Question

All the remote learning and telecommuting during shelter-in-place means and increase in residential energy use from more people being home. Assume that a 60 watt incandescent lightbulb in each of the approximately 128 million U.S. household just burned out, and everyone is debating whether to replace it with another 60-W incandescent bulb or a 8.5-W light-emitting diode (LED). Assume that the 60-W incandescent and the 8.5-W LED deliver the same quantity of light. Assume an average emission factor for U.S. electricity of 119 gC/kWh and an average cost of $0.13.3/kWh. A typical LED bulb costs $2.37 and has a lifetime of 15,000 hours. A typical incandescent bulb costs $1.79 and has a lifetime of 1,000 hours.

1. Calculate the annual electricity savings from lighting if everyone chose the LED bulb. Assume the light is on for an average of 15 hours each day. Express your answer in kWh/year. [2 points]

2. Calculate the cost-of-avoided-carbon associated with investing in the LED rather than the incandescent (i.e., what is the cost of implementing this efficiency measure and what amount of carbon does implementing this efficiency measure avoid?). Express your answer in $/kgC.[Hint: Assess the relative costs and savings over a 15,000-hour time horizon. Note that you would need to purchase 15 incandescent bulbs to equal the lifetime of one LED.] [3 points]

3. Suggest two other energy-use energy efficiency strategies that could help avoid the shelter-in-place increase in residential energy use [2 points]

Answer 1

Ans) Number of houses = 127 million

Power consumed by incandescent bulb = 60 W

Power consumed by LED = 8.5 W

Total power consumed if incandescent bulb is used = 127 x 10^6 x 60 W = 7.62 million kW

=> Electricity consumed = 7.62 million kW x 15 hr/day = 114.3 million kW-hr /day

Number of days in year = 365 days/yr

=> Annual electricity consumption = 114.3 million kW-hr /day x 365 day/yr = 41719.5 million kW/yr

Total power consumed if LED bulb is used = 127 x 10^6 x 8.5 W = 1.0795 million kW

=> Electricity consumed = 1.0795 million kW x 15 hr/day = 16.1925 million kW/day

=> Annual electricity consumption = 16.1925 million kW-hr /day x 365 day/yr = 5910.3 million kWh/yr

Annual Electricity savings = 41719.5 - 5910.3 = 35809.2 million kWh/year

Ans) Emission factor of carbon = 119 gC/kWh

Average emission Cost = 0.133 $/kWh

Time = 15000 hrs

LED needed = 15000 /15000 =1

=> Average emission cost = 0.133 $/kWh x 1 = 0.133 $/kWh

Cost of carbon associated = (0.133 $/kWh) / (119 g C/kWh) = 0.0011 $/gC or

Number of incandescent bulb needed = 15000 hr / 1000 hr = 15

   => Average emission cost = 0.133 $/kWh x 15 = 1.995 $/kWh

Cost of carbon associated = (1.995 $/kWh) / (119 g C/kWh) = 0.0168 $/gC

Cost saved = 0.0168 - 0.0011 = 0.0157 $/gC or 15.7 $/kgC

Ans) To avoid increase in residential energy use following strategies can be used :

1) Installation of solar panels can reduce energy use significantely

2) Drying of clothes by using solar energy instead of using dryers or heaters