Julieta and Andy's adventures in solar power

Some background

In the early 2000s we were using about 10,000 kWh of power per year (27 kWh per day on average) for our 1,200 sq ft home and paying $2,200 per year. After switching over to LED bulbs, and more efficient appliances and HVAC we got that down to 3,500 kWh per year (10 kWh per day on average), and $1,500 per year. Then in 2017 we started using an electric car most of the time, and in late 2018 added a second electric car, so we were using electric cars for all our driving. That pushed our usage back up to around 7,000 kWh per year (19 kWh per day on average) and $2,300 per year.

We had been buying renewable power since 2014, and decided in July 2019 to switch over to generating our own power from solar. We had been keeping track of the prices and performance since the early 2000s and it seemed like the time had finally come that we could produce enough power to offset our usage at a reasonable price. People we knew had started installing solar at home so we could get some pointers on the process. The federal tax credit of 30% was also going to be reduced in 2020, so that motivated us to get this done in 2019.

Overview of our system

We had 19 solar panels installed in October 2019 on the roof of our bungalow. Each panel is about 5' by 3' so in total they take up about 2/3 of the south side of our roof. We also have several boxes installed on the side of the house near our ComEd smart meter.

Over a year we should produce about as much energy as we use, but we will be producing more than we need in the summer, and less than we need in the winter. Production will also vary with how much sunlight we get. We are still connected to the grid. Forest Park had smart metering installed years ago, so that means that any excess energy we produce goes back through the smart meter into the grid to help others and we get a credit. When we aren't producing enough power we can pull power from the grid using the credits we built up.

If the power from ComEd goes out then we do not continue to get power from the panels. Power from the solar panels is automatically shut off as a safety measure for people working on the power lines. However, if we add in a battery solution like a Tesla PowerWall, then we would be able to use our solar system during a power failure. More on this coming in the future.

View from the
          street  View from the

Boxes added to the side of the

For Christmas 2020 we build a gingerbread version of our house with the solar panels
Gingerbread House


There are several different ways to get solar installed, including buying the system or leasing it. We decided to buy ours. The size of the 'solar system' and its price are mostly based on the amount of power you want to generate and available southern facing roof space, but also on the potential rebates you want.

The federal renewable energy tax credit for those buying a solar system has been 30% from 2016-2019, but drops to 26% in 2020 and down to 22% in 2021. Illinois has its Illinois Shines program in which you can get money up front for installing solar in exchange for giving up 15 years worth of Renewable Energy Credits from your system, but you can only install solar up to 110% of what you used the previous year. You can also choose to sell your Renewable Energy Credits yourself over the next 15 years and install a bigger system, but that seemed overly complicated.

We had a 5.9 kW system installed, which should have offset 100% of our usage from the last 12 months with 7,500 kWh of power generation, though we've really only been getting about 4,800 kWh generated. This cost us a little over $20,500 up front, but then we received $6,500 back as part of the Illinois Shines program in early 2021, and we received over $6,100 back as a federal tax credit on our 2019 taxes in 2020, so the entire system cost us around $7,900.

We still pay ComEd monthly ($15) for being connected to the grid.

We figure in about 8 years the system should pay for itself.

Timeline (2019 - 2021)

Production (kWh)


2021 75
60 215 475 545 640 740 690 655 550 415 170
485 670
740 740 680 495
190 95
75 380 545 635

Our panels produce roughly six times as much energy per month (in kWh) in the summer as in the winter with the longer daylight hours and the sun being higher in the sky (especially with the two story house to the south of us).

The numbers for 2020 (4,750 total) are lower than expected. Apparently Illinois has been much cloudier than usual this year according to the Illinois climate network. In 2021 we made it almost to 5,000. In summer 2021 a tree in the yard to the south of us was cut down and that probably helped our numbers in 2022 to get up above 5,200.


ComEd's 'View My Usage' on their web page or smart phone app gives data on production and usage with a day or two delay, so we can see an overview of how our system is working. We have a relatively constant background use of power (blue) but during daylight hours our energy production (green) is enough to offset that usage and supply excess power back to the grid.

Visualization of power data from ComEd

We can also see live data from the system itself showing how production varies over time and how much each panel is producing.

Another nice device for this kind of thing is the Rainforest Automation Eagle-200 which can wirelessly connect to our utility meter and to our home WiFi for real-time monitoring of the to-grid and from-grid power through a web page or mobile app/

Adding in Battery Storage

Since Illinois has net metering and our electricity rates aren't crazy expensive here, adding in a battery like Tesla's Powerwall isn't needed from an economic point of view, but it does allow us to use more of the excess power that we are generating by storing it for later usage (minus a 10% loss in the conversion), rather than sending it to the grid and then using grid power at night. Adding a battery also allows us to keep running if there is a neighborhood power failure and grid power is unavailable, although we haven't had any serious power failures here for many years.

We started the process for getting a single 13.5 kWh Tesla Powerwall 2 in early November 2019 after our solar system went live. In early February 2020 we had the contract and the installation took place in early May 2020. The total cost was $12,000 including changes to our circuit breaker box, and we were able to get 26% of that back on our taxes in Spring 2021 (and since we ordered in 2019 Tesla gave us the 4% we missed as the Federal rebate decreased, getting us back to the 30% federal rebate from 2019) bringing the final cost down to $8,400. Our entire house is connected to the Powerwall but the Powerwall can only generate 5kWh maximum at a time. That should be OK as the only thing that draws that much power is recharging the Tesla. The install took most of a day and added three more boxes with red stickers to the side of our house.

The Powerwall itself is sitting in our basement. Its very quiet and has a green glow in the dark.

The Powerwall is connected to our home WiFi and we can monitor it from the very nice Tesla app. Here the app shows a typical spring day. The Powerwall (green) supplies power to the house through the night, then the solar (yellow) starts to producing in the morning and begins powering the house and also recharges the Powerwall until it is full at mid-day. Then the excess solar power goes out to the grid (grey) for the rest of the afternoon. As the sun begins to set the Powerwall takes over again for the rest of the night, giving us an entire 24 hours without relying on grid power. In early May 2020 we were able to go 11 days straight, and in mid July 22 days straight without needing power from the grid until a couple days in a row with storms drained the Powerwall.

General Resources

- Google's Project Sunroof - https://www.google.com/get/sunroof
- Illinois Shines program - http://illinoisshines.com/
- Home Energy Tax Credits - https://www.irs.gov/credits-deductions/home-energy-tax-credits
- Homeowner’s Guide to the Federal Tax Credit for Solar Photovoltaics - https://www.energy.gov/eere/solar/homeowners-guide-federal-tax-credit-solar-photovoltaics
- Tesla Powerwall -

More Technical Resources

- NREL's PVwatts Calculator - https://pvwatts.nrel.gov/pvwatts.php

Other Resources

- Rainforest Automation EAGLE-200 manual -

last updated May 31, 2024