Transcript Newton’s second law of motion

Example of the Final Project
Possible Reduction of Greenhouse Gas Emissions
by Replacing Incandescent Lights with Compact
Fluorescent Lights (CFL)
Outline
• Introduction
• What are CFLs and why are they more
efficient than incandescent bulbs?
• How much energy can be saved per year
in British Columbia of all incandescent
light bulbs are replaced with CFLs?
• What is the effect on the CO2 emissions?
Introduction
• Government web pages and media suggest
replacing incandescent light bulbs with compact
fluorescent light bulbs to save energy.
• We want to know how much energy is saved per
household and estimate the energy savings in
BC if all the home lights were replaced by CFLs.
• We also estimate the corresponding reduction in
CO2 emissions.
• In our estimates, we take into account energy
used to manufacture incandescent bulbs and
CFLs. For the estimate of the BC energy
savings, we assume that ½ of all lights could be
replaced by CFLs on average.
What is a CFL?
• Ordinary incandescent light bulbs emit light
due to electrical heating of a thin tungsten
wire. They convert only a few % to visible
light (Lab 8). 90% – 95% of the electrical
energy is converted into heat.
• A CFL is based on light emission from a
gas discharge: An electric current is driven
through a gas ionizing the gas molecules.
The recombination of ions and electrons
results in light emission.
• For the same light output as a 60 W light
bulb a CFL needs only 13 W of electrical
power.
• (Source: Wikipedia)
How much energy would be saved
annually due to replacing these bulbs?
• Assume each bulb is switched on an average of
4 hours/day
• Average power 60 W. Replaced by 13 W CFL
= Savings of 47 W per bulb replaced
• Each home would save
10  47 W  (4 h/d  3600 s/h  365 d/y)
≈ 2.5109 J per household per year.
• For the whole province:
2.5109 J  1 600 000 households
≈ 41015 J per year
What would be the total reduction
in CO2 Emissions?
• CO2 emissions in the US are 1.34 pounds (0.608 kg)
of CO2 per kWh averaged over all methods of
generating electricity
– (1998 – 2000, Source: US Government, DOE).
• Conversion between kWh and J
1kWh = 1000 J/s  3600 s/h  1h = 3.6106 J
• Annual reduction in CO2 emissions is:
41015 J per year  (1kWh / 3.6106 J)  0.705 kg/kWh
= 8108 kg of CO2 per year in BC
What would be the percentage
decrease in energy consumption?
• Total BC power production
≈ 53 000 GWhours
≈ 53109kWh  3.6106 J/kWh
≈ 21017 J
– (http://www.bchydro.com/rx_files/info/info46749.pdf)
• The savings of 41015 J by switching to
CFLs would decrease our provincial
energy consumptions by 2%
Conclusion
• Replacing incandescent bulbs with CFL
leads to significant savings in energy (and
money).
• BC’s energy consumption would decrease
by approximately 2% if all households
would replace.
• Higher production cost of CFLs are offset
by much longer lifetime.
• Concerns about mercury content in CFLs
could be addressed by mandatory
recycling programs.