Tesla's Powerwall will not piss off your utility company

The headlines over Tesla'a Powerwall have been nothing short of hyperbole: Tesla just made nuclear power obsolete. Elon Musk just seriously pissed off your utility company. Your whole concept of electricity has been turned upside down.

Let's do numbers for a bit. The high-end Powerwall is a 10kWh battery. If you have solar, this is what's meant to keep you going between dusk and dawn. And to illustrate the beauty of this new battery, we see this image of a Powerwall in a garage with a Tesla Model S:

Image Credit: Tesla/EboMike
A Tesla! Now let's see. On winter solstice in San Diego, the sun sets at 4:47pm and rises again at 6:48am. So we have over 14 hours without sunlight, i.e. without electricity from solar panels. And that's actually mild - Seattle would be 4:21pm until 7:56am, over 15 1/2 hours!

Tesla's own website says that a single refrigerator takes 1.6kWh per day, so 14 hours would be 1kWh. Since the sun sets early, you'll have lights running for a while. And a TV. Maybe you'll nuke some food with your 1100W microwave. Better not run the clothes dryer!

Adding everything up, you'll probably still end up under 10kWh, which is nice. But what about your EV? My puny Volt eats up 10kWh if I were to use a full charge. But this picture here shows a Tesla with a 85kWh battery, so if you happened to deplete it, you'd need 8 Powerwalls just for the car alone!

Chances are that if you work a 9-to-5 job, you'll arrive at home after 4:47pm, and you'll leave for work before 7, so charging your car will be entirely up to the Powerwall, which is completely and utterly incapable of doing that. Or, assuming you don't drive to much, it is, at the expense of having refrigerated food.

Look at how much energy my solar system generated in December 2014:

2.40kWh over 24 hours on a rainy day! Yeah, there's this thing. It sometimes rains in California in winter, and on those days you won't get much solar energy. Over the year, we're generating more than we use, but that's over the course of 12 months, not a single day.

I love the idea of a Powerwall. I'd love to get off the grid entirely and just take care of our own needs. Especially because of the ridiculous fact that SDG&E will leave us in the dark if there is a power outage, even during broad daylight when we're generating our own electricity.

However, the Powerwall is not the tool for that. It's a step in the right direction, but it's not the solution yet. In winter, the solar panels don't create enough to sustain the daily consumption, so you'd have to draw from the utility company.

If you have an EV, it's completely out of the question. A Tesla in particular would take its big 40A straw and suck the Powerwall dry like a milkshake.

And there's the other problem - the Powerwall isn't really designed to be constantly filled and emptied - it's meant to go through no more than 50 charging cycles per year, according to a SolarCity spokesman.

At best, it's a tool for non-solar users to avoid using electricity during peak hours, which is great. But why not go solar then? That's more economical in the long run, and more environmentally friendly.

Don't get me wrong - I'm a huge Tesla fan, and I can't wait to get off the grid. But a 10kWh battery in the garage isn't going to get you there. Maybe in a California summer if you don't have an EV. But over the course of an entire year? No.


Mellzah said…
It wouldn't be an ideal situation, but if you were looking to get entirely off grid with your home and had an EV, couldn't you do a partial charge at home and supercharge at a station?
Michael Krehan said…
Depends on the circumstances. Some companies like Google have chargers for their employees to use free of charge, so in those cases, it would feasible. In general though, charging stations are few and far between - check plugshare.com. Plus, logistically it's a bit odd - how do you do it? Do you spend an hour every day driving to a charging station to fill up your car?

It's particularly bad with a car like the Volt, the range is so small that you essentially have to charge it every day.

But again, the whole EV aspect isn't even the biggest issue - even without one, you wouldn't be able to get off the grid in winter.
Santokes said…
Get your studio to provide chargers.

Mine does and I don't even have an EV. So I just plug my battery into the EV chargers and leave it for the day. When the sparks die down that's when I know my car is ready.

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