# How to efficiently charge 48V battery-motor system with solar panels

I'm wondering how to efficiently charge and use the following system with standard 18V solar panels:

• 1kW electric motor

To charge the battery with either PWM or MPPT, the solar panel voltage should be more than 48V, if I understand correctly. Thus I can either boost the voltage to more than 48V (inefficient), or connect multiple solar panels in series (e.g. 3x18V=54V). The panels will not necessarily be oriented in the same direction, and shadows may be cast on individual panels, so I guess connecting them in series will make the whole array highly sensitive to the environment.

Alternatively, would changing the battery-motor system be an option? The 48V battery is made up of 4x12V packs, so I could connect them in parallel to form a 12V system that could easily be charged with the 18V panels. But I guess I'd require a new motor, right?

Any tips are appreciated!

• A boost solution could be just as efficient as any other. It’s very dependent on how long cables you intend to run. Can you show with a simple block diagram? If you have them in different locations, I would consider three separate boost converters, one for each panel. Commented Jul 22, 2018 at 11:49
• The current source will be limited by the weakest panel in series but combine in parallel , so aim for high noon Commented Jul 22, 2018 at 12:06
• @winny: The cables will be very short, less than 2m in total I'd guess. What kind of boost device would you recommend? Total power will not be very high (<150W). Commented Jul 22, 2018 at 18:51
• @TonyEErocketscientist: Yes, but if I wire the panels in parallel, I'll not achieve the voltage I need. Commented Jul 22, 2018 at 18:51
• Of course then if you aim in 3 directions, the weakest will limit the current of all 3. So to clarify it must be all aimed to sun or high noon in series!! Commented Jul 22, 2018 at 19:55