# How Much CO2 Can You Save by Switching Light Bulbs in Canada?

• theone
In summary: You have to determine what the "gC/MJ" figure means, and convert it to a "gCO2/MJ" figure.A bit of searching makes it appear that the "gC/MJ" figure is for all the carbon in the fuel, including that which will become CO2, and that the "22 g/MJ" figure is a reasonable average for the carbon in the fossil fuels used for generating electrical power in Canada. So I think you can proceed with your "22.65 gC/MJ" figure and use it as if it was a "gCO2/MJ" figure, as long as you clearly indicate that you've done so. So I think you are good to go
theone

## Homework Statement

Using the above result, estimate the annual CO2 emission savings (in kg/yr) associated with replacing one 60W incandescent bulb with one 13W fluorescent bulb, in one typical Canadian household. Do this calculation from “first principles” using the following assumptions:

(The "above result" was the answer to "How many hours per day must the replacement and original light bulb be left switched on (on average over the year) to save a certain amount of money per house". The answer was found to be 4 hours)

- The GHG savings are entirely CO2 and result from the reduced combustion of fossil fuels in electric power plants.Canada’s electrical power generation mix is 23 % from fossil fuels. Assume electricity from other sources (hydro, nuclear and renewable) have approximately zero carbon emissions. The carbon intensity of this fossil fuel usage is 22 g/MJ
- Assume the overall efficiency for the fuel energy to electrical power conversion process is 35 %
- Most light bulbs are located indoors, in an occupied living space. So, the net carbon emissions savings will be approximately zero for six months of the year.

## The Attempt at a Solution

so (60-13)= 47W worth of carbon emissions is saved by replacing the bulbs,

47W=47 j/s so

47 j/s * (4hours*3600)s * 22(g /MJ) * (1MJ/10^6J) =

14.9g

since carbon savings is zero for half the year, then 14.9/2

= 7.45g?

I'm not sure where to use the info of 35% or 23%?

Hi. Your 4 hours is not 4 hours but 4 hours/day. Dimensional error !

theone said:
The carbon intensity of this fossil fuel usage is 22 g/MJ
That is rather low. Coal is about 88g CO2/MJth. See e.g. https://en.wikipedia.org/wiki/Emission_intensity.
theone said:
I'm not sure where to use the info of 35% or 23%?
The 22g/MJ is for thermal energy (22g CO2/MJth). Light bulbs need electrical energy. The conversion from thermal to electric is only about 35% efficient.
As against that, only 23% of the electricity used by the bulb will come from fossil fuels.
For each Joule used by a bulb, how many Joules come from fossil fuel electricity? To make that many Joules of electricity from fossil fuels, how many Joules of thermal energy were produced?
theone said:
since carbon savings is zero for half the year, then 14.9/2
I thought the 4 hours/day was already the average over the year.

The 22 g/MJ appears to be for fossil fuel used. So divide by the efficiency to get g /MJ electricity generated. That way we agree a bit better with Haru's number.

I also agree with him about the factor 0.5 already in the 4 hours/day calculation -- you could check that with the äbove"calculation !

And if only 23% of the electricity is from fossil fuel, then the savings are only 0.23 of what would be saved if ALL electricty is from fossil fuel...

theone
BvU said:
Hi. Your 4 hours is not 4 hours but 4 hours/day. Dimensional error !
And you get rid of the 1/day by multiplying with days/year, so you end up with something with a dimension of mass/year

BvU said:
The 22 g/MJ appears to be for fossil fuel used. So divide by the efficiency to get g /MJ electricity generated. That way we agree a bit better with Haru's number.
No, my 88g is fuel per MJ thermal, so about 300g/MJe, or 1t/MWhe. That's a fairly standard number.

88g/MJ of fuel could well be correct. However:
theone said:
The carbon intensity of this fossil fuel usage is 22 g/MJ
is given in the problem statement as a known. Perhaps 22g/MJ is the carbon emitted as smoke, after accounting for scrubbing and ash.

haruspex said:
That is rather low. Coal is about 88g CO2/MJth. See e.g. https://en.wikipedia.org/wiki/Emission_intensity.

the actual info from the question was:
"Canada’s fossil fuel based electrical generating capacity is comprised of 70% coal and 30% natural gas (EIA, 2010). Use these percentages to compute the weighted-average carbon intensity, based on the LHV of the three fuel sources given in the class notes"
From the notes: LHV Carbon Intensity (gC/MJ) of natural gas is 15.3, petroleum is 20 and coal is 25.8"

so I did (25.8*0.7)+(15.3*0.3) to get 22.65 gC/MJ.
was that right?

theone said:
the actual info from the question was:
"Canada’s fossil fuel based electrical generating capacity is comprised of 70% coal and 30% natural gas (EIA, 2010). Use these percentages to compute the weighted-average carbon intensity, based on the LHV of the three fuel sources given in the class notes"
From the notes: LHV Carbon Intensity (gC/MJ) of natural gas is 15.3, petroleum is 20 and coal is 25.8"

so I did (25.8*0.7)+(15.3*0.3) to get 22.65 gC/MJ.
was that right?
Not sure what this gC/MJ actually means. I can't find it defined anywhere. The worry is that when we talk about greenhouse gas emissions it's always in terms of equivalent CO2 mass. But one gram of C produces about 3.5 g CO2.
The table at http://cta.ornl.gov/bedb/appendix_a/Lower_and_Higher_Heating_Values_of_Gas_Liquid_and_Solid_Fuels.xls shows 24g anthracite per MJ. According to https://en.m.wikipedia.org/wiki/Anthracite, anthracite is about 75% carbon, so that's 18gC/MJ, or 65gCO2/MJ.
As I posted, around 80gCO2/MJ heat is the figure I'm familiar with.

Last edited by a moderator:
theone
theone said:
so I did (25.8*0.7)+(15.3*0.3) to get 22.65 gC/MJ.
was that right?

Yes, the math and the approach are right, from the way I understood the given information.

However, as haruspex pointed out, there is the question of is it "Carbon" or "CO2" indicated in the original problem statement. Your OP says "CO2" and the "first principles" clause may indicate that calculation of CO2 is expected. So it looks like you need that one extra step.

theone

## 1. What are carbon emissions?

Carbon emissions refer to the release of carbon dioxide (CO2) and other greenhouse gases into the atmosphere, primarily through human activities such as burning fossil fuels, deforestation, and industrial processes.

## 2. Why are carbon emissions a concern?

Carbon emissions contribute to the greenhouse effect, trapping heat in the Earth's atmosphere and leading to global warming. This can have negative impacts on the environment, including rising sea levels, more frequent and severe natural disasters, and changes in weather patterns.

## 3. How do carbon emissions affect the environment?

Carbon emissions contribute to climate change, which can have a range of environmental impacts. These include melting of polar ice caps, ocean acidification, loss of biodiversity, and disruptions to the natural balance of ecosystems.

## 4. What can be done to reduce carbon emissions?

There are many ways to reduce carbon emissions, including switching to renewable energy sources, using energy-efficient technologies, improving transportation systems, and promoting sustainable agriculture and land use practices. Additionally, individuals can make small changes in their daily lives, such as reducing energy consumption and supporting companies that prioritize sustainability.

## 5. What are some consequences of not addressing carbon emissions?

If carbon emissions continue to increase at current rates, the consequences could be catastrophic. These include more frequent and severe natural disasters, displacement of populations due to rising sea levels, decreased access to clean water and food, and significant economic impacts. It is crucial to address carbon emissions now to mitigate these potential consequences.