My first idea for the glass window on the front of the oven was to use a recycled microwave oven turntable held in the center of the stainless steel mixing bowl with a clip so it would be free to expand and contract. An online seller of replacement turntables mentioned ceramic glass and regular glass, but I imagine this one is regular glass. It is not clear, and has bubbles in it, and probably reflects lots of energy, but I wanted to try it. (I am in the process of making a frame to hold three inch strips of very clear optically good glass from some junked Xerox Copy machines.) Here is a photo of the turntable window:

The oven reached 450 degrees today, and we baked some bread and two meatloaves, plus boiled some water (during the warm up) and dried some wood (after it was shut down.) Here is a photo after shutdown:

We pulled the Helios out into the bright sun so the mirrors could be pointed and adjusted.

Finally, all the spiders are welded, sand blasted, painted, glued, and mounted on the array. The pulleys and cables are hooked up, and the three double rows of mirrors can be adjusted up and down on the front side of the oven. Here is a photo taken shortly after pulling it out of the barn.

Completed Engine

Over half the people on earth (3 billion people) rely on fire wood directly for essentially all their daily energy needs such as cooking and heating. Though burning wood is sustainable in small quantities within a sustainable relationship with the ecosystem, burning in too much quantity degrades the land. Moreover, with the increase in the price of fossil fuel, more and more people will turn to fire wood for energy, causing further pressure on our trees and ecosystems precisely when we need our trees and ecosystems to heal the damage caused by fossil fuel burning.

Also, for the over 3 billion people that rely on fire wood for cooking, often this done indoors and the smoke causes serious health problems for the (usually) women that keep the hearth as well as accompanying children. In some places plastic and tires are also burned for cooking which causes even more diseases.

However, when 1 kg of wood is turned into 400 grams of charcoal, 50 % or more energy is extracted from the 400 grams of charcoal than if we burn the 1 kg of wood in the average fire [1].

This is a word description describing the construction steps of the Batant (SFT Training Model). When refined and complete (hopefully with help from your feedback, leave a comment or email eerik(at)solarfire.org directly) I will make a new pdf will be made containing the descriptions.

Here is what I came up with for the control wheels for adjusting the mirrors.

March 28, 2010

The wheels and track have just been welded. I found two iron cots (sleeping frames) that were being used for the last 25 years to keep wild dogs and coyotes from entering our chicken pen. These cots were constructed with rivets which I ground out with a hand grinder, and ended up with four rusty angle iron pieces to use for the "U" channels. The wheels came from a scope cart (Not a Tektronix cart!) constructed for the Gov’t under contract about 50 years ago. Very heavy duty. I cut the metal cart right down the middle with a metal cut-off blade in an old Skilsaw, and then welded it back together with a wider wheelbase to fit my tracks. Here’s a photo:

Saturday, March 13, 2010.

Another beautiful low humidity 75 degree Winter day! It was even warm enough to get some nice warm shower water from our Solar Water Heater. Between sessions of helping to prepare the garden, and sifting compost, I managed to sandblast and paint 4 more spiders, as well as the 54 brackets that hold the spiders to the 6 ten foot long "bars". The plan was to work on the pulleys, but it was too good of a day for painting to pass it up. This time I used the paint sprayer using the small "dash" pot, and sprayed the Rustoleum thinned slightly with mineral spirits. Really works well, but I plan to inspect all cracks/crevices and touch up with a good bristle brush before calling the painting finished. Here is a photo of the 54 tabs that hold the spiders. (You know what? THERE ARE 54 of many things to make in this project!)

Feb 21, 2010

Those six 1 1/2" square tubes have end plates that get welded on, and then have a threaded rod or a threaded hole in each one. The photo below shows how I cut the little squares that will be welded to the ends of the tubes.

When I cut the 3" squares out of 1/8" plate for the spiders, some of them were not exactly square, and were placed in a "reject" pile, so I cut some of these into four pieces using my chop saw. Since they were small, it was hard to figure out how to hold them. I ended up using the two C-Clamps, as shown in the photo.

Feb 15, 2010

After welding enough spiders for two rows of mirrors, I decided to paint them so I could start gluing the mirrors to the frame. Since the raw steel is covered with a black grease or oil, I decided to construct a sandblasting booth using some canvas tarps. First, I removed all the bolts from the spiders (they were installed so I could "adjust" them using the C-Clamp.) and put them in a large pile on a metal grate, and then blasted them with the sand. Hopefully, the sand would hit more than one spider during its flight, so it wouldn’t take as long to sandblast the ones that were in the stack. The sandblasted spiders are very light-colored, and the part that gets attached to the mirror back has a "tooth" and almost feels like sandpaper. This really works the air compressor, so I did several, and then moved to the bench to paint them using a small brush. I’m using oil based premium RUST-OLEUM enamel that is supposed to provide excellent rust prevention when applied over bare metal. (The can says that for even longer lasting protection you can use a STOPS RUST primer.) After painting and sandblasting for most of a nice 70 degree F day, I had nine of them hanging up to dry. The second day, I got six more done, when a cold front arrived with a tremendous wind that blew down my sandblasting booth, rained on my sifted sand, and sent me looking for my jacket. It froze the water in buckets on the porch. Until it warms up, I can’t do any more painting outside. The strong wind got me to thinking about what would happen if I had a completed Helios sitting out there when the cold front arrived? I wonder if the wind would break the mirrors?

I am currently writing a book detailing a society based on solar concentration. The Solar Concentration, or Solar Fire Society.

Since it may take some time to complete, in the mean time interested parties may read my first outline and summary, The Solar Fire Economy, click here or on the icon below to download the PDF.

The current working draft has a radically different organization and content than the above outline and summary but the basic spirit is the same.

Feel free to enjoy and comment below.

Ray Menke is building a Helios in Texas (see blog) and had some questions on the focal drift and mirror calibrating process that are not well explained in the existing material so I wrote back a fairly long diatribe about the issues, and in case others have the same questions I’m posting the response here.

I also drew up an image explaining focal "cross over" which happens with the spiders: the light from one corner will cross the reflection and hit the other corner but the focal point size stays exactly the same. What does change however is that the internal stresses in the mirror increase leading to breakage. I think most of the mirror breaking is caused by this sort of thing as shown bellow.

Response to Mr Ray Menke 25 Mar 10:

This is part of an architectural project by Nadim, who’s studying architecture in Sweden, to design an ecological house. Here we have bit of an idea of what a Prometheus would look like on the roof.