Comment by powerbroker | Hacker News Reader

Comment by powerbroker | Hacker News Reader

This Sparks Nevada presentation suggested that the Tesla mega-packs would play a role in delivering 1 MW in charging capacity (4X the rates of the newest Tesla cars).

The older (Austin?) introductory presentation (2017-2018) of the semi spoke of ridiculously low 7¢/kWh electricity availability (which even in Texas is a ridiculously low rate). I can't help but think that when you tack-on the added expenses of:

  1. Site acquisition and leasing;

  2. Permitting;

  3. Design;

  4. Trenching and installation;

  5. Charger manufacturer;

  6. Ongoing maintenance;

  7. Added feature of a giant battery to feed the semi batteries

I'm finding it hard to imagine:

  a) that 7¢ was even realistic for grid power backing in 2018;

  b) that the enumerated costs above;

will be cost-competitive with current diesel prices.

Lastly, if its 30 minutes at 1,000 kW to reach 70% state of charge, then the battery is 500 kWh < x < 714 kWh. I'm thinking my math must be wrong somewhere... But if this is the ballpark, then this is going to be one expensive battery.

If we isolate the battery pack cost it is likely between $100,000 and $150,000. This comes from some data suggesting Tesla was purchasing cells around $140/kWh a year ago. Lets assume the rest of the truck costs the same (it won’t) and the Tesla Semi is $100,000 to $150,000 more expensive than another diesel Semi truck.

Average semi trucks get 6.5 miles per gallon and diesel fuel is around $5.00 per gallon right now. This translates to 77 cents a mile in fuel. Tesla semi uses 2kWh per mile. We can assume a hefty 20 cents/kWh price for commercial off peak power which translates to 40 cents a mile. With a delta of 37 cents a mile the $100,000 to $150,000 expense is paid off in ~300,00 to ~400,000 miles.

Semi trucks are built to last around 750,000 to 1 million miles and drive an average of ~50,000 miles a year. Thus the payback comes in around year 6 or 7 of a ~15 year lifespan.

I think $70/kWh on the cell level is closer to truth than $140. Might even be less at this point. A pack will of course have additional costs.

The battery is even larger than that. They did a 500 mile drive and claimed a slightly less than 2kWh/mi average efficiency. The peak charging rate is around 1MW.

7 cents/kWh is still doable with a large commerical solar farm and megapacks. My residential rooftop solar at over $3.00/watt installed is generating power at around that price (based on 25 year system lifetime). A commercial solar+storage solution should be able to hit that price.

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