I've got a bunch of solar cells whose maximum power point is at around 18V and a battery-powered system that uses 3S LiPo batteries (9-12.6V). I would like to interface these solar cells to the system in order to increase the endurance (i.e. operation time from battery full to battery empty) compared to the battery-only setup.
What are the minimal electronics required to achieve this?
I'm aware that the proper way to go is to use a MPPT, including possibly one that support recharging LiPo batteries. What I'm after is the minimal effort required to a working prototype where part of the system's power requirement is provided the solar cell. In particular, I don't require battery charging capability and it would be ok if the solar cells don't operate the maximum power point (i.e. it would be ok if it operated at battery voltage instead, which would yield about half the efficiency). Also, since the solar cell can provide only ~30% (~8W) of the total average power (~25W), the battery cannot be completely replaced and the power supply cannot be simply switched from either battery or solar cell depending on battery charge or lighting condition.