Why do you need a low ttl for those? You can add multiple IPs to your A/AAAA records for very basic load balancing. And DNS is a pretty bad idea for any kind of failover. You can set a very low ttl, but providers might simply enforce a larger one.
While the price of energy production is likely to continue to fall, I fear that this will be completely overshadowed by the necessary investment in the grid. Both energy storage and the need to adapt the grid to the more decentralised nature of renewables could lead to a plateau in end user prices.