Mirrors must be placed in a circular shape around a Solar Turbine within a certain distance. The distance limit is not measured in blocks, but in actual distance, with the result that mirrors can go as far as 8 blocks in straight lines along the x or z axis, but they must be within five blocks on the diagonal.
Mirrors that are active will look like this, with the mirror facing the turbine:
While mirrors that are inactive will look like this, with the mirror facing the sky:
If a mirror is inactive, it needs to be either moved closer to the turbine, or have an obstruction removed.
Extra mirrors will cause the solar turbine to go faster and generate more Charge. The mirrors must have line of sight and will be blocked by all blocks, including blocks otherwise considered transparent like glass, or other mirrors.