[hackerlight]

The shape of the curve is a bit of a red herring, unless additional context is considered. Decay could mean we have succeeded in decarbonizing the entire power sector, which is a signal of success. Or decay could mean California has finally built all the solar it needs but no other states are following in California's footsteps, which is a signal of failure. Both are instances of decay that signify very different situations.

You are correct though that a naive prediction of constant doublings is definitely wrong. China is showing signs of slowing over the last month due to transmission and storage bottlenecks in a few locations. BNEF has an article about this.