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 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.