ground sun little
You have very little space to build, and there is one block the creeper can destroy to get to the surface, so you'll need to be quick and deal with being energy hungry.
On the biggest size, there are six emitters, and the decaying ground will connect them all. I tried it with the highest complexity, and the emitter right beneath the surface had the rotating flow effect, which is probably what makes it difficult, so try that if you want a challenge.
I have to digress about the difficulty of that map... compared to some of the possible ones on the Impossible Code Maps (http://knucklecracker.com/forums/index.php?topic=7236.0) thread, this one's rather easy. rain to water (Small/High), for example.