Thinking out loud

[Mike Gleason jr Couturier]

Hi Dacian,

I was wondering for a future DMPPT, instead of switching the number of panels, how about always have a constant number of panels and switching the cable length instead? (provided we have a single cable)

I had an idea about a crude MPPT water heater with 2+ elements inside with different resistance that we could switch from one another or do combinations to get to the nearest maximum power point of the panels.

With a single wire in concrete it could be the same. There still would be a single wire so the cost is about the same, and we could put a fixed number of panels. We could then put terminals at different length: 100% - 90% - 80% - 70%- 60% - 50% etc.. the mppt would switch to the proper wire length. The wire could be laid out in a way that it always cover the entire surface wherever it is shorted, it would be just sparse when let's say 50% is connected. And the shorts terminals could be near the same place.

What do you think? Just throwing ideas, I don't think I will ever build that water heater :P

[Dacian Todea]

Mike,

This is how the DMPPT450 actually works and all panels are connected at all times.

The confusion is probably because there are two functionalities in the DMPPT450 one is the heating where the entire PV array is always connected and a number of heating elements are switched ON or OFF to keep the PV array at max power point.

The other functionality is to divert some of the PV array to battery charging and there is where some of the PV panels are diverted to an SBMS for charging a battery and there say you have a 200Ah battery and want to keep the charging to 50A max you will need to divert different number of panels based on the amount of solar light available. So in a sunny day maybe 6 panels are enough to be diverted to SBMS in order to charge around 50A while in a cloudy day the entire 30 or 40 panels may need to be diverted to be close to 50A.

All the panels that are not diverted to battery charging will be used for heating so no panels are even disconnected. 

[Mike Gleason jr Couturier]

Oh thank you very much I didn't I didn't know it was working like that thank you very much that's awesome. I don't need an mppt right now but I will keep it in the back of my mind!