A new battery-powered electric bus pulled out of the driveway at SamTrans San Carlos headquarters Monday morning, its motor purring as it turned left onto El Camino Real. Designed by Burlingame manufacturer Proterra Inc., the bus is a replica of 10 that will roll out on the Peninsula next year, the first batch in the agencys effort to convert its entire fleet to zero emission vehicles by 2032. It wont be easy. SamTrans operates more than 300 diesel commuter buses that crisscross San Mateo County, each with a life span of about 12 years. The new electric buses cost $700,000 a piece about $200,000 more than a diesel-guzzling model and the agency will put a contract out for bid each time they order a new bundle. The electric buss motor weighs less than 200 pounds but does the work of a 2,000-pound diesel engine burning about a quarter-gallon of fuel every mile, Popple said. The emissions from that fuel build up, with typical city buses driving up to 40,000 miles a year. So, just one electric bus saves SamTrans 10,000 gallons of diesel fuel annually, which is enough to offset the added cost of the bus over a four-year period.

To calculate the height of the bar, we need to know CO2 abated from the electric switch and how costly it is. Do everything on an annual basis.

Discount Rate: 5%

Lifespan of electric bus: 12 years (or 6 years)

$ per electric bus: +$200,000 annual ownership cost is $22,565 every year for 12 years or $39,403 every year for 6 years (I used the =PMT function)

Diesel

Gallons of diesel used /year: 10,000

Cost: $3/gallon

CO2/gallon: 22.4pounds/gallon

Electricity

kWh used per year for the same distance: 2.5/mile100,000 per year

Cost per kWh: $.10

CO2 per kWh: 340grams/kWh

If we replaced every single public transit bus that burns diesel (just diesel, not gasoline, CNG, etc.) in the US, how much carbon could we save? i.e. what's the width of the electric bus abatement option for diesel buses? Assume half are using clean electricity like Sam Trans does (340 grams CO2/kWh, and half are using dirty (700 grams Co2 / kWh), and that otherwise they travel the same distance as a Sam Trans bus. Leave your answer in metric tons.