Very nice. Thank you for sharing. Have you considered taking some servers out of load balancing while energy is short, and also running them at lowest energy use settings during that time as well?
And curious - are you running redundant Internet links? Fiber and 4G for example. Emails can queue if your server is off and DNS doesn’t eat much.
Pretty low power already, just 2 nameservers passing mail to the mail server, it has more to do with extended power outages longer than an hour.