Our household is on a mission to achieve net zero greenhouse gas emissions from operating our home. In doing so, we are helping to build a climate-safe future and demonstrating how every home can become a low carbon home.
To achieve zero emissions, our home must generate enough onsite renewable energy over the year to offset the total energy that it uses in a year. Our solar panels may not meet all our needs all of the time, but so long as it all balances out over the year, we can claim net zero energy and emissions.
Although energy efficient and fully electrified, our home was still responsible for operational greenhouse gas emissions because our electricity supply is not yet zero emissions. In fact, recent decisions by our provincial government mean emissions will rise as more gas-powered electricity generation is added to the grid in Ontario. Fortunately, all-electric heat pumps will remain a lower carbon option than gas furnaces despite this increase because they are so much more efficient at heating.
To make sure we could get to net zero, we used our electric utility bill to calculate our total annual energy needs. Since our home is fully electrified, it was a simple matter of adding our annual kWh of electricity from our utility bills.
Next, we used PVWatts to estimate the size of solar panels needed to generate our target renewable energy. The calculator used our location plus roof orientation and tilt to estimate the electricity that a 1 kW array can generate over a year. Our installer performed a more accurate calculation but knowing the rough size needed helped us get quotes faster and easier.
For our home, the average annual energy use was 7000 kWh, including electricity used to charge our EV. At 3000 kWh/yr, our heat pump was responsible for the lion’s share of the electricity usage – thank goodness it is so efficient! We added 10% to our total as a buffer and to compensate for the emissions associated with manufacturing the solar panels.
In December 2021, after investing in a new roof, we had an 8 kW array installed for total cost of $16,850 after applying a $5,000 Greener Homes Grant. Our utility shifted us to a net meter that subtracts the electricity generated from the electricity used and only charges us for the difference. When we generate more than we use in a month, we get a credit that can be carried over for up to a year.
The panels have been up for over a year now. Despite near zero generation in December and January when the panels were covered in snow, our panels generated a total of 8500 kWh in year 1, saving us more than $1,000 in utility costs and saving the planet 264 kg of greenhouse gas emissions from electricity.
In summary, our home achieved net zero emissions by a) performing relatively easy building envelope upgrades including attic insulation, insulation over concrete floors, simple air sealing, and window replacements; b) electrifying the home by installing a cold climate air source heat pump (we already had an electric water heater); and c) installing enough rooftop solar panels to offset our total electricity use over a year. Most of these upgrades can be cost effectively done in all homes and they not only reduce emissions, but they also lower utility bills and make homes more comfortable.