Question

Many college students have a mini-fridge in their dorm room. A standard mini fridge costs roughly $100, uses about 100 watts of electricity per hour when it is running, and can be expected to last for 5 years. The refrigerator is plugged into an electrical socket 24 hours a day, but is usually running only about 12 hours per day. Assume that electricity costs $0.10/kWh.
(a) Calculate the lifetime monetary cost of owning and operating the refrigerator.
(b) Assume that the electricity used to power the refrigerator comes from a coal-burning power plant. One metric ton of coal contains 29.3 GJ (8,140 kWh) of energy. Because of the inefficiency of electricity generation and transmission, only one-third of the energy in coal reaches the refrigerator. How many tons of coal are used to power the refrigerator during its lifetime?
(c) Assume that 15 percent of the mass of the coal burned in the power plant ends up as coal ash, a potentially toxic mixture that contains mercury and arsenic. How many tons of coal ash are produced as a result of the refrigerator's electricity use over its lifetime?
(d) What externalities does your answer from part (a) not include? Describe one social and one environmental cost associated with using this appliance.
(e) Describe two ways a college student could reduce the electricity use associated with having a mini fridge in his or her dorm room.

Answer 1

The amount of coal burnt to operate the mini fridge is 0.81 metric tons.

What is energy cost?

The term energy cost refers to the monetary cost of operating a particular electrical appliance. Let us now answer the questions one after the other.

a) Power consumption per hour = 100 watt or 0.1kW. To operate it for an hour we have  0.1kWhr × $0.10/kWh = 0.01$ Since it operates for twelve hours a day 12(0.01$)= 0.12$ per day. In five years; 0.12$× 5 × 365 = 219 $.

b) Electricity used for the five years = 5 × 365 × 12 × 0.1kWhr = 2190 kWhr

Since 1 metric ton of coal produces 2713 kWh(considering energy losses)

x metric tons of coal produces 2190 kWhr

x = 1 metric ton × 2190 kWhr/2713 kWh

x = 0.81 metric tons

c) In part 1 we did not include the cost of the environmental damage caused by the mining of coal and the social inconveniences caused by the sound of the mini fridge.

d) The college student could reduce the electricity use associated with having a mini fridge in his or her dorm room by turning it off for some hours within the day.

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