[pavanred]

Edit: ...2GW in 2015 and is about 20GW in 2018...

Typo, and HN doesn't allow me to update it now. Anyway, my point was that in the past 4 years we achieved 20GW and we expect to achieve 80GW in the next 4 years.

[rohit2412]

But it isn't linear. Price is falling exponentially (15% every year). And adoption will be more rapid as solar suddenly becomes economically viable.

For a benchmark, look at China's adoption. https://en.m.wikipedia.org/wiki/Solar_power_in_China . Not at how many years they too from 20gw to 175 gw, but how much solar became viable for them last year.