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The sun is a reservoir of power almost beyond description. Man's Dream of tapping this mammoth source of energy has only started to become a reality and this is the century of science. WGBH FM in Boston presents the century of science produced under a grant from the Educational Television and Radio Center in cooperation with the National Association of educational broadcasters. This is an exploration of developments in 20th century science and of the implications they present for contemporary American society. Your host Volta Tory former editor of Popular Science and now director of radio television programming for the Massachusetts Institute of Technology. We have more energy at our fingertips now than ever before. All sorts of things can be done by pressing buttons. The energy that has made this possible has come largely from coal and oil. We're using such tremendous quantities of these fuels that people wonder how long the supply will last. It would not occur to
any sensible person to waste fuel oil by simply letting it flow out of a garden hose under bare ground. But the sun burst as much energy onto an acre of land noom as such a stream of oil would contain the sun in fact freely gives every square mile as much energy per day as there is in a couple of atomic bombs. If this solar energy could be captured and tamed it could save us tremendous amounts of work and worry. Professor height see Hottel of the Massachusetts Institute of Technology is one of our country's leading authorities on fuels combustion radiant heat transmission and industrial furnaces. He has been honored by both the American and British governments for his work. He is the director of the fuels Research Laboratory at MIT and chairman of the MIT research committee on solar energy. He is here now to tell us about efforts to harness solar energy. Professor Hoddle Why is solar energy so much more difficult to handle than
the energy and fossil fuels. Well Mr. Troy I assume you mean by difficult to handle difficult to handle economical way or with good economic consequences. This analogy to the garden hose can be continued by pointing out that unfortunately the flow isn't all at one spot from the acres accumulation it's distributed over the acre and it is that low density of energy or dilute mists of sunlight. That makes it so hard to devise a means of cheaply using it. The mean intensity of sunlight in the United States is about 13 hundred units falling on a square foot in a day a 24 hour day. That's to be compared with. Almost.
2000 times that great energy transfer in the devices that are involved in our converting fuel power over to fuel energy over to power. As solar energy. Something that scientists have been trying to capture or shall we say concentrate for a long time or is this a comparatively new field of research. It depends on how old you are the effect they have or the main stream of effort started back in the 1870s with some French and some American research. I think when my properly say that in the present the more intensive attack on the problem. Started in the 1930s with. The foundation by I got for a cab. Of a project at MIT and another at Harvard
and by the formation and rush of the helio Technical Institute. I have to assume there are various approaches to this problem like the professor I have. How many are being pursued and how many are of interest. Well you might broadly divide the field into. About. Three. Divisions photochemical attack on the problem is one photo electrical studies institutes another. And then comely thermal studies with or without focusing devices to increase the intensity. Could you define those just a little bit more just what do you mean by the photochemical for example. Well I referred to the possibility of in some way imitating nature's use of sunlight. To grow. Food. The storage of solar energy in the form of chemical
energy and something that I think by combustion or by being eaten can furnish energy. Photo electrical I suppose would be more like a solar battery that we have yeah absolutely. The exposure meter of the camera and those just as an example of the. Photo electrical conversion on a minute scale. The solar battery is a. Is the same device developed as far as it's been possible so far some 11 percent I believe is the efficiency of the best of the present solar batteries and other thermal On the other hand that would be to use the heat directly not to transform it into chemical energy or unless this thermal approach refers to the absorption of the heat by a blackened surface either a surface of the full extent of the solar beam being intercepted are a smaller
surface at the focus of some concentrating device for the purpose either of obtaining energy at a modest temperature level. For house heating or refrigeration RS distillation are possible a far obtaining heat at a higher temperature level and using it to run what. In. Thermodynamic parlance we call a heat engine. It's basic to our present power plant which is this approach as Professor hostile to you think is the most promising. Or can you say. Well in the long run. Believe thought a chemical on photo electrical approaches are the interesting and intriguing ones the ones that would constitute the neatest solution to the problem. But there aren't any good ideas at present on how to. Convert. Soil and sunlight by either of these means at a cost which is
attractive in competition with him. The thermal method on the other hand is much closer to being economically sound today and I suspect that within the next few years perhaps the next decade or more. The one of the thermal approaches will be one which is economically the soundest. What kinds of basic research would be most helpful in overcoming some of these difficulties. You know other words what is there that the scientists and engineers don't know. That would be very helpful if they knew more about. Course when you mention basic research there's always the question how basic you're asking when we don't know the answer what do we need to know and what is out. And that's always a tough one but it's very safe to generalize that.
Since we haven't today any knowledge which is very impressive from the standpoint of applicability to an immediate solution of the problem of using sunlight. It follows that whoever. Presents a solution will do so as a result of. Having a fundamentally broad education. Well I've studied. Physics and chemistry and mathematics if we're talking about young people. He will have become an expert in one of those fields rather than set for himself. The goal of becoming a solar engineer let's say. What tends to be the way. Young people think they way they back out a narrow field and think they can prepare themselves for it. When an educator would say that. They should use it simply as the impetus to study but not an hour of their.
Curriculum to subjects the results of which they can see applicability out. Well wouldn't this really cover quite a variety of so-called I think Demick disciplines. If you are really going to get into the fundamentals of utilization of solar. Yes I'm quite sure it does. For example if we are to find the info to chemical reaction that will produce energy storage we must know. More than we do today about the kinetic set of chemical reactions involving both a chemical acts and the energy storing reaction and the dissipating reaction the dark reaction so call the one that undoes the job that the sunlight is trying to do. That's intriguing what you have in the dark reaction that's new to me. Well suppose a plant a leaf is growing in the
sunlight. This means that CO2 and water are being synthesized to form a carbohydrate. Using energy from the sun. At the same time look this is going on a degradation is going on and using up some energy in the case of the plot belief of the degradation is not very great so there's a net growth that is quite considerable. When we try to imitate this in a test tube such as Professor Heights experiments with the use of Siri I'm Salt's to cause sunlight to decompose water in the hydrogen oxygen. About thirteen hundred and ninety nine fourteen hundredths of the energy of that is used. Usefully is destroyed by a back reaction that does what we would like to have done. And
the kinetics of the dark reaction must be known in order to exploit the reaction that we want to have. Take place. That probably entails a great deal of laboratory work yesterday. It calls for a general knowledge of photochemistry rather than on knowledge that's based on any specific desire to use the photochemical process to make chemicals out of sunlight. Similarly in the field of physics. There are a number of places where we now see need far more knowledge of solid state physics for example. To improve. Our knowledge of how to build a blocking layer of photos so a battery are to improve our knowledge of how to make surfaces. Selectively black. These are only two examples of where solid state physics. Would
be a significant contributor to that is a familiar territory. Ever buy a TV but whatever I bench that other people they always ask me what is solid state physics. Could you explain a little why you designate a part of physics as solid state physics and what it really covers. Well I'm a chemical engineer rather than a physicist so you should perhaps be asking someone else to define this and in any detail as an example in the. Thermoelectric generation of electrical energy from heat. The use of the same principle that. Is involved in measuring the temperature with a thermocouple. Except that here we would like to feed heat into the hot junction of a thermocouple and take out some useful electrical energy. We need to know the effect of the structure of the solid. On the tendency to
produce this voltage at the junction of the two dissimilar metals. And we find sometimes that. The maximum voltage is generated when the two metals. Are quite similar except for a minute quantities of impurities indicating the. Profound effect of these impurities only structure of the solid crystal in the case of the blocking layer photos. The two parts of the thin wafer. Silicone used in the Bell Telephone solar battery. Are very similar except for parts per million of contaminants which affect the crystal structure of the solid. It's knowledge of the nature of that structure to which people refer when they speak of solid state physics.
Well is this in general an area in which more qualified people are needed. Are we where we are in solar energy because of lack of money or because of lack of people. Well I think it's much more lack of people than lack of money it's it's a lack of people. With. Ideas. It's lack of able people. Many things can be done with fairly modest funds. But. One. Caught my kid way without good people in the field and we have a great need for. More good people. Is there a current demand in the laboratories and research institutions for. People especially trained for this sort of work. No I think it's fair to say that that. We have not made enough headway in the solar field. To present today very many applications that are economically sound house heating. Looks as though it may be
a sound way to use the sun. Domestic air conditioning as a possibility. Hot water supply for. Houses for domestic use is a possibility. There is no present. Evidence to me of that solar power and come dressed to solar heat will be economical a son very soon and consequently there is no requirement for. Engineers trained in this field that many people have heard of course about the solar houses that have been built by MIT and others. Some here near Boston and others in other parts of the country. You had to dissipate that many more of these houses I take it they are all experimental as of now will be built in the next few years. MIT will probably follow the present one with a better design
what's our objective continuously to improve these. We have to work in the Boston area with the. Knowledge that solar heating is much further from being economically sound here than in other parts of the country with fixed charge on the investment in the solar plant is generally greater than saving the fuel. We have hope that the improvement in solar collectors will be such as to reduce their cost to the point where. So housing is economically sound even in New England. Even before that day comes though we can buy experiments in New England reach generalizations concerning the economic position of solar housing in other parts of the country where the solar climate is more favorable.
Is it possible to say draw a light on the map. And that's much closer to the equator of this much further north solar heating. Is there is not likely to become economically feasible. Well that's a little bit of an oversimplification that has been done by various people in the past. But not by those who have been involved in quantitative calculations of what can be expected to happen. It isn't the CO ness of the winter so much as the intensity of the sunshine which counts how much you get back per square foot of collector. Is the important number. A sunny climate in a high altitude in a fairly northern latitude. Could produce a position of. Greater economic soundness for solar heating. Than a mild climate. In a more temperate zone accompanied let's say
by a high humidity which produces absorption in the atmosphere. So this way you would do best where you have some altitude. Good dry right there. That's ideal sea hostile solar engineer and chairman of the MIT research committee on solar energy as described three theoretical approaches for the possible utilization of the sun's power. Robert J Pelletier research associate in civil engineering at MIT will tell Mr. Torrey of an actual use of the sun's energy in the solar heated house in Lexington Massachusetts. Then I'm going to ask Mr. Robert Jay Pelletier to describe the newest of the MATV solar heated houses. Mr. Pelletier is a research associate in civil engineering at MIT assigned to the project at one of the popular magazines is called the Solar experts dream house. How big a house is this Mr. Pelletier.
Well it contains three bedrooms two baths a kitchen dining room living room. All in about fifteen hundred square feet of living area not too small by a conventional family standards. And the houses of course two stories in height. Does it look very different from the outside. Yes it does a little especially from the south side except for the south side however it looks just like a conventional contemporary design. Few of the collectors. That's right the collector forms the entire south side of the house. And what is that like. Well the collector is composed of 60 rectangles of glass separated by metal frames and the whole bank of collectors is sloped at an angle of 60 degrees to the horizontal. Is this black or does it look like a skylight or what. Actually the background of the collector behind the glass is black but it appears to reflect sky formations out as clouds birds trees and so forth and is not at all attractive.
Well how does this collector work. Well let's start from the bottom as an absorbing surface. We have aluminum sheets with copper tubes clamped to them at intervals of about five inches. The side facing the sun is painted dull black to absorb the radiant energy and above that we have two layers of glass separated by an air space. Is this ordinary glass special for us. This is a somewhat special glass. We control it or have had the amount of iron put into the glass controlled to a low level so that it does not absorb very much of the oncoming radiation. In effect as light or heat comes through this glass under the aluminum plate. That's right and then it is collected in the pipes as a part. Well the radiant energy is absorbed by the black surface and then heats the plate. We have water flowing up through these tubes clamped to this plate and the water picks up this heat or energy in the form of heat and is
carried off down into the basement of the house to a large insulated tank and there it is kept until needed by the living space. This tank is much larger than ordinary oil take which should have a poster of a bag as well. It's a fifteen hundred gallon tank which sounds large however when you see it in the flesh it doesn't appear to be much larger or any larger than the old type called Pan the water from this tank is then used to heat the house. Yes we have a water to air heat exchanger and we pass warm water from the tank through the heat exchanger. We then blow air by means of blower over the heat exchanger and the warm day or is passed through a system conventional system of ducting into the living space. So actually they get warm air that has been heated by hot water. That's it exactly. We choose a water. Heating system for convenience of collection and also because we can then provide domestic hot water with great ease. How hot does the water get Mr both here during the heating season the
heat will probably not exceed one hundred fifty degrees during the summer however the water could get considerably hotter than that. Would you normally have enough heat in this water for a dishwasher or a hot shower. We probably will for most of the year but for this reason and for the reason that it's only economical to design for 100 percent solar heating in a cold climate such as New England when the amount of sunshine that we receive during the worst part of the heating season is the least that we receive at any time during the year. We feel that an auxiliary. Method of heating is a must as an economic must. How much of the necessary heat for the house would you actually get from solar energy. But we hope. And have designed for about 80 percent 75 to 80 percent depending on the pattern of the weather during the year. Some years we may get more and other years we may get less.
But you have an exhilarating system there so that you burn oil as well as our engine to refuel That's right. And if you had a real co-slept for a long period without sunshine this suffices to keep the house work. Yes as a matter of fact it has to be of a size sufficient to do the entire job by itself. Because just as you mentioned we can get the coldest weather and the worst sunshine simultaneously so that we can't get much of any help from the solar system in a situation like that is this is just a Mr Pelletier where you can use this energy to cool the house for air conditioning in the summer. Not at present we don't seem to have developed a good practical method of refrigerating with low temperature water such as we are a low temperature in the in the conventional sense that we obtain from a collector of this type. Well how much fuel do you normally need in this house and doing what.
Well let's first say how much we would require if we didn't have a solar collector. Yes and that would be about twelve hundred young ones. That's well insulated house and uses somewhat less fuel than a conventional house of its size would anyway. With the collector However we should be able to reduce the oil consumption to about 250 gallons. This means that we're only using about 20 percent of the fuel ordinarily required. Did you have to use unusual materials or especially skilled labor to build this Mr poeta. Not really the collector itself was the only unusual piece of equipment in the house as such and even the collector was made of conventional sheet metal and conventional tubing put together in a slightly unusual fashion but nothing beyond the range of steels ordinarily employed in building construction. The rest of the system the heat storage system and the distribution system are all formed of conventional components that is components readily available in the
present market. They are hitched together in unusual ways and this caused a little complication. Is this something that ordinary plumber or heating engineer can handle lower. Once the plans have been worked yes we think so there are really no unusual situations occurring in the system that haven't already occurred in other types of heating systems. Well Buster but I gathered from Professor Hart of his remarks a little earlier that solar heating is not regarded as economically attractive yet. What made the heating system that you have used in this house unusually expensive. I think I would attribute most of the expense to the fact that we haven't ever built one of just this form before. The first time through any design is always necessarily expensive. We usually have to backtrack from mistakes or wrong direction somewhere in the building of the thing. I think
in this case we could say that the collector itself was the most expensive although it perhaps shouldn't be. And when put into reasonable scale production what do you see as the future potential of this house Mr. Botha. I think one of the chief things to look for in the future is refrigeration of the solar energy this will enable one to use the collector to its fullest capacity all year long and will be able to pay for itself in much shorter order and also gain a lot of use in areas where there is abundant sunshine but only a moderate need for heat. At present time they certainly could use a lot of cooling. It is a great deal of work being done. That method of cooling the US by means of solar heat. There is some work being done at present and I'm sure there's going to be a great deal of work done in the future. You have heard Robert J Pelletier one of the designers of the solar heated
house in Lexington Massachusetts. And research associate in civil engineering at MIT earlier voted Tory talked with C hostile solar engineer chairman of the MIT research committee on solar energy and professor of chemical engineering power from the sun has been a part of a century of science a recorded exploration of developments in science and their import for the 20th century American. This series is prepared by WGBH FM in Boston for the Lowell Institute cooperative broadcasting Council. Your host Volta Torre a former editor of Popular Science now director of radio television programming for the Massachusetts Institute of Technology Director for the series Lillian Ambrosio producer Jack the Summerfield Bill kavanah speaking century of Sciences produced under a grant from the Educational Television and Radio Center and distributed by the National Association of educational broadcasters. Next week Harlow Shapley Payne
professor of practical astronomy emeritus at Harvard University will answer the question why study stars. This is the end E.B. Radio Network.
Century of Science
Power from the Sun
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WGBH Educational Foundation
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University of Maryland (College Park, Maryland)
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Episode Description
Hoyt C. Hottel, solar engineer, MIT; Robert J. Pelletier, designer of the Lexington, Mass., solar house, MIT.
Series Description
Discussions of aspects of science affecting modern America. This series is hosted by Volta Torrey, the director of radio and television programming at Massachusetts Institute of Technology, as well as the former editor of Popular Science.
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Director: Ambrosino, Lillian
Guest: Hottel, Hoyt C. (Hoyt Clarke), 1903-1998
Guest: Pelletier, Robert
Host: Torrey, Volta, 1905-
Producer: Summerfield, Jack D.
Producing Organization: WGBH Educational Foundation
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University of Maryland
Identifier: 59-9-3 (National Association of Educational Broadcasters)
Format: 1/4 inch audio tape
Duration: 00:29:14
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Chicago: “Century of Science; Power from the Sun,” 1959-01-01, University of Maryland, American Archive of Public Broadcasting (GBH and the Library of Congress), Boston, MA and Washington, DC, accessed December 8, 2023,
MLA: “Century of Science; Power from the Sun.” 1959-01-01. University of Maryland, American Archive of Public Broadcasting (GBH and the Library of Congress), Boston, MA and Washington, DC. Web. December 8, 2023. <>.
APA: Century of Science; Power from the Sun. Boston, MA: University of Maryland, American Archive of Public Broadcasting (GBH and the Library of Congress), Boston, MA and Washington, DC. Retrieved from