Energy

There are two angles to energy use in a household: production and consumption.

Consumption

With the addition of the heat pump added a significant amount of electrical load during the winter months. You can see this clearly by looking at this chart of our monthly consumption:

The above chart includes both energy drawn from the grid and self-consumption from our solar system. For more information on that calculation, see the next section.

The system comes with a 10kW backup strip, but honestly we probably didn't use it much (if at all) based on the data I'm seeing. Unfortunately we aren't measuring regular consumption patterns but one day in January 2024 I got curious, went outside, and periodically checked the meter:

That works out to an average of about 1.91 kWh per hour on a very cold day. Between 9:24 and 12:46 (when the weather was coldest), we used only about 4 kWh. The specifications on the heat pump suggest that the maximum output of the heat pump itself is 3kW, leading me to suspect that we just didn't need the electric backup. It's probably good to have for insurance purposes (e.g. if the heat pump breaks down) but I don't think it was necessary otherwise.

Production

To offset the increased energy use of the heat pump, we installed a 6kW solar system. As mentioned, it's a 6kW system with a 5kW inverter. Its peak output is far more than what we would consume at any given time.

In Ontario, we use a system called "net metering", which allows you to resell excess solar power at the retail rate that you buy it (not including the delivery charge, which works out to a few cents per kWh).

We'll get more into the economics in the finance section, but the birds eye view of a system like this is that it produces a lot more in the summer than in the winter. If you're trying to fully offset your electricity use over a full year (not a possibility in our case) you'd size so as to produce enough in the summer to offset your winter.

The other variable here is of course self-consumption: by default, my solar system will first try to power the house. What's left over at any given time is what's sold to the grid. The utility only measures the latter, of course, what we use ourselves is only visible to us.

To get a handle on these variables, I sourced information from two different sources:

• We can get the kWhR values we send to the utility from our utility bill
• The SolarEdge inverter I have has telemetry values which tell you how much it produced over a given hour.

By subtracting the second from the first, we can get a rough idea of how much we used ourselves.

You can watch as our net consumption (total produced subtracted from total produced) goes down over the course of the year as the days get longer and our need for heating goes down:

It's also interesting to look at "self consumption" on its own. This is electricity directly consumed by our household, without being sent to the grid.

You'll note that only in September 2024 did we actually produce more than we consumed. This is due to two factors:

1. Our system is a little undersized. Unfortunately we ran out of useable south facing roof space! Such is life.
2. We were continuously running an inefficient dehumidifier in the basement until August 2024 which was using a lot of power. Oops 🤦. I wrote about this on mastodon last year.