No, that answer is incorrect or at least incomplete. Can you post the link where you got it?
The only kind of personal loan interest that his deductible is a mortgage loan. A mortgage loan must be secured by a lien on the real property, so that the property could be foreclosed if you stopped payments. Real property is land, plus any permanent structures that are attached to the land.
If this loan was secured by a lien on your house and land, it would qualify as a mortgage, and it would be deductible to the extent that it was used to pay for improvements. However, if the loan is only secured by a lien on the solar panels themselves, so that the company can foreclose on the solar panels but can’t foreclose on the land that the home is attached to, then it is not a mortgage and it is not deductible.
