The killer feature of Tesla's Powerwall is the price

If you're not closely following the world of renewable energy, Tesla's big announcement Thursday might have been a bit of a letdown

In the simplest of terms, Tesla Powerwall is a big battery. You mount it on your wall, and you have power even when power fails (which, in most Western countries, is rare). Weren't there similar products like that before? Don't most people with solar-powered homes already have an energy storage solution? And is Tesla's Powerwall really worth $3,500 for a 10 kilowatt-hour (kWh) model)?

The answers are yes, yes and yes.