The image above does not lie. Installing a 5-kW solar system eliminates as much carbon pollution as 5.6 acres of mature trees. It’s like waving your magic solar wand and spontaneously creating a new forest.
Solar energy replaces electricity from the utility company, which comes from a mix of fossil fuels, nuclear, and renewables. Utility energy represents a great deal of greenhouse gas pollution that comes from mining and burning fuels, transporting and processing raw materials, and building and operating power plants.
As we can hopefully all agree, more greenhouse gases in the atmosphere leads to more rapid changes in climate. You know what’s good at capturing that CO2 and keeping it from getting into the atmosphere? Trees! Specifically, mature trees in a forest.
Some really smart folks across several national and international scientific organizations have performed calculations that show how good trees are at capturing that carbon. Other scientists spend time calculating the estimated greenhouse gases, measured in terms of CO2 equivalence (but we’ll just say CO2 for short) that come from all manner of industrial processes, like mining, transportation, and burning of fuels.
We used numbers from both sets of scientists, including CO2 that is caused by traditional energy and solar panel production (yes, we know making solar panels creates greenhouse gases, too), as well as how much CO2 can be captured by a mature forest.
We grabbed the two images in the gif above from Google Maps via a special tool that calculates area using those maps. What see in the image is 5.6 acres surrounding a typical home in a Santa Rosa, California subdivision, and also shows what the neighborhood would look like if the CO2 savings from the solar panels on the home were translated into trees.
Here’s how we calculated our numbers:
- Solar Energy Production – Based on numbers from the National Renewable Energy Laboratories (NREL), we calculate the average annual amount of energy generated per kilowatt of solar panels in every state in the country. For California, it’s about 1,360 kilowatt-hours (kWh) per year. And our 5-kW system would produce a total of 6,800 kWh (1,360 kWh x 5 KW of panels). For more on these numbers, read our full-length article on calculating energy produced by solar panels.
- Carbon dioxide savings per kWh – The EPA lists the carbon dioxide avoided by not using each kWh of gird power is about 740 grams.
- Carbon pollution from solar panels – Of course, manufacturing, transporting, installing and decommissioning solar panels produces carbon pollution, too (this one’s for the nitpicky members of the audience). NREL did a study of the lifecycle greenhouse gas emissions from solar panels, and found they cause 40 grams of CO2 per kWh. So the net CO2 savings per kWh of solar electricity is 700 grams.
- Total CO2 savings from solar in one year – Multiplying those 700 grams of CO2 saved per kWh by the 6,800 kWh produced by our panels equals 4,760,000 grams. That’s a lotta grams! Now we’ve gotta figure out how much forest that equals.
- The carbon sequestration of mature forest – Sequestration means “keeping carbon dioxide out of the atmosphere,” and trees are really good at that. The EPA, with the help of the Intergovernmental Panel on Climate Change (IPCC) and the U.S. Forest Service, has determined that the amount of carbon dioxide pollution sequestered by an acre of mature forest in one year is 850,000 grams.
- Putting it all together – Our 4,760,000 grams of CO2 avoided divided by 850,000 grams per acre gives a final number of 5.6 acres.
Fun Solar CO2-killing thought experiments
Calculating the number of acres of trees your home solar system would equal is actually pretty easy. Given that we use standard measurements for carbon sequestration of forest and the carbon pollution from every kWh of electricity and solar panel lifecycle, the only variable is how much electricity your solar panels can generate.
If you already have solar panels
If you’re a solar lover who’s put your money where your mouth is, just take your annual production and plug it into the formulas above. Remember, it’s 700 grams of CO2, multiplied by your annual kWh, then divide that number by 850,000 grams per acre of forest.
If you haven’t gone solar yet
One strategy for how estimating might be to look at your electricity usage for one year. That number is exactly what your panels would produce if you were to design a solar system that made all your energy for one year.
Of course, designing a solar system to meet your energy needs might not be in your wheelhouse, but we know solar experts in your area. They can take a look at your roof and tell you exactly how many kWh you could make with those magic panels on your roof.