I think that means while they are installing it on your property, you’re not paying for the assets, and will pay for the electricity you use but at a rate discounted compared to the regular utility? So it still makes economic sense.
They could word that better.
“We sell you the electricity generated that you use at a discounted rate compared to utilities”
No, that's not it. You're still buying and selling electricity to and from your utility company. The 12¢/kWh that you're paying to Tesla is the rental on the solar panels.
Why it seems confusing is that you're paying based on how much electricity is produced, but it's still simply a rental.
If you sell your electricity to the utility for 16¢/kWh, and are paying Tesla 12¢/kWh, you will make 4¢/kWh. Which is not a lot, but it's with no upfront costs.
They could word that better.
“We sell you the electricity generated that you use at a discounted rate compared to utilities”