Solar Charge Controller | What is it and How it works in a Solar Power System

Hi. I’m Amy from the altE Store. I’m going
to go over the basics of solar charge controllers with you.
First let’s take a look where a solar charge controller fits into an off-grid solar system.
The charge controller goes between the solar panel and the deep cycle battery.
A Charge controller is an important component in battery based systems. They are not used
in straight grid-tied systems, as they do not have batteries to charge.
Their primary role is to manage charging the battery bank. It prevents it from overcharging,
and many of them control the rate of the current and voltage at which it charges. More on that
in a moment. Some charge controllers have load control,
where you connect the DC load right to the charge controller instead of to the battery,
and it will turn it on and off based on voltage of battery and/or time of day, for example
turning the load off if the battery gets too low or turning on a light from dusk to dawn.
At night, the voltage of the battery bank is higher than that of the solar array that
is connected to it. Since electricity flows from high voltage to low, without a charge
controller, the tendency would be for the electricity to flow out of the battery bank.
A charge controller prevents that from happening, allowing the flow to only go one way, into
the batteries. Many charge controllers manage charging the
batteries by varying the voltage and current to the battery bank based on how full the
battery is. Much like pouring a glass of water, when the glass is fairly empty, you can have
the faucet on full blast, but when it starts to get full, you want to turn down the flow
to prevent overflowing. Likewise, a charge controller sends a lot of power to the battery
when it is low, but as it approaches full, it slows it down. Once it is full, it will
send a smaller amount of power, a trickle charge, to keep it topped off.
This is called multi-stage charging. Here’s an example from Morningstar of 4 stage charging.
With Bulk Charging, when the battery is low, it will accept all the current provided by
the solar array. At Absorption, the battery has reached the
regulation voltage, the controller begins to hold the voltage constant. This is to avoid
over-heating and over-gassing the battery. The current will taper down to safe levels
as the battery becomes more fully charged. Equalization is done with flooded batteries,
not sealed batteries like AGM and Gel. Many batteries benefit from a periodic high voltage
boost charge to stir the electrolyte, level the cell voltages, and complete the chemical
reactions. Your battery specs will tell you how often and at what rates it wants to be
equalized. Float charge is when the battery is fully
recharged, the charging voltage is reduced to prevent further heating or gassing of the
battery. There is a wide variety of features that are
optional on some, but not all controllers. In most cases a display does not automatically
come with the controller, but can be added separately for a remote display. A few even
have Ethernet connections, allowing you to monitor your system across the web.
Temperature compensation will improve the battery bank charging, by adjusting its output
based on the temperature. Low Voltage Disconnect is a great feature
that allows you to connect your DC load to the charge controller. If the battery voltage
gets low, it will turn off the load, preventing the batteries from becoming too low and getting
damaged. Some controllers can be used as a diversion,
or dump, load controller, turning power on to a heater to burn off excess power. There
are others that have light control functions, turning lights on and off automatically based
on dusk and dawn. You’re going to hear me talking about Nominal
Voltage, Voc, and Vmp. Voc is Open Circuit Voltage, or what you will measure from a solar
panel in perfect test conditions with nothing but a volt meter connected to it. Vmp is voltage
at Max power, or what the solar panel will put out when it is connected to equipment
like a charge controller or inverter. Nominal voltage is a way to categorize battery based
solar equipment. Because a higher voltage is required to charge a battery, nominal voltages
are used to help see what equipment goes with what. So a nominal 12V panel, which actually
has a Voc voltage of around, 22V, plus or minus a volt or 2, and a Vmp of around 17V.
And if you count the number of cells, or silicon squares on the front, it will likely have
36 cells. Likewise, a panel that was designed to charge
a 24V battery bank will have a Voc of around 44V and a Vmp of around 36V. Counting the
cells will come up with 72, twice as many as a 12V panel. If you wire 2 24V panels in
series, or 4 12V panels in series, you can charge a 48V battery bank.
This was all well and good for battery based systems, but then along came grid-tied systems,
and 12, 24, and 48V became meaningless. So the industry sort of standardized on 60 cell,
20V nominal panels. Alone, they are too big to charge a 12V battery, and too small to
charge a 24V battery. An MPPT charge controller solved that, by reducing the voltage down
to the required range, and in doing so, increasing the current output, so you are not losing
power. There are 3 main types of charge controllers.
Shunt controllers, that just turn the flow to the batteries on or off are rarely used
anymore, so we won’t go into them. The 2 main types you’ll find these days
are PWM and MPPT. Let’s discuss them in greater detail.
PWM are generally the less expensive option of the two. A PWM charge controller pulses
the power sent to the battery bank, allowing it to do the different charging stages we
discussed. When using a PWM charge controller, the nominal
voltage of the solar panel must be the same nominal voltage as the battery bank.
So if you are using a 12V battery, you must use a 12V solar panel. If you have a 24V battery
bank, you must wire two 12V panels in series, or one 24V panels to make 24V. If you have
a 48V battery bank, you must wire four 12V panels in series, or two 24V panels in series,
to make 48V. Make sure the charge controller you select is designed for the battery bank
voltage. Some can support multiple voltage ranges, others are designed only for 1 voltage.
Note if a PWM charge controller says it can support 12 or 24V, both the panel and battery
bank must be one or the other. It is NOT saying it can take a 24V panel to charge a 12V battery.
It is saying it can work in EITHER a 12V or a 24V system.
Selecting the right charge controller for a PWM system is pretty simple. For a single
string, we check the label or datasheet and confirm with the Voc of 22.1V that it is a
nominal 12V panel, and the Isc is 8.68A . We then multiply the Isc by the number of parallel
strings, 1, and multiply it by NEC’s safety factor of 1.25, to get 10.85A minimum charge
controller amperage requirement. Great, I’ll round up to a nice 15A Morningstar
ProStar 15M with a meter. Now let’s try it with 2 parallel strings
of the same 140W panel. Notice I’m not talking about how many panels are in each string,
because I’m using a PWM charge controller, I know that I’m using the right number to
match the voltage of my battery bank, so I’ve got 1 for a 12V, 2 in series for a 24V, and
4 in series for a 48V battery bank. In this example, I have 2 parallel strings of 2 in
series for a 24V system. 8.68A short circuit current x 2 strings x
1.25 NEC required protection, equals 21.7A, so I’ll round up to the Midnite Solar 30A
Brat charge controller. Now we move on to MPPT charge controllers.
A Maximum Power Point Tracking, or MPPT, is the more sophisticated, more expensive type
of charge controller. It tracks the output of the solar array and
adjusts itself so that the output is always maximized. In doing so, it can increase the
production of the array by up to 30%. Another great advantage is that most MPPT
charge controllers can take a higher voltage array, for instance a 60 volt array, to charge
a lower voltage battery bank, like a 48V. This is required if you have a 60 cell, 20V
grid tied solar panel, that are common, and thus less expensive, and use it to charge
a 12V battery. It’s also very useful if you have to go a distance from your array
to your battery bank. The higher the voltage of the solar array, the lower the current
going across the wire. Therefore, you can use smaller gauge wire, which will cost less,
and have a lower voltage drop, which gets more of your power to the batteries.
There are also a few MPPT charge controller that can take a lower voltage panel and charge
a higher voltage battery bank. These are great to use a 12V panel to charge a 36V golf cart.
But MOST MPPTs require a higher or equal to voltage panel. Be sure to read the specs carefully.
To see how an MPPT charge controller works, let’s look at a system with one 60 cell
PV panel and one 12V battery. The charge controller takes the 30 volts from the solar panel and
converts it down to around 14V to charge the battery. Unlike a PWM charge controller, it
doesn’t just throw away the extra voltage, it increases the current on the output to
maximize the power out. So if it is taking 30V in and sending 14V out, that is a decrease
of 2.14. Since it is taking 9A in, it will INCREASE that by the 2.14, and output 19.28A
out. So power in equals power out. So the simplest way to size an MPPT charge
controller is to take the total watts of the array and divide it by the voltage of the
battery bank. So 270W panels times 4 panels divided by 24V battery bank times 1.25 for
NEC equals 56A charge controller. Cool, I’ll use an Outback Power FlexMax 60.
In addition to amps, Solar Charge controllers are also rated by voltage.
A typical 150V charge controller can support up to three 20V panels in series. You may
be saying, but three 20V panels in series equals 60V, that’s waaay below 150V. But
the voltage the specs are referring to are the Voc voltage, the actual voltage the panel
puts out. That is much higher than the nominal 20V or the Vmp. The Voc of a 20V panel is
actually around 38V, so three in series is 114V. Also note that cold weather increases
the voltage output of a solar panel. So if we also figure in the cold temperature in
the winter, we increase the volts. At -5 degrees Fahrenheit, it adds 20% to the voltage, bringing
us up to 136Voc. So you can see why at least in cold climates, three 20V nominal panels
would be the max for a 150V charge controller. There are now higher voltage charge controllers
available, with some accepting as much as 600V in. This is very useful if the array
is a long distance away from the battery bank. So again, check the specs to find the right
charge controller for you. That’s it for a quick summary of solar charge
controllers. Check out our website for a great selection
of solar charge controllers and all of the other components needed for a solar power
system. Also watch more of our Videos on our web site
to learn more. We’ve got a team of highly trained Technical
Sales Reps available to help you plan your system, give us a call. And don’t forget to check out the rest of our website at where we’re making renewable doable!

68 thoughts on “Solar Charge Controller | What is it and How it works in a Solar Power System

  1. doesn't most panels these days have a blocking diode to prevent that reverse current flow at night?
    Also are there solar setups that use this reverse current flow to melt ice build up the the panels? in this case that blocking diode would have to be removed? what charge controllers have this function?
    can you talk about sometime the relationship between windturbine and charge controller like the midnite classic?

  2. I really need your help here. I have a small solar panel that I would like to use just to keep a charge on one 12 volt battery. I will give you all the information from the back of the panel, and hopefully you'll be able to tell me what type of controller I will need in order to use the panel. Panel Information: Zamp Solar Panel: Model # ZS-M-20Cell Type: Monocrystalline Peak power (Pmax): 20 WattPower Tolerance Range: (%) -3% to +5% Open Circuit Voltage / Voc (V): 21,0 Max Power Voltage / VMP (V) 17.5 Short Circuit Current / ISC (A) 1.23 Maximum Power Current / IMP (A) 1.14 Maximum System Voltage (V) 600 V DC Dimension (MM) 345*470*25

    Above Specification At Standard Test Conditions
    (STC) 1000W/m* , cell temperature 25*C,am1.5

    This is all of the information from the label on the panel. I'm sure this may help you to figure out what type of charge controller I need in order to put the solar panel to use. Thank you very much for your time, and all of your videos. I hope to learn from all of them.

  3. +altE store thanks so much for the info,i would like to know what is the limit to the number of panels that i can connect in series for a 12v system so that i can have lots of charging current using an mppt.Can i have 114v into an mppt charging a 12v battery

  4. +altE I must say this is a fantastic video and an eye opener for me. I currently use twelve 130W solar panels on a 12V inverter system. The solar panels are connected in 2 different arrays with each array connected to its own PWM solar controller and then to a 12V battery bank. The solar controllers are each 12/24V 60A . Now I want to change my inverter to a 24V inverter, which means I would upgrade my battery bank to 24V. Since my solar controllers can handle 24V, how do I connect my solar panels to the charge controler. Do I need to increase the number of charge controllers? How will the modification affect the charging rate of my batteries, will it charge them faster or slower?

  5. thanks for this!!! now i know the difference between charge controllers!!! great help!! i will go to mppt charge controllers!!

  6. Hi, Mrs. Amy!
    Wonderful your explanation!
    Would it be possible for you to make a video explaining the MPT-7210 Minghe charge controller. I put one in my electric car. It seems that it's working fine but I would be much happy if you make a video explaining how it works and I would understand it better.
    Thank You and have a nice day.
    Best regards!

  7. Would it be possible to send you some photo of the charge controller working so you can tell me if it is really working in mppt mode? So you will see our Kalnoit( Electric Vehicle) Direct from Israel! Maybe by email or Whatsapp?
    Thank You and best regards!

  8. Hi, Friend!
    I need your help, please. As I told you I am using Minghe mppt charge controller and here in Israel now is very hot. The display is showing that the voltage of the two Batteries is 31volts nearly 32, is that normal? Can the voltage of one battery reach more than 15 volts and is there any danger? When I turn off the charge controller or at night the voltage goes down to 26.4 volts? What should I do? Can you explain to me what us constant current and what is constant voltage?
    Thank You very much!
    Best regards,
    Emmanuel Távora Freire.

  9. Hi Amy I have a smart harvest charge controller  SCCM20-100   MPPT  outback is it ok to wire up 3 x 100watt  12 volt panel in  parallel to a 300 to 400 WH  battery bank Many Thanks.Brian

  10. Now from all info I've picked up from your video's the system I was looking to buy is just not going to work or did I get lost in the mppt's and series /parallel . Can you tell me if this system will work? 8 Renogy 250 w 24 v panels (voc 30.37,vmp 30.20, vmp 8.29, isc 8.84) with a Midnite Classic 200 (79 amp output) with a 24v battery bank.From what I found it should be a 48v battery bank and that controller wont work. I'm confused

  11. If a had a 12 volt battery and provide it 30 volt through a PWM charge controller, only 14 volt will reach the battery meanwhile the other 16 volt is wasted? Correct me if I'm wrong

  12. If the PWM charge controller with matching nominal voltage between PV and batt, the efficiency is equal to the MPPT CC since there is no voltage drop?

  13. Hi, nice video, thanks !
    I have a question :
    If you connect the solar panel to the charge controller and the load to the charge controller too. On a sunny day should your load get power ? Note there are no batteries !
    What do you feel ?

  14. as long as solar is marketed in the diy or a-la cart fashion by breathless geeks it will never be embraced by the public at large… all your vids are excellent and informative. but when buying a car does the average shopper need to contemplate compression ratios, cam lift, brake chamber viscosity, cooling cavitation… no they want seating, color, leg room etc… solar needs a deep rethink on how to package and sell.itself…

  15. I got a free grid-tie 20V nominal 60 cell 250W panel that has a smashed glass but is still working, can I safely use it with a PWM controller to charge a 12V battery bank (even though I'm loosing efficiency?) My first thought was to use it with a 24V battery and a UPS that I have lying aroung but then I learned that the 60 cell won't top off the battery.

  16. one question.
    will mppt charge controller work if the voltage from panels are not in the mppt range what is mentioned in the mppt charge controller manual? i mean TO ask will mppt totally shut off giving Power or it will work like PWM? thank-you for your answer in advance.

  17. hello , But I do not understand how the battery feeds the load when the irradition is unavailable, Plz explain me how the current flows in the other way

  18. Very good. I have à confusion, I live in indian States Uttar Pradesh. The highest temperature is recorded 43 degree C. I want to use Monocrystaline solar panel or should I use polycrystline panel. I mean temperature is between 15 degree C to 43 degree C. Please suggest. Thanks

  19. hi , please to explain to me something that confuses me .
    first i understand that ;
    (Vabs = 14.7v, Vfloat = 13.5v ):
    Bulk – full solar power until battery reaches Vabs
    Absorption – The battery is allowed to come to full state of charge at the Vabs
    Float – Vfloat low maintenance levels

    1) Is the controller discarding power during the absorption phase? I mean it can only control either I or V – and the other follows, right?

    2) Absorption confuses me a bit. Firstly because it just runs for a fixed time – not based on any sensors or anything. So how does it know it comes to a "full state of charge"? Is it that there's a typical SOC when bulk hits 14.7v and transitions to absorption? I realize it's triggered by 14.7v voltage, but is that usually 60% or 90% SOC?

  20. I am working on a camper solar system. I have C60 21.8% eff, vmpp (v) 0.574 cells, i am thinking to put on as much solar as I can fit. Here is my question: I am considering volts vs. amps, is there anyone who can tell 30 cells would produce enough volts to charge 12v batteries? Thanks in advance.

  21. Amy,, thank you for all your videos you are really our solar queen <3

    I have simple question , I saw some MPPT charge controllers say in their specifications that for example the MPPT CC is 60 A , and max PV input (24v battery): 1600 W

    but when I calculate it 1600 W / 24V = 66.67 A > 60 A

    so is it ok to follow their recommendation about the 1600 W PV maximum input for 24 V battery???

    TriStar TS-MPPT-60 is good example

  22. i have 12 volt 5 watt solar panel…so what would be suitable solar charge controller for me? please suggest me specific charge controller!!

  23. Nice explanation, I have one fundamental question. I understand that the PV power will always go from the charge controller to the battery before it goes on to the load. This means the load is always fed by the batteries.
    My question is: Let's say the load is 100 W, and produced solar power is 200 W. Would the battery still be charged or will the power just go through the battery and directly to the inverter without charging the battery. Or will the PV power first charge the battery, and then deliver the necasarry power? When the battery is fully charged I assume PV power will still provide power to the load while keeping the battery fully charged, and only start discharging the battery when the load exceeds the PV power?

  24. what happen if the battery is fully charged, does the power coming from the pv module directly supplies the connected load?

  25. Hello,

    I'm slightly confused about your two calculations when sizing the mppt controller.
    In your first example you give a 1panel 30Vmp, 9Imp, 270W. You then divide 30Vmp/14V (voltage controller outputs)= 2.14. Then multiple this by the 9Imp to find current output by the charge controller stepping up the Amps = 19.28 to the batteries, correct? so to take into consideration the 1.25 possible increase in voltage at colder temps you would do 30*1.25= 37.5 V/14V= 2.67, then multiply by 9Imp =24.1A
    In the second calculation you then simply take 4 x 270W panels / 24V battery bank x 1.25 for safety to determine rating for the controller. = 56.25
    Given the scenario of 4 X 270W panels using method one 60Vmp * 1.25= 75 /28V =2.67, mutiply by 18A = 48.21A max output by mppt.
    Can you explain why you wouldn't use the first/last calculation to determine the Amp rating for the controller?

  26. super cool video! Does anyone know how a charge controller handles the excess power if its not transferred to the battery. (like after the batter is full?) Does the solar panel just stop generating without a place for the excess to go? does the controller burn it all of as heat or something? I'm really curious to find out what happens to all that uncaptured energy if it can't be put to use somewhere. Could an excessive solar panel array melt a charge controller if its producing way beyond your storage capacity?

  27. Hi all loved the video, clear and concise. We have an urgent problem, we have a 120 watt panel on the Land Rover, there is power going into the control panel but not going out to the battery. What would cause this please

  28. If each solar panel has its own wire (which is the case with Harbor Freight amorphous panels), then it doesn't matter much if they are series or parallel connected, cuz the current flow in them should be about the same, such as 12V 1.5A (each panel) or 48V 1.5A all 4 panels in series. You mentioned higher voltages reduce the current but that is misleading. There is no current reduction in this case, especially if you have 4 separate charge controllers, one for each of the four 12V batteries.

  29. Are the 24V,100W solar panels available n market? And are they efficient to give the required voltage. I want to charge a 48V battery pack but not getting the panel of 24V 100W capacity in market. Please suggest ideas.

  30. i have a 48v 18ah battery bank ( 4 batteries in a series) . i power a 48volt 750 watt (max draw) motor. i want to recharge this system using solar…..i simply cannot find anyone who can or will explain this to me. can i wire the solar panels to the controller…not use the controller for output..have the batteries wired to both the solar controller and the motor controller ? do i need to turn off the solar to use the motor ? i am completely lost in this regard……
    also- my solar array would only be 50 watts…two 25 watt panels @ 12 volts….unless i can mix wattage of the panels– due to the area available for the placement of the panels…..
    i looked at a mppt converter or two on amazon and i saw a couple that accept assorted input voltages and will give the 48volt output for my battery bank…
    i simply do not wish to buy a bunch of solar related equipment just to simply watch it all go poof the 1st time i try it out.
    I am lost…need help…

  31. Amy looks like the Stereotypical super achieving Female Nerd, but a cool nerd that we envision when we think of someone like the astronaut Sally Ride, or many other heroins in the field of Science, Medicine, Sports, etc. It wouldn't surprise me if she had a PHD in Thoeretical physics, and/or electrical engineering and graduate some ivy league college like MIT or UC Berkeley.

  32. I have 2 300w panels. I've noticed the 40a controllers are a lot cheaper than the 50's. Not sure how to go about it.

    Also the 600watts are 24v so I wasn't sure if I should make the whole rig 24v or not.

    Any help would be much appreciated.

  33. You know that the charge controller prevents the battery from getting discharged, that is it prevents the current flowing from the battery to the PV panel and instead lets the battery supply current to the DC load via charge controller in the night-time or in the absence of sun. In the daytime, the charge controller allows the battery to get charged via PV panel and at the same time, powers the DC load. Now the question is: if the battery gets fully charged in the daytime, then will the battery gets discharged during the daytime? Or does the charge controller disconnects the battery from the system? Please let me know asap because I'm extremely confused about it.

  34. The math annotations in the video are weird at 7:15… the way it's explained is terrible. The example should read, if you want to run 1500w heater for an hour, you need to generate at least 1500w in one day. Since you only make 300w, you will need 4 more panels (totaling 1500)to generate the 1500w your heater consumed.

    the formula should be 1500w demand – 300w supply = 1200w deficit… 1200w (deficit) / 300w (generated per panel) = # of panels needed to get 1500w

    the second example is worse. 1500w x 5hrs = 7500w demand. 7500w demand / 300w supply= 25 PANELS not 2500w. 2500w is the total W generated for you system…again it's the same information but annotation doesn't match the explanation.

  35. In that MPPT charge controller example we are having a 30V panel charging a 12 V battery what should be the voltage of charge controller ?

  36. Please help me I want to charge two different batt 175 and 250 ah 12 v each with a single 50 A PWM and separate wires to each batt

  37. On my sail boat with variable shading from the boom Can I parallel a 24v 100w and a 24v 200w panel to a 100/30 controller to a 12 volt house bank

  38. I counted and have one 60 cell solar pannel. I have 1 brand new 12v agm deep cycle battery. Should I have 2 batteries for this?

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