Info about night operation:

The upside of wind power is that some areas such as coasts offer energy almost around the clock. Combining solar energy and wind energy can be advantageous in most areas to reduce the cycle effect of photovoltaics (energy abundance during the day, scarcity at night). Combining various forms of energy usually reduces the necessary storage capacity of our type of system.

Why do we need energy at night?
Well, for one it is often advantageous to water plants at night or in the early morning hours, when it's still cool. This lets the ground saturate before the daytime heat sets in.
Also, maintenance personal should have a source of energy for service 24h/day, just in case.