You bring up heated water as a method of storage, and it reminds me of a neighborhood in Alberta, Canada that uses geothermal + solar heated water storage for 52 homes. They’ve been able to successfully heat the entire neighborhood with only solar over the winter in 2015-2016 and have gotten > 90% solar heating in other years.

https://en.wikipedia.org/wiki/Drake_Landing_Solar_Community

There’s a huge number of new storage technologies being developed, and the fact that some even work on a seasonal basis for long term storage is amazing.