Experimental Solar DIY (and commercial) Projects

Solar and renewable energy ideas and projects that look promising (or at least interesting).


One of the appealing aspects of the solar thermal area is that "garage inventors" can make meaningful advances.   Some of the factors that make it possible to keep coming up with new ideas and innovations in this centuries old field are:

  • Innovative ways of combining collection, storage, insulation, and distribution of solar energy

  • New ways to integrate solar features with architectural features

  • Opportunities provided by new materials

  • Opportunities provided by increasing prices in conventional energy sources

  • Opportunities provided by the pollution consequences of conventional fuels

If you have a concept that you think should be here -- please send it in!


Directory for this page:

Note: New section on measurement techniques for solar thermal experimenters.


 Solar Inventor Resources
New Inventions in Low-Cost Solar Heating

William Shurcliff

Click here for Extensive Extracts from this book

My all time favorite solar book.  Published in 1979, but still has many interesting concepts that are well described.  Out of print, but available at BookFinder, Amazon used books, etc. 

The picture here is one of a hundred concepts in the book, each interesting and well explained.

David Delaney's Site

David's site has gone offline, but still available on the Wayback Machine: https://web.archive.org/web/20181103113700/http://davidmdelaney.com/

Original Website: http://davidmdelaney.com/

This is David Delaney's site.  He usually has some new and interesting ideas cooking.
Phase Change Materials Homepage


One PCM supplier


The latest on the application of phase change materials for heat storage.
Potential DIY Phase Change Material for Heat Storage


Nick Pine posted this note describing a phase change material for heat storage that was developed by George Lane some years ago.  It appears to have some potential for use as a low cost, home made heat storage material in solar heating systems.
Electric Bicycle Experiments



A large collection of experimental electric bikes and trikes.  Some with fairly detailed descriptions.
Backyard Inventor Projects   -- modest to moderate size projects that any of us could think about working on
Looking for a good overwindow collector design...

an overwindow solar collectorThis is a first cut at finding a nice looking over window solar collector design that produces a worthwhile amount of home heating.

It has a ways to go, but maybe you have some suggestions to make it better? Lets hear from you.


An Easy to Build Earth-Sun Simulator for Optimizing Reflectors and Shawdowo Studies...


Also, see the new section on reflectors, including reflector performance ans sizing tables, reflector desgin notes, and several examples of using reflectors ...

Earth sun simulator for reflector designThis is an earth-sun simulator you can build to test reflector designs or to understand sun and shade patterns on anything you can build a model of.

It allows you to see the sun and shadows for any location on the earth and any season and for any time of day. By rotating the turntable you can quickly play the sun over your model for a full day and see the sun and shade patterns. You can take readings on the model with a light meter and get a quantitative idea how much (for example) a reflector is increasing radiation.

Waterbag Solar Water Heating Collector Using Inflatable Film Cover and Soap Bubble Insulation....

A unique new design proposal from Nick Pine for an inexpensive solar water heater that may be capable of very high solar fractions and short payback.

It uses an inflatable cylinder made from poly film over a water bag heat storage. Soap bubbles are used for night insulation.

Off The Shelf Solar DHW -- Cheap and Easy DIY Solar Water Heating


All the details on the prototype...


Update March 2013: A glazed version of this system...


off the shelf solar dhw diy systemThe goals of this system is to provide an easy to build and inexpensive solar water heating system that uses all off the shelf components (i.e. nothing to build yourself -- just assemble).

This is a four season drain back system.  While the parts are inexpensive, they are high quality and the life and reliability should be comparable to commercial systems.

Total cost is projected to be about $1300, and the system qualifies for federal and some state rebates.

The system is in the design and prototyping stage -- comments and suggestions are most welcome.
All the details on the prototype...
Building and Using a Blower Door -- A DIY Blower Door you can Build for $30

All the details on our homemade blower door...
DIY blower doorThis is our homemade blower door that uses a furnace blower for the fan.

The writeup gives all the details on building and using the blower door,furnace blower base blower door and the methods you can use to compare your house tightness to others as well as estimate the heat loss and carbon emissions associated with infiltration.
With a little scrounging, the blower door and instrumentation can be built for $30.

DIY Blower Door Plans -- North Dakota Sate University Extension


Plans for blower door....


URL for NDSU Extension service -- many free plans...


DIY blower door tester NDSUThis is a set of plans from the North Dakota State University extension for a DIY blower door.

I ran into these plans after building the blower door just above -- not sure which is easier or cheaper or better.


A $6/sqft solar collector using Copper tubing and Aluminum fins

Full Details ...


This collector is an offshoot of the collector just below.  It uses the same scheme to transfer heat from the aluminum fin to the heat transfer tubing, but copper is used instead of PEX for the tubing.  This adds a modest amount to the cost per sqft, but provides performance that is quite close to all copper commercial collectors.

This is a cut at a solar water heating collector that offers a combination of high performance with a low cost per sqft, and an easy build.
See what you think!

The fin to tube thermal connection is similar to the collector above, but copper is used for the tubing instead of PEX.  This provides performance within 4% of an all copper collector in an easy to build package.

Extensive build, testing, and performance information is provided...


A $4/sqft solar collector using PEX tubing and Aluminum Fins

Full Details...



There has been a lot of interest in a collector that uses PEX tubing rather than copper to convey the heat transfer fluid.  Here is a cut a collector that does this -- with careful attention to the PEX/fin joint, it can perform surprisingly well. 

This is a cut at a solar water heating collector that uses PEX tubing instead of copper to convey the heat transfer fluid.   The fins are aluminum, and a lot of effort was put into attaining a good thermal bond between the PEX and aluminum.  Testing indicates that the collector performs at 84% of and all copper commercial collector at about 1/7th the price.

Extensive build, testing, and performance information is provided...

A $1000 solar water heating

Full Details ...



This is a cut at a system that performs well, lasts a long time, and is easy to build.
As of 9/29/2008, the system has been in operation for about 3 weeks, and is working well, and has supplied 100% of our water heating needs.

This is a cut at $1000, cold climate, high performance, long life, low maintenance, and easy to build solar water heating system.

It combines one of the two collector designs just above with a very simple drain back scheme.  A unique heat exchanger that is inexpensive and very efficient is used.

Extensive build, testing, and performance information is provided ...

Serpentine Drainback Solar Space Heating Project and Design Manual...

large serpentine drain back collectorThis is a very unique solar space heating collector. The absorber covers the entire south wall right to the peak -- this is made possible by using an absorber that is plumbed with tubes in a serpentine pattern rather than they usual vertical riser pattern. The serpentine pattern allows the absorber to be fit to the entire wall area and to extend all the way up to the peak. The full wall glazing makes for a very nice looking collector.

Several other unique features on the system, including a partitioned tank for more efficiency.

The builders provide a very complete 36 page manual that details the design and build in great detail...

How to make collector fins and evaluate collector fin designs

How to make and evaluate collector fin designs...

This article covers the various ways people have worked out for making the heat absorbing fins for collectors, fin performance, and some construction tips.

How to make and evaluate collector fin designs...

The Sungrabber Unglazed Solar Water Heating System

Description and some thoughts...
Sungrabber solar water heating systemThis is an innovative solar water heating system that uses unglazed collectors with drain back for freeze protection.

It appears to offer some advantage for milder winter climates. 

Description and some thoughts...
Build a Solar Attic,
Rob, www.IWillTry.org





This is a very nice project to incorporate a solar heating collector into a home's basic roof structure.

Rob describes in detail the first stage of incorporating the collector glazing into his new roof. 
He will now experiment with various sort of collector designs behind the glazing.  Add a comment into his blog to encourage him to keep us up to date on how he is doing! 
(thanks to Erik for suggesting this link)
Thermosyphon Solar Water Heating System Tests,


Test of the PEX/Aluminum collector...

Test of the Copper/Aluminum collector...


Some tests to determine how well two of our homemade collectors perform in a simple thermosyphon solar water heating system -- and, just to learn a bit about thermosyphon systems.
There are some questions here for a passing thermosyphon expert to answer for extra credit.

Test of the PEX/Aluminum collector...

Test of the Copper/Aluminum collector...

Converting a Clothes Dryer to Use Solar Heated Attic Air

All the details on Randy's solar dryer conversion...
hooking dryer up to an attic hot air supplyRandy has worked out  a way to convert a conventional d dryer so that rather than using an internal heater to make hot air do dry the clothes, he uses hot air produced by his unique solar attic collector.

This cuts the cost and energy use and CO2 emissions to do a dryer load by a factor of five!
Solar Cooking After Dark  -- A Stored Heat Solar Cooker 

Full construction details...
solar cooking with stored heatThis is a very interesting project from Mik that gives the details on building a solar cooker that stores solar energy in a bundlecooking with stored solar heat of steel rods during the daytime, and then uses the stored heat for cooking after sunset.

Mik is looking for ideas on improving the prototype.

Full construction details...
Solar Heated Livestock Watering Stock Tank Prototype

Details ...



NOTE that this project has progressed through a couple new versions -- see this section for the latest "production" version...

This is a first cut at a livestock watering tank that is insulated and solar heated to keep the water above freezing.

The usual approach around here to keeping stock tanks from freezing is to use an electric stock tank heater, which uses a lot of electricity.    This approach might eliminate or greatly reduce the need to such heaters and the cost and GHG's that go with them.

Details ...

DIY Heat Recovery Ventilator (HRV)

Details on the DIY HRV ...HRV/ShurcliffHRV.htm

This is another brief description of a potential DIY HRV from the RedRok site...
DIY HRVThis is a short description of a DIY HRV design that was developed at the University of Saskatchewan in the 1980. 

The description is from a book on HRVs for homes written by William Shurcliff in 1982 that gives a very readable description of how HRVs work and quite a bit of design information.

If you know of any other DIY HRV designs, please le me know.
Optimal Solar Air Collector Design



Careful design of air collector baffles and fins may allow high efficiency solar air heating collectors that are still simple and cheap to build.

These collectors have the potential for 1 to 2 year paybacks on material costs in cold climates.

Horizontal Pond Domestic Hot Water Heater

Gary and Nick


An experimental concept for a domestic solar water  heating that uses a pipe coil in a glazed pond to collect energy.
The goal is to provide a full four season solar water heater with the simplicity and low cost of a batch solar heater.
It is looking promising, but still some issues to resolve.
Comments welcome.
SunCache Solar Water Heating -- Harpiris Energy


Video: https://www.youtube.com/watch?v=dnKD0A3p7xk

SRCC OG-300 certification results for CA zone 3:


This design was developed by the Davis Energy Group in an effort to lower the price of solar water heaters.  The unique design allows more use of plastics resulting in a lighter and less expensive design.

This is a soon to be commercially available, low cost, Integral Collector/Storage solar water heater.
The retail price for DIY installations is estimated to be $2200.

The collector has been SRCC certified, and will qualify for incentive programs that require SRCC certification.   There is a CARB program that CA residents may want to check on.

The unit is designed for easy DIY installation -- for instance, the plumbing connections to the collector are made with two Sharkbite push in style fittings, and there are no controllers, or heat exchangers to install.
The collector contains 50 gallons of water for thermal storage that remains in the collector forever.  Fresh water that is to be preheated passes through a copper pipe heat exchanger immersed in the collector water.

Note that the freeze tolerant temperature for this collector is listed as 20F, so it is not intended for cold climates.  The testing indicates a savings for about 75 therms of NG per year for a family of 4.

Greenward Ridge Vent Water Heating System



Article with a bit of detail...


A new idea for solar water heating.  An antifreeze fluid is circulated through  the attic ridge vent to pick up heat from the hot air exiting the ridge vent.  The fluid is routed through a heat exchanger that is embedded in a solar preheat water tank -- this preheats the water before it gets to the regular hot water tank.

more (including a diy alternative)...
(Thanks very much to Chris for finding this!)

A unique solar water heating design using flexible tubing compressed between absorber plates


Full details:


This new design uses silicone tubing that is compressed (squashed) between two aluminum sheets.  This is a unique approach to providing a good thermal connection between the water carrying tube and the aluminum absorber plate. 

By squashing the tube, David gets a larger contact area and a good tight fit of the aluminum to the tubing with no air gaps.

There is no test data comparing the thermal performance of this arrangement to a metal tube with soldered or welded fin, but based on the tests I've done with PEX tubing and aluminum fins, I think the performance is likely to be somewhat less than the metal tube/fin, but still quite good.

The way in which water systems are plumbed in the UK results in low water pressure in the silicone tubing, and silicone has a high temperature capability, so this may work out very well.

Double Play -- An Experimental Solar Heating and Cooling System
Steve Baer

How to get articles from Home Power ...

and the Zomeworks site


Roof Integrated Solar Absorbers: The Measured
Performance of “Invisible” Solar Collectors
Preprint (700K pdf)

Roof Integrated Solar Absorbers -- slides

Roof Integrated Solar Absorbers
Home Power magazine article, issue 102

This innovative system uses unglazed collectors that are integrated with the roof structure and a unique thermal storage system to provide solar thermal heating in the winter and radiation cooling in the summer. Amazing!

The pdf report provides detailed performance measurements from the FSEC & NREL.

Theoretical Evaluation of the NightCool Nocturnal Radiation Cooling Concept
Danny S. Parker
Florida Solar Energy Center (FSEC)

New report on the NightCool performance in test buildings:
Experimental Evaluation of the NightCool Nocturnal Radiation Cooling Concept: Performance Assessment in Scale Test Buildings,
Danny S. Parker, John R. Sherwin
Florida Solar Energy Center (FSEC)

Daily performance of the test buildings,

Note: I would tend to NightCool  in the Experimental area, so, if you go after this, bear in mind you may suffer the "being a  pioneer" learning curve.  Please let us know how it comes out.

This is a simple, building integrated, cooling scheme that uses nighttime  radiation cooling from a metal roof to cool air in the attic space.  Attic air is then circulated into the living area to provide cooling.
A simulation model is used to predict performance in various climates -- the scheme works very well in dry areas, and fairly well even in very difficult moist-warm climates (e.g. Florida).
One of the attractive features of this system is that the roof is very conventional -- no massive ponds or moving insulation.
There is the potential in some climates to use the same metal roofing/attic system for space heating in colder weather.
The new test report shows the results for two 10' by 16' structures that were built to compare NightCool performance to conventional AC in Florida.  Very interesting and promising results.
Tests of a a simple dehumidification system using  desiccants are now underway.
The Rotating Solar Boiler

The Whole Story...


A new idea for low cost, high temperature solar collectors.
Simple Pool Heating Idea



This is an idea for a simple, cheap and efficient homemade pool heating collector.


Solar Shed for Space Heating House

Solar Shed



This idea uses solar collectors and heat storage tank installed in a multi-purpose outbuilding to provide space heating for the nearby house.

Night Air Thermal Mass Cooling Using Water Barrels


All the details on water barrel space cooling...

water barrel space cooling

This is a scheme that I am experimenting with to cool my shop.  It basically blows cool night time air over a collection of 50 gallon barrels filled with water to store "coolth" in the water. 

The method looks like it might provide cooling with a COP of 42 (SEER 140) or more!

While I am using the scheme in my shop, it could be used to cool any interior space.   The basic question is: does it make sense to use a fan forced flow of cool night air over thermal mass to store "coolth" for later use in daytime cooling?  Details...

Evapro-radiative Cooling Thoughts


Full Story ...

This is exactly the same collector listed just above, but used for cooling instead of heating.  The idea is that at night water from a storage tank is pumped over the collector surface to cool.  The water cools by radiation to the night sky and evaporation.  The chilled water in the storage tank would be used for space cooling the next day.
And, some thoughts on practical cooling and heating applications using this scheme.     Full Story ...
Full Scale Version of Evapro-radiative Cooling System


This is a first cut at a full scale implementation of the evapro/radiative cooling system described just above.

It uses our existing solar space heating system as a base, and manages to add the cooling function with very little additional work or cost.


Using Your Lawn Sprinkling Water to Cool the House

lawn water to air heat exchangerRick uses a water to air heat exchanger to extract some "coolth" from the water he is using to water the lawn.

Its basically free cooling.

All the details on Rick's cooling setup...
Nathan's Low Tech, High COP Air Conditioner



Nathan's low tech AC uses a tank with cool water coupled to an air to an efficient air to water heat exchanger (car radiator).

It occurs to me that this could be coupled with the Evapro-radiative cooling just above to make a very pretty cool system.

Experimental Solar Collector Made from Twinwall Panel

www.instructables.com/ ...


This is an interesting idea for a collector.  It uses the channels in a Twinwall glazing sheet as flow passages for water.  Slotted pipes fit over the ends of the twinwall sheet to act as manifolds.
I'm a bit skeptical of the temperature capability, leak sealing, and life of this panel, but its certainly an interesting idea.
Finding a twinwall that holds up to long term exposure to hot water may be a issue -- GE says that polycarb does not.
(thanks to Brent for finding this)
The Quest for an R15 Thermal Window Shade Some thoughts on developing high R value thermal window shades.

Such shades have the promise of greatly reducing window heat loss, while still being convenient to use.

Details here ...

An Over and Around the Window Solar Air Heating Collector First Cut Prototype


All the construction and performance details...

A first prototype of a solar air heating collector that fits over an existing window, and uses the window to get air into and out of the collector.

This is a simple collector that could be installed seasonally. 

The collector must, of course, be significantly larger than the window itself.

First try prototype and performance...

Combined Solar Collector and Window Shade


The Story


An insulating window shade that also acts as a solar collector, and that automatically transitions from one to the other depending on conditions.
Flow Organizer A try at the Saunders/Delaney/Pine  flow organizer.
The Integral Passive Solar Water Heater Book, David Bainbridge

Download this book

Even though the batch water heater design is an old one, I think there is a great deal of opportunity for improvement.  How about an all season, $300 solar water heater with a payback of one year -- this seems reachable to me with some refinement of the designs. 

This book is book is a great place to get up to speed on the potential.

This is a really fine book on all aspects of designing and building a wide variety of solar batch water heaters.

The book has a great mix of how-to and engineering design information -- great for builders and experimenters.

Thanks to David, the full content of the book is available here as a free download.

Low Tech Garage/Barn Heater (pdf)





An experimental idea for heating barn or workshop spaces.  Inexpensive and easy to build (honest!).


Solar Water Collector from CPVC Pipe

CPVC Collector Test



This is a try at a very easy to build and cheap solar flat plate collector that uses CPVC pipe, and extruded alum radiant floor heat spreaders.

Mixed results.

The Rutgers Solar Heating System for Greenhouses
Mears, Roberts, Simpkins, and Kendall
Rutgers University

The Rutgers Solar Heating System for Greenhouse - 1977 (0.8 MB pdf)

Greenhouse Solar Heating-1981 (2.5MB pdf)


The solar collector shown here was developed in the 70's as a very inexpensive greenhouse heater.  It works well for situations in which only low temperatures are required (like greenhouses and pools).

While I do not know of anyone who has tried this as a pool heater, it seems to me it might work well, and it would be very inexpensive -- perhaps $2 per square foot?

The papers give information on a several greenhouse energy schemes, so you have to wade through all this to find the details on building the collector.  The collectors described in the paper a quite large, but could be scaled down.  Note that even though this is a very simple collector, there are details that you must get right for it to hold together -- so read all the construction notes.

If you build one of these PLEASE let me know -- Gary

A number of other interesting commercial greenhouse related papers at the Rutgers Horticultural Engineering Website: http://aesop.rutgers.edu/~horteng/

Solar Closets and Sunspaces

Nick Pine and Paul Bashus




An interesting idea for coupling a low thermal mass solar collection area with a well insulated, high temperature  heat storage area that is used as a "solar battery" to heat the attached house during cloudy periods.

DIY Grey Water Heat Exchanger for Showers...



diy pex shower gray water heat exchangerThis is a simple and effective grey water heat exchanger from Tyler that captures some of the heat from your shower drain water in order to preheat water on its way to the shower.



Grey Water Heat Exchanger In A Barrel

Nick Pine (with a little help from Gary)


Canada study and test of grey water heat recovery system for a residence ( 3 MB pdf)

An innovative version of a grey water heat exchanger that may be able to recover a large fraction of the heat that normally goes down the drain.  It is inexpensive and is constructed inside  a standard steel barrel.
The Amazing Heat Scavenger Experiment

www.voltscommissar.net/ ... .pdf



An interesting and simple experimental setup to show the potential (and some of the problems) of capturing heat from grey water from the shower.
Recovering Heat From Shower Drain Water for Space Heating


A potential simple scheme for recovering heat in shower water for use in space heating is described.

Data from a small test to assess the feasibility of the scheme is presented.


An Approach to Developing a Very Low Energy Use Shower

A odd ball, but very low energy shower...


An approach that was looked into for implementing showers onboard commercial airplanes is discussed as a potential very low energy approach for home showers.
Recirculating Showers -- Yet another way to save shower water and energy

Thoughts on a very efficient shower design...

Ken's implementation of a recirculating, high flow shower...

A Kohler add for a (sort of) recirculating shower...

Thoughts and schemes to allow endless hot water showers at high flow rates with very little energy use.


Integral Stagnation Temperature Control For Solar Collectors (pdf)
S.J. Harrison, Q. Lin, and L.C.S Mesquita
Department of Mechanical and Materials Engineering, Queen's University, Kingston, ON, Canada

SESCI 2004 Conference

A passive approach to automatically decreasing the stagnation temperature of solar collectors.  An air channel behind the absorber plate is used to ventilate the collector when the temperature exceeds a set value.   A valve at the top of the air channel opens automatically at a set temperature.



A scheme to use soap bubbles as insulation on greenhouses (or other structures) to prevent night heat loss.
Solar Bubble Build



Pretty detailed description of a building using the soap bubble insulation scheme.  An interesting site -- with some new ideas.

How to Build a Heliostat for Solar Heating and Lighting,
Rob, www.IWillTry.org

http://www.iwilltry.org/ ...


Rob's heliostat -- reflects solar light and heat into a window in your house.
An interesting idea if your house is lacking in south windows.
Some detail provided on the construction.

Inflatable Heliostat

Download full report pdf (3.5 mb)

Mithra and Gary


 Surya -- a cylindrical tracking inflatable concentrating PV solar collector...

Patent for the Surya...  (pdf)

An experimental, low-cost heliostat design that uses air pressure to focus and support the mirror.




NEW This is the follow on version of the inflatable heliostat design that uses a tracking inflatable reflector to concentrate energy on a line of PV cells --->

RIC Enterprises ...


This is the site of my friend, co-worker, and very creative inventor -- Mithra.  We have worked together on several projects, including the inflatable heliostat just above.

The Inventions page on Mithra's site has some very interesting ideas.
Paper on PV powered irrigation system has a unique(?) combination of fixed reflectors and 1 axis tracking to increase PV panel output

Helikson, Haman, and Baird

The Paper (pdf)



This paper on a PV powered irrigation pumping includes an interesting scheme to increase PV output.  It has fixed reflectors on each side of the PV panels, and a single axis tracking system to point the entire rig toward the sun.  The reflectors are said to increase panel output by 33% (not counting the tracking benefit).

Does this seem like a good idea?

Solar Heated Home Using An Attached Greenhouse and Woodburning Stove

David Mears

The Paper (pdf)


A short article in Live Science on David's house

This 1981 paper with a 2004 update describes a solar heated house with a "flooded subfloor" thermal storage area. 

Seems like an interesting concept.  Test data for a real house is provided.

Papercrete Construction






PaperCrete is a building material made from a mixture of recycled paper, sandy dirt, and a little cement.  It has an R value of 2.8 per inch, good strength, and is lightweight and inexpensive.   While PaperCrete has been around quite a while, it has just started to be used for home construction, so this is for adventurous experimenters.
Roof Sprinkler Cooling System,

Full Details ...


Roof sprinkler system lowers roof temperature and cooling bills by keeping the roof cooler through water evaporation.

Added a description of another similar system 3/6/07

An Experimental Trickle Down Solar Water Heating System


Lu has designed, built and tested a version of the Thomason trickle down collector with some unique features.

The system includes a unique trickle down collector, a storage tank with a new liner design, and an innovative version of a copper heat exchanger.


The mb-soft compost heating schemes

Details here...

This is an interesting set of concepts that use the heat generated through the decomposition of organic mater for space and water heating.


Interesting New Projects
Drake Landing  -- Community with Solar Seasonal Storage for Water and Space Heating


Modeling of Borehole Storage:
www.trnsys.com (pdf)

YouTube Video on Drake Landing ...

New Alberta community uses 2300 sq meters of solar thermal collectors to collect heat in the summer for use in the winter.  Heat is stored in a field of 144 boreholes, and distributed by a common heating loop serving the 52 houses.
Vertigro Oil From Algae


On "The Energy Blog" ...


This looks like a pretty simple way to get sustain high growth rates and oil production from algae?

The video has the best description of the process.

MIT's Warm Light Wall System






An interesting solar wall/window construction that was used on the MIT Solar Decathlon entry.
The wall uses a layer of aerogel insulation (which transmits light) and a glass block that is apparently filled with water to act as thermal mass.  It appears to have an insulation layer on the inside as well (to control the heat transfer rate to the interior?).
It may provide some combination of solar gain, light, and storage in one unit.   As usual with solar decathlon projects, its hard to find any details or performance -- if you find something, please let me know.
Road Energy System -- solar heating from your parking lot




A system from Invisible Heating Systems Ltd that embeds plastic pipe in asphalt pavement to recover heat.
No detail on what weather conditions lead to successful heat recover, but maybe they will tell us how its working out in a while.  Seems like it might work well for public swimming pools with large parking lots?
Elisolar Thermal Shad Structures



Eliosolar makes a line of architectural shading structures that double as solar water heaters.  So, potentially you get the double benefit of reducing the building AC bills and also making free hot water.  They are in the process or getting SRCC approval, and it will be interesting to see what the efficiency as solar water heaters comes out to, but even if its quite low (as one would expect from the unglazed design), maybe the double benefit makes it worthwhile.
Eco Wave Power -- Simple Wave Power Generator

wave generatorEco Wave Power is developing a couple types of simple wave powered electric generators.

The designs are simple and might form the basis for a simple DIY wave power generator, or at least provide some ideas.
Cable supported heliostat from Solaflect Energy

For power generation stations that use a central tower to collect sunlight reflected from a field of heliotstat, the heliostats are the major cost element, so simpler and cheaper heliostat designs have a big payoff.

This new design by Solaflect Energy supports the heliostat mirrors using mostly tension cables rather than the traditional heavy bending structure.

Working on more efficient heliostat designs seems like a good backyard inventor challenge.
Magenn Power Air Rotor System

An Helium inflated wind generator

As of Feb 2020, the Magenn site does not appear to exist anymore, but Googling Magenn wind turbine brings up some descriptions



An interesting idea for a helium inflated wind generator.
Night Sky Roof Water Spray Cooling system


EERE report (pdf)


ORNL gov report

The first link above provides the most complete design information, and describes three different roof spray system designs. 
While these papers seem to be aimed primarily at commercial applications, residential applications may well be workable, simple, and energy efficient.
Most beneficial for dry climates.

"This innovation spray-cools water on the roof at night and applies the cooled water to reduce subsequent cooling loads. On clear nights, the sky is much colder than outdoor air, contributing to high water cooling rates through a combination of evaporation and sky radiation. Overnight, NightSky systems can typically cool a large storage volume (preferably two gallons per square
foot of roof surface) to a final temperature as much as 12 degrees below the minimum night air temperature."

Seems like a very promising way to reduce the energy cost of cooling.  The 5600 sqft prototype described in the first link achieved an EER of 149.

It seems like this system while currently used for commercial buildings is simple, and might well be adapted to cooling a residence??  The first link gives some useful design guidance on cooling per sqft, tank sizes, ...

Solar Thermal Electric Power Plant





A new solar thermal electric power generation installation in Nevada with some improvements.



Michael has shows some interesting concepts in home/building design.  Some of these have the potential for good energy efficiency -- as in the Home-Scape pictured here.
Mobile Window Thermal Test (MoWiTT) Facility





An interesting test rig to measure the side by side performance of two test windows under actual field conditions.
Interesting New Products
Solarcentury solar thermal and solar electric roof tiles



The data sheet, brochure, and video show pretty good installation detail.

An interesting new UK product.  These are standard roof tiles that are solar collectors.  There is a solar thermal version that heats water, and a solar PV version that generates electricity. 
The thermal versions appear to come in pre-plumbed horizontal runs of several tiles.

(thanks to Doug for finding this) 

May 2011: It looks like the solar thermal version is no longer offered?
Advanced Thermal Solar System With Heat Storage For Residential House Space Heating (pdf)
Kazimierz Szymocha

SESCI 2005 Conference



An interesting concept for a solar wall heater.  The absorber has integrated heat storage in the form of Phase Change Material.  The objective is to store heat during the day in the PCM, and let the PCM warm the wall that the collector is mounted on at night -- this reduces heat loss through the wall.  More...
Vacuum Insulation Panels


More on vacuum panels:




These panels have R values that are about 10 times greater per inch that conventional insulating materials.

They are made by placing a gas tight film over a porous but rigid material.  The air is then evacuated from the porous core to make the high R value panel.
There are some obvious questions regarding accidental punctures and leakage rates, but, none the less, a potentially very useful material.

Aerogel Insulation





Aerogel is a rigid, low thermal conductivity material that holds great promise for very high R values in very little space if the price can be brought down.

"Currently the popular insulation material is fiberglass. Three-inch thick fiberglass insulation has an R value of 13 while six-inch has an R value of 19. However, only a half-inch thick piece of silica aerogel will have an R value of 40. Both are are made of silica, but with radically different structures, yet this structural difference makes a drastic difference in thermal insulation performance."

Hot Harry

Gough Industries


download Hot Harry pdf

This Australian design has some features in common with the Horizontal Pond scheme just above, and some new features.  The case is rotationally molded PE, it incorporates two layers of glazing with a transparent honeycomb material between them for insulation.  The sun heats the bath, and transfers heat to an immersed coil of copper pipe.  The prices seem on the high side given what looks like a cheap manufacturing process?
Combined PV - Air Collector as Heat Pump Air Pre-heater

H. A. Zondag

Download details pdf

An interesting idea to use the normally wasted heat from PV panels for thermal heating.   Should about triple the useful energy output from the PV panel.
PVT Solar, Inc -- Echo Combined PV and Thermal System

PVT Solar Website...

Demo Video  -- this is probably the best overview of how the system works...

Some pdf downloads that provide a little (very little) detail...

An Inhabitat article that has some pictures of the system...

There is an SRCC report on a "Cleanline PV" that may be this system...


This system is a combined PV and solar thermal system.  Conventional PV panels are mounted above the roof plane leaving a space between the roof and the bottom of the PV panels.  The top and sides of the PV array are sealed to the roof.  Fresh air is drawn in under the PV panels along the open bottom edge, and is heated as it progresses up between the hot PV panels and the roof.  Vents at the top of the array take the heated air into the house and use the heated air to heat domestic water and/or for space heating. 

The PVT website does its best to not provide much of any useful detail on how the system is built -- the links to the left are the best I could find -- let me know if you find a more detailed description.

From a thermal point of view, the system is basically an unglazed collector that takes in ambient air and heats it all the way up to temperatures good for space heating (most solar heating systems get a head start by heating room temp air up).  I would think that this might work well in some climates, but the combination of unglazed collectors and heating all the way from ambient would seem to limit its use in cold climates?  The SRCC report (link at left) would seem to confirm this if it is for the same system -- the efficiency curve intercept is 0.24.

This is a very simple concept, and could certainly be implemented on a DIY basis.   While the thermal performance is likely to be well under a good dedicated thermal collectors, the extra "free" thermal energy would likely be more than the electrical energy the PV array generates.

Would love to hear from anyone who has one of these systems, or know more about them.

SolarWall PV/T

Overview SolarWall PV/T...


A Discovery Channel video on the system...


This is a variation on SolarWall's well know transpired solar air heating collector system.  In this version, PV panels are spaced over the transpired collector absorbers.  The SolarWall collectors draw in the heated air behind the PV panels.

It would be interesting to know how the thermal efficiency of this PV version of the solar wall compares to a regular solar wall.  I would think the addition of the PV panels may reduce the thermal efficiency of the SolarWall because PV panels would not be as efficient an absorber as the SolarWall absorber they are shading?
I did not see any detailed performance numbers.
(thanks to Paul for suggesting this)

Sunflower 250 -- Concentrating PV,
Energy Innovations




An interesting concentrating PV design.  First deliveries for early 2007.

"Now standing at a little over five feet square and five feet high, the 25X Sunflower™ is able to meet our targets for both energy generation and cost. Each of the 25 1'x1' mirrors is separately aligned, and yet all are attached to and moved together by an undercarriage controlled by just two motors. The receiver is approximately the size of one mirror and contains a collection of small cells that are wired together to produce electricity. It is backed by fins that dissipate heat and keep the cells operating within 30°C of ambient temperature at all times."
Greenway -- a PV system designed for DIY installation


A little more detail on the system:

Greenway is developing a PV module with an integrated inverter.  Detail is a bit sketchy, but it appears that the intent is that these modules can be strung together, and then plugged into an outlet.  They are specifically designed for easy DIY installation.
This seems somewhat similar to the Enphase system, but with even more straight forward installation.
Its hard to tell how far along they are, but the do have some gov and private funding.
Home CoGeneration Units

Honda Version:
Honda Micro CHP Home Cogeneration System

Article on home CoGeneration:

The Marathon Version:

www.infiniacorp.com/ ...

An assessment of CHP from ToolBase.org:

Some early testing in US:

Capstone Micro Turbine -- turbines for CHP, hybrid vehicles, power generation, ...

Home cogeneration systems offer the possibility of putting the waste heat produced when generating electricity to a useful purpose (heating your home).  The end result could be some cost saving, and an about 30% reduction in green house gas production.
As seems to be usual with any new technology to reduce energy use and pollution; availability and adoption in the US is slow.

Whisper Gen  -- CoGeneration




Another residential cogeneration system that comes in either an on-grid AC version or and off-grid DC version.
The website provides quite a bit of detail.
Not currently available in the US?
Some Test Results
This  just a place to put the results from some random tests that were run to settle some burning issue.

DIY Solar Air Heating Collectors: Pop Can vs Screen Absorbers...

test of solar air heating collectors: pop can vs screenA side by side test of two of the most popular solar air heating collector designs: the pop can absorber and screen absorber.

Detail on:

- Collector basics and measuring performance
- Building each collector
- Side by side testing and performance
- Flow distribution and thermal images
- Cost of materials


Testing the Transmittance of Some Common Solar Collector Glazing Materials

This is a test of the transmittance of a few glazing materials that are commonly used in DIY solar collectors.

It also looks at loss in transmittance with age.

TMeasuring Heat Transfer Coefficient for Solar Heating (Cooling) Systems Using Water Container

This test is a cut at measuring the heat transfer coefficient between the air surrounding a container of water and the container. The test is done for still air and for air velocity of 260 fpm.

This heat transfer coefficient is important for estimating the amount of heat that can be added to or removed from water heat storage containers by flowing hot or cold air over them.


Stagnation test on vertical double glazed collector...

stagnation test on solar collectorThis is a stagnaton test on our $2K vertical double glazed collector.

Comparing the Performance of Two DIY Solar Water Heating Collectors -- CPVC vs Copper


All the details on CPVC collector performance test...

cpvc solar collector testI did a side by side test of  Scott's new design cpvc solar collectorof the CPVC/aluminum collector comparing it to the  copper/aluminum collector. 
The performance of the CPVC collector was good, and I think that this CPVC design offers another option for DIY solar collectors.

The CPVC collector is easy to build and would make a good first solar project. 

All the details on CPVC collector performance test...

CPVC, PEX and PEX-AL-PEX in a short elevated temperature test

This was a quick test to see how CPVC and PEX faired in elevated temperatures up to about 260F.
A Sun Simulator for Collector Testing

The details...
sun simulatorThis is a project to do a sun simulator that will allow indoor testing of collectors up to 2 by 4 ft.

This is an active project and I could use some help on the reflector design -- have a look and see if you have some ideas...

Deep Mesh Solar Air Heating Collector -- Test 1

Deep Mesh collector test 1...


deep mesh solar air heating collector testThis is a first test of a collector design that Nick Pine has proposed that promises to provide higher collector output temperatures without as much degradation in efficiency as usually occurs.

The higher collector output temperatures are helpful in systems with heat storage as more heat can be stored in a smaller space with higher temperatures.
Testing on our shop heating thermosyphon collector -- including efficiency, flow rate, and effect of smaller vents...

shop heating solar collectorSome new testing on our nearly 10 year old thermosyphon solar shop heating collector.

Testing includes the performance effect of reducing vent size, and measurements of efficiency and flow rate....

Air flow distribution for a horizontal solar air heating collector with screen absorber


An attempt to get an idea whether the flow distribution in horizontal collectors with horizontal airflow tends to be distorted by the buoyancy forces on the heated air.
Done with IR pictures of the glazing.


Testing a conductive silicone in the collector fin to tubing thermal bonding.

Test of using conductive silicone in the fin to tube bond...

test of conductive silicone in solar collectorOur collector design uses an alum fin that is bonded both mechanically and thermally to a copper tube using ordinary silicone caulk.  This was a test to see if changing to a conductive silicone would improve the performance of the collector.

Twinwall Polycarbonate vs Plexiglas Glazing for Solar Collectors


Twinwall vs Plexiglas glazing for solar collectors...

twinwall vs plexiglas glazing for solar collectors testThis is a test to compare the performance of twinwall polycarbonate glazing to single wall clear Acrylic glazing for solar collectors under cold weather conditions.

Pop Cans for Solar Water Hating Collector Fins?


pop cans for solar water heating collector finsThis is in answer to a question of whether alum pop cans could be used to make a solar water heating collector  -- Maybe.


Solar Air Heating Collector Performance Tests -- Which DIY Collector Design is Most Efficient?

All the details on DIY solar air heating collector comparisons...

solar air heating collector side by side testsThis is a full winters worth of side by side testing of several DIY solar air heating collector tests.downspout solar air heating collector

Scott and I did independent testing of several designs, with each design tested side by side with the same baseline collector.
The surprising outcome was that the simplest and cheapest design did very well.
Measuring Sunlight at Earth's Surface: Build Your Own Pyranometer,
David Brooks


Update: I built one of these kits and tested it against my Apogee Pyranometer for recording solar radiation during collector tests.... 


Information on making and using pyranometers. 

Material on how to order and assemble a $20 pyranometer kit.

The References section at this link contains some in depth papers on measuring and modeling solar radiation at the earths surface.

My new Thermal Imaging Camera

Some tests and impressions of my new thermal imaging camera...
FLIR thermal cameraThermal imaging cameras offer an unmatched capability to view the temperatures over a whole surface.  They are a great tool for things like improving solar collector designs.

They have been almost prohibitively expense, but over the last few years have come down a lot as some entry level lines have been introduced with lower prices that have been steadily dropping.  The lowest priced ones are now a bit over $1000 -- still a lot, but much better than $10,000.

I recently took the plunge and got a FLIR IR camera.  My impressions of the FLIR so far are here... 
Heat Transfer in Solar Air Heating Collectors Made from Gutter Downspouts... thermal imate downspout collectorA simple test to see how much heat gets transferred around to the back side of solar air heating collectors made from gutter downspouts.

If heat transfer to the back side of the collector is efficient, then the effect heat transfer area from absorber to air is significantly increased, and this should improve the efficiency of the collector.
More PV Array Shading Tests

All the details on PV shading test...
PV array shading testThese are some simple tests to try to determine the effect of shading from nearby power or telephone wires that cast shadows on a PV array.
Effect of Tree Shade on Solar Collector Efficiency
A Simple Way to Test All Kinds of Collector Design & Placement Variations

All the details on solar tree shade test...

This is a simple way to test the effect of tree shade on collector efficiency.  It uses two identical collectors each with a bottle of water inside to collect heat.  You place one collector in full sun, and the other in the shade of the trees you are concerned about.   The difference in water temperature rise at the end of the collection period tells you how much the shade is hurting.

This same method could be used to compare glazing materials, compare different collector orientations, ...   and all sorts of other variables.  Its simple, practical, and accurate.

Screen Absorber Test...

A Second Set of Screen Absorber Tests...
(this one has an observation on the suitability of FG screen for absorbers)

This is a simple to test to try to understand a little more about how solar collector absorbers made from multiple layers of window screen actually work...


Adventures in Measuring Airflow for a Solar Collector... Some notes on various ways to measure airflow for a solar collector, and how well they work (or don't).
Effect of partial snow cover on PV panel output


This little test shows the effect of having your PV panels partly covered by a thin layer of light snow.

Power output of cleared panels is compared to the panels with some snow.

Test of a Collector with Horizontal Risers

All the details...


This is a rough test of a collector in which the "risers" run horizontally instead of vertically.

It has been suggested that this arrangement might work better for the large and wide collectors that DIYers build for space heating.

The results look encouraging to me...

Best paint for solar collector absorbers

The test...


This is a quick test to compare the temperature reached by small samples of aluminum painted with Flat black, Gloss black, and Thermalox paint.
Idea being that sample that reaches the highest temperature will have better performance as a solar collector absorber finish.
Variation in Riser Flow for Wide Solar Water Heating Collectors



A test of the variation in riser to riser flow rate for a wide collector with 3/4 inch top and bottom manifolds....
Using Attic Heat
Logged Attic Temperatures

Details ...




This page goes over some potential ways of using attic heat, including preheating water, space heating, a source for pre-heated dryer air, and pool heating.

It also provides long term plots of my attic temperature, which is probably typical of cold many cold northern US climates.  These give some feel for the potential.

An FSEC paper on measured attic temperatures...
note the dramatic reduction in attic temps for a white roof.

Effect of edge gaps on the performance of insulating shutters and shades,
William shurcliff,
Thermal Shutters and shades, 1980

Details ... (pdf)

Some simple tests that William Shurcliff did for his book Thermal Shutters and Shades to determine how tight insulating shutters and shades need to fit in order to not have excessive heat loss.

Extracted from "Thermal Shutters and Shades", William Shurcliff
with permission.
 Effect of vent size on thermosyphon collectors ...



This is a test of the effect of changing the size of the the inlet and exit vent for a thermosyphon collector.

The airflow through thermosyphon collectors is driven only by the buoyancy change of the air heated in the collector, and is sensitive to changes in the collector flow path.
Small panel tests to compare collector designs


Follow on small panel tests:
Air gap vs silicone gap...
Conductive vs regular silicone...

This is a method for comparing the performance of alternative collector designs.
It does not require much in the way of instrumentation, and it appears to produce solid results.


Large plastic pipe coil as heat exchanger




This is a simple test of the thermal effectiveness of a large plastic pipe coil used as a heat exchanger in a solar water heating system.


Serpentine Collector Drain Back Testing,

Details ...


This is a quick test to evaluate how see how well a serpentine plumbed solar collector will drain back once the pump is stopped.

Basically the tests attempt to determine if a serpentine collector can be used in a drain back system.

Details ...

EPDM Collector Test

Details Here ...


This is a test I did some time back in trying to see if a collector absorber constructed from EPDM (rubber) sheet would work for my Solar Shed project.

While the results were not good enough to use it on the Solar Shed, they were not totally discouraging, and I think that the idea has some promise. 
There have been successful commercial collectors made from EPDM in the past, so there is probably some combination that works.   A lower tilt angle would also help with the water spread problem.
The appeal of an EPDM collector is that the cost could be south of $3 per sqft -- compared to $30 per sqft for commercial collectors.
Transmittance of Corrugated Glazing

The Test


Do the corrugations in corrugated glazing (e.g. SunTuf glazing) reduce the solar transmittance compared to flat glazing?
Here is a little to test to find out.
Temperature Stratification in Tall Rooms




This little test was done to settle a "discussion" about how much the hot air tends to rise and stratify at the top of a tall room.  You may be surprised by the answer.


Flow Organizer




A try at the Saunders/Delaney/Pine  flow organizer.
Radiant Floor Heat Spreader Plates Test

Heat Spreader Plate Test

DIY Press to make Heat Spreader Plates


A little test to determine how best to install heat spreader plates for radiant floors.
Shower Temperature Drop



I'm sure you were dying to know how much the water cools from the shower head to the shower drain -- here is the answer.
This drop is of interest because it is heat that cannot be recovered using a grey water heat exchanger:
Shower Temperature Drop

A shower design that might reduce the temperature drop:  http://www.sunfrost.com/efficient_shower.html
Effect of Air Filter on Thermosyphon Collector Air Flow


Test measures the effect on air flow and heat output of a thermosyphon solar air heating collector with and with out dist filters on the inlet vents.


Optics Experiments On The Cheap



This is a very clever and simple test setup for experimenting with curved mirror shapes.

It allows you to quickly and easily fully visualize how a given mirror shape will do in focusing incoming sun.  It allows you to very quickly see the effect of mirror shape changes.

While the video is aimed at refining solar cooker designs, the technique could be used for any kind of concentrating solar application.