If you decide to finance or lease your solar panels, the finance or leasing company will place a claim, known as a 'lien', on the solar equipment itself. They make this official by filing a form called a 'UCC-1', or Uniform Commercial Code Financing Statement, as well as a county fixture filing.
Now, it's important to understand that this lien is not against your home itself. It doesn't affect your mortgage or home ownership in any way. What it does do is appear as a 'UCC-1 fixture filing' on the title of your property.
Why does the finance company do this? It's a way of ensuring that if, for any reason, your home was to be foreclosed, the finance company would still have a claim to the solar system. The UCC-1 filing prevents your mortgage lender from taking ownership of the solar system if your home is foreclosed. So, it's simply a way for the finance or leasing company to protect their investment in the solar system.