Which solar controller is for me MPPT or PWM?
These are the two most popular types of solar charge controller, and although they both do the same job of taking the energy generated by your solar panel and safely ensuring it's stored in your battery. They go about it in a different way and have different features.
What's the difference?
A PWM controller is the cheaper and more basic of the two. They are however robust in their simplicity. As it's basically a switch, the voltage of the solar panel is often dragged down to a similar voltage of the battery.
The MPPT controllers don't do this. They adjust the input voltage (to the battery). This transformation of the power means that you can run a different voltage solar array to your battery bank (as they are no longer linked), ideal for joining multiple panels in series or using larger "24V" panels.
MPPT controllers excel when the temperature of the panels is below 45 Celsius and above 75 Celsius, meaning if you use your van in low light conditions or colder climates they will give you between 10% and 40% higher yield. (see UK panel temperatures). The other great advantage in campervans is that when a flexible panel is used, because they don't have much of a cooling gap, they run a lot hotter, so the MPPT controller can harvest a lot more power than a PWM controller in this situation.
A comparison
| Item | PWM | MPPT |
|---|---|---|
| Relative cost | Low | High |
| Efficiency | 60-80% | 95%+ |
| Parallel panel connection | Yes | Yes |
| Series panel connection | No | Yes |
| Performance in low light | poor | Good |
| Warranty | Typically 1 year | Victron offer 5 years |
Due to the variation in the performance based on temperature. Here in the UK, if you want to get performance out of your panel during the winter months, although the return will always be way down on the summer, (see here for expected solar yields), then an MPPT controller really comes into it's own here. Some studies suggest the variation in power harvested can be as large as 40%, whilst others more conservatively suggest 10-20%. Either way. It's quite a big difference.
To summarise
If you're using your van regularly or have high power demands, then the MPPT can't be matched. For a one off investment the upgrade from PWM to MPPT would make more difference than adding a second lead acid leisure battery or even going up one solar panel size.
However if you're just looking for something simple and cost effective to give you a little more power, then a PWM can be great. If it has all week to charge up your battery bank, and you're only using it for a weekend at a time in the summer, the PWM will do just fine. It can always be upgrade in the future if your needs change.
Thanks for reading. Have a good day!
Resources used to compile this article;
https://www.victronenergy.com/blog/2014/07/21/which-solar-charge-controller-pwm-or-mppt/