Change begins at home. Having come home due to coronavirus, I figured it was time to look at my home’s energy usage and its emissions. For context, I’m currently staying in a 1500 sq ft townhouse in the SF Bay Area with two occupants. Based on our utility bills from the last four years, we’ve used an average of 175 kWh of electricity and 14.5 therms of natural gas per month.
How do we compare to the average?
The US Energy Information Administration (EIA) occasionally conducts a Residential Energy Consumption Survey (RECS) household energy usage patterns. The most recent RECS is from 2015, for which they sampled 5,600 households out of the 118.2 million households in the US.
Based on the 2015 RECS, the average household in the US consumes 893 kWh of electricity and 48 therms of natural gas per month. Apparently, our household footprint is far lower than the national average: one-fifth of the electricity and one-third of the natural gas! That’s good, but that’s quite an easy bar to beat, given that:
- Our house’s square footage (1500 sq ft) is 25% lower than the national average of 2008 sq ft.
- Our household size or occupancy (~0.9 due to travel) is much lower than the average household size of 2.5.
- California households use 31% less energy than the US average, among the lowest in the nation. One big reason is that California’s mild climate reduces the need for heating and air conditioning.
On top of this, beating the US average isn’t something to be proud of, as the average American uses more than double the energy of the average European, and nearly four times as much energy as the average person on earth. And one big reason is that Americans love big houses, and space heating and air conditioning use a lot of energy.
Nonetheless, PG&E, our regional utility company, tells me that our household still has lower energy usage than other houses in our neighborhood. That’s certainly a good thing, but much of the different must be due to the fact that the occupancy in our home is much lower than other homes here.
PG&E reports that in 2018 their CO2 emissions rate was only 93 grams of CO2 per kWh of electricity generated. I found this astounding, as the national average is 449 grams of CO2 per kWh! It appears that PG&E generates 69% of its electricity from nuclear and renewables, 17% from natural gas, and none from coal or oil (the dirtiest sources). The remaining 14% is marked as “unspecified,” meaning it cannot be traced to its source. That’s intriguing. Based on this figure, our household emissions from electricity amount to 0.54kg CO2/day or 195.3kg CO2/year.
The EPA reports that burning one therm of natural gas releases 5.3kg of CO2. Thus our household gas usage results in 2.56kg CO2/day or 922.2kg CO2/year, bringing our total emissions to 3.1kg CO2/day or 1,117.5kg CO2/year.
For comparison, the average American emits about 17 tons of CO2 per year (not including other greenhouse gases, such as methane) of which 6.1 tons come from electricity and natural gas. Europeans emit about 8 tons in total per year and the global average is about 5 tons.
The most interesting result here is that natural gas makes up 82.5% of our household emissions! The fact that PG&E generates most of its electricity from nuclear and renewables means that our natural gas usage has an outsized carbon footprint.
Reducing our footprint
If we wanted to reduce the carbon footprint of our home, it seems the most effective solution would be to switch our heating sources (central heating, water heating, and stove) to electric alternatives. However, most people prefer gas heating because it’s considered to be cheaper to operate. What would the cost difference be for us, with PG&E?
For the sake of simplicity, let’s just assume all the natural gas we currently use is for central heating. We currently use an average of 14.5 therms of natural gas per month. One therm contains 29.3 kWh of power, so that comes out to 5098 kWh of energy per year. Compare that to 2100 kWh of electricity that we use per year. Our central heating furnace has a annual fuel-utilization efficiency (AFUE) of 80%, basically meaning that it’s 80% of the 5098 kWh of energy contained in the natural gas is actually being converted into heat. In contrast, electric furnaces have higher efficiency, as high as 100%.
We currently pay $0.24/kWh for electricity and $1.41/therm for natural gas. Over the course of a year, the $245 we currently pay for natural gas would be replaced by a $988 bill for the added electricity. In reality, the bill would likely be more than that, due to the fact that the rate of electricity increases to $0.30/kWh when we cross a baseline threshold that we currently do not cross but would likely be crossed on days we use central heating. The exact numbers will depend on a variety of factors, but the overall point is that the cost of heating would roughly quadruple from switching to electricity.
Of course, there are many other ways to reduce our overall carbon footprint significantly without having to pay more. Reducing flying, eating less meat and dairy, and driving less would all have a substantial impact on our carbon footprint. In particular, for those of us who do fly more than a few times a year, flying is likely to make up the majority of our individual carbon emissions.