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Most solar panels are 12 volts, but 24 volt PV modules are becoming more commonplace. If you have a 24V solar panel though, will it work on a 12V battery? Or do you have to use 12V panels as well? The answer is yes, 24V panels can charge 12V batteries, but there are conditions.
24 volt solar panels can charge a 12 volt battery because when you wire the system, the panel voltage drops to match the battery. To avoid wasting power, use an MPPT charge controller because it will run the solar panel at maximum power before adjusting the voltage to work with the battery.
Solar Panel Volts and Battery Volts Explained
24V solar panels can work with lower voltage batteries because the voltage is not as important as the current. While this setup can work, you will waste a lot of solar panel energy unless you have a the proper charge controller.
Whether it is a 300 watt or a 150 watt solar panel , the connection will pull the panel voltage downwards so it is compatible with the battery. There is no risk of overcharging the battery because the voltage output is reduced.
Most 12V solar panels consist of 36 cells, with a 22V open circuit voltage and power up to 18V. A 24V solar panel has double the cells at 72 and the maximum power with 36V. Some 24V systems are even 48V.
So a 24V solar panel like the Newpowa 120W can charge up to 36V and generate a minimum 30% more power than the battery they are required to charge. This works for solar panels because they provide constant current. As long as the solar panel is at least 4 volts higher than the battery, it will provide a charge.
Solar panels have two important values, maximum current (LMAX) and short circuit current (LSC). These two numbers are close and is the current by which the panel charges, regardless of the voltage.
A Lot of Wasted Solar Energy
However, you are wasting the energy potential of a 24V solar panel by using it on a much lower voltage battery. The following example shows you why and what the solution is.
Suppose you have a 300 watt 24V solar panel. It has 72 cells and the Maximum Power Point Voltage (VMP) is 36 volts and the maximum current is 8.3 amps. To get the LMAX you divide the watts by the volts, in this case 300/36 = 8.3 amps.
If you charge this 24V solar panel to a 12V battery, it will charge at 8.3 amps and draw the voltage down to what the battery can handle. A 12V battery usually charges at 14.5 volts.
To get the watts, multiply volts by amps.
14.5 volts x 8.3 amps = 120 watts
Only 120 watts of the possible 300 watts from a 24V solar panel are charged to a 12V battery because of the low voltage. The rest of that energy – 180 watts – is lost and wasted.
This is where you need an MPPT charge controller.
Why You Need an MPPT Charge Controller
Charge controllers keep batteries from being overloaded when a battery is being charged. As the name makes clear, the device controls the charge going through the battery.
There are two types of charge controllers, MPPT and PWM. MPPT charge controllers are ideal when charging 24V solar panels with 12V batteries because the MPPT allows solar panels to run at the highest maximum power point (Pmax).
There are certain instances where PWM (pulse width modulation) controllers are sufficient. But in this case, MPPT (maximum power point tracking) is the better option. One we can recommend is the Suyima 60A MPPT Charge Controller, as it is affordable yet capable of handling high end solar panels and batteries.
PWM vs. MPPT Charge Controllers
PWM charge controllers are widely used because they are low cost. It is suitable for charging USB phones and simple appliances like lighting.
PWM charge controllers are directly connected to the solar panel and battery. A basic transistor is used to control the charge. It works fine, but a PWM controller pulls the solar panel voltage down to the battery voltage level. This prevents the solar panel from charging at maximum level.
An MPPT controller allows solar panels to run at the optimum level for the highest possible output . This translates to greater efficiency when charging a battery bank. An MPPT controller also works well with 48V batteries.
Your 12V battery could potentially receive up to 30% more power from a 24V solar panel using an MPPT charge controller. To understand why, we have to take a look at how an MPPT charge controller works.
How an MPPT Charge Controller Works
The amount of sunlight that reaches a solar panel varies throughout the day. This is why the current and voltage are always changing too. Whereas a PWM controller simply drops the panel voltage, an MPPT goes over the system to locate the best current and voltage combination to generate power.
That is why it is called a maximum power point tracking device. It literally tracks the maximum power points on a solar panel so it can adjust the voltage. Regardless of the time or the solar panel size , the controller will make the necessary adjustments to produce the highest output possible.
Bottom line: if you have a large solar array or charging solar panels and batteries with different voltages, use an MPPT charge controller. The money you spend will be well worth it, and you will recover it by reducing energy loss.
Can a 12V Solar Panel Charge a 24V Battery?
What if the situation was reversed? Can you use a lower voltage solar panel to charge a higher voltage battery?
You cannot charge a 24V battery with a 12V solar panel because the panel voltage must be higher than the battery. Even though 12V solar panels are really 18V, that is still insufficient to create a charge.
By connecting at least two 12V solar panels in a series, you will be able to power a 24V battery. Connecting solar panels in a series increases the voltage, so two 12V modules become 24V.
Setting up solar panels in a series is easy. Just connect their positive and negative terminals together, that’s it. Doing this not only charges the battery but prevents it from being overloaded by the solar panel.
Two 12V solar panels is the minimum required to do these charges. If you can hook up three for 36 volts that is even better. Remember too that the charge controller must still be the right size for the battery and solar panels to work.
Frequently Asked Questions
What charge controller should I use for my battery?
Most 10A to 40 charge controllers are compatible with 24V and 12V batteries. Charge controllers with higher voltages also work with 24V and up to 48V batteries. Some charge controllers are suitable with 12V all the way to 48V, and there are dedicated controllers for 120V batteries.
What is the maximum solar array size for a 24V battery bank?
The battery voltage determines the maximum solar array size. For a 24V battery, 1040W is the maximum recommended size for a solar array. For a 12V battery it is 520W. For a 48V battery it is 2080W. All of these can be managed by a 40A MPPT charge controller.
What battery and solar panel voltage does an MPPT charge controller need to work?
An MPPT charge controller will work as long as the solar panel voltage is 4 to 5 volts greater than the battery voltage. Note that this is the charging voltage, not the nominal voltage This is necessary because solar panel voltage levels drop when the temperature goes up or the sky gets overcast. The solar panel voltage must always be greater than the battery for MPPT charge controllers to function.
Can a 24V solar panel charge a 24V battery?
Technically it is possible, but it is best not to. A 24V solar panel charges at 30 to 40 volts. It is higher than the 14.5 volt range where 12V batteries charge. A 24V battery however, charges at around 28.V. That is lower than the 30 volt charge of 24V solar panels.
However, solar panel voltage levels can drop by as much as 6 volts in hot temperature. This means the solar panel voltage will be lower than the battery, making it impossible to produce a charge.
A lot of these elements may be confusing for someone new to solar, but it is essential to learn these. All these volts, currents and amps have to be fully optimized for your solar system to work. Once you know how different solar and battery volts work, you longer have to fear the unknown.