I agree with Wolfhound that imports (needs) and exports (abundance's) of planets.
As to energy importer, I guess to me it would say that the planet is one of the following; not that advanced tech wise, does not have that many people so it does not need advanced infrastructure, planet lacking in resources, a frontier world or throw back planet or the planet is an extreme environment.
I think that I would need or would like to see more info about the planet in some way as net energy importer is very vague. I hope that advances in tech can be able to build basic energy supplies from the following, dramatic changes in temp (low level electricity), wind, solar, water (hydro and wave) and even something like vacuum power from SM:P or Dark Energy power.
Then there are things that might be possible such as Psionic Power or Magic Power depending on your game universe. Those can be a really interesting universe plot line or plot point, IMHO
MDC