Monday, November 24, 2008

How much energy is used for a 140 degree latte?

We are not talking about the Rio Grande but the mid-size coffee serving at Starbucks. Yes Starbucks has Short, Tall, Grande and Venti sizes for their coffee and lattes. The Grande is a 16 fluid ounce size. I was recently in the Strawberry Starbucks when I overheard the patron in front of me ask for a 140 degree latte. Being a thermodynamics and green expert I of course had to ask the Barista what this meant. The Barista replied that the milk in the 140 degree is warmed less than the normal 160 degrees. Of course my mind started doing mental arithmetic as to how much energy Starbucks could save if all patrons became green and asked for the 140 degree Grande non fat latte with one Splenda and no foam single cupped.

Yes there are over 15,000 Starbucks stores and Starbucks has yearly revenues of nearly ten billion dollars. Soon there will be fewer stores as Strabucks has hit hard times with the terrible global economic downturn. I estimate they must sell something like 3 billion Grande equivalent drinks a year. Twenty degrees difference on a drink that weighs a pound and using a specific heat of 1.0 means 60 billion BTUs could be saved each year by Starbucks moving to the 140 degree latte. Each of the Starbuck espresso machines is powered by electricity. There are 3412 BTUs in a kilowatt hour. The added warmth of the drinks therefore equals 19.096 million kilowatt hours. The average heat rate of a coal fired power plant, the most common form of power plant in the world is about 10,000 BTU per kilowatt hour. This means about 1.25 pounds of coal needs to be burned to generate a kilowatt hour, therefore the 19 million kilowatt hours required 23.870 million pounds of coal. Coal is composed of approximately 50% carbon, the remainder is ash and moisture with a little hydrogen. Therefore 11,935,000 pounds of carbon are emitted each year to increase the temperature of the Grande cups of Starbucks from 140 degrees to 160 degrees. This is almost 6,000 tons of carbon. Expressed as carbon dioxide we have to multiply the amount of carbon by 3.67. Now that I have bored you all with tedious math, we have that Starbucks is emitting and additional 21,881 tons a year of carbon dioxide simple because the average patron did not request their 140 degree Grande non fat latte with one Splenda and no foam in a single cupped option. This is about the same amount of carbon dioxide that 4,000 cars emit in a year. Of course just driving to Starbucks to get the 140 degree Grande non fat latte with one Splenda and no foam single cupped drink causes an untold amount of carbon emissions.

Starbucks will be able to claim a lesser environmental foot print now that their business is stalled and they are closing stores. As for me I have to say I like my non foam Venti soy latte at 150 degrees. The cost of this drink is about half the price of Starbucks stock that now trades at $9.29 a share. Maybe soon Starbucks will give out warrants for their shares instead of coupons and they will change their name to Star with not so many Bucks.

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