What Size Charge Controller Do I Need For Solar Panels?
What size charge controller for a 100 watt solar panel? Or 200w, 300w, or 400 watt solar power system? Or more than that?
(A charge controller installs between the solar panel array and a battery bank)
(description below)
There is a simple way to figure out the size (its rating).
Ready? Lets go…
Take the number of panels x watts to get the total watts of the solar array.
You then divide it by the voltage of your battery bank to get amps.
Add 25% to allow for margin (e.g. cold temperatures) and as always, round up.
Examples:
1 x 100 watt solar panel / 12 VDC battery bank + 25% = 10 amps.
2 x 100 watt solar panels in series = 200 watts / 12 VDC battery bank + 25% = 21 amps.
3 x 100 watt solar panels in series = 300 watts / 12 VDC battery bank + 25% = 36 amps.
4 x 300 watt solar panels in series = 1200 watts / 48 VDC battery bank + 25% = 31 amps.
10 x 300 watt solar panels in series = 3000 watts / 48 VDC battery bank + 25% = 78 amps.
Okay, you get the idea… it’s just simple math.
Note that the most common solar pv charge controllers come in 12, 24 and 48 volts. High power systems will utilize 48 volt battery banks to advantage smaller cables and losses than otherwise on lesser voltage battery systems.
There’s more to it than what I’ve described (what size charge controller). However the calculation above is the most determining factor for the rating.
Other factors include:
- input specifications (voltage & current from the solar panels)
- MPPT (Maximum power point tracking – the most common) or PWM (Pulse width modulation)
- temperature compensation
- ability to charge varying types of batteries
- user adjust-ability of charge parameters
Most manufacturers have sizing tools to help the decision process.
What is a charge controller?
It is a device which most importantly properly charges a battery or battery bank, enabling as long a life as possible.
A solar charge controller is designed to receive power from a solar panel or array of panels and use it to charge a battery or bank of batteries.
The charge process is performed in a ‘smart’ or ‘intelligent’ way. This involves varying charge stages, voltages, and current — depending on the type of battery and other factors.
Not to be confused with an inverter, a charge controller is specifically designed to charge batteries in a controlled fashion.
Low power charge controllers are widely available, commonly used on 12 volt battery systems. Amzn has lots of them, for example.
However if you are considering a higher powered system, such as for an off-grid cabin (or whatever), I recommend that you contact Iron Edison in Denver. They will be happy to help determine your needs (they distribute charge controllers). They also specialize in battery banks, particularly Lithium Iron and Nickel Iron. Regardless, they are a sponsor here and will surely be glad to help.
Continue reading: The Four Essentials of Off-Grid Solar
Thanks Ken, good photo. Nice assortment of ‘solar’ power parts…. We have a garage where the roof faces south. Are considering some solar.
Good photo of solar connects?
I, myself, like the rifle and flag.
Hehe
Joe c,
The rifle (an old Marlin 880, .22 caliber), sets at its resting place (as shown) which is near the back door. It’s for dog-potty duty at night. Coyotes. My Sampson is just a little feller. Though he has no idea he’s little.
👍
Don’t blame ya one bit. Nasty yotes
….and the Marlin is pretty cool, too!
Note that the example numbers listed above are simply the “ratings” (the max that a given charge controller can do).
It’s not the actual charge profile parameter(s) — which will vary depending on one’s setup.
For example my ‘MidNite Solar’ brand ‘Classic-200’ MPPT charge controller (as shown above) has a multitude of user-selectable settings and tweaks. This allows me to perfectly adjust the charge parameters for my particular battery bank.
Just because my charge controller is rated for 79 amps and up to 48 VDC, doesn’t mean I’m going to push that through a single battery! (for example). Rather, it means that it’s able to pump out that current — which in my particular series/parallel combo 48 volt battery bank of 24 batteries — is perfectly fine.
Make sense? Someone contacted me, apparently confused about it, so this is my attempt to clear it up.
As mentioned by Joe C:
Do guns and solar systems go well together?
Neat set-up Ken. Is your system off-grid? Does your state allow or grant permits for an off-grid system?
I know some states like California did not allow for off-grid systems and now PG&E is bankrupt so depending on your location, solar systems may make financial sense.
Calirefugee,
No special permits required here where I live. And yes it is off-grid in the sense that I have installed individual transfer switches for most of my electrical panel circuit breakers from the grid. This enables me to choose which circuits I want to be solar powered rather than grid. During the summer I can run whole-house on solar. During the winter, the essential systems (unless a long period of clouds – thus draining my batteries over several days). So I play with it throughout the year.
Ken,
Very nice set-up. Mine is in an outdoor building which is just attached to the side of the house. It’s not really a building, as there is not room for a person to enter it. Matching hardi-plank siding so it looks OK. Gotta keep the wife happy. When the power goes out, she keeps her smile, for a while at least.
hi, and thank you. would 2 separate controllers be a good idea for 4 100amp hr lifeion batteries to split the loads