This unit stores 8MWh of energy with 100 tonnes of sand. Gravity is about 9.8m/s*2. If you put the calculation into google "8MWh / 9.8m/s*2 / 100 tonnes", it t

This unit stores 8MWh of energy with 100 tonnes of sand. Gravity is about 9.8m/s*2. If you put the calculation into google "8MWh / 9.8m/s*2 / 100 tonnes", it tells you that you need lift those 100 tonnes 29.39km up, which is over 3 times the height of Everest. And the mechanics of the system are much more complicated, more expensive to build and maintain. However, pumping water uphill is done in many places, and is more practical because a lake of water can easily weigh millions of tonnes. The problem is finding places with suitable hill top lakes. Also, if you are using it for district heating output, storing it as heat is convenient. There might scope to increase efficiency by using some sort of heat pump, but getting a heat pump to go up to 600°C is quite hard.