The Medium Voltage Solar Array is an Industrial Craft 2 generator. It is a more efficient version of the Low Voltage Solar Array, producing 64 EU/t instead of 8 EU/t in the same amount of space. This is the equivalent of 64 Solar Panels or eight Low Voltage Solar Arrays. It is still bound by the same placing restrictions, working only in direct sunlight and generating far less EU in rain and thunderstorms.
The Medium Voltage Solar Array is part of the crafting recipe for the High Voltage Solar Array. Medium Voltage Solar Arrays can also be crafted with an Iron Helmet to create the MV Solar Hat, which acts as an upgraded version of the LV Solar Hat.
MV Solar Hat Shapeless Recipe