12 volts *  0.61 DC off grid system eff * 4.89 hours of sun = 162 AH @ 12 volts per April day
  

Of course, you should not "plan" on using 100% of predicted power per day...

Do you have any way of measuring current in your system? Using a DC Current Clamp DMM is really nice. In the US, you can get a "good enough" meter for ~$60 USD.

For AC loads, look at a Kill-a-Watt type meter.

For smaller DC loads, there are lots of DC AH/WH meters out there.

Questions?

-Bill

Canadianinjapan

First, Thank you very much Bill...

I greatly appreciate your response...

It is a shame that I am still a bit clueless in regards to the math required to fully understand your response...However, I  do have a vague understanding...
If you could perhaps recommend a reading or article to get a better idea on the math for batteries, amps and watts.... I will spend some time to research it. That being said ...

Yes to both of your questions that you had asked regarding the batteries and panels being in parallel and the panels being at 17.5 volts at 5.6 amps each...( I believe that parallel is all negatives joined together and positive joined together.)

I agree that I may be running more than I can chew in regards to the amount I am drawing from the battery bank...However it seemed to work better before with the old batteries. Mind you I have increased my inverter from 450 watts to 600 watts...Which is why I added two more 100 watt panels. I also run lights for my home and charge my cell phones from the charge controller directly.  Recently I also added a security camera to the load as well...What I had done before was when the charge controller shut down due to low battery level then I would switch to AC and usually by the middle of the next day the panels had given enough charge to use again...( of course it depended on the weather as well.)

Unfortunately there really is not too much I can do for angling the  panels for maximum sun absorption... I live in a really confined area and have my panels setup on a balcony roof...Fortunately, the panels do face south and have quite a good amount of exposure...( the other roofs don't make any shadow just barely ...very lucky)... The panels have done a fairly good job so far...Recently I have made some upgrades to my system in order to handle the bigger load...
These include
1. I shortened the wires running from the panel to the charge controller by trimming excess wire
2. I had the panels all attached to a 2mm solid wire...( which is usually used for AC wiring here in Japan.) to 5.5 mm wire...running about 10 meters (again it worked quite well before the upgrade)
3. I checked every panels output and they all were putting out about 20.9 volts at the time...So I believe the panels are all functioning unless I had messed something up when wiring them to the 5.5mm cable...( I had triple checked but weird things happen.)
4. I had added two more panels ...
5. I swapped out the PWM charge controller ... However it is a used one and rated at 20 AMPs...I am considering purchasing a new one now at 30AMPS...I am aware the MPPT are more efficient but the cost is much more substantial ...( a 10 amp one is not too expensive at about 60 dollars but I feel I need more amp)...Again I need to study more about it...

I am considering purchasing a cheap DC CLAMP but not really sure how to use it...I will research the use on the internet...

I wonder if the charge controller is off or do I just plainly need a few more panels...Also I would like to ask how should I tie the panel output wires to the 5.5 mm wire cable that runs to the charge controller ? Now they are connect together with a screw and bolt that runs through the ( I do not know the term for a flat bit that ties to the wire and has a hole through it to run the screw through)...

I believe that you had also responded to me regarding my being accidentally being banned by the program Vanilla...I thank you for responding to that issue so quickly and I figured that it was a software issue...Also it could be my fault because I do use a VPN occasionally so the system might have picked that up as suspicious...I will try not to run it again while connected to Wind and Sun...Should I stay with this handle or should I use Pangea...

Anyway Thank you again and I am sorry to have such a long response...

Johann

Canadianinjapan said:

Hello , I have a small off grid solar set up and recently made a few upgrades...I live in Japan and am trying to save a little on electricity by using the system daily...However my 4 new 12 volt batteries at 100 amps are just not getting enough charge during the day...I have six 100 watt panels and one 50 watt panel at 5.6 amps each...SO I was wondering how much panel would I need to use the batteries on a daily basis ? I know that clouds and exposure to sun make a difference in the amount charged...Recently it has been quite sunny...

I am sure you nice folks need more info ... Please let me know what you may need to know...

You have six 100watt panels that could produce 5.6 amps each. You need to add those amps from all those panels together in a parallel system.
6 panels times the 5.6 amps = 33.6 amps total max which could get even higher if conditions are right.  Your 20 amp charge controller will charge your batteries with about 20 amps max if you are lucky and could  even burn up when max amps are switched all the time. Depending on the charge controller, your 20 amp charge controller may even shut down when it reaches close to 20 amps to protect itself and your system and the batteries may not get charged in the meantime.

I would suggest to load a charge controller no more than 75% of it's name-tag rating. 

Canadianinjapan

Hello Johann

Thank you for the heads up about the charge controller and how it works...After reading your comment I realized that I should have bought a bigger charge controller...You were right on the money about the 20 amp one melting...It did ....and sadly I already replaced it with a 30 amp one...Now I think I should get 60 ...Of course Mppt is better ...In addition I added yet another 100 watt /17.5v/5.7amp panel just to teach that darn charge controller a lesson...( OOPS)

Thank you again and the hunt for a reasonably priced charge controller at 60 or more amps is on...

Johann

Canadianinjapan said:

Hello Johann

Thank you for the heads up about the charge controller and how it works...After reading your comment I realized that I should have bought a bigger charge controller...You were right on the money about the 20 amp one melting...It did ....and sadly I already replaced it with a 30 amp one...Now I think I should get 60 ...Of course Mppt is better ...In addition I added yet another 100 watt /17.5v/5.7amp panel just to teach that darn charge controller a lesson...( OOPS)

Thank you again and the hunt for a reasonably priced charge controller at 60 or more amps is on...

I don't know if you know.
You can use two 30 amp controllers to charge one battery bank.
Two 30 amp controllers may be cheaper than one 60 amp controller.

For example....
You could use #1,#2,#3 panels and wire to controller #1 and then to the battery bank and then wire #4,#5,#6 panels to controller #2 and then to the same battery bank .