Plug-in Load - Estimating Carbon Emissions

In the first part of Unit 1, you found out how much energy devices at the schools use (in kWh) and how much that electricity costs. What is the environmental impact of that electricity use? How to measure or calculate it?

As you will see in Unit 2 - Energize NB!, many forms of electricity generation result in the emission of the greenhouse gas carbon dioxide (CO2). CO2 is a major product of combustion, whether you are burning coal, oil, wood pellets, gasoline, or anything else with carbon in it. CO2 accumulates in the atmosphere and achieves a state of equilibrium as some of it is absorbed by plants for growth. The CO2 that isn't absorbed can trap heat in the atmosphere and lead to global warming and climate change. Therefore, being able to measure the amount of CO2 associated with the energy we use is very important.

Measuring the CO2 emissions from a combustion process is quite straightforward. If you know the quantity of fuel you burn and it's chemical composition, you can calculate the amount of CO2 with a simple calculation. What about electricity? Electricity is a form of energy, but it clearly isn't combustion. What are the CO2 emissions associated with it? In New Brunswick, not all of the electricity we generate required something to be burned in the process. Water power, wind power, and nuclear power are the three major forms that don't involve combustion directly. It should be noted however, that some of the processes involved with those three generation types like the trucks that have to drive the uranium to the nuclear reactor, or the energy that was required to produce the raw materials like cement and steel, have CO2 emissions associated with them. Electricity from coal, oil, diesel fuel, biomass (like wood chips, waste wood chemicals from pulp mills, natural gas leaking from landfills) have direct CO2 emissions associated with them. So how to pin down a single number to represent all the diverse ways we generate electricity?

NB Power tracks all the fuels used, as well as all the resources put into the operation of its power plants and uses a single number to estimate the CO2 emitted from a kWh of electricity. You should keep in mind the bathtub analogy in regards to using electricity across the province:

Power plants put electricity onto the grid like separate faucets into a bathtub. If you were to use electricity from the grid, it isn't coming from a specific power plant, but from a mix of all power plants. Like taking a cup of water from the middle of the bathtub, you can't be sure of which faucet it came from.

With this in mind, over the year 2014, a typical kWh of electrity in New Brunswick was associated with the emission of 290 grams of CO2. Or:

  • 290g CO2/kWh

CO2 is a gas, so 290 grams is the mass of that gas, not it's volume (which depends on temperature and pressure). 290 grams is very close to the weight of 290ml of water, or close to the weight of a small milk/chocolate milk carton.

So what can you do with this information? In a way very similar to how you calculated the cost of the electricity used for certain devices, you can estimate the carbon associated with the electricity used. Consider "Mr. B's computer" from worksheet 4 of the Plug-in Load Audit document. It used 390 kWh per year. How much CO2?

  • 290g CO2/kWh x 92.5 kWh = 26,825 grams of CO2 or 27kg

That's a lot! Make a simple table and calculate the CO2 emissions associated with all the devices you measured. Find the totals for all the devices combined, for a whole year. Surprising?

But how much CO2 is that? It was mentioned above that plants absorb CO2 to grow. How many acres of trees (or grass, or rainforest) would it take to absorb the CO2 emissions associated with the devices you measured? Use the internet to find out. There is a lot of information, you can find the CO2 absorbed by a single tree, or a whole forest. Find one that you find interesting and relevant and include it in the table you made. Don't forget to give credit to the source of where you find your info.

This Greenhouse Gas Equivalencies Calculator by the US EPA is a good start. Click the "If you have emissions data" tab and enter the amount of CO2 you found from the device you are measuring, then click calculate. The page produces a variety of comparisions based on this amount of CO2

Last modified: Tuesday, 12 January 2016, 11:59 AM