Re: tracking with a counterweight

Subject: Re: tracking with a counterweight I relayed Stan's posting about tracking devices on to a couple of the engineers in my office -- neither of whom wants to be a full-time participant on this list -- but like to read the technological-oriented postings nonetheless. Here is one response (caution: a sense of humor is necessary). ---------- Thanks. I particularly like the statement that there has not been much innovation in tracking since Farrington Daniel's 1964 book. The truth is, there has not been much innovation in solar at all since the book (in fact, since the turn of the century). This is especially true for solar thermal - PV has had some incremental advances. The reason is that, as always, solar energy is extremely diffuse, making it very low quality. What makes work is high quality energy. It's simple high school physics. Solar concentration is obviously an answer to real energy problems and indeed is technologically proven, but until we as a society want to pay for the solution, low-cost, dead-dinosaur energy is going to abuse the earth for our children. I believe in saving the earth for our children, but not for our children's children - I don't believe children should be having sex. :- ) ---------- From: Jim Arwood To: Jeff Jowett Subject: Re: tracking with a counterweight Date: Monday, December 30, 1996 9:46AM Jeff, Thought you would find this posting interesting from a technological point of view. ---------- From: sandler To: solarcooking-l --=====================_851758021==_ Content-Type: text/plain; charset="us-ascii" Barbara Kerr wrote: >Regarding tracking systems, I saw one built on a related design >back in the 1970s. There was a 6 inch square of plywood. On it >were erected two solid pieces crossed at the center of the >square. This partitioned the space into four shielded areas with >the top and outside planes open. In each section there was a >small PV cell which ran one of the four small motors. The motors >would run gently all the time until its solar cell was shaded by >the partitioning. It was actually directed by shadows, not by >sun. When a motor went into shadow, the motors in the sun were >left to dominate until they pushed the device so there was sun on >all cells.The small amount of electricity was sufficient to work >little motors placed to rotate a device in four directions. The >square was mounted on the solar device so when the sun changed, >the activated motors repositioned it on focus. > >I do not know how long it functioned. I wonder about how long >little electric motors would last for this work. Hi Barbara and All: I have just finished reading all of abstracts of the solar tracking devices patented from 1976 to the present in the U.S.Patent Office. There are 65. By comparison in the same time period there were only 16 solar cookers patented (one of them being your solar wall oven, Barbara). If anyone is interested you can search any ideas and find the abstracts of the patents on the internet at http://patents.cnidr.org There have been surprisingly few innovations in solar tracking since Farrington Daniel's book "Direct Use of the Sun's Energy" was written in 1964. He wrote: "Tracking the sun can be accomplished in several different way by clockwork mechanisms, by leakage using the principle of the hourglass, by shadows and electrical circuits and by manpower." He did not include thermal expansion in this statement but dealt with it a few paragraphs later after expanding on the above methods: "Another method of automatic tracking is to use a weight on a rope on the rotating axle and controlled by a ratchet wheel and escape mechanism which is released by the thermal expansion of a metal heated by the focussed sunlight when the sun passes the target." The factor that makes all these SIMPLE methods possible is the type of mounting. If the mounting is the equatorial type then only a single rotation (controllable by any of the above means) is required to track the sun. But if the mounting is azimuthal then you need the kind of tracking that Barbara has described with two separate rotations. I found it interesting that less than half of the solar tracking patents were for equatorial mountings and the remainder were for azimuthal and some very similar to what Barbara noted (differential lighting on photocell or photovoltaic arrays). In an equatorial mounting the axis of rotation is set to perpendicular from the solar altitude (angle between the sun and horizon) at midday. Since this angle changes through the year the only disadvantage of this mounting is that the axis should be readjusted periodically (once a week probably for most solar cooking applications would be plenty). I have included as an attachment to this post the abstract of one patent idea for a solar tracker that I thought was truly innovative. I converted it from html format to ASCII and I hope members of the list can read it. It has no moving parts (except the collector itself) and uses no electricity, valves or thermal sensor. I imagine that it would be very sensitive to wind however and the collector would probably have to be well protected (perhaps dug into the ground). I am ordering the full patent with its diagrams, and will inform the list of my impressions when it comes. There was a second patent using expansion rams that was based on a similar principle, but would be more wind stable (though more complicated). My final remark is in a rather different vein. It concerns solar tracking and sprituality. It is my opinion that low tech and appropriate tech methods of solar tracking are available and if you choose to incorporate them into your solar cooker you might remember that you are linking yourself with ancient cultures of sun worshippers (such as the Egyptians and Aztecs) who built such solar devices as sundials and solar event predicting temples. They were very aware of the movements of the sun, and when I change the axis of my collector each week I plan to have a little indicator on it with "solstice", "equinox", "unpack the beehives", "cut the hay" and so on marked on it. I think probably most of us on this list "worship" the sun's life-giving energy, and see its potential in helping us try to fix the mess we have made of this planet. Wishing you all a Happy New Year Stan --=====================_851758021==_ Content-Type: text/plain; charset="us-ascii" Content-Disposition: attachment; filename="ABS1.TXT"

A solar tracking device for causing a solar collector to track the sun during the course of the day and for automatically reorienting the collector to the east at the end of the day. The device (11) includes a pivotal support (13, 17) having a center of gravity below the pivot axis 16. The device further includes closed containers (25, 27) being an eastern container (25) and a western container (27). The closed containers (25, 27) are interconnected for fluid communication therebetween and contain a volatile fluid. The containers are mounted on the pivotal support (13, 17) one on each side of the pivot axis (16). A shading means (31, 32) is provided for shading the container nearer the sun more than the container further from the sun to provide unequal solar radiation on the containers when the rays of the sun are not at a predetermined relation to the containers thereby causing fluid transfer between the containers and rotation of the containers and the support about the pivot axis until equal radiation is received by both containers. The containers (25, 27) are so positioned relative to each other that the western container (27) is higher than the eastern container (25) when the device is at the rotational position which it assumes at midday. http://www.uspto.gov/ http://www.cnidr.orgi/