I have a set of Dakota Alert sensors - basically an IR sensor setup with a radio transmitter to base, used to alarm for people/vehicles approaching.  https://dakotaalert.com/product/bba-4k-plus-solar-powered-wireless-infrared-break-beam-kit/.  I've connected to a Raspberry Pi to provide a push alert to my phone when people are coming: https://technpol.wordpress.com/2021/01/22/arriving-visitors-alerted-to-your-phone-or-watch/ 

They are solar powered, and installed in a shaded area.  The retailer reckoned the solar panels would still be sufficient, but they were wrong (which I suspected).  The solar panels are vertical, so even in full sun I think would be working hard to keep the unit powered (although they are quite large for my assumed power draw).  They are therefore running flat and stopping working.

They have a charging port, and can be charged with the 12v 0.5A wall charger that also runs the radio receiver.

I am working to plug in a larger solar panel to them, on a wire, so that I can put the extra solar panel in a sunnier position more oriented towards the sun.  I have so far installed this panel https://www.jaycar.co.nz/12v-5w-solar-panel-with-clips/p/ZM9050?pos=17&queryId=ed57dc8a769c96d4073fa7cd57546211&sort=relevance, plus this charge controller: https://www.jaycar.co.nz/miniature-12v-3a-pwm-solar-charge-controller/p/MP3762?pos=2&queryId=d7df5dce5cb3b1db7954ab0440b3b9cc&sort=relevance, plus some cabling, waterproof box etc.

The panel is often shaded, and looks to provide about 3-5v a lot of the time.  I don't think it's sufficiently charging.  My hypothesis is that although the charge light comes on, it actually isn't getting enough voltage to charge at all (it doesn't look to need much current, but clearly if you don't have enough voltage it won't charge).

So, with that background, the question.  I want to increase the voltage I'm getting, and I understand I still won't get much current.  My schoolboy electronics knowledge says I can wire two solar panels in series to in theory give me 24V total.  My reading and observation of the panels tells me that the rated voltage and actual delivered voltage bear little resemblance, and the delivered voltage depends on sunlight.  So, I have two situations:

1. The panels are shaded, and deliver about 5-6V each, so by wiring in series I get 12V total.  I think the units actually need 7.5V to charge (and are therefore limiting the 12V input to 7.5V internally anyway), so this would work fine

2. The panels get full sunlight for a while, in which case they deliver 12-15V each, and I get a total of up to 30V.  As I understand it the charge controller will automatically cap this to 12V, so I still won't fry my equipment.

Is this sound logic, or am I missing something obvious?

Thanks,