The best comparison to explain the thermal mass would be a cheetah running after a gazelle. From 11am to 3pm usually you have infinite amounts of energy from the sun.
You can make electricity with it, you can heat up water or air in the pipes. It’s “limited” to 3,4 hours and then it’s gone.
It’s like a cheetah running after the prey. It catches it and it has unlimited amount of food. More food that it can eat.