Hemispheres by Mark Everglade

Light is currency, light is big business on Gliese 581g, the last remaining colony of the human race.

Severum Rivenshear hunts those who steal it in the form of fireflies, just to have enough light to live by. He works in the icy, eternally dark hemisphere of Evig Natt, the sun an absent deity. The rest of the world pursues every pleasure beneath a sun that never sleeps.

Thalassa Latimer will rotate the tidal-locked planet faster, or die trying. Dedicated to bringing light to everyone, rich and poor alike, she will stop at nothing to achieve her goal, even if it means destroying the environment and toppling the economy.