Much Narrower Than It Used to Be

If you want energy independence, buy two.

On the way to the Stanford Apple Store we stopped by the Tesla showroom, which had a steady stream of curious passersby. Everyone else looked at the cars, but I was interested in the Powerwall. Had consumer-level battery storage progressed to the point where solar-energy owners could be off the grid? (Normally excess electricity is "sold" to the utility during the day and is "bought back" at night. Capacious batteries would greatly reduce or even eliminate this relationship with the utility.)

I had phrased my question poorly. Tom, the Tesla salesperson, explained that while every home is legally required to maintain a connection with PG&E, two battery banks are sufficient not to have to draw electricity at night. Two Powerwalls installed would cost about $15,000, and a solar-panel system, as quoted by Tesla's competitors will run $20,000. Spending $35,000 when our electricity bill is about $2,000 per year doesn't make much sense, but the decision is much narrower than it used to be. Besides, showing off signaling virtue to neighbors doesn't come cheap.