Finnish City Inaugurates 1 MW/100 MWh Sand Battery

Helsinki did the same thing but storing the energy in water instead of sand: https://helsinkismart.fi/worlds-largest-cavern-thermal-energ...

Several cities in Finland have water based thermal batteries already, connected to local district heating networks. They have been previously used to store energy from existing combined heat and power plants, but now that wind power build up has created a lot of excess cheap power period, have been modified to include electric boilers.

Helsinki has advanced integrated district heating and cooling. Over 300 MW of heat pumps by 2025.

Collecting heat from wast water is free energy. When you defecate, wash clothes or dishes, or take shower there is warm water and solids going down the pipes. That heat can be used. In the summer stored cold sea water can provide district cooling.