equinitry, thanks for comments.I chose cone shape for simplicity, with center of mass in lower end and 20m drop, it should do the job on moderate hard ground.Solar is the way to go, as it is cheap, durable(with a bit of clear epoxy) and fairy predictable with power output.Maybe I add a few on sides to get at least some power when deployment goes in fugazi mode.

For this one, grid shape will change, but it will be definitely grids.Weight/material reduction,automatic opening,space savings and this spaceX/soviet missile scent ;)

For comms LoRa and mesh networking is the way in my opinion, gps goes out because you have one on drone, is power hungry and you know where you made the drop from logs.

Thermoelectric I have in mind for very simple sensor that stays for looong time.Minimal power,slow brusts of data. Space blanket with Peltier and simple pcb. It works on Antarctida, we will see how well it goes on 50degN :)

Geophone is interesting thought, but it feels like order of magnitude smaller that already weak TE.I will look into it.

Mmmmh sounds interesting, would use more like a rod hat for penetrating the ground with leg mechanism that it stands verticaly. Depending on you deploy system (with pressure or just release them and let the gravity do the job) solarcells in back might not be the best idea. You guidance fins dont look very good...make some normal one with actual use and maybe some moveable to guide it to a specific position. LoRa and gps to get and send data (just let em do it every hour to save energy). Thermoelectric sounds interesting but im not sure if cost/space/energy efficincy will be sufficent. Depending on size, maybe you could use geophone principle and get some energy out of it or use it as sensor hence you already penetrate ground (piezo/magnet coil)