Refrigerator Cost

Question

Your refrigerator uses an average of 350watts and your utility company charges $.10 per kilowatt-hour of energy (including taxes and fees). How much does it cost you to run your refrigerator for a year? Explain.

Answer 1

The cost of running the fridge for a year = (Cost of energy per hour) x (Energy used in 1 year)

 

We are given the cost of energy per hour: $0.10 per kW-hr

 

Let's get the power used in 1 year in terms of kW and hr

kilowatt -> 1000 watts (kilo = a thousand)

350 W x (1 W/1000 kW) = 0.35 kW

So, the fridge uses 0.35 kW of power.

 

1 year = 365 days = 8760 hours

 

Now multiply it out with your calculator:

( 0.35 kW )( 8760 hr )( $0.10 /kW hr)

$306.60 

Hope this helps!

Answer 2

Watts are a unit of power (unit energy per second in this case). 

The utility company charges $0.10 per kilowatt-hour, or 0.10/kW*hr. To do the conversion correctly, we need to convert watts to kilowatts. So 350 W = 0.350 kW. Over the course of one yr:

$0.10  x 24 hr x 365 d x 0.350 kW
kW*hr    1 d     1 yr

 = $306.06/yr

Which seems like a reasonable number over the course of a year. Notice that all the proper units cancel out, leaving only the units of money per yr (this can help you set the problem up, by letting the units work for you).