Trickle Down Solar Heating


In the 1950’s, Harry E. Thompson, a North Carolina engineer, had a dream about a low cost solar heating system that used of the entire surface area of a south facing roof. His invention became known as the ‘Trickle Down Solar Thermal Roof”. It involved a corrugated metal roof covered with glass. Cold water from a large insulated tank in the basement was pumped to the top of a specially prepared roof where it was allowed to "trickle down”. Solar heated water from the roof was than collected in a gutter and returned to the basement storage tank. This innovative solar heating system is still functioning in numerous households along the US/Canadian border, but there is now a  new improved, more cost effective, more efficient, more DIY friendly modification of Thompson's invention called: Modified Trickle Down Solar Heating.  Upon close examination of the Thompson thermal roof we notice that water flows over the steel corrugations. The underside of the corrugated steel is  insulated to prevent heat loss, but a lot of heat is still lost through the cold outer glazing surface.  


      Harry Thompson’s “Trickle Down” dream became a reality but it was never fully realized until now with the invention of the “Modified Trickle Down” solar heating system. TD and MTD are alike in that they are both open loop systems that pump water to the tops of collectors but there are significant differences between them.


              Trickle Down                                                            Modified Trickle Down          

Open loop

Open loop

Trickles water on absorber

Trickle water through absorber

Glazed in glass

Glazed in polycarbonate

Unit construction

Modular construction

Corrugated steel absorber

Polyester felt absorber

Not portable

portable array

Has no inner film

Has inner film


 My first MTD collector looked something like this, but the screen has been replaced with polyester felt along with numerous other modifications so that now MTD is more cost effective and more reliable than oil heating systems. I have experimented with dozens of collector designs over the last three years and have settled on a steel stud slots construction. The magic of MTD has a lot to do with the way they are pressed together to form arrays. The  fundamental parts of the MTD collector include the Trickle Down Matt, the Gutter and the TDD or Trickle Down Distributor. To make the first TDD I used a 2" PVC pipe with .25" holes , next I decided to use a 1" copper pipe with .25" copper tubes soldered in place. Now I use a 3/4" Heater Hose with .25" drip irrigation spigots. Uniform distribution of water from the TDD is very important.




MTD collectors have been designed for flush mounting on a house roof, but don't give up if your roof is oriented in the wrong direction. Build an MTD sun shed. and use a multi drum heat storage system right inside the shed.  


The top and bottom 2”x2” mounting supports provide an ideal platform for flush mounting MTD collectors. An eight collector system would require four 2’x2’x9’ supports screwed into the roofs rafters. Use a level to position the top supports so that the collectors have a slight slope towards the center. This will help to channel the gutter water into a central drain connected with a 2” rubber T boot. Water will never freeze inside a properly installed MTD collector, because it drains back into the storage tank when the pump is off.


Richard Heiliger and I both believe that energy from sunlight can and should be a practical investment and we both encourage the reader to gain hands on experience through experimentation and discovery. There is only so much to be learned from reading. Dreams are given wings not only by our thoughts and understanding but also by the actions we take to turn them into reality. The MTD construction starter kit along with the MTD construction guide and video CD will help clarify the construction experience of this innovative solar thermal application..  Energy independence is possible but it will only become a reality if we make it so.  


Richard Heiliger's MTD solar heated home in Northern Utah


Bob Gering's MTD solar heated year round greenhouse in Canada  


John Canivan's MTD sun shed used for manufacturing Differential Controllers

STARTER KIT...The starter kit is designed to give the reader some hands on experience with a Low cost 2'x4'MTD collector. The kit contains a construction guide book, TDM materials (24"x48" polyester felt, two 29"x48" sheets of 5 mill Mylar, EDPM Bibs, a Trickle Down Distributor, a gutter end cap, a gutter compression support, an MTD gutter, a 3/4" L connector, end caps. and rubber bumper supports. The kits  comes with an instruction booklet for a steel stud slot MTD collectors and a CD with an MTD construction guide video. This video CD runs on standard PC computers. An MTD kit is the best way to gain the hands on experience needed to build MTD collectors. On line technical support is part of the MTD kit purchase experience.

MTD Starter Kit with MTD construction guide              USA only                      $ 99               


Trickle Down Solar Heating
MTD Solar Heating

MTD Solar Home 
MTD Data

Oil Alternative Articles
Carry Barrel Solar Hot Water

Collector Efficiency

Energy Alternatives 

Green Collar Work

Solar Heating in December
Solar Heating in January
Multi Tank Heat Storage

DIY Solar Heating Panels
Sustainable Living Homesteads
Gallery of Solar Homes

Solar Heated Workshop Plans
Sustainable Solar Heated Workshop

Sun Money from a Solar Workshop 
Solar Thermal Roof