Thursday, November 5, 2015

How far can you ride an electric bike on the power it takes to produce a Model S battery pack?

A truth of modern industrial society is that it takes energy to make things.

Sometimes, that energy is better spent doing things than making the thing to save energy or "be green."

Let's consider a Tesla Model S battery pack.  The shiny new one is 90kWh.

How much energy does it take to build a 90kWh pack?

http://www.lowtechmagazine.com/2015/05/sustainability-off-grid-solar-power.html makes some claims about lithium battery embodied energy.  It claims:
According to the latest LCA's, aimed at electric vehicle storage, the making of a lithium-ion battery requires between 1.4 and 1.87 MJ/wh
How much is that?  1MJ = 0.278 kWh = 278WH.

I'll be nice and use the lower end for Tesla's batteries. 1WH of lithium battery takes ~390WH to produce.

A Model S 90kWh pack, therefore, takes ~35MWh to produce.

http://seekingalpha.com/article/1261431-why-batteries-are-too-valuable-to-waste-on-solar-power-integration-and-electric-cars also does some math on the Tesla packs.  Their number is 472WH per WH of battery.
Based on an embodied energy of 472 kWhe per kWh of battery capacity, the Tesla's 85 kWh battery pack will have 40,120 kWhe of total embodied energy.
Well, 40MWh is within a reasonable tolerance of my numbers, so I'm happy enough with my back of the envelope calculations.

How far can that 35MWh take an electric bike?

A throttle-based ebike will consume somewhere around 35Wh/mi.  So... a million miles. :/

What if we use a pedal assist bike at 15-20Wh/mi?  Near as makes no difference, two million miles.

A typical American car travels 12k miles/yr.  If you drive for 80 years, that's 960,000 miles.

So... for the energy involved in creating one Tesla Model S battery pack, you can ride an ebike for your whole life.

Ouch.

7 comments:

  1. You can probably walk a million miles with the energy it takes to make an electric bike.

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    Replies
    1. Some studies have found electric bikes, even with a high carbon grid, to be better in terms of emissions than straight pedal bikes or walking.

      Bikes are significantly more efficient than walking.

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    2. That makes sense. Plus, electric bike owners put more miles on their bikes and use their bikes more often than those who ride non-electric bikes, and every trip you take on an e-bike is one less car trip.

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    3. (citation needed)

      The cyclists I know ride a lot more than the ebikers I know.

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    4. Your 100 mile weekend rides don't generally replace a car trip. They're recreational.

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  2. And that's just to make the pack!

    An ebike is on my medium term savings plan. I think it will help me stick with the bike versus car on several common longish trips I make with loads, but especially during winter, because I won't have to worry as much about getting sweaty underneath all my cold gear layers. (Yes, I'm the weird biker who complains much more about sweat when it is cold than when it is hot.)

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    Replies
    1. It's quite nice in the winter for that exact reason!

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