Even the Energizer Bunny stopped to take notice of expansive thinker, futurist and entrepreneur Elon Musk’s announcement of Tesla home batteries for use with rooftop solar installations. Launched as the “PowerWall” the battery comes in two sizes — 7 kWh and 10 kWh, priced for purchase at $3,500 and $7,140 respectively. SolarCity, Musk’s rooftop solar company, is pairing the larger battery with rooftop solar systems as backup storage for use during grid power outages.

According to Musk, the demand for the Tesla batteries has been “crazy off the hook” as solar customers search for ways to complement their rooftop solar systems and become less dependent on the power grid for “pulling” power when their solar panels aren’t producing.

Although similar battery technology has been available for some time, the Tesla batteries are priced lower than most others and have the prospect of going even lower once Tesla’s battery mega-factory in Nevada starts production.

Besides – it’s Elon Musk!

Customers self-generating a portion of the power from solar panels would have a choice whether to store energy for their own use or sell the excess power back through the grid at a profit under net metering arrangements.

In Arizona, however, with utility proposals to lower net metering credits under consideration, the Tesla battery announcement has been called a game changer for solar. Paired with the new batteries, many believe solar companies and their customers can now thumb their collective nose at the utility companies seeking to charge more for grid access and lower net metering subsidies.

Not so fast.

The batteries have limited capacity and it would take more than one Tesla battery linked together to provide sufficient and reliable power at levels approaching what the grid offers. According to Bloomberg Business News, (LINK) the large Tesla battery, which SolarCity is offering “. . . puts out just 2 kW of continuous power, which could be pretty much maxed out by a single vacuum cleaner, hair drier, microwave oven or a clothes iron.”

Taking supplemental and backup power from the grid is not only more reliable, it’s less expensive, especially here in Arizona where retail electricity prices are lower on average than in states like California or Hawaii.

Nevertheless, with lower net metering credits and rate designs with demand charges for new solar installations being discussed and implemented, rooftop solar customers in Arizona could benefit on the margin by adding battery storage. Maybe.

Can they economically pull the plug from connection to the grid entirely?

No way. Not yet.

So, while battery storage for rooftop solar offers the promise of greater savings for consumers and less dependence on the traditional utility, it cannot yet replicate the cost advantages of the electricity grid.

But, that day will come – maybe even before Musk settles his first colony on Mars, where what little atmosphere exists is 95 percent CO2 and connecting to the grid never an option.