In this comparison of solar charge controllers, I would like to explain the differences between MPPT and PWM in more detail using a practical example and some theory. How do MPPT solar charge controllers work and is it even worth converting?
What does a solar controller do
Solar controllers establish the connection between the solar module and a battery. As the name charge controller suggests, solar controllers regulate the charging current to the battery. An IUoU charging characteristic is now standard and ensures fast and at the same time gentle charging of a mobile home battery.
IUoU charging curve, what is it?
IUoU is the extended IU charging method to which a third phase, trickle charging, has been added. The IUoU charging characteristic is made up as follows:
I= main charge with constant current
U= Equalizing charge (absorption charge) with constant voltage over a certain period of time
oU= trickle charge with reduced voltage
Lithium RV batteries can be permanently charged with this charging characteristic. The charge controllers described here in comparison also have a state of charge detection, which measures the battery voltage at sunrise and then adjusts the time of the U charging phase according to the previous state of charge.
Why not connect the solar panel directly to the battery?
As already described above, a charge controller monitors the voltage when charging a 12V battery. If you connected your solar panel directly to a battery, it would be charged, but you then have to monitor the charging voltage yourself. Once the final charging voltage has been reached, you must disconnect your module from the battery – if the voltage drops again, you must reconnect it. You can repeat this several times a minute over the entire absorption period.
If the module were not disconnected when the battery was full, the battery voltage would continue to rise. Sooner or later that would destroy the battery. Solar controllers primarily protect against overcharging a battery.
MPPT charge controllers also use the full power of the solar module and bring a higher charging current than if the module were connected directly to the battery.
Difference between PWM and MPPT solar charge controller
A solar module supplies electrical power. Solar modules consist of several cells which are connected in series. Each individual cell delivers a voltage of 0.5V. A 12V solar module with 36 cells results in a working voltage of 18V. 24V solar modules have 72 cells, which results in a working voltage (Umpp) of 36 volts.
PWM solar controller:
A PWM controller connects a solar panel to a battery, the current then flows through the controller to the battery. The module voltage collapses almost to the battery voltage. Basically nothing different than in the example above happens when we connect a solar panel directly to a 12 volt battery. However, when the battery is full (the absorption voltage is reached), the solar controller starts to work. It separates the module and battery from each other and when the battery voltage has dropped a few millivolts, the solar module is switched on again. This process takes place several times per second. This type of control is called pulse width modulation (PWM).
Solar modules deliver a certain current depending on the solar radiation. This current is independent of the module voltage. Consequently, the same current flows at 18V or 13V.
However, the module delivers power (measured in watts). Power is the product of voltage and current. Anyone who was paying attention in physics back then knows that electrical power can be calculated simply by multiplying voltage and current. As a result, the power at 18V is higher than at 13V, assuming the same current.
Calculation of electrical power:
Watts (W)=Volts (V) x Amps (A)
A = W : V
V = W : A
W = V x A
Can you already guess what I’m getting at? Now the MPPT controller is used.
MPPT solar controller
MPPT = Multi Power Point Tracking – in German something so much multi-point tracking.
An MPPT controller scans the power curve of the solar module and finds the highest power point. As a rule, a module delivers its maximum power at a voltage of 16-18V. The output of the module is now converted to the battery voltage, like a voltage converter that converts 12V to 230V or generates 12V from 24V. This type is so effective that, despite the losses in the controller due to the voltage conversion, significantly more power goes into the battery than with a PWM controller.
Here is a short example:
Bring 100Wp (example!!) in the sun 18V and 5 A (corresponds to 90W)
With a PWM charge controller you could charge a 13.5V battery with 5A charging current. Which corresponds to a power of 67.5W (at exactly 13.5V).
With an MPPT controller, the 5A and 18V are converted to battery voltage and at 13.5V 6.66A (90W) flow.
That’s the theory. Of course, our solar charge controller has this work paid for and the result is always a little less than what is put into it. But even if the bottom line is only 6 A, that’s 20% more power compared to a PWM trickle charger controller!
Comparison of MPPT to PWM charge controllers in practice
Brings MPPT really?
I tried it out for you once, what is true of the MPPT myth. A simple test setup with a battery, solar regulator and a measuring device reveals the difference.
MPPT to PWM solar charge controller – experimental setup
In comparison, two high-end solar charge controllers from Steca (PR1010) and Renogy Energy (Blue Power MPPT 75/15) are used. A 36 cell 55Wp BP solar module provides the solar power.
As a battery I use a 12.8V Lithium LiFePo4 battery, which I have equipped with a battery computer. With the battery computer, the effective charging current and charging power can be easily displayed.
The sun is shining, there are no clouds in the sky, ideal conditions for a comparison under real conditions.
The battery voltage is slightly lower during the first attempt with the Steca charge controller, which is why I will also state the charging power in watts so that the two tests can be better compared.
Experiment 1: Steca PR1010 PWM solar charge controller
The following data is determined:
Battery voltage 13.21V
Solar charging current 2.8A
Solar charging power 37 watts
Experiment 2: Renogy solar charge controller MPPT
Battery voltage 13.5V
Solar charging current 3.26A
Solar power 44 watts
20% more power with the MPPT charge controller – determined under real conditions in the sun and not in the laboratory! The emptier the battery is, the more effective the MPPT charge controller becomes. Or to put it another way, the further apart the battery voltage and module MPP voltage are, the more useful the MPPT controller is. An MPPT controller works with the MPP voltage from the solar module. This voltage is also always specified on the nameplate, usually as umpp to the no-load voltage. With the 12V modules, this voltage is usually around 18V, which results from 36 solar cells that are distributed on one module and each deliver 0.5V voltage.
Solar charge controller comparison
PWM charge controller
MPPT charge controller
Renogy MPPT 75/15
Solar charging current
Solar charging power
In normal charging mode, an MPPT controller will be able to achieve an average of 20% more power. In the worst case, when the plates are very hot and the battery is already quite full, the gain from MPPT technology will not be quite as great. On cold days, with empty batteries, a gain through MPPT can easily exceed 30% more power than PWM control.
Thanks to MPPT technology, 24V solar modules with 72 cells can also be operated at full power on a 12V battery system. These modules from building technology are usually cheaper and ideal for building large solar systems on the mobile home. For example, I have three 190Wp modules on the mobile home. They deliver an MPP voltage of 36V, which is first reduced to the 12V battery voltage by the Renogy MPPT controller at the battery. Because of the high voltage, the current in the solar cables is low. I can lay thinner cables and still not have such high losses.
Renogy MPPT charge controller
The Renogy MPPT 75/15 is a very simple controller, but shines with inner values. You will look in vain for a display, but it has very effective electronics with a very high degree of efficiency. The unbeatable price of less than 100 euros makes it the perfect solar controller for solar systems up to 250Wp (lying flat on the roof).
All data can be conveniently read out from the charge controller using a smartphone or tablet via a Bluetooth dongle. All Renogy MPPT controllers can also be adapted to any battery type with the Bluetooth dongle. Alternatively, there is also a USB data cable with which the controller can be connected to the PC. The PC software and mobile app are structured identically. Midnite solar classic 250 not starting. If you don’t need either, you can also connect a remote display (MPPT Control) in the design of the BMV battery computer to the Renogy charge controller.
Despite the many display options, it must be noted that only one option can be used at a time. So either MPPT control display or Bluetooth dongle (or USB data cable).
Renogy controllers do not offer a charging option for the starter battery, but a standby charger can easily be retrofitted in any vehicle for less than 30 euros. So I wouldn’t consider this a disadvantage.
All Renogy charge controllers are for 12V and 24V, the larger models even up to 48V battery voltage.
Alternative manufacturers for solar charge controller 12V
Except for the MPP 165 Duo Dig, all Votronic MPPT solar charge controllers have a built-in fan. Moving parts break down over time, I don’t like that much. Furthermore, they cannot be freely programmed, but you have to select preset charging programs. But what’s nice and that’s why I also offer the regulators: they have a charging output with 2A for the starter battery. Votronic controllers work just as effectively as the Renogy charge controllers.
Steca solar charge controller PWM
Steca builds great charge controllers with displays. The PR series (PR1010 – PR3030) has a nice LCD display and provides information about battery voltage, daily yield and charging current. But just for that reason it is not worth doing without 20% more power of an MPPT controller. Steca MPPT controllers are not bad for lead-acid batteries, but cannot be configured sufficiently for special requirements and do not have a graphic display.
In short, this practical test more than confirmed the theory. I am referring solely to the comparison results, in some other situations I have measured performance gains of 30% with MPPT controllers, especially when the battery voltage is very low or it is particularly cold and windy. MPPT controllers have also become significantly cheaper in the meantime and buying a conventional solar controller is not really worthwhile. Why give away expensive solar power with outdated solar controller technology?
My favorites are Renogy solar charge controllers. Renogy devices are passively cooled and you won’t find the beautiful Bluetooth display anywhere else.
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