MTD Solar Heating
Trickle Down solar heating is a revolutionary, low cost solar heating
concept that heats water directly rather than transferring heat indirectly
through copper absorber plates or copper flow tubes. It’s a trickle down open
loop system similar to Harry E. Thomason’s original “Trickle Down Solar
Roof” with a few exceptions. Harry used the entire surface area of a
corrugated metal roof covered with glass to heat water. An
MTD solar roof also uses the trickle down method to harvest heat, but individual
MTD collectors are pressed together in an array to form the solar roof.
Instead of a black metal roof a
black polyester material is used to distribute a thin sheet of water.
· Instead of transferring heat through a metallic absorber plate heat is transferred directly to the water through a “Trickle Down Mat" or TDM
Instead of using a heavy, fragile,
expensive glass glazing an inexpensive, polycarbonate material is
used as an exterior glazing and a thin, inner Mylar film is used to
One problem with Thomason’s trickle down roof was the heat loss through the outer glazing material. Although the heat gain of a large solar roof is more than the heat loss due to hot water condensing on the outer glazing surface I felt that an inner film would improve the net heat gain.
Well it does increase the cost of the collector a little but it also increases collector efficiency a lot. The TDM is the heart and soul of the MTD concept. It provides a waterproof envelop that traps heat inside a water soaked polyester material. From here the solar heated water is channeled into a gutter and drain at the base of the collector array. MTD collectors may now be built for about $4/ sq ft.
MTD heat collection efficiencies vary between 40% and 60% depending on temperature differential, flow rate and the method of heat storage. Large, multi tank heat storage systems work best with MTD systems.
Mounting MTD collectors is a
beautiful thing. They are designed for flush mounting on a south facing roof
where they may be pressed together to form an array. Gutters and Trickle
slide into position after mounting. Soldering expensive copper pipes is not
necessary. Easy to install heater hoses are used instead.
about freezing? Is antifreeze required?
Freezing is not a problem because there are no flow tubes. Antifreeze is not required or desired with this open loop system. When the pump shuts off water simply drains back into the heat storage tanks.
Copper and aluminum and
other metals have a high thermal conductivity, but there are other ways to
transfer heat. Take a moment and consider wet clothes drying on a clothes line.
On a humid day clothes take longer to dry than they would on a dry day. This is
because evaporation is accelerated in a dry environment. Next time you wash
clothes in an
sunlight will make your clothes hot and cause them to dry faster.
My clothes are hot and so am I but the temperature difference between your wet clothes under that tree and my wet clothes in this bright sunlight is insignificant. Why do you think this is so?
it be evaporation?
It could! Evaporation has a cooling effect. My clothes will not overheat because the heated water vibrates fast enough to become airborne. What do you think would happen if we placed a clear plastic bag over my black shirt?
think that would put a damper on the evaporation process.
True, but what about the temperature of my wet shirt?
Take a reading with this digital thermometer and tell me what you find.
shirt is now 1400 F.
I told you my shirt is hot.
So what does this have to do with the
Trickle Down Mat?
Well, my wet black shirt incased in a plastic bag traps solar heat the same as a TDM by preventing evaporation, but the TDM does more than trap heat it also transports heat.
does it do that?
Water flows through the TDM like water flowing over Harry E Thompson’s corrugated solar roof, but the thin film of water through the TDM is more uniform than the water trickled on top of a corrugated roof and the heat exchange is direct so that more heat may be collected at a lower flow rate. This heated water is then collected in a gutter and drained into a solar storage tank.
does it do that?
Thompson used one heat storage tank. How many will
Well that all depends on the number of collectors, the size of the tanks, the heating requirements, the flow rate of the pump, and the location. Personally I like to see about one 55 gallon recycled, plastic drum for each 2’x12’ collector
do you need more than one heat storage tank? The MTD system takes
Harry’s low cost solar heating concept to a new level and places it in the
hands of the do-it-yourselfer. A major expense associated with the solar thermal
industry has to do with shipping, assembly and installation. These expenses can
be eliminated by the invention of "Trickle Down Mat" materials that facilitates
MTD construction and also keeps the expense of shipping down. The
original 150 page, 8.5"x11", illustrated, MTD Solar Heating book with slide
shows is no longer in print, but I do have a few coppices left that are being
sold at a discounted price. Contact me if you are interested.
Multiple heat storage tanks are capable of storing more heat than one tank through a process known as heat stratification. Hot and cold water may be separated to some degree by differences in density but the turbulence inside an open loop system has a mixing effect. The following illustration demonstrates the entire MTD solar heating concept. as well as a method of stratifying heat.
MTD collectors are modular. In other words they may be pressed together and connected with trickle down tubes and gutters. Antifreeze is unnecessary and the plumbing is simple and inexpensive. Most of the parts needed for an MTD project may be purchased from a building supply house such as “Home Depot”
The MTD system takes Harry’s low cost solar heating concept to a new level and places it in the hands of the do-it-yourselfer. A major expense associated with the solar thermal industry has to do with shipping, assembly and installation. These expenses can be eliminated by the invention of "Trickle Down Mat" materials that facilitates MTD construction and also keeps the expense of shipping down.
The original 150 page, 8.5"x11", illustrated, MTD Solar Heating book with slide shows is no longer in print, but I do have a few coppices left that are being sold at a discounted price. Contact me if you are interested.
MTD Collector Kit new
Take me Home
Strawberry Fields Solar Book
How to Build a Solar Hot Water System
Energy Independent Housing
Solar Thermal Energy
Solar Energy Center
World Without Oil
Solar Energy Alternative
Plant Bed heating
Solar Thermal Energy Group
Active Solar Passive Solar
Heat Storage Vaults
Gallery of Solar Homes
Photovoltaic Electricity Animation
Solar Water Heating Animation
Our Sun and Our Future
Solar Politics for a Small Planet
Five Solar Thermal Principles
Solar Energy Facts
MTD Solar Heating