Harnessing the sun ’s extraordinary energy all begins with radiation . Radiation is used to heat water, and it’s water that will heat the air that flows through ducts to heat cold winter rooms. Solar thermal water heaters gather the sun ’s energy to heat water for sinks and showers, and also to heat the air in a solar heating system. Solar energy collectors soak up the energy from direct sunlight. That energy is used to warm up cold water. That water, now hot from this process, is