Homework answers / question archive / G3900 SP21 Exercise 5 Name: ____________________________   DUE: Monday, 29 March 2021, 11:59 PM   National Energy Impact: The power of small choices (Total: 20 points) What would be the collective impact be to our national electricity consumption, carbon emission, and ultimately $$ savings if we all made a deliberate choice to lower computer power use? Personal computers (PCs) consume about 65 to 250 watts (W) of electricity

G3900 SP21 Exercise 5 Name: ____________________________   DUE: Monday, 29 March 2021, 11:59 PM   National Energy Impact: The power of small choices (Total: 20 points) What would be the collective impact be to our national electricity consumption, carbon emission, and ultimately $$ savings if we all made a deliberate choice to lower computer power use? Personal computers (PCs) consume about 65 to 250 watts (W) of electricity

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G3900 SP21 Exercise 5 Name: ____________________________

 

DUE: Monday, 29 March 2021, 11:59 PM

 

National Energy Impact: The power of small choices

(Total: 20 points)

What would be the collective impact be to our national electricity consumption, carbon emission, and ultimately $$ savings if we all made a deliberate choice to lower computer power use? Personal computers (PCs) consume about 65 to 250 watts (W) of electricity. It turns out that a “screen saver” does not use any less power than a full screen, and with LCD screens, we don’t need to “save” the screen from burn in like old CRT screens. It is much better to put a PC to sleep then leave a screen saver on. So, let's consider: What would happen if all US homes put their personal computer (PC) to ‘sleep’ and turned off ‘screen savers’ when not in use at night?

Given the assumptions below for Case A and Case B, answer the four questions on page 4 as you calculate the energy required in Case A and Case B. You might find useful energy and carbon emission information at bottom of page 4.

Assumptions for both Case A and B:

· There are 50 x 106 homes in the U.S.

· Each home has one desktop PC; assume all U.S. PCs use 100 W at full power, and only 1 W in sleep mode.

· Case A: All homes leave PCs always on with screen saver on (full power all day).

· Case B: All homes put computers to sleep for 8 hours/day.

Hint: As you set up your calculations, pay close attention to the units! How the units cancel each other in the calculation will help you use logic to construct your equations.

Show all work (use a separate sheet if needed) and be sure to include proper units.

(1) How much electrical energy per year (in kWh) does it take to power all U.S. home PCs in: (a) Case A? (b) Case B? (5 points)

 

 

 

 

(2) How much energy (in kWh) is saved per year in Case B vs. Case A? Solve for both: (a) energy saved per PC, and (b) total energy saved for all U.S. homes. (5 points)

 

 

 

 

 

(3) Given the average cost of electricity in the U.S. is $0.12 per kilowatt-hour (kWh), how much money is saved Case B vs. Case A? Solve for both: (a) money saved per PC, and (b) total money saved for all U.S. homes (5 points)

 

 

 

 

(4) Given that the average CO2 emission for electricity generation in the U.S. (see below), how much total CO2 (in tons) is saved in Case B v. Case A? (5 points)

 

 

 

 

Basic units and references for electricity usage and Carbon emission

These will help you with the energy conversions you need to calculate the answers.

· Kilowatt-hour (kWh) - measures electrical usage (power used over some length of time). For example, 1 kWh operates one 100 watt bulb for 10 hours (100 W x 10 hr = 1000 Wh = 1kWh)

· Although the actual U.S. emissions of CO2 per kWh varies by fuel source: (i.e. http://www.eia.gov/tools/faqs/faq.cfm?id=74&t=11), we can assume an average national rate given the U.S. sources of electricity. The national average CO2 emission for generated electricity in 2016 was:

· 1,211 lbs CO2 per megawatt-hour (EPA 2017): https://www.epa.gov/energy/ghg-equivalencies-calculator-calculations-and-references)

· Remember, one megawatt-hour is 1000 kWh, and there are 2000 lbs in a ton.

· Handy calculator (to check work): http://energy.gov/energysaver/estimating-appliance-and-home-electronic-energy-use