Solar hot water is water heated using natural energy from the sun. Solar energy heats up large panels called thermal collectors. The energy is transferred through a fluid (often water) to a reservoir tank for storage and subsequent use. It is then used to heat water for commercial or domestic use and also as an energy input for heating and cooling devices and for industrial 'process heat' applications. Despite an excellent solar resource, the penetration of solar water heaters in the Australian domestic market is only about 4% or 5%, with new dwellings accounting for most sales.