Everybody knew that Tesla was going to be announcing some kind of home battery at a press conference on April 30. In fact, Jim Motavalli wrote about it last week. But nobody knew what a game-changer it was going to be. Overnight, the world order in the electricity industry has changed.

The big utilities that supply our homes and offices with electricity can’t store the stuff; they have to make it to order. That means the electrical system has to be sized to meet peak demand, usually in hot evenings in August when all the air conditioners are running. The utilities also can only handle so much renewable energy — not knowing when the wind is going to blow or when clouds might shade the solar panels. The utilities have to plan for the worst.

Tesla Powerwall battery

Here are the nitty-gritty details. (Photo: Tesla)

It's long been known that batteries are the solution to this problem, but they've been too expensive and the systems for managing them too complicated for the average homeowner. Now Elon Musk and Tesla Energy have done for batteries what the iPod did for the MP3 player: make them simple and elegant. They have also made it astonishingly affordable at $350 per kilowatt/hour, or $3,500 for a 10kWh battery system.

Before you plan on cutting the cord to your utility, note that the unit feeds out only 2,000 watts on a continuous basis and 3.3 kW at peak load. To put that in perspective, a hair dryer can burn 1,500 watts and a clothes dryer can consume 4,000 watts running at the hottest setting. (I joked over on TreeHugger that Tesla should ship a clothesline with it, because the dryer is the biggest load in the house.) But things have changed: lighting consumes almost nothing now because of LEDs, and if you think like an off-gridder and reduce your electrical demand as much as possible, you can get awfully close. 

Peak solar and how the grid works

Think about how your day evolves: You use more power at home in the morning and at night — simply because that's when you're there. (Photo: Tesla)

The system isn't designed for going off grid. Its main function is to even out the load curves. We all use a lot of power in the morning and the evening, but the sun shines brightest at midday. Many utilities charge a lot more for power at those times, so if you can fill up the battery at night when power is cheap and at midday if you have a solar panel system, you can save money by using only the power from the battery during peak times.
As Musk noted: 

The battery can store surplus solar energy not used at the time it is generated and use that energy later when the sun is not shining; It is very important to smooth out energy generation.
The real magic starts to happen when these batteries start popping up in thousands or millions of houses and when the bigger power pack units that start at 100kWh are installed in offices and stores. As Musk said in the news conference, this leads to “a fundamental transformation of how the world works.” Utilities can more confidently invest in renewables. Musk notes that there are 2 billion cars and trucks on the world’s roads, and that 2 billion of these batteries could switch the world over to renewable power. That will take a while to achieve, but it's doable. (After all, it took a while to clog the world with 2 billion cars.)

If we keep driving down the demand side with better houses, more efficient appliances and lighting, and we keep cleaning up the supply side with renewable energy and the batteries to store it, we might be able to decarbonize our electrical system in a reasonable timeframe. That’s truly world-changing. 

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Lloyd Alter ( @lloydalter ) writes about smart (and dumb) tech with a side of design and a dash of boomer angst.

Tesla's new Powerwall battery could be world-changing
Build enough Powerwall batteries and you can run the world on renewable resources.