MPPT or PWM charge controllers?
MPPT or PWM charge controllers - quick decision
The decision between MPPT or PWM charge controllers has changed over time. In the past, the standard advice is to use a PWM controller for small solar systems and MPPT for large solar system. This advice doesn’t necessarily hold due to the reduction in price of MPPT charge controllers.
We recommend MPPT type solar charge controller when:
- Limited amount of space for solar panels (and want to use the energy as efficiently as possible).
- Shade conditions e.g. boat, campervan or caravan.
- Cloudy conditions (like the UK).
- You want to use less expensive solar panels (the cost of less expensive solar panels is often offset by the more expensive MPPT controller).
- Cold conditions like the UK (since PV panel voltage gets relatively higher than battery voltage – this makes MPPT even more efficient than PWM).
In many situations the benefits of MPPT outweigh the extra cost.
Visual appearance
They can look absolutely identical – they just have slightly different electronics inside.
PWM
Lumiax SMR10-R5
MPPT
Lumiax SMR-MPPT1050
PWM vs MPPT - Conclusion based on use case
Campervans and caravans
Why?
- They often experience shade – MPPT produce more energy in shade.
- Limited space for solar panels – MPPT maximise the output.
Recommend ideally using one MPPT charge controller for each solar panel.
Boats
Why?
- Boats often experience shade, especially yachts with booms and stays – MPPT produce more energy in shade.
- Limited space for solar panels – MPPT maximise the output.
Recommend ideally using one MPPT charge controller for each solar panel.
Shed/cabin with shade
Why?
- Shade reduces the output of a solar system significantly – MPPT trackers reduce this impact.
Shed/cabin without shade
Why?
- Without shade the diffence in output is very minimal and not worth the extra cost of a MPPT solar charge controller. Unless you want to use potentially less expensive 60+ cell solar panels.
How solar charge controllers work?
PWM
Pulse Width Modulation (PWM) solar charge controllers use an alogorithm to switch frequency to modify the output current over time. They operate at battery voltage.
MPPT
Maximum Power Point Tracking (MPPT) solar charge controllers asseses the maximum power voltage of the solar panels and modify the PV voltage to match the required charge voltage of the batteries.
Comparison
The decision as to whether to buy MPPT or PWM charge controllers can be summerised in this table:
