Typical mixtures use eg potassium nitrate, sodium nitrate, and calcium nitrate. Salts are one of the most produced substances on earth. For instance, potassium nitrate is in virtually every fertilizer. I couldn't find how much is used annually, but it's made from potash, and US reserves of that are ~270 million tons[1]. At 40 to 110 kWh/ton[2] that's a minimum of 10.8 billion kWh (10.8 TWh), or a full day of storage.
This design also needs almost double the amount of hexane...
Not so environmentally friendly...
Neither are used up though, and probably won't devalue with time, so the financial cost of them is just interest payments, and the environmental cost is zero.
