I would like to share a little bit about these windows with you, all. While these are just a prototype and are not yet commercially avalailable they will be in the near future. The windows or rather the window system contains glass blocks filled with water, along with a specific exterior glazing that covers the entire block assembly. The exterior glazing is a fixed unit with a u-value of .29 and a SHGC of .76, pretty good balance for a solar window. The blocks are 16" x16" and 4" thick and weigh in at 50# a piece. For this house we have 85 of these blocks along the due south facing wall. The total area of coverage is about 150 sq/ft and the total water weight is around 3,000#. They have been installed in the house since last october and have been performing better than expected. The heating system for the house did not get up and running until Feb 15th, 2009 and the windows were the sole source of heat thru the winter before that. The water in the windows acts as thermal mass storage for the thermal energy and then releases it into the house as night approaches. While I didn't start data logging the windows and house until late Feb, we did take notes of high and low temperatures thru the winter. The coldest temperature reached inside the house was 41.9F and the windows were still at 48F. This was only after 3 consecutive days with no sun, low's around -5F and high's in the upper teens. January 15th-17th 2009 ( historical data )  The average high temperature reached in the windows was 85-90F on a good sunny day, even without the heat in the house running yet, and the windows not only warmed the house over the course of the day, but the house actually got warmer until about 10pm and then moderated over the night. Most days the interior temperature would rise a degree or two between 5pm and 10pm and then slowly moderate and then decline until 9am. Around 9AM, in the middle of winter, the sun starts to hit the windows  and the windows quickly start to rise.   
  I don't know if they will ever freeze, but this winter was a good test for them. As for over heating, the window will have an exterior shading system. Why exterior you might ask? Well, you need to stop the suns energy from reaching the water in the blocks. The inventor of this window, Wendell Colson, is the VP of research and development for Hunter Douglas, the window shade manufacturer. He has developed an exterior shade that will block 70% of the solar gains while allowing for view and light to enter the space. The shades are being built right now and should be installed in a few weeks. Take a look for yourselves and let me know what you think.
                                         Thanks, Tom Pittsley
                                                       ecobuilder@aol.com 
                                                     
I have been documenting the project from the start and posting it online for all to see. Here are some links to the videos showing the performance during the winter and explaining how the windows work. http://www.youtube.com/user/eebuilder 
 
I have also been posting blogs and pictures for the project as well.
http://tompittsley.blogspot.com/
Pictures

   

Interesting, how do you keep the heat from radiating back out?

Aerogel has an insulation value of about R10 per inch, very good for blocking conducted heat even in relatively thin layers. (An inch thick wall of aerogel outerforms a 2x4 studwall full of fiberglass.)

It's mostly UV-absorbent, but has a few bands of transparency to UV:

http://eetd.lbl.gov/ecs/aerogels/sa-optical.html

There will be some radiative loss, but with properly-emissive glazing on the interior side the net flux of heat (both radiant & conducted) will be strongly toward the interior.

When/where will the stuff be commercially available?

...or are these glazed with something less exotic than the daylighting blocks used on the Solar Decathlon project?

The exterior glazing for these windows is a combination of glazings that have a U-value of .29 and a SHGC of .76 . Having the mass located on the interior side of the window system allows the heat to move along the path of least resistance. I wasn't sure just how well it would work but the IR pictures show the story. http://picasaweb.google.com/TomPittsley/PassiveSolarHomeMiddleboroMA# . The inventor has moved away from the aero-gel window, due to the lack of transparency and cost issues related to aero-gel. The aero-gel worked really well but people want to see out their windows and this didn't provide for any visibility. The windows I have in this house, are not the final product, he has already moved on to a more cost effective solation that will also eliminate many of the problems with the long term storage of water. His latest development also reduces cost signifcantly, one of the problems found while building these windows. The exterior glazing that covers the 5 windows for this house cost $8,500 for the exterior glazing alone and they were not user friendly upon installation. If you want to see his latest version. you will have to wait for the 2009 solar decathlon, Team Boston (http://www.livecurio.us/index.html) will be using his latest and greatest system. I can tell you this, these windows provide incredible visibility and without knowing it you would never guess that they are filled with water, most people don't believe me when I tell them. So far the windows have remained free from any kind of growth in the water a problem experienced with previous versions. I think he is getting close to having a final product, and they will hopefully be comercially available soon. His goal is to reduce the cost of the system to an affordable level, he thinks $50 sq/ft but I don't see it. I am guessing that upon introdction the windows will cost in the $100 sq/ft range. The prototypes used for this house cost $300 sq/ft, not a feasable number in the real world. Granted the cost to build a prototype is much higher than producing them in quantity, but without changes the cost would still have been to high.

Tom Pittsley
ecobuilder@aol.com
www.eebt.org