Why don’t renewable energy systems simply produce standard 120-volt AC power like the utility companies? It’s simple. No technology exists to store AC power; it has to be produced as needed. For a utility company, with a power grid spread over half a state or more, considerable averaging of power consumption takes place. So it can (usually) deliver AC power as demanded. A single household or remote homestead doesn't have the advantage of power averaging. Batteries give us the ability to store energy when an excess is coming in, and dole it out when there’s a deficit. Batteries are essential for remote or back-up systems. Utility intertie systems make do without batteries, by using the utility grid like a battery to make up shortfalls or overages. But this requires the presence of grid power and doesn't provide any back-up ability in case of a power outage caused by grid failure.