Boron Power Plant

Solar Power Plants produce Energy Cells, the basis of the X universe economy. They require Crystals to accomplish their task.
NPC plants buy Crystals as a secondary resource only, and do not require them to produce energy. This provides an uninterruptable stream of Energy Cells, ensuring that the X-Universe economy is unable to run down and collapse.
A sector's Sun rating only affects the temporal interval of Energy Cell production. Higher Sun ratings do not make a Solar Power Plant more efficient in terms of Crystals used or Energy Cells produced, only that more Energy Cells are created and more Crystals are consumed in the same amount of time.