Choosing the Correct Charge Controller
Selecting an efficient and properly designed charge controller is key to the longevity and efficiency of your entire battery based photovoltaic (PV) system.
Selecting an efficient and properly designed charge controller is key to the longevity and efficiency of your entire battery-based photovoltaic (PV) system. By optimizing the power coming in from your solar modules, you will get that much closer to offset your use of traditional grid power or another source of energy. In addition, you will be protecting your battery bank and thereby you protect yourself from any unforeseen and needless replacement costs. Your solar charge controller is an item well worth investing in and researching as you design your system. You'll need to choose an option that is scalable and appropriate for your power needs, as well as making sure that you have ample battery storage for the solar modules you have selected to install. CED Greentech can advise you on everything from optimizing your current system, to how to install your solar modules, to choosing the right equipment tailored to your needs.
Solar charge controllers are rated and sized by the solar module array current and system voltage. Most common are 12, 24, and 48-volt controllers. Amperage ratings normally run from 1 amp to 80 amps, voltages from 6-600 volts.
For example, if one module in your 48-volt system produces 8.05 amps and two parallel strings of modules are used, your system will produce 16.1 amps at 48 volts. Certain factors such as light reflection or cloud effect at irregular intervals can increase current levels. This is quite common. Therefore we increase the charge controller amperage by a margin of 25% bringing our minimum controller amperage to 20.13. We migrate over to our catalog and we find a 30-amp controller, which is a very close match. There is no problem going with a larger controller, other than the additional cost. This would allow you to expand the size of your system later on down the road if your load demands change or you find you need a little more power.
MPPT Charge Controllers
Top: Schneider Electric’s Conext MPPT 60 150 Charge Controller
Bottom: Outback Power's FlexMax 60, an MPPT Charge Controller
In the past, you would assume that the nominal voltage of your battery and your solar module array would be the same and that you would also choose that voltage for your charge controller. However, this school of thought is no longer commonly used as more efficient charging technology called Maximum Power Point Tracking (MPPT) has become widely available on many models of charge controllers. The primary feature of this technology is that it allows you to have a solar module array with a much higher voltage than your battery bank's voltage. The MPPT charge controller by design converts the higher voltage down to the lower voltage.
MPPT Charge Controllers have the added benefit of saving you a little bit of cash on wiring costs. A big advantage to having a higher voltage solar module array is that you can use smaller gauge wiring into the charge controller. Many times a solar module array can be over a 100 feet away (or more!) from the charge controller, keeping the cost of the wiring down to a minimum is usually an important target for the whole project. When you double the voltage (e.g. from 12 to 24 or 48 volts), you will decrease the current going through the wires by half each time which means you use much less copper, saving you money.
Example of Sizing an MPPT Charge Controller
For example, you could have a 3,000-watt solar module array that operates at 93.3 volts DC and your battery bank is 48 volts DC. MPPT charge controllers are rated by the output amperage that they can handle, not the input current from the solar module array. To determine the output current that the charge controller will have to handle we use the very basic formula for power in Watts:
Power = Volts x Amps
Here we know the power is 3,000 Watts, the battery bank is 48 volts, so:
3,000 Watts = 48 volts x Amps
which gives us:
Amps = 3,000 Watts/ 48 volts
Amps = 62.5A
We still want to adjust this value by 25% to take into account any special conditions that might cause the solar module array to produce more power than it is normally rated for (e.g. due to sunlight's reflection off of snow, water, extraordinarily bright conditions, etc). So, 62.5A increased by 25% is 78.13A. In this case, we'd probably choose an 80 Amp MPPT Charge Controller, like Outback Power's FlexMax 80.
Another Benefit of MPPT Charge Controllers
Because MPPT charge controllers can handle a higher input voltage from the solar module array than the battery bank's voltage, you can also use these charge controllers with solar modules that have voltages that don't match your typical system voltage (i.e. 12, 24 or 48V). For instance, you could have a solar module that has a nominal voltage of 31.1 volts and charge controller and battery bank that's 48 volts efficiently with an MPPT charge controller.
Keep in mind that MPPT charge controllers have a maximum system voltage limit that they can handle from the solar module array. It's important that you make sure there is no condition that the solar module array voltage will go above this limit or you could potentially harm the controller. You want to make sure that the open circuit voltage of the solar module array does not go above this value. You also want to give yourself a little bit of a margin for safety to take into account for the potential that an array's voltage will actually increase the colder it gets. If you give yourself a 25% margin of error you will be alright.
Here's an example:
We'll use twelve 31.1 volt SolarWorld 250 Watt solar modules with four parallel strings of three in series for a nominal voltage of 93.3 volts and a 48-volt battery bank. We'd like to use a Schneider Conext MPPT 60 150 charge controller. If we look at the module's specification page we see that each module has an open circuit voltage of 37.8V. That means the array has three times that because there are 3 modules in series. So the array open circuit voltage is 37.8V x 3 = 113.4V. We'll increase this by a safety factor of 25% and we get 141.75V. Now we'll look at the Conext MPPT 60 150's specifications and we see that it can take a maximum of 150 volts. 141.75V < 150V, so you’re good to go!
Hi i would like to ask. If i have a 30A solar charger controller, is it able to fully charge a 100A drycell battery? Thanks in advance
For solar charge controllers, it's more of sizing these to the solar system than the battery size. Their really isn’t a cap on battery size to solar charge controllers, really charge controllers need to be sized to the solar amperage and the battery voltage. Thanks.
Please can i connect parallel 60amp and 80amp all mppt charge controller to charge a battery bank with different solar panel array input.
Thanks for the question. The charge controller voltage output rating needs to pair up with the battery voltage and the current rating needs to match up with the amount of DC potential so as to properly convert the energy of the system for the battery to safely receive. We suggest that any configuration questions of specific charge controllers be directed to their manufacturers so as to not void any warranties or specific nuances to individual systems.
I got to tell you that your explanation of the charge controller left me a little confused because I always understand that the first number on a charge controller pertains to its voltage and the second to its amperage. For example the MPPT 60 150 controller has a rating of 60V input and 150A output.
Sorry for the confusion. Yes you can parallel charge controllers but the voltage outputs need to match up so there isn’t electrical conflict within the system. Thanks.
I have a 3Kw off grid solar system which uses the Conext MPPT 60 150 Charge controller, it is normally charging my batteries at 1A and 36V, we are in peek sunshine and therefore my system is generating only 36 Watts, why does the system not utilize the remainder of the 3kw.
The way the off grid system is designed is such that all power for the house is via the batteries, most of solar power is lost, resulting in a semi charged battery for the night time, and over a few days with only a fridge running the batteries are loosing there charge, with a full 8-10 hours sunshine. Is it just me or has this system got a fault or has it been badly designed?
I am currently looking to modify the system so that it works as a hybrid grid tied system (without being tied to the grid), buying another inverter and generating AC to the conext XW+ 7048 inverter to charge the batteries from the AC generated.
my other idea is to split the solar panels into a 2kw system for AC production and a 1Kw for DC production using the MPPT controller.
this way I will have 2Kw solar power (with additional boost support from battery for large loads) and a fully charged battery system for the night time.
All advice welcome
Hello. I cannot speak to how your system is designed since details are not provided, but I would suggest that there is likely either a design error and/or an issue with some piece of equipment within the system.
In regards to the notion of going hybrid on-grid + Storage, Hybrid systems are a personal preference and there are financial decisions that should weigh in the benefits to best make choices that could help make the most sense.
I have a 150watts solar panel with maximum current of 10AMP at peak
My solar charge controller is 30AMP
So my question is does choosing of a higher amperage controller affect the rate(charge at a fast rate) at which my 75 Ampere battery bank is charged
Does this aid in damaging my battery
Thank you for you comment. In general oversizing, a charge controller is not harmful and shouldn’t have any negative effects on the battery. As this relates to the charge rate, you’ll only get out what you put in less any efficiency loss or necessary wakeup/startup power requirements. It is always best practice to refer to the specific data sheets and manuals of both the charge controller and batteries to qualify your intended design.
Let us know if you have any additional questions. Thanks again.
I have two different mppt charge controllers , is it ok for the system? Thank you
Yes, you can have two different MPPT charge controllers on the same system and battery bank, but it is best to consult with the manufactures to ensure proper setup and that there will not be any issues. Thank you for your question.
I have an MPPT charger that is rated for 40 amps. The data sheets says it has a max rated charge of 520 watts and a max PV Array power of 1520 watts. I currently have one 12 v, 100 amp battery connected to the MPPT. I was hoping to run a 600 watt appliance with two 400 watt solar panels. The volts and watts of the panels falls well below the max for the MPPT. My question is, if the max rated charge is 520 watts and my solar panels can provide a max of 800 watts will the excess of 520 watts be wasted?
Thank you for your question. While your charge controller is capable of connecting with a maximum of 1520w of solar power it will only produce the rated 520w at the given voltage, which means yes the excess of your 800w system will not be utilized; however, most solar panels do not operate at their peak rating all day every day, which is why a charge controller would be designed to take up to almost three times its export.
I want to install 100 pieces of 350 watt solar panels to power an off grid premises. How many charge controllers do I need?
Thank you for your questions. We need to get more information before we can help. It would be more efficient if you complete a contact us form on our site and outline the problem then we can refer you to the right local sales person that can support you needs. Thanks again.
I have 400watts 24v solar pannel and 12v 200AH battery, what charge controller will be good for it.
Good morning. Many charge controllers could handle the problem you are raising. We need more information to properly answer your question. It may be best to reach out to us and we can put you in touch with a design professional that can assist you. Thank you.
Can you explain why a mppt cc has a limit on size of solar array? Obviously it can be advantageous to have excessive solar array for size of charger and bank to maximise power gain in suboptimal conditions. And I would have thought as long as the solar output voltage is correct, the size of the array should be irrelevant to the mppt charge controller as there is nothing to drive excessive current beyond its rating? (talking specifically mppt as opposed to pwm)
Generally, charge controllers need to limit intake power due to the internal components they used which have specific ratings. Excess energy can’t just be instantaneously released it has to be managed by the hardware within the charge controller so there must be limits. Thank you for your qusestion.
I guess I’m confused. you’re not calculating the open voltage per panel, but only per series. I thought that whenever you connected the panels in series it increases the voltage per panel. Example, four 12 volt panels in series equals 48 volts. So you are using the open circuit voltage of 1 panel per string instead of 4 panels? How is it that the open circuit voltage does not increase?
This article focuses on sizing the charge controller to the battery system using the total power of the solar array. The Voc and Isc of the panels do need to be considered in regards to the PV system construct feeding the charge controller so as to not overwhelm the input ratings. As the article states “Solar charge controllers are rated and sized by the solar module array current and system voltage. The most common are 12, 24, and 48-volt controllers. Amperage ratings normally run from 1 amp to 80 amps, voltages from 6-600 volts.” This is saying that the output voltages to the battery system are 12, 24 and 48Vs and the input voltage from the solar array ranges from 6-600V. Hopefully, this answers your questions. Thank you for reaching out.
Thanks for the article.
If the only variable to change in a system design is the input voltage (so I increase the solar panels from 12v to 24v, but they are rated for the same wattage), and assuming the correct mppt controller, and a 12v battery... Should the charging rate effectively double? I.e. will a 24 v input charge a 12v battery twice as fast as a 12v input, given the same wattage? (I understand there may be some loss in order to operate the controller.)
I've been trying to research this for a couple hours..
The simple answer is no, theoretically changing the voltage alone and not increase the total power won’t increase the charging rate. It easiest to look at it like the power going into a charge controller will be the power out(minus efficiency losses), so if you aren’t changing the power in, then you won’t change the power out to the batteries to charge. Thanks again for the comment. Hope this answers your question.