Sunlight is heating the air and also heating the copper tubes in order to function the solar energy system. It's using the heat of the sun to power the panels.
This is because hydroelectrical energy is produced from hydropower – the force created by running water. Hydroelectric energy is usually generated by constructing a dam on a river, such that the water which flows through the dam is used to power turbines that generate electricity.
The expression or comment "Brain Freeze" means that the roof of your mouth is getting so cold that its affecting some of the nerves in your brain making it feel like a brain freeze.
