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

  • 48V lead-acid battery
  • 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!

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  • \$\begingroup\$ 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. \$\endgroup\$ – winny Jul 22 '18 at 11:49
  • \$\begingroup\$ The current source will be limited by the weakest panel in series but combine in parallel , so aim for high noon \$\endgroup\$ – Sunnyskyguy EE75 Jul 22 '18 at 12:06
  • \$\begingroup\$ @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). \$\endgroup\$ – Lennart Jul 22 '18 at 18:51
  • \$\begingroup\$ @TonyEErocketscientist: Yes, but if I wire the panels in parallel, I'll not achieve the voltage I need. \$\endgroup\$ – Lennart Jul 22 '18 at 18:51
  • \$\begingroup\$ 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!! \$\endgroup\$ – Sunnyskyguy EE75 Jul 22 '18 at 19:55
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After the discussion in the comments above and asking some electrical engineers, I decided to go with the following setup:

  • leave the 48V battery-motor setup as it is
  • wire three 18V panels in parallel. While this is not optimal, the change in voltage due to shading or orientation should be much lower than the loss in current, so the total power output should be higher than wiring them in series
  • use a MPPT boost solar charge controller that will handle the panel output, boost the voltage to the level needed for battery charging and prevent overcharging of the battery

This is the low-cost version that will hopefully still yield good results. After construction and testing, I'll update you how well it works (or not).

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  • \$\begingroup\$ I'm interested in the results, as I'm planning to do the same thing. Is it for a boat? \$\endgroup\$ – Carl Löndahl Aug 7 '18 at 13:35
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    \$\begingroup\$ It's for a mobile application, but not for a boat. I think I'll have the results ready within a month from now. If you're looking for solar applications for boats, there are many resources out there in the internet \$\endgroup\$ – Lennart Aug 7 '18 at 15:10

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