I have been put onto a project that needs to be powered by a small (1-2 W) solar panel trickle charging a battery pack. The product will be located on rooftops.

We have reviewed similar products and have found them to be using NiMH batteries so are planning on following suit. I have reviewed many similar posts, particularly the below, but still have some unanswered questions, apologies if I am repeating the questions of others.

* [Charging 6 NiMH batteries in series via solar](https://electronics.stackexchange.com/questions/312101/charging-6-nimh-batteries-in-series-via-solar)
* [Charging NiMH batteries with 1W solar panel, charge controller needed?](https://electronics.stackexchange.com/questions/157069/charging-nimh-batteries-with-1w-solar-panel-charge-controller-needed)

The battery needs to supply power to a 12 VDC motor and a 24 VDC actuator (planning on boosting 12 V to 24 V) but these will only be active for a small amount of time each day, so overall energy requirement is quite low.

At this stage we are planning on using 10xAA NiMH 3600 mAh in series to get a 12 V output. I plan on using a Zener diode between the battery and panel to prevent back discharge at night.

The solar panel will be something like the 12 V model at the bottom of this page:
<https://www.futurlec.com/Solar_Cell.shtml>

I understand that trickle charging NiMH batteries is not ideal, but it seems to be commonly done and NiMH seems like the ideal chemistry for the application.

My questions are:

* Is a 12 V panel the best choice for trickle charging the 10 batteries in series?
* The panel linked outputs a peak of 80mA, 80/3600 = 1/45C, my understanding is that this is well within the safe limits for solar charging of NiMH, is there a benefit in regulating this to a constant current (with LM317 for example)?
* Should we be considering including an IC such as the DS2715 to monitor battery level and prevent overcharge, or is this completely unnecessary given the low output of the panel?

Happy to provide any more information that would be useful.