If batteries are used, then technically yes. But in practice, when grid power is available, it is recommended to use solar power in combination with the grid. Solar power can be integrated with your existing power sources (such as grid power, inverter, generator, etc.) so that the solar power to be consumed first is always automatically given priority. However, if you are using photovoltaics for night-time use or in a remote location, it is quite common to have solar systems that run on batteries.

Unless your solar energy system includes battery storage and you are fully off the grid, you will still receive a bill from your utility. However, you can dramatically reduce your bill, or even cut the amount you owe to $0, with a solar panel system that matches your energy use.

Solar panels are a highly proven, durable, and reliable technology and have been in use since the 1950s. A solar system that is designed, installed, and maintained well will operate for 25-30 years. Moreover, since there are no moving parts (unless you are using tracking devices to move modules that tilt with the movement of the Sun), there is practically negligible wear and tear.

Each roof is different. In general, the number of panels needed depends on the amount of electricity used and the amount of sunlight hitting the roof.