I've been on a huge mining kick lately and the sheer volume of places I've been that had no electromagnet power led me to figuring out an optimal, portable solution. "Just wire up solar panels and batteries" you say. Well yes, but did you know that each length of electrical wire takes away three points of your account-wide base creation limit? Also it doesn't look very nice. So here's what I came up with.

Make two Glass Cuboid rooms attached to each other in any orientation you like. The glass cubes are better than regular cubes because they don't draw any power during daylight hours, and also look nicer. Inside one cube put 4 solar panels. Inside the other put one solar panel and three batteries. On top of one of the cubes put your teleport gate. This rig will run 2 mineral or gas extractors and the teleporter forever. And it only uses 2+8+1+2+6+6 = 25 of your build limit, pipes and wires included. If you did it running wires it would use up 8 (panels and batts) + 1 (teleporter) + 2 (extractors) + 39 (inter-battery connections) + 18 (solar panel connections) + 6 (wires out to extractors) + 6 (long supply pipe and connector) = 80 of your build limit. More than three times as much.