Could my home go net zero?

Written by Heather McDiarmid

The Bottom Line: The climate crisis threatens the future well-being of my kids

Waterloo Region has committed to reducing greenhouse gas emissions by 80% below 2010 levels by 2050.  I want to do my share because the potential impacts of runaway climate change on my kids’ future is the stuff of nightmares. My family of 4 lives in a 1992 semi-detached, 1500 square foot home, eats a vegetarian diet, and drives a small car.

According to Project Neutral, my carbon footprint is 13.9 tonnes of greenhouse gases emitted yearly. My family’s biggest source of emissions is food, but since the agricultural sector’s emissions are not exactly within my control, I need to reduce my emissions from other sources to get close to near-zero impact.

My Goal: To reduce the carbon footprint of my home to near zero

The Project Neutral tool estimates that my home’s carbon footprint is 4.5 tonnes of greenhouse gas emissions per year. My own calculations, based on actual natural gas and electricity usage, suggest that this number is closer to 3.4 tonnes (1.888 kg CO2/m3 natural gas and 0.1 kg CO2/kWh in Ontario).  Regardless, I want to see what it will take to get that number to near zero. This will mean generating enough renewable energy on my property to offset the emissions from the energy that my home uses in a year.

I approach investigating net zero energy as a three-step process:

  1. Calculating how much renewable energy I can generate onsite with solar panels.
  2. Calculating how much energy I currently use.
  3. Exploring how to get those two values to match to achieve net zero energy use.

Step 1: Calculating the solar potential

Since the solar potential of our roof is a limiting factor, I started there. Using PVWatts, a calculator put out by the US Dept of Energy, I calculated my roof’s solar potential.  The program used my geographical location, the slope and size of my roof (tilt) and its North-South orientation (azimuth) to estimate how much energy rooftop solar panels could generate in a year.

Since my home is on the north side of the semi-detached building, I maximized the space on the roof facing east and west. In total, the calculator estimated my annual solar potential at 8,692 kWh from an 8 kW array. Therefore, 8,692 kWh is the maximum amount of energy that I could use in a year if my home were net zero energy.

Step 2: Calculating my current energy use 

The next step was to figure out how much energy our house currently uses for daily operation. I felt confident that our energy use would be low.  After all, we have already made efforts to improve the energy efficiency of our home: air sealing, adding insulation to our attic and basement floors, upgrading windows, upgrading to a highly efficient induction cooker (I love my induction cooker!).

I used my electricity and natural gas bills from the last three years to determine our average energy use per year.  On average we use 3,051 kWh of electricity per year and 17,365 kWh of natural gas per year (10.55 kWh/m3 of natural gas) for a total of 20,416 kWh.

We currently use 20,416 kWh per year and, if we made no changes, we could only offset 8,692 kWh using renewable onsite energy. Yikes!

Step 3: How we could reach net zero energy

My first thoughts were: it will take major renovations to our walls and basement to achieve the energy efficiency needed to reach net zero. Then I remembered that modern, cold climate, air source heat pumps are capable of an average of 300% efficiency in our climate. Yes, 300%! That’s possible because heat pumps move heat, they don’t generate heat.

Since all of our natural gas is used for space heating, replacing our natural gas furnace with an air source heat pump would mean that we would need roughly 5,788 kWh to heat our home (17,365 kWh in natural gas/300%).

That brings our total energy use to only 8,839 kWh (3,051 kWh for regular electricity use and 5,788 kWh for heating). And as a bonus, we wouldn’t be burning any fossil fuels in our home – wow! Of course, even with these changes, our home would still have a carbon footprint without solar panels. Ontario’s electricity supply, while mostly from nuclear and renewables, includes electricity from natural gas power plants, hence the need for solar panels to offset our emissions from electricity.

Finally, there is still a difference of 147 kWh/year, since we would have the ability to offset 8,839 kWh with solar while our usage would be about 8,692 kWh. That leaves one last question: could we cut our energy use by an additional 150 kWh/year? That is about the energy that a typical fridge uses in 3 months.  I am not going to unplug my fridge but I do think we can do it!  There are many options: heat pump water heaters are up to 350% efficiency, we can do more to address air leaks, we could add insulation, add a drain water heat recovery pipe or we change habits to reduce our hot water usage. There are many possibilities and a Reep Energy Audit can help to find them!

Conclusion

Reducing my home’s carbon footprint to near-zero will mean adding solar panels to my roof, replacing my natural gas furnace with a cold climate heat pump, and making some other minor energy efficiency improvements. I am saving up and looking for opportunities to make these improvements organically when appliances and equipment reach their end of life or when making other renovations.

For some homes, especially older homes, achieving net zero energy may require major energy efficiency renovations. Reep Green Solutions’ home energy audits can help to identify which renovations to prioritize. Some homes may be unable to bridge the gap between solar potential and energy use because of low solar potential or high energy use. But a warming planet will affect us all and I believe we must do all that we can to ensure we keep global warming within safe limits: our kids deserve the best future we can give them. So, what would it take to get your home to net zero energy?

Heather McDiarmid is the founder of McDiarmid Climate Consulting, which offers research and analysis to help communities, organizations and everyday people chart a course toward a healthier, more equitable and low-carbon future.

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