Solar is already down to $0.065/kWh for industrial applications [1]. That's $3.90/gallon at today's prices, and solar prices continue to fall.

The DOE's 2020 targets came three years ahead of schedule. Their 2030 target is $0.04/kWh [2], which would work out to $2.40/gallon. Mix in the fact that a bunch of countries (and US states) have implemented carbon taxes and you've got yourself a good long term investment.

[1] http://solarcellcentral.com/cost_page.html [2] https://www.energy.gov/eere/solar/articles/2020-utility-scal...