It turns out that if you place the Seeed SenseCAP Solar P1 Node strategically, it can withstand the harsh Dutch winters.
https://meshcore.jorijn.com/year.html
In mid-January, we experienced two or three weeks of no sun, only snow and rain. The charge dropped to 65%, but a few hours of sun brought it back to over 90%.
It hasn't fallen below 85% since then. What a neat little device.