Fully automatic 6-star in-line gas booster provides plenty of hot water all year round. The Solargain double panel roof mount with in-line gas booster is the workhorse of solar hot water systems. The cooler water at the bottom of the cylinder is denser than the warmer water at the top. As the cooler water flows through the panels, the sun’s energy heats the water via the highly efficient all-copper collectors, and rises up into the storage tank. This cycle will continue while the sun is shining and will cease once the sun goes down.