100 W Solar charging 12 V Prius battery while running

Hello board,

I’m planning to do this in an attempt to increase the MPG of my 2011 Prius. My car doesn’t have the roof solar panel, so I plan to add a flexible 100 W panel on it. The output of the panel will be connected to 2 solar charge controllers. One controller will charge an auxiliary deep cycle battery while the other one will charge the 12 V Prius battery. The + terminals of the two batteries will also be connected together via a blocking diode to allow current to flow only one way from the deep cycle battery to the 12 V Prius battery. Please see the attached diagram. I’ll also connect the charger in a way that when the 12 V Prius battery is disconnected, the charger will not energize the car.

My theory of operation is that while the car is running under the sun, the two batteries will be charged. The power from the solar charge controller to the 12 V Prius battery should supplement the charging power from the hybrid system and be used by the car’s 12 V systems, resulting in a higher MPG. When the car is parked or put on standby (not in READY), if the 12 V Prius battery becomes depleted, then the current (with higher voltage) from the auxiliary deep cycle battery will flow via the blocking diode to top it up. Power from the auxiliary battery can also be used when the car is off and not affecting the main 12 V battery because the blocking diode will not allow current to flow backward.

My main concern is that do you think the Prius’s 12 V power supply system (that gets power from the main HV battery) to charge the 12 V battery will be affected by the voltage and power from the solar charge controller? Or will the charge controller provide any output power at all because it will sense a high voltage from the Prius’s 12 V power supply system and interprets that the battery is full all the time? Any comments, suggestions or warnings will be highly appreciated before I proceed to actually doing this. In any case, if this is successful, I plan to do the same thing on my Alphard, with 2x100W solar panels instead of just one. Thanks everyone for your time!

 

Thank you very much for everyone's reply. I highly appreciate it. I believe that we do have a law on reverse engineering here in Thailand (but, honestly, no one takes it seriously). But, yes, as you pointed out, it will require a tremendous amount of effort and I'm sure that no one here would want to do it.

I really don't want to do anything with the HV battery. It seems too much for the amount of effort that I plan on this project. Thank you for your suggestion anyway. We don't have the Optima available here in Thailand, although I could buy it from Amazon and have it forwarded by sea to here. Having one in my Prius would be nice. And as you know that here in Bangkok it is hot to very hot for most of the year, so I'm sure that the warmup mode must be very quick or must never have been activated here.

So I'm not sure if I should proceed with my plan. There's a risk of burning my 12 V power supply system. Maybe if I finally decide to do it, I'll surely report the results here so that it will benefit everyone. Thanks everyone a lot for your reply!