MPPT controller vs PWM

[lw395]

If you are loking to trickle charge batteries at a mooring, then PWM and a smaller panel are adequate. If you're looking to run the boat from solar power completely, with a daily requirement of 1kWh or more then a MPPT is going to do a better job.

It's down to percentages.

A MPPT controller is perhaps 15% more efficient than a PWM in northern climes ...

15% of a 50W panel would mean 7,5W lost by using a PWM instead of MPPT.
15% of a 400W array would mean 60W lost - here, MPPT is a better choice.

MPPT makes alot of sense if you need alot of power from your solar installation, PWM is fine for trickle charging on a mooring or marina berth or for low power applications.

You also need to look at the efficiency of the charging regime.
If your controller goes to float after 3 hours of CV charging, will it have charged your batteries enough?

The efficiency of extracting energy from the panels and converting it to charging volts only matters while the system is current limited. As soon as the battery reaches 14.4V or whatever, it ceases to matter how efficient the power conversion is (provided you don't increase the loads further).
If you run big loads in the daytime, then the system will take longer to get to 14.4V, so efficiency will matter more. It often comes down to how hard the fridge has to work.
You can balance paying for efficiency against buying more/bigger panels or better batteries perhaps?
If you can only make space for a panel that's smaller than ideal, efficiency will matter more.

 

[Baggywrinkle]

You also need to look at the efficiency of the charging regime.
If your controller goes to float after 3 hours of CV charging, will it have charged your batteries enough?.....

Sorry, you're right. My assumption - which I didn't mention in the post - was that both controllers have the same abilities in terms of 3 stage charging (bulk, absorb, float) algorithms and the only difference being PWM or MPPT.

It is often the case that PWMs being so much cheaper, also don't tend to be as sophisticated (e.g. ability to change battery type and target voltages/times to suit) - but this is also not always the case.

 

[rszemeti]

Be aware that it is not unknown for cheaper controllers marketed as MPPT to be the PWN type.

Ummm .. ALL the MPPT systems use PWM on the primary side to track the maximum power point, you simply could not do it with a linear regualtor, the thermal losses would be excessive and negate the purpose.