# Am I saving a ton of cash by using Starbucks' power?January 28, 2008 9:55 PM   Subscribe

How much money am I costing, say, Starbucks if I charge my laptop there every day?

Hypothetically speaking, let's pretend that 300 times per year, I plug in at the local Starbucks and charge the battery on my MacBook from 0% to 100%. How much, broadly speaking, will this cost the Starbucks in electricity? In other words, how much would it save me if I never, ever charge the battery at home?

I recognize that there's probably some variables here, like the actual cost of electricity, but if someone could ballpark it for me, I'd be much obliged.
posted by terceiro to Work & Money (14 answers total) 4 users marked this as a favorite

It depends on the laptop, of course....

A quick google search puts Powerbook battery energy at around 50 watt-hours. Look at your power bill; it will give a rate for energy in terms of kilowatt hours. Divide that price by 20. That's how much you're saving each day by avoiding one at-home recharge of your laptop battery.
posted by mr_roboto at 10:10 PM on January 28, 2008

Probably around half a cent per day, given typical US energy costs.
posted by mr_roboto at 10:11 PM on January 28, 2008

Let's say your MagSafe power brick is the 60W variety instead of the 85W variety.

That's like one 60W bulb running fulltime for the maybe 4 hours it takes to fully charge the battery.

For 4 hours of a 60W power supply, you're using 240Wh.

My energy costs plus fuel costs are about 11¢ per kWh. Based on your profile, your kWh charges are about 4.7¢ (I don't know if Ohio charges fuel charges like Florida does, but Ohio is supposed to have some of the cheapest power in the US)

So, you're using roughly 1/4 of 1kWh, or about 1.2¢ of electricity per charge based on 4.7¢/kWh.

posted by tomierna at 10:13 PM on January 28, 2008

You have to assume a lot of variables here. Let's assume your battery is 10.8 V and 5000 mAh, and that the switchmode converter is 75% efficient, and that each charge is 1C, and that power costs Starbucks 20 cents per kWh. Using those figures and 300 charges, I come out with \$4.32 for the year.
posted by Rhomboid at 10:14 PM on January 28, 2008

My laptop charger is speced at 2A @ 120V. Assuming it takes around an hour to charge your battery, thats 1h * 240W = 0.24kWh. Assume 10cents/kWh, you are saving 2.4cents every time you charge up at Starbucks. At 300/yr, you can buy yourself another coffee every 6 months or so!! Hooray!!
posted by jpdoane at 10:16 PM on January 28, 2008

To put it in perspective, from a financial standpoint, you simply being there and taking a seat costs the company much more than your laptop recharge.
posted by geoff. at 10:18 PM on January 28, 2008

To put it in perspective, from a financial standpoint, you simply being there and taking a seat costs the company much more than your laptop recharge.

Unless of course, you're buying coffee
posted by jpdoane at 10:20 PM on January 28, 2008

You should also account for the charging efficiency of your laptop, which is typically 60-70% according to this document (though it is a few years old). So, 50 watt-hours takes about 77 watt-hours of electricity to charge. Since your profile puts you where electricity is cheap, that would still be around half a cent.
posted by ssg at 10:25 PM on January 28, 2008

Your filling a window seat to make the store look alive and attractive to other prospective patrons may or may not be worth less or more than the rough five-spot that we figure the actual electricity costs.
posted by kcm at 10:27 PM on January 28, 2008

So if you're really trying to put a dent in Starbucks' bottom line, charge your laptop there daily...but don't be pretty about it. Wear a gorilla suit or speedo every time you do this, scare some people away, and you'll provide a much bigger ripple in their water than just a power-suck.
posted by diastematic at 10:33 PM on January 28, 2008 [2 favorites]

If you'd like to make a difference, why not charge your 5kVa server UPS while you're at it?
posted by zippy at 11:52 PM on January 28, 2008

How much money am I costing, say, Starbucks if I charge my laptop there every day?

Significantly less than the profit they make on the coffee you buy while you're there.
posted by missmagenta at 3:43 AM on January 29, 2008

Not meant to be a de-rail, but I've often wondered about essentially the same question as it relates to the possibility of plug-in hybrid cars in the near future. Think about how many unguarded exposed outdoor plugins you see everyday.. I think alot of people would be very tempted to leech energy if the alternative was to pay for gasoline.
posted by jlowen at 10:29 AM on January 29, 2008

jlowen: Well, according to this article, you can go for 50km on a 5kWh battery in a plug in Prius, which assuming a 65% charging efficiency (these are the same batteries as laptops generally use), would be \$0.40-\$0.80 depending on local electricity prices. Considering you'll pay about \$2 for gas to go the same distance, I don't think people would object too much to a system in which you dropped \$1 in the meter to charge your car or something similar, though some people, as always, would be leeches if they could.
posted by ssg at 1:24 PM on January 29, 2008

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