I have been using a fully off-grid solar system for over four years now. For my setup, I have a 15kWh battery paired with a 5kW inverter. I consume nearly 330 units per month from my off-grid system. Additionally, I own a BYD Dolphin, which I charge during the daytime. On top of this, I still pay the CEB nearly 6,000 Rs per month for my remaining grid electricity consumption.
The main advantage of going off-grid is that I never experience power cuts, which is a huge benefit for my job. When it comes to battery degradation, I believe you can easily use these batteries for more than 10 years; so far, I haven't noticed any degradation at all.
The only downside is the risk of lightning strikes. You must install Surge Protection Devices (SPDs) and carefully manage the system to ensure long-term benefits. Ultimately, I don't think you can earn a direct income from an off-grid solar setup, but it is incredibly convenient and cost-effective.