According to many renewable energy experts, a stand-alone hybrid system that combines generation sources, such as wind and PV, offers several advantages over a single generation system.
In much of the United States, wind speeds are low in the summer when the sun shines brightest and longest. The wind is great in the winter when there is less sunlight. Since the greatest operating times for wind and PV occur at diverse times of the day and year, hybrid systems are more likely to yield energy once you need it. For the times when neither the wind generator nor the PV modules are producing electricity (for example, by night whilst the wind is not blowing), most stand-alone systems provide energy through batteries and/or an engine-generator powered by fossil fuels.
If the batteries run low, the engine-generator can be run by full power until the batteries are charged. Adding a fossil-fuel powered generator makes the system more complicated, but new electronic controllers can run these complicated systems without doubt. Adding an engine-generator can furthermore reduce the quantity of PV modules and batteries in the system. Keep in mind that the storage capability should be generous enough to supply