It uses molten salt to store heat to generate power when the sun has set. This was indeed a milestone. It’s the first ever solar plant to generate for 24 hours continously. However, it can only do this in the summer and when the sky is cloudless. Plus, the output Â is just 20 MW. So, while this is a nice little test demonstration and shows it can be done, solar has a long way to go before it is grid scale.