A co-worker and I discussed the feasibility of swapping out batteries
of electric cars in an effort to reduce charging time (from hours to
minutes). Curious, I searched the web (and newsgroup) to see if this
has been discussed before, and it has:

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm 94Jul11.183022.9498%40ultb.isc.rit.edu&rnum=1&prev=/groups%3Fq%3Delectric%2Bcar%2Bremovable%2Bbatteries%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26selm%3D1994Jul11.183022.9498%2540ultb.isc.rit.edu%26rnum%3D1

Let's do a preliminary economic analysis. Got some numbers to crunch. For a hypothetical service station between SF and LA, assume:

(1) 10 cars can be serviced simultaneously

(2) 15 minutes needed per battery change/fillup (i.e. full-service attendants on forklifts)

(3) each car battery holds 100 kW-hrs (3.6E8 J)

(4) each charging station in the "charging warehouse" will be 10 ft by 10 ft.

(5) attendants are paid $20/hr (burden rate: workers comp, OASDI, SS, income taxes etc.)

(6) $0.15/kw-hr electricity

10 cars every 15 minutes is 40 changes per hour. Let's assume the "charging warehouse" must hold double this: enough for 80 batteries.

At 10' by 10' per charging station, that's 100 ft^2 x 80 batteries 8000 ft^2, or about 90 ft by 90 ft of charging warehouse.

Charging 80 batteries per hour, at 100 kW-hr per battery: 3.6E8 J/charge x 80 charges/hr x 1 hr/3600s = 8 megawatts of electric power needed.

For 15 minutes of service per customer, the station spends $5 (at $20/hr employee burden rate), cost passed on to the customer.

With electricity at $0.15/kw-hr, 100 kw-hr/battery is $15 per battery.

So, the customer spends a minimum of $5 + $15 = $20 per battery change.

This amount excludes any profit, and also excludes loan amortization for the charging equipment, "charging warehouse" engineering/construction and forklifts.

Any thoughts?

Mike Darrett

http://groups.google.com/groups?hl=en&lr=&ie=UTF-8&oe=UTF-8&threadm 94Jul11.183022.9498%40ultb.isc.rit.edu&rnum=1&prev=/groups%3Fq%3Delectric%2Bcar%2Bremovable%2Bbatteries%26hl%3Den%26lr%3D%26ie%3DUTF-8%26oe%3DUTF-8%26selm%3D1994Jul11.183022.9498%2540ultb.isc.rit.edu%26rnum%3D1

Let's do a preliminary economic analysis. Got some numbers to crunch. For a hypothetical service station between SF and LA, assume:

(1) 10 cars can be serviced simultaneously

(2) 15 minutes needed per battery change/fillup (i.e. full-service attendants on forklifts)

(3) each car battery holds 100 kW-hrs (3.6E8 J)

(4) each charging station in the "charging warehouse" will be 10 ft by 10 ft.

(5) attendants are paid $20/hr (burden rate: workers comp, OASDI, SS, income taxes etc.)

(6) $0.15/kw-hr electricity

10 cars every 15 minutes is 40 changes per hour. Let's assume the "charging warehouse" must hold double this: enough for 80 batteries.

At 10' by 10' per charging station, that's 100 ft^2 x 80 batteries 8000 ft^2, or about 90 ft by 90 ft of charging warehouse.

Charging 80 batteries per hour, at 100 kW-hr per battery: 3.6E8 J/charge x 80 charges/hr x 1 hr/3600s = 8 megawatts of electric power needed.

For 15 minutes of service per customer, the station spends $5 (at $20/hr employee burden rate), cost passed on to the customer.

With electricity at $0.15/kw-hr, 100 kw-hr/battery is $15 per battery.

So, the customer spends a minimum of $5 + $15 = $20 per battery change.

This amount excludes any profit, and also excludes loan amortization for the charging equipment, "charging warehouse" engineering/construction and forklifts.

Any thoughts?

Mike Darrett