You will more than likely get this naturally as you play through the game, however for the purpose of this achievement you can get this one easily right from the start.
All you need is 1x steel plate in order to build the foundation for a solar panel, just the foundation for one is enough to count towards the achievement without having to fully construct a panel. Simply build one foundation (or as many as your steel inventory allows), grind it down to destroy it and get your materials back and repeat! You do not need to have 25 in your world at once, you just need to have "built" 25 total throughout your save.
Edit: Additionally you can get this through the use of the admin panel (brought up by pressing
+
) and clicking to "Enable creative mode tools". With this on you can then simply drop the required 25 solar panels into your world. Thanks to
markhamfists for pointing this out to me.
Note: This achievement may also need to be done in your own world in order for this to pop.