An MTD (modified trickle down) solar heating system is a good DIY project because it uses less expensive materials, and because of its simplicity to build. It heats water directly, instead of using absorber plates or flow tubes. It uses the same concept as Harry E. Thompson’s Trickle Down Solar Roof. With a MTD solar heating system, an array of MTD collectors forms a single solar roof.
The MTD solar heating system utilizes a black polyester material to distribute a thin sheet of water. Then a polycarbonate material acts as the exterior glazing with a thin, inner polypropylene film, to help conserve heat. The inner film helps prevent the water from condensing on the outer surface.
The inner film, or the Trickle Down Mat, might make the MTD solar heating system more expensive, but it also increases its efficiency. This film acts as a waterproof envelop that traps heat inside. The solar heated water is diverted to a gutter and drain at the bottom of the collector array.
A 2×8 MTD collector can be constructed for less than $100.
MTD collectors can easily be mounted on a south-facing roof. They can be pressed together to form a large array. The gutters and distributors are slid into position after the collectors are mounted. Lastly, heater hoses are used to bring the water into the holding tank.
The orientation of your MTD collectors depends on your location. Those living in the northern hemisphere should mount their collectors in the south. That maximizes the amount of solar radiation absorbed.
Freezing during winter is not a cause of concern because MTD solar heating systems have no flow tubes. An open loop system does not require any antifreeze. Once the pump shuts off, the water goes back into the heat storage holding tank.
The size of the heat storage tank depends on the number of collectors, the flow rate of the pump, and the location. A 55-gallon plastic drum should be enough for every 2’x12’ MTD collector. Multiple heat storage tanks are capable of storing more heat than a single tank is.
Most parts needed for a MTD solar heating system can be purchased from a building supply store or home depot. They are modular and can easily be pressed together. The gutters and drain tubes can be connected with simple plumbing know-how.
The video below shows you how a MTD solar heating system works: