We bought a set of solar garden lights, they come with ground spikes, but we wanted to put them onto a wall. So I built a base that friction fits into the hole on the bottom where normally the ground spike fits into. All dimensions of the base are easily customizable in the SCAD file.

To get the right amount of friction fit, I measured the hole on the bottom of the solar lights, and then created different versions with 0.1mm diameter increase (30.3mm - 30.6mm) and tested them. The 30.5mm version was the best for my case. This will probably differ with each manufacturer of solar light. I had a previous type of light that needed a 28.1mm base, but I did not use them for unrelated reasons. So you will need to experiment yourself to find the right size.

The screw hole is sized for a countersunk screw with 5mm outer diameter thread.

The SCAD file references the library af-basics.scad which can be found here: https://www.printables.com/model/175914-openscad-library-for-more-basic-shapes

The base is printed in black PETG at 0.3mm layer height. I does not need to be pretty, but it should withstand summer temperatures.