The announcement of Tesla’s Powerwall last week has been a long time in the making. The Solar industry in one of the fastest growing industries in US right now and a large number of energy conscious households are installing roof mounted PV systems. As discussed in a previous post (https://modern-off-grid.com/2013/12/30/to-grid-or-not-to-grid-thats-the-question/) the economics for a residential PV system is great – 8 year ROI on average. Producing and consuming your own power makes great sense. However overproducing power and selling it back to the grid does not, since your sell price is only a fraction of your buy price.

Now enter Tesla Powerwall.

Think of it as a small “off-grid-like” system that allows you to store your excess power from the peak sunny hours of the day and use them in the evening or at night when your PV system does not produce any power. Much like what my off-grid system does but with one major difference: You are still connected to the grid as your plan-b. If your Tesla battery runs dry it’s not the end of the world – you’ll have to buy some power from the grid to hold you over and wait for the sun to rise – so what!

In contrast, an off-grid system has no plan-b other than a noisy generator that starts as your batteries deflates. The required redundancy and spare capacity needed to avoid power failures makes an off-grid system much more expensive and complex.

The Tesla 10kW battery costs $3,500. I would need 7 of those to match my capacity = $25,000 or about 30-40% more than my “old school” lead-acid batteries. They are both expected to last 10 years+ only time will tell.

Again, for households on the gird there is no reason to have this much extra capacity and a 10kW battery will hold most normal house over for the night so $3,500 is a great investment and a great step towards energy independence for the average home.