In the previous two posts of our photovoltaic system, we reviewed the amount of kWh we used and produced, and our electrical cost. But how does our electrical consumption and cost compare to other homes in Illinois?
To find out, I took the data per solar year for our 4,500 sf building (kWh used and cost) and divided it by the three apartments to have a per-household baseline, which I compared against the residential average monthly bill data for Illinois published by the U.S. Energy Information Administration (EIA).
Since we activated our solar array on December 24, 2019, I show data starting with solar year 2020. The latest EIA data available is for 2023. 2024 data has not yet been published, so I will skip that year.
Electricity consumption
Broadly speaking, our electricity consumption per household/apartment is about half of that of the average Illinois household, or less.
What these numbers show is that our investment in the building envelope improvements paid off by significantly reducing our overall energy load. I am talking about good insulation, good air sealing, good quality triple glazed windows, good exterior doors, a high quality and highly efficient ventilation system, etc.
What also helped was us being picky about what appliances we bought. They were almost exclusively Energy Star rated appliances. And not just any Energy Star appliances. We picked the ones that had the best (or one of the better) efficiency ratings.
Cost and bills
If I use solar year 2020 as a baseline, the Illinois average annual electricity cost per household was 8.4 times our cost, thanks to our solar roof array. And 2020 is the best year to focus on, since the only heating source was our air source heat pumps.
This significant cost reduction reflects that our investment in the building envelope improvements reduced our overall energy load, plus the electrical production from our 8.58 kWh solar roof array reduced the amount of electricity we had to purchase.
Let me say this again:
I started two posts ago with bragging rights because we generated a surplus two years in a row. That is an encouraging data point. The real bragging rights, however, are less in the surplus and more in the relatively low electrical load that we have been able to achieve and maintain.
We were not distracted by the low hanging fruit: “Let’s switch to all LED lighting…”. I credit our motivation to eliminate unnecessary energy hogs (such as the proverbial old refrigerator in the garage), our selectiveness in picking right-sized and efficient appliances, AND most importantly, our laser sharp focus on the building envelope improvements during the deep-energy-retrofit. The latter gave us, without a doubt, the biggest bang for our buck.
In the next post I’ll explain, at least partially, why the building envelope improvements were such an important investment by using our air source heat pumps as an example.