World's first fully solar-powered airport is in India. The Cochin International Airport is powered by a solar plant comprised of over 46,000 solar panel units.
Unearned revenue is the money or revenue earned for the product or the service that is not yet sold or provided to the customer. Hence, it comes under liabilities.
The words "asset" and "liability" are two very common words in accounting. Liabilities are legally binding obligations that are payable to another person or entity. Accounts payable, loans, mortgages, deferred revenue,... come under liabilities.