Solar energy conversion system

A solar energy collection and conversion system is disclosed in which a cassegrain mirror system is rotated about a diurnal axis, which axis is adjusted for seasonal variations in the incidence of the sun's rays on the earth's surface. A black body absorption cavity filled with translucent or transparent fluid material is used for direct absorption of the sun's rays. The incident solar energy is absorbed directly by the fluid medium. The fluid within the cavity may be maintained under extremely high pressures and temperatures in order to utilize this fluid as a heat storage medium. Such heat storage is facilitated by apparatus which permits a change in the volume of the reflective cavity in response to the temperature or pressure of the fluid within the cavity.

BACKGROUND OF THE INVENTION 
All of the earth's conventional power sources such as oil, coal, and 
running water are originally derived from the sun. For many years attempts 
have been made to use the heat of the sun directly for power and domestic 
needs. Outside the earth's atmosphere, an average 1350 watts per square 
meter is available. Under good conditions, such as a cloudless desert, 
approximately 1000 watts per square meter is available at the earth's 
surface. 
Solar energy conversion systems described in the prior art are generally 
either so complex as to require enormous capital investment, making their 
utilization virtually impractical; or are so unsophisticated that their 
efficiency in absorbing and converting solar energy is too low to make 
their application practical. In the first extreme, there are numerous 
prior art disclosures of complicated heat storage systems utilizing state 
changes in various salts and other materials, many of which are extremely 
caustic in one state or the other, and all of which are subject to 
significant losses through the fundamental inefficiency of heat transfer 
apparatus used for transferring heat absorbed by collection units to the 
storage materials. Other costly aspects of complicated prior art systems 
include the use of multiple heliostats for redirecting the sun's rays, 
each of which must be individually controlled in order to track the 
relative motion of the sun and the earth's surface, the use of critical 
reflective or refractive surfaces often in shapes and forms which are 
extremely expensive to manufacture, and through the use of exotic 
materials which substantially increase the capital investment required for 
the collection of solar energy. Another example of the first extreme has 
been the use of solar power in solar furnaces. These are very large arrays 
of optical elements which concentrate sunlight into a small area producing 
very high temperatures at the focus. These elements are often unique, very 
large and expensive installations, with only a few operating worldwide. 
They are principally used for materials experiments and limited production 
of ceramic and abrasive materials, which cannot be readily produced in any 
other way. A typical working temperature for a solar furnace is 
3,000.degree. K. This first extreme also includes the direct generation of 
electricity from solar radiation falling on solar cells such as are widely 
used in the space program. Because each cell can produce only low voltage 
and current levels, a great number of cells are needed to produce 
substantial amounts of electrical energy. Each cell requires two 
individual electrical connections and labor costs for millions of 
connections become prohibitive except for critical uses in inaccessible 
places. There are also inherent problems in transmitting low voltage 
direct current, and storage of large amounts of power in batteries is not 
presently economical. 
In the other extreme, most relatively simple or unsophisticated collectors 
are flat plate collectors which expose large flat heat absorbing surfaces 
of the sun's rays. These collectors are extremely inefficient in that a 
substantial portion of the collected energy is reradiated, the surface 
which forms an efficient collector also forming an efficient radiator. 
Substantial heat is also lost through convection to the atmosphere. In 
addition, such systems, by definition, must operate at relatively low 
temperatures which make the storage of heat extremely expensive, since an 
enormous bulk of low temperature storage must be provided. Nonetheless, 
the main current thrust of solar energy research an development programs 
is directed toward production of low grade power at relatively low 
temperatures for domestic water and space heating. There is also 
considerable interest in solar powered air conditioning using the Servel 
process. Extensive commercial use of low grade solar power awaits the 
development of efficient and economical collectors so that vast areas are 
not needed to collect sufficient power. The basic technical problem is the 
development of an economical material which will absorb sunlight with an 
effective temperature of 6,000.degree. K. (10,000.degree. F. and not 
reradiate at a working temperature of around 350.degree. K. (170.degree. 
F.) to typical surroundings at 300.degree. K. (80.degree. F.). 
In summary large scale utilization of solar energy for replacing energy 
presently produced by depleting natural resources such as fossil fuels has 
not been practical in the past since no system has been produced which 
combined efficiency and economy, so that both capital expense and 
operating expenses could be maintained at a sufficiently low level that 
the solar energy produced could compete economically with fuel burning 
systems. 
SUMMARY OF THE INVENTION 
The present invention provides a very significant advance in the solar 
energy collection and conversion field, since it permits the manufacture 
of reasonably priced collection equipment which operates extremely 
efficiently and incorporates self-contained heat storage capabilities 
sufficient to overcome the inherent deficiency of solar energy, that is, 
the absence of the energy source at night and on cloudy days. 
Fundamentally, these advantages are accomplished through an efficient, low 
cost optical system for the concentration of solar energy and through the 
direct absorption of this energy by a working fluid. Such a system permits 
the storage of the working fluid itself at extremely high temperatures and 
pressures to provide energy during time periods of total or partial 
darkness. 
The preferred embodiment of this apparatus includes a cassegrain optical 
system incorporating a primary reflective concave mirror directed toward 
the sun and including a central aperture. Attached to and spaced from this 
primary mirror is a secondary convex mirror coaxial with the primary 
mirror and aligned to collect and focus through the aperture of the 
primary mirror solar rays reflected by the primary mirror. 
This entire optical system is rotated about a diurnal axis and adjusted for 
seasonal variations so that the focal point of the entire optical system 
is fixed relative the earth's surface. 
Along the average diurnal axis, that is, the diurnal axis at equinox, a 
high pressure vessel in the form of an elongate pipe conducts a 
transparent or translucent working fluid. The portion of this pipe 
adjacent the focal point of the optical system is provided with a toroidal 
lens system which refracts the incident focused solar rays along the axis 
of the pipe. The entire inner surface of the high pressure pipe is highly 
reflected so that rays entering the pipe cavity are reflected to pass 
through the working fluid repeatedly until the radiation energy is totally 
absorbed by the fluid itself, the reflective walls substantially 
prohibiting absorption of the energy by the pipe itself. The toroidal lens 
system is contained in a highly reflective shutter which rotates so that 
only the sun's image falls on the aperture. The optically closed pipe acts 
as a black body cavity, rapidly distributing the incident radiation 
throughout the transparent or translucent medium contained and quickly 
raising this medium to temperature equilibrium. Energy cannot be 
reradiated through the aperture to the much hotter sun without violating 
the first law of thermodynamics. Because energy is absorbed from radiative 
transfer in the bulk of the material contained in the pipe, the outer 
walls of the container may be kept cool as, for example, by insulation. 
Since radiative energy transfers occur in accordance with the following 
formula .DELTA.E=.sigma.(.DELTA.T).sup.4 where .DELTA.E is the energy 
transferred, .sigma. is the Stefan-Boltzmaun constant, and .DELTA.T is the 
difference in absolute temperatures, radiative losses predominate. Thus, 
maintaining the outside of the container cool eliminates most losses. The 
system provides energy collection and absorption efficiencies near 90%, 
which is 10 times or more greater than that for a typical solar power 
system. The maximum temperature available on the earth from solar heating 
is 6,000.degree. K. (10,000.degree. F.). Because of the high efficiency of 
this system, working temperatures approaching this limit are possible for 
relatively small amounts of material. The flow of working fluid through 
the cavity is adjusted to give the desired working temperatures and 
pressures in that part of the system. 
The optical concentration system may be mounted on the high pressure pipe 
or separately, but rotates about the pipe in accordance with the daily 
rotation of the earth to assure that the solar radiation is focused 
through the toroidal lens system. 
During periods of substantial incident solar energy, when the entire energy 
capacity of the device is not necessary for producing power, the working 
fluid within the high pressure pipe may be heated and pressurized, thus 
absorbing a large amount of solar energy. This energy may be removed from 
the system by permitting flow of the working fluid from the high pressure 
pipe. Thus, in those instances where water is selected as the working 
fluid, a substantial bulk of water may be elevated in temperature and 
sufficiently pressurized so that the water absorbs a large amount of 
energy. By permitting this heated, pressurized water to escape from the 
high pressure pipe to a lower pressure cavity, the water will immediately 
vaporize to produce high pressure steam which may be used, for example, to 
run a turbine system for generating electricity. 
It will be understood that during periods of substantial incident solar 
energy continuous flow of working fluid to the system may be maintained by 
a high pressure pump, the black body cavity being maintained at very high 
pressure to prohibit vaporization of the working fluid within the cavity. 
This working fluid is continuously removed from the system and permitted 
to vaporize for operating, for example, a turbine. At the same time the 
cavity itself may store sufficient working fluid to form a substantial 
energy reserve. 
The reflective cavity formed by the walls of the high pressure pipe may be 
changed in volume during such use to provide for the storage of different 
amounts of thermal energy. This is accomplished through the use of a 
mirror positioned within the high pressure pipe and moved along the pipe 
by a control system. If this mirror is properly ported for the through 
flow of working fluid, no pressure differential occurs across the mirror 
so that a relatively simple and preferably remotely actuated driving 
system may be used for positioning the mirror. As this mirror is moved 
away from the toroidal lens, the portion of the high pressure pipe which 
forms the reflective reservoir is changed in volume, permitting a servo 
system to maintain the pressure and temperature of the working fluid 
within the high pressure pipe by storing additional thermal energy when 
the source energy exceeds the demand. 
In a typical installation, a high pressure pump supplies the working fluid, 
such as water, to the downstream end of the high pressure pipe. This water 
flows through the movable mirror into the reflective cavity and directly 
absorbs energy reflected through it by the cavity walls and the optical 
system. The water temperature is raised and the pressure within the vessel 
is maintained at a level prohibiting vaporization of the water. The outlet 
or upstream end of the high pressure pipe is connected through a control 
valve to a turbine, the control valve separating the higher pressure and 
lower pressure zones within an outlet pipe and permitting the working 
fluid to vaporize on the downstream side of the valve, the steam thus 
produced being used to operate a turbine. The system may be totally self 
contained if the exhaust steam from the turbine is condensed to provide 
water supply for the high pressure pump or may be operated on available 
water supply with the exhaust steam from the turbine vented to atmosphere.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring initially to FIG. 1, the solar collection and conversion system 
of the present invention includes a high pressure cavity formed, for 
example, from a pair of high pressure pipes 11 and 13 joined by a toroidal 
lens 15. The high pressure pipes 11, 13 include inside walls which are 
polished or coated to provide a highly reflective interior surface. The 
pipes 11, 13 are supported from a base 17 which may be, for example, a 
concrete foundation pad, by plural supporting struts 19, 21, 23 and 25 as 
well as concrete pylons 27 and 29. Each of the struts 19, 21, 23, 25 and 
concrete pylons 27, 29 illustrated in FIG. 1 are duplicated by identical 
supporting structures on the opposite side of the high pressure pipes 11, 
13, as specifically shown in FIGS. 6 and 8 so that the structure is braced 
against static loads as well as wind forces. The system is arranged such 
that the pipes 11 and 13 and their supporting structure are rigidly 
mounted on the foundation 17 and neither move nor rotate, so that high 
pressure fittings connecting working fluid to and from the pipes 11 and 13 
need not include expensive rotating or articulating couplings. 
An optical collection and focusing system is arranged to rotate about a 
diurnal axis coincident with the stationary pipes 11, 13. This optical 
system is a two-mirror cassegrain system including a primary mirror 31 and 
secondary mirror 33. The primary mirror 31 has a parabolic concave surface 
which is highly reflective for collecting and reflecting parallel solar 
rays 35 toward the secondary mirror 33, as shown at 37. The secondary 
mirror 33 is a much smaller, convex, paraboloidal mirror which in turn 
reflects the rays 37 toward a single focus, as shown at 39. The rays 39 
pass through an aperture 41 at the center of the primary mirror 31 and 
converge on the toroidal lens 15, so that substantially all of the 
incident radiation 35 is concentrated at the lens 15. 
In order to maintain the focus of solar radiation at the toroidal lens 15, 
it is necessary to maintain the axis of the primary mirror 31 parallel to 
the incident radiation 35. This is accomplished by mounting the entire 
optical system, including the primary mirror 31 and secondary mirror 33 
which is attached thereto by plural struts 43, for rotation about a 
diurnal axis formed by the high pressure pipes 11, 13. The details of this 
mounting and rotational system will be explained below. 
The entire solar energy conversion system is mounted on the foundation 17 
such that the high pressure pipes 11, 13 are parallel to the rotational 
axis of the earth. This is accomplished by mounting the inlet end of the 
pipe 13 lower than the outlet end of the pipe 11, so that the angle 
.alpha. is equal to the earth's latitude at the installation location. The 
concrete pylons 29 are placed due north of the concrete pylons 27 in the 
northern hemisphere, and due south of the concrete pylons 27 if the 
installation is in the southern hemisphere. When installed in this manner, 
and with the axis of the cassegrain mirrors 31 and 33 perpendicular to the 
axis of the pipes 11 and 13, all incident solar radiation will be focused 
through the toroidal lens 15 at each equinox. 
In order to adjust for seasonal relative movement of the sun and earth, 
hydraulic actuators 45 and 47 are used to pivot the cassegrain system, 
including the mirrors 31, 33, about a pivotal axis coincident with the 
toroidal lens 15 and perpendicular to the pipes 11, 13. A pair of struts 
49 and 51 are connected at the rotational axis to support flanges 53 and 
57, respectively, extending from the rear of the primary mirror 31. It 
will be recognized from the remaining figures that each of the actuators 
45 and 47 of FIG. 1 are duplicated by an identical pair of actuators on 
the opposite side of the high pressure pipes 11, 13, there being four 
spaced support flanges 53, 57 on the rear surface of the mirror 31. In 
addition, an identical pair of struts 49, 51 exist on the other side of 
the high pressure pipes 11, 13 so that these struts 49, 51 and actuators 
45, 47 cradle the primary mirror 31 and support its entire weight. 
A clock drive 59, in conjunction with a gearing system 61, to be described 
in detail below is utilized to rotate the cassegrain mirror system about 
the diurnal axis formed by the pipes 11, 13 on a daily basis, the mirrors 
31 and 33 rotating through approximately 180.degree. during each day and 
being recycled through the same 180.degree. rotation at night to begin 
another daily diurnal rotation on the following dawn. This diurnal 
rotation of the mirror system, combined with the seasonal adjustments made 
by the actuators 45 and 47, assures that the rays 39 are always focused at 
the stationary toroidal lens 15. The incident radiation 39 is refracted by 
the toroidal lens 15, in a manner described in more detail below, to 
travel the length of the pipes 11 and 13 as shown at 63 and 65, 
respectively. Because of the reflective surface on the inside of the high 
pressure pipes 11, 13, this radiation 63, 65 is repeatedly reflected from 
the walls of the absorption black body cavity formed by the pipes 11, 13 
so that, after passing repeatedly through the working fluid within the 
pipes 11, 13, the solar energy is totally absorbed directly by the working 
fluid. The reflective interior surfaces of the pipes 11, 13 substantially 
prohibits absorption of this energy by the pipes themselves. Input working 
fluid, such as water, is supplied through a valve 67 and high pressure 
pump 69 to the inlet end 71 of the high pressure pipe 13. This working 
fluid is heated through direct absorption of the solar energy reflecting 
throughout the interior volume of the pipes 11 and 13, but is preferably 
not vaporized within the pipes 11, 13. Rather, the pressure supplied by 
the pump 69 is sufficient to permit substantial heating of the working 
fluid without vaporization. In an exemplary installation wherein the 
working fluid is water, the pressure and temperature maintained within the 
high pressure pipes 11, 13 is 665 PSI and 500.degree. F. Under these 
conditions, substantial energy may be stored within the high pressure 
pipes 11, 13 themselves. Thus, for example, in this same exemplary system 
wherein the diameter of the primary mirror 31 is 20 meters, the system is 
designed to produce 300 kw of thermal power. The pipes 11, 13 have a 
combined length of approximately 30 meters, a diameter of 20 in., and thus 
the capacity to store 1.6.times.10.sup.7 BTU of thermal energy. This 
substantial storage capacity permits the solar energy system to store 
thermal energy during peak solar energy hours and to liberate this energy 
during hours of total or partial darkness. It will be noted that, contrary 
to the storage systems used in the prior art, the storage of energy in the 
present system is in the working fluid itself, so that no intermediary 
heat transfer is required. The present system permits an extremely dense 
storage of energy so that the entire system may be installed on site 
without substantial subsurface storage. In addition, the use of caustic 
chemicals for heat storage is avoided, so that both the safety and life 
expectancy of the system is enhanced. 
From this brief description in reference to FIG. 1, it will be recognized 
that the cavity formed by the high pressure pipes 11, 13 performs, in 
essence, the function of a black body collection cavity. This is 
accomplished by maintaining the energy entrance port defined by the 
toroidal lens structure 15 relatively small in comparison with the volume 
of the high pressure pipes 11, 13. The difference between this black body 
absorption system and those of the prior art, however, is the use of the 
reflective surface on the inside of the cavity defined by the high 
pressure pipes, 11, 13, which forces the solar radiation to be directly 
absorbed by the working medium rather than by an intermediary plate or 
heat exchanger. This direct absorption substantially increases the 
efficiency of the system without detracting from the black body absorption 
characteristics of the device. In addition, those skilled in the art will 
recognize the fact that, through the use of the toroidal lens structure 15 
and a shutter to be explained in detail below, any energy which would 
escape from the system must be directed back through the cassegrain mirror 
system at the sun. Since the effective solar temperature always exceeds 
the temperature within the black body system, no energy can be redirected 
at the sun and the system becomes totally absorptive, with the exception 
of minor convection losses from the pipes 11 and 13 to the atmosphere, 
which losses can be effectively controlled through insulation as described 
in detail below. The overall system thus effectively converts solar energy 
at an efficiency of approximately 90%, ten times the efficiency of typical 
prior art solar collectors. 
From the foregoing discussion and the exemplary embodiment described and 
depicted in the drawings it will be apparent that a central feature of the 
invention resides in the adaption of the black body cavity principle in a 
way not previously contemplated. The classic black body cavity, e.g., as 
conceived by Lummer and Pringsheim, ideally absorbs all radiation which 
enters and radiates none. Of course, there is some radiation in practice 
but a hollow body in which the entry window is a small fraction of the 
total interior wall area will act as an effective black body cavity with 
negligible or insubstantial loss. Whether or not a given cavity acts as a 
black body cavity may be determined by known scientific principles, e.g., 
by measuring the radiation at the opening with a given body temperature. 
Thus, scientifically, a black body is an ascertainable structure and it is 
sufficient definition simply to call the cavity of the present invention a 
black body cavity absorber, thus incorporating the classical criteria for 
black body cavity structures. 
In a prototype embodiment of the black body cavity of the present 
invention, the cavity was a cylindrical tube four inches in diameter and 
ten feet long. The window for receiving concentrated solar radiant energy 
into the cavity was three inches in diameter. The opaque wall area of the 
cavity was approximately 200 times the area of the window and the longest 
dimension of the cavity was approximately 40 times the diameter of the 
window. In practice, of course, considerable design variation is possible 
within the criteria for a black body cavity, including variation in shape, 
as well as size, of the cavity. A spherical cavity, for example, could not 
accomodate as large a window as an elongate cavity. In general, a window 
diameter of less than one tenth or less the maximum linear dimension of 
the cavity, and preferably no greater than one twentieth the maximum 
cavity linear dimension is required for the cavity to perform as a black 
body. In area terms, the opaque wall area should be at least about seventy 
times the window area, preferably at least one hundred times the window 
area, and, for optimum efficiency, in the general range of about 200 or 
more times the diameter of the window. The overriding criterion, of 
course, is that the cavity be so configured and arranged, in respect to 
size, shape and dimension and wall-to-window ratio as to act effectively 
as a black box absorption cavity for incident solar radiant energy. 
In this respect, it is recognized that Goddard, U.S. Pat. No. 1,969,839, 
sought to bring about absorption in a fluid in a chamber. Goddard, 
however, did not contemplate a black body cavity. Goddard's device is 
inherently limited to comparatively low temperatures because, as will be 
apparent from the placement of the window at the largest lateral dimension 
of the cavity. At temperatures where emissivity of the medium is 
significant, there would be extremely large losses through the window. The 
placement of the large window at the large end of a funnel-shaped chamber, 
as in Goddard, is antithetical to the present black body cavity concept. 
In summary, then, the absorbing cavity is so configured and arranged as to 
act, in basic principle, as a black body cavity absorber. The radiant 
energy which is concentrated and focused into the cavity is retained in 
the cavity and ultimately absorbed in the fluid in the cavity, either on 
the first pass through the cavity or on one of the multiple reflected 
passes through the cavity, in either case being directly absorbed by the 
fluid. In the classical black body cavity, absorption occurs primarily at 
the walls of the cavity. In the present instance, however, the absorption 
preferably occurs primarily by the fluid as the radiant energy traverses 
the cavity. Any energy absorbed by the walls, however, immediately is 
conducted to the fluid; hence, at steady state, there is essentially no 
net absorption of energy by the walls. 
The cavity may be of any shape, but the relationship of the cavity size and 
shape must be such that the cavity acts as a black body absorber. In 
general, the effective diameter of the window, i.e., the diameter of a 
circular window which would transmit the same amount of radiation as is 
transmitted by the window in the cavity, must be a small fraction of the 
largest linear dimension of the cavity as in classical black body 
cavities, thereby presenting to the incident radiation essentially all 
opaque walls, with less than about one percent, and preferably less than 
about one tenth of one percent, of the incident radiation being 
re-radiated out the window. 
Fluid is, in the preferred form, pumped through the cavity under such 
conditions as to maintain the fluid at liquid density. In low pressure 
systems, a simple pump is all that is required. In high pressure systems 
wherein highest efficiency is achieved, the fluid is maintained under high 
pressure sufficient to keep the fluid at essentially liquid density, e.g., 
at the critical point of the liquid, even though the fluid may behave as a 
gas when allowed to expand. The most effective absorption occurs when the 
body of fluid in the cavity is at liquid density. Localized pockets of 
vapor, and other minor losses, such as heat leakage through the walls, 
etc., may, of course, occur without altering the mode of operation. Water 
is the preferred fluid, but any other transparent or translucent fluid may 
be used, if temperatures other than conventional steam operating 
temperatures are desired or if special phase change temperatures, heat 
capacities, absorption characteristics or other characteristics are 
desired. Heat from the absorption fluid may, in a less preferred mode, be 
extracted by heat exchange in the cavity, but this is less efficient than 
flowing the fluid through the cavity. 
Turning now to the detailed aspects of construction, FIGS. 2 and 3 show a 
rotating support system used for supporting the actuators 47 on the high 
pressure pipe 13. Each actuator 47 is a double-acting hydraulic cylinder 
having first and second hydraulic input lines 73 and 75 (FIG. 1). The 
actuator 47 is mounted by means of a mounting lug 77 onto a support plate 
79. A second mounting lug 81 mounts the second hydraulic actuator 47 (not 
shown), the pair of hydraulic actuators forming a cradle for one side of 
the primary mirror 31 and attached thereto at spaced support flanges 53 
(FIG. 1). The mounting lugs 77 and 81 are rigidly clamped to the support 
plate 79 by bolts 83 and nuts 85 so that the hydraulic cylinders 47 and 
mounting plate 79 form a rigid cradle structure for one side of the 
primary mirror 31. An identical support plate and mounting structure is 
used for the pair of hydraulic cylinders 45 (FIG. 1) at the other side of 
the primary mirror 31 to support and cradle that side of the primary 
mirror 31 at support flanges 57 (FIG. 1) from the high pressure pipe 11, 
so that the entire weight of the cassegrain mirror system is supported 
from the high pressure pipes 11, 13 at the support flanges 53 and 57 (FIG. 
1) through the hydraulic actuators 45 and 47. 
While the mounting plate 79 bears the weight of the cassegrain mirror 
system, it is designed to freely rotate about the high pressure pipe 13. 
This high pressure pipe 13 is surrounded by a coaxial pipe 87 of larger 
diameter. The pipe 13 defines the walls of the high pressure reflective 
cavity, while the pipe 87 defines an evacuation chamber 89 between the 
pipes. The chamber 89 is evacuated, and the inside walls thereof made 
reflective to thermally insulate the high pressure pipe 13 from the 
outside atmosphere. This insulation is preferably further increased by 
making the outside walls of pipe 13 reflective. Thus both the inner and 
outer walls of the high pressure pipes 11, 13, as well as the inner wall 
of the pipe 87 are made reflective, the inner reflective wall of the pipes 
11, 13 used to form a reflective black body cavity and the remaining 
reflective walls used for assisting the insulation of that cavity. By 
evacuating the space 89, the high pressure pipes 11 and 13 become, in 
effect, a high pressure dewar for storing energy which has been converted 
by the system. 
The support plate 79 is guided to move in an arcuate path along an arcuate 
rail 91 which is supported, as by brackets 93 and a reinforcing ring 95, 
to the pipe 87. The arcuate guide rail 91 is formed as a C-channel in 
which a pair of rollers 97 and 99 are guided. A third roller 101 is 
mounted to an L-shaped bracket 103 which is attached, as by welding, to 
the support bracket 79. Each of the rollers 97, 99, 101 is mounted on the 
support plate 79 or bracket 103 by a bearing mounted on screws 105, 107 
and 109, respectively, clamped in place by nuts 111. The rollers 97 and 99 
bear against the inside surface 113 of the lower leg of the arcuate 
C-channel 91 while the roller 101 bears against the outer surface 115 of 
the channel 91 to maintain the rollers 97 and 99 positioned within the 
opening of the C-channel 91. It can be seen that the support plate 79, 
along with the actuators 47 and the cassegrain mirror system, are thus 
guided for rotational movement around the axis of the pipes 11 and 13 for 
diurnal movement. An identical mounting system 117 (FIG. 1) is used for 
guiding the actuators 45 for rotary motion about an identical axis. Thus, 
the pipe 87 is used to support the cassegrain mirror system, including the 
primary mirror 31 and secondary mirror 33, for rotation about the axis of 
the pipes 11, 13, guided by the rail 91. 
The actuators 45, 47 may be, for example, hydraulic actuators which are 
connected by means of lines 73 and 75 to a control system which supplies 
hydraulic fluid to tilt the cassegrain mirror system about an axis 
perpendicular to the pipes 11, 13 and passing through the toroidal lens 
structure 15 to account for seasonal variations in the relative position 
of the sun and earth. Rotation about this axis is facilitated by the use 
of struts 49 and 51 (FIG. 1) which are connected to a pivot point 
coincident with the toroidal lens 15, as will be described in more detail 
below, which axis defines the center of rotation of the cassegrain mirror 
structure when the actuators 45 and 47 are energized. 
Referring now to FIG. 4, the detailed construction of the high pressure 
pipes 11 and 13, the toroidal lens structure 15 and the surrounding pipe 
87 will be explained. The toroidal lens 15 forms, in effect, a bulged 
cylindrical section of fused quartz interconnecting the high pressure 
pipes 11 and 13. Radiant energy 39 concentrated by the cassegrain mirror 
system enters one face of the lens 15 and is refracted, as shown at 65, to 
propagate along the length of the high pressure pipes 11, 13. This energy, 
due to the highly reflective inner surfaces of the high pressure pipes 11, 
13 will be reflected repeatedly from the inside walls of the black body 
cavity until it has passed a sufficient distance through the transparent 
or translucent working medium to be totally absorbed thereby, thus 
directly heating the working fluid. Since the entire inside of the cavity 
formed by the high pressure pipes 11, 13 is reflective, the working fluid 
will achieve a uniform increasing temperature throughout, the entire 
cavity being uniformly illuminated by the incident collected radiation and 
by reradiation from the fluid and walls. 
The high pressure pipe 13 is open at one end 117 facing the toroidal lens 
15 and is mounted at this open end in an annular mounting plate 119. The 
mounting plate 119 may be grooved to receive the open end of the pipe 13 
and may be welded thereto to insure the pressure integrity of the vessel. 
The outer pipe 87 includes a similar open end 121 which is likewise 
attached, as by welding, to the annular support plate 119. This attachment 
may be strengthened by plural reinforcing webs 120, which webs 120 also 
serve to rigidify the mounting plate 119. The other end 71 of the high 
pressure pipe 13 is closed, as by a hemispherical end cap 123 welded to 
the end of the pipe 13. The hemispherical end cap 123 includes an opening 
which is attached to an inlet pipe 125 and mounted by means of this inlet 
pipe 125 and a vacuum gasket 127 to an end support plate 129. The 
remaining open end of the outer pipe 87 is also attached to the end 
support plate 129 concentric with the pipe 125. The pipes 13 and 87 are 
thus concentrically mounted between the plates 19 and 129 to form a dewar 
housing for the black body cavity, the space 89 between the pipes being 
evacuated to insulate the pipe 13. 
A support plate 131 identical to the support plate 119 is positioned on the 
other face of the toroidal lens 15, and the pair of support plates 119 and 
131 is clamped to the lens 15 by a plurality of bolts 133. Annular gaskets 
135 and 137 may be used to seal the lens 15 to the plates 119 and 131, 
these gaskets 135, 137 compressed between the elements by the bolts 133. 
This entire structure thus forms a rigid cavity formed by the pipes 11, 
13, plate 119, 131 and lens 15, the lens 15 having substantial structural 
strength to resist the extreme pressures within the cavity. 
It will be noted that, in addition to the bulged outer surface of the lens 
15, the inner diameter of the lens 15 includes a pair of intersecting, 
coaxial, truncated conical surfaces 139 and 141 which form a second 
refractive surface to assist in refracting the incident radiation to a 
path approximately coincident with the axis of the pipes 11, 13. 
A third relatively lightweight cylindrical enclosure 143 may be used to 
surround the pipe 87 and to support therebetween a layer of thermal 
insulation 145 which reduces the thermal convection losses of the system. 
The pipe 87 may be attached to the end plate 129, if desired, by an 
L-shaped annular bracket 147 and plural bolts 149, so that the end plate 
may be made removable from the system to allow access to the evacuated 
cavity 89. 
As previously explained, the entire cassegrain mirror system is rotated 
about an axis coincident with the center of the lens 15 and perpendicular 
to the axis of the pipes 11, 13 to accommodate seasonal changes in the 
relative position of the sun and the earth. As shown in FIGS. 1 and 4, a 
conical-shaped tube 151 interconnects the opening 41 in the primary mirror 
31 to a shutter system adjacent the toroidal lens 15. This tube 151 is 
used to exclude foreign objects from the area of intense radiation between 
the aperture 41 and the lens 15. 
The shutter system completely surrounds the outside of the toroidal lens 15 
and includes a reflective inside surface to eliminate to the greatest 
extent possible the loss of solar radiation through this lens 15. The 
shutter is formed as a bulged cylindrical sleeve 153 mounted at its open 
ends on a plurality of rollers 155 so that the shutter 153 may rotate 
about the diurnal axis during daily movement of the lens system about the 
pipes 11, 13. One side of the shutter 153 includes an opening 157 which 
cooperates with an overlapping flange 159 extending from the lower 
extremity of the conical tube 151. As can be seen from FIG. 4, as the 
cassegrain mirror system and its attached tube 151 rotate in the direction 
indicated by the arrow 161, the flange 159 will move beneath the opening 
157 of the shutter 153 to permit seasonal adjustments, while at the same 
time maintaining a reflective surface surrounding the lens 15 over the 
greatest surface area possible. The inner surface of the shutter 153, as 
well as the flange 159, are made highly reflective so that any energy 
which is directed toward the shutter system will be reflected. Thus, the 
only aperture for escape of radiant energy is through the conical tube 151 
which, as explained previously, requires a radiation directly at the solar 
source, which is impossible. Since the entire shutter system, including 
the shutter 153, flange 159, and tube 151 are rotated by movement of the 
primary mirror 31, the shutter rotating on the rollers 155, the aperture 
157 remains directed toward the axis of the cassegrain mirror and system 
at all times. 
Apparatus is included within this system to change the effective size of 
the black body cavity bounded by reflective surfaces. This apparatus is 
best understood through a reference to both FIGS. 4 and 6 and includes a 
cylindrical ferrous member 163, the outer diameter of which is slightly 
smaller than the inner diameter of the pipe 13. Between these diameters is 
positioned a ball bearing structure including a bearing spacer ring 165 
and plural balls 167. The bearing spacer ring 165 is maintained in 
position between the ferrous cylinder 163 and the pipe 13 by a first 
plurality of positioning plates 169 which are attached to the ferrous 
member 163 by plural screws 171, and a second annular positioning ring 173 
which is similarly attached. The ring 173 has a highly reflective outer 
surface 175 and includes a central aperture 177 which is smaller than the 
inside diameter of the ferrous cylindrical member 163, the ring 173 
forming a mirror which extends from a position adjacent the inside 
diameter of the pipes 13 to the aperture 177. 
A second flat mirror 179 is mounted, as by a spider member 181 which is 
attached to the inside diameter of the ferrous member 163. The outer 
diameter of the circular mirror 179 is larger than the diameter of the 
aperture 177 so that the pair of mirrored elements 173 and 179 form a flat 
mirrored end for the pipe 13. A space exists between the mirror 179 and 
the inside diameter of the ferrous cylindrical member 163 to permit the 
flow of working fluid around the outside of the mirror 179. Since fluid is 
allowed to freely flow around the mirror 179, no pressure diferrential 
exists across this element and, regardless of the pressure within the pipe 
13, the entire mirror assembly is free to roll on the ball bearings 167 
along the axis of the pipe 13. 
Movement of this flat mirror assembly is accomplished by moving a pair of 
annular permanent magnet segments 183 and 185, each of which is mounted on 
and threaded to a pair of threaded rods 187. Each of the rods 187 is 
mounted for rotation in a first end bearing 189 mounted on the support 
plate 119 and a second bearing 190 mounted within apertures within the end 
support plate 129. The threaded members 187 extend beyond the end plate 
129 to support sprockets 191 which are each engaged by a chain 193. The 
chain 193 is additionally engaged by a sprocket 195 attached to the rotor 
of an electrical motor 197. The electrical motor 197 thus serves to rotate 
each of the four threaded rods 187 in the same direction, these rods in 
turn threading along the magnet segments 183 and 185 to move the magnet 
segments along the length of the pipe 13. The magnetic force between these 
segments 183, 185 and the ferrous element 163 is used to draw the flat 
mirror structure along with the moving magnet sections 183, 185. A 
rotation of the motor 197 thus moves the flat mirror partition, including 
the mirrors 173 and 179, along the length of the pipe 13 to change the 
effective size of the black body cavity 11, 13. Since only the magnetic 
force of the magnets 183 and 185 traverses the high pressure pipe 13, the 
pressure integrity of the pipe is not affected through a system of this 
type. Numerous alternate methods for moving the magnet segments 183, 185, 
such as linear motors, may be used, but in each instance the magnets are 
preferably positioned between the pipes 13 and 87 to remotely move the 
flat mirror structure. 
With the flat mirror structure, including the mirrors 173 and 179, adjacent 
the toroidal lens 15, the black body cavity in which elevated constant 
temperatures are maintained by solar radiation is limited to the area 
between the flat mirror 173, 197 and the upper end of the high pressure 
pipe 11. As will be explained in more detail below, as the pressure or 
temperature within the black body cavity increases, the storage capacity 
of the system may be adjusted by moving the flat mirror 173, 179 toward 
the inlet 125 of the pipe 13, effectively doubling the black body cavity 
volume when the flat mirror 173, 179 reaches its other extreme. In 
operation, the flat mirror 173, 179 is positioned adjacent the toroidal 
lens 15 in the morning, before dawn. When the sun rises above the horizon 
and heats the working fluid within the cavity to a predetermined 
temperature, the motor 197, under control of a temperature sensor and 
servo system, operates to move the flat mirror 173, 177 along the axis of 
the pipe 13, enlarging the volume of the solar collection cavity. It will 
be appreciated that, while no pressure differential exists across the flat 
mirror 173, 179, a substantial thermal gradient exists at this point in 
the system since the fluid upstream of the flat mirror 135, 179 is not 
subjected to solar radiation and is therefore relatively cool in 
comparison with the high temperature fluid within the mirrored walls of 
the adjustable sized cavity. Some thermal convection may occur through the 
spaces around the flat mirror 179 to heat the inlet water, but it is 
assumed that, under normal operating conditions, there is a continuous 
flow of working fluid through the inlet 125, limiting the convection 
upstream through the spaces around this mirror 179. 
Referring now to FIGS. 4, 5, 6 and 8, the mechanism for supporting the 
struts 49 and 51 of FIG. 1 and for controlling diurnal rotation of the 
cassegrain mirror system will be explained. A pair of reinforcing rings 
199 and 201 encircle the pipe 87 at locations adjacent the toroidal lens 
15. These rings 199, 201 are attached to the pipe 87 through plural 
circumferentially spaced brackets 203, and are attached to support a pair 
of facing, annular C-channels 205 and 207. The C-channels 205 and 207 are, 
in turn, attached, as through brackets 208 (FIG. 6) to the mounting struts 
23 and 25 mentioned in reference to FIG. 1. The mounting struts 23 and 25 
thus directly support the C-channels 205 and 207 from the foundation pad 
17 and, through the brackets 203, serve to support the central portion of 
the high pressure pipes 11, 13 so that undue strain is not placed on the 
toroidal lens 15 by the weight of the cassegrain mirror system. 
A pair of hemispherical gear segments 209 and 211 are supported for 
movement along the C-channels 205 and 207 through plural rollers 213. Each 
of the rollers 213 is mounted by a bolt 215 and nut 217 to one of the gear 
segments 209, 211 for rotation. The gear segments 209, 211 are 
interconnected by plural channel members 218, attached thereto, as by 
welding, to form an integral structure. Thus, the entire structure, 
including the gear segments 209, 211 and channel members 218 is free to 
rotate about the axis of the high pressure pipes 11, 13 through movement 
of the rollers 213 within the channels 205 and 207. The gear segments 209 
and 211 engage with spur gears 219 and 221, respectively, these gears 
mounted on a common shaft 223 which is rotationally mounted in bearing 
pillow blocks 225 and 227 from a stationary support structure 229. The 
shaft 223 is attached to a sprocket 231 engaged with a chain 233 which is 
driven by a sprocket 235 attached to the rotor of the motor 59 through the 
gear box 61. The motor 59 is preferably a synchronous, clock-type motor 
which, through the gear box 61 drives the gear segments 209 and 211 at a 
rate equivalent to the rate of rotation of the earth. 
An opposing pair of the channel members 218 support a pair of coaxial axles 
241 extending outwardly from these channels 218. Mounted, as by bearings 
243, to these axles 241 are a pair of support plates 245, one on either 
side of the lens 15, which are in turn rigidly attached to the struts 49 
and 51 as through bolts 247 and 249. It will be appreciated that a pair of 
struts 49, 51 is thus attached on either side of the lens 15, and these 
struts are, in turn, attached to support flanges 53, 57 (FIG. 1) located 
at spaced locations on the primary mirror 31. The axles 241 thus provide a 
rotational axis for the entire cassegrain mirror system about the center 
of the toroidal lens 15, the movement introduced by the actuators 45 and 
47 (FIG. 1) thus confined to a rotation about this axis 241. It will be 
appreciated that this axis is directly supported through the supports 19, 
21, 23, 25 from the concrete foundation 17 so that the weight of the 
mirror system is not directly borne at the center of the black body cavity 
formed by the pipes 11 and 13. As the clock motor 59 drives its sprocket 
235, the entire assembly, including the gear segments 209 and 211, the 
channel members 218, and the attached axles 241 rotate in accordance with 
the diurnal rotation of the earth, inducing a rotation through the members 
49 and 51 in the cassegrain mirror system, causing this mirror system to 
follow the relative motion of the sun and earth. 
As best shown in FIGS. 1, 4, 7 and 8, the primary mounting for the solar 
energy conversation system of the present invention is preferably 
accomplished through the end plate 129 attached to the inlet end of the 
system and a similar end plate 247 mounted in identical fashion, though 
inverted, to the outlet or upper end of the high pressure pipe 11, as 
shown in FIG. 7. These end plates 129, 247 are supported on the concrete 
pylons 27 and 29, respectively. As previously explained, it has been found 
advantageous to mount the system so that the axis of the high pressure 
pipes 11 and 13 is parallel to the earth's axis at the location where the 
system is installed. In order to facilitate such installation, as 
particularly shown in FIG. 8, the end plates 129, 247 may be attached to 
pillow blocks 249 and 151, respectively, and thereby rotationally mounted 
on a pair of axles 253 and 255, respectively. The axles 253 and 255 are, 
in turn, supported by pairs of pillow blocks 257 and 259, respectively, 
which are attached to the top of the concrete pylons 27 and 29. Through 
the use of this rotational mounting, the height of the concrete pylons 27 
and 29, as well as their spacing, may be specified by the manufacturer for 
a particular site. The concrete pylons may then be poured to the desired 
height so that the system may be directly installed thereon by attachment 
of the pillow blocks 257 and 259 to the concrete pylon. If the 
installation is carried out properly, the axis of the cassegrain mirror 
system, when properly tracking relative solar movement, will be 
perpendicular to the axis of the pipes 11, 13 at equinox and will vary 
therefrom to accommodate seasonal changes through actuation of the 
actuators 45 and 47. 
As shown in FIG. 7, the mounting of the upper end of the high pressure pipe 
11 is substantially identical to the mounting of the lower end of the high 
pressure pipe 13. The high pressure pipe 11 includes a hemispherical end 
cap 261 which is connected to an outlet pipe 263, which outlet pipe 263 is 
mounted through vacuum gasket 265 to the end plate 247. The outer pipe 87 
is connected by an L-shaped annular flange bracket 267 welded thereon to 
the end plate 247 by a series of bolts 269, and the outer insulation 
supporting jacket 143 may be mounted to the bracket 267 as well. 
Referring now to FIG. 9, an alternate embodiment of the toroidal lens 15 
will be described. In this embodiment, the entire structure is identical 
to that described in reference to FIG. 4, except that the inner diameter 
of the lens 15, rather than including intersecting truncated conical 
refracting surfaces, includes a cylindrical inner wall, ruled or grooved 
to form a Fresnel lens 271. This lens 271 operates in a manner 
substantially identical to the lens structure of FIG. 4, refracting 
incident radiation 39 to bend the solar radiation to a direction more 
closely aligned with the axis of the high pressure pipes 11, 13 as shown 
at 65. It will be recognized by those skilled in the art that the Fresnel 
lens of FIG. 9 is the optical equivalent of the lens structure of FIG. 4. 
Referring now to FIG. 10, a typical overall system installation utilizing 
the conversion device of the present invention will be described. As 
previously explained, solar radiation incident on the primary mirror 31 is 
reflected from the secondary mirror 33 to enter the optical cavity defined 
by the small opening provided in the shutter 153 surrounding the lens 15. 
This solar energy is repeatedly reflected from the reflective inner 
surfaces of the optical cavity defined by the inner walls of the pipes 11 
and 13 and a movable flat mirror structure including the mirrors 173 and 
179. At all times during operation of this system, the entire volume of 
the pipes 11, 13 is filled with fluid, the density of which is equal to 
the liquid density of the working medium. Thus, once the triple point has 
been exceeded, the fluid within the optical cavity will have the 
properties of a gas, but will nevertheless have the density of liquid 
since a sufficiently high pressure is maintained on the system to maintain 
this density. For the purpose of the remainder of this description, the 
fluid within the black body cavity will be referred to, therefore, as a 
liquid, regardless of its temperature. Water is supplied from a reservoir 
273 through a manual control valve 67 and high pressure pump 69 to the 
inlet pipe 125 of the pipe 13. The pump 69 may be designed to maintain a 
given pressure head within the system and this pressure head will be 
selected to maintain the density of the working fluid within the system 
equal to the liquid density of the fluid. Fluid pumped into the system 
will pass through the flat mirror 173, 179 to enter the black body cavity 
and be heated through direct absorption of solar energy. The extremely 
high temperature, high pressure liquid resulting from this absorption is 
conducted by means of the outlet pipe 263 through an automatically 
controlled valve 275 to a steam turbine 277 used to drive, for example, an 
electrical generator 279. The rotational rate of the turbine 277 and 
generator 279 may be controlled, for example, by an electronic control 
system 281 used to regulate the valve 275. It will be understood that a 
pressure differential exists across the valve 275, such that a much lower 
pressure exists at the inlet 283 of the turbine 277 than within the black 
body cavity, so that the liquid immediately vaporizes to produce a high 
volume, high pressure vapor source for driving the turbine 277. It will 
likewise be recognized that the exhaust steam or other gas from the 
turbine 277 may be exhausted to atmosphere or may be condensed to supply 
water to the reservoir 273. 
The clockwork motor 59, which through the gear box 61 drives the cassegrain 
mirror system about the diurnal axis on a daily basis, is typically 
energized from an electronic motor control system 285 which may be 
connected, for example, to the generator 279 as a source of power and 
which operates in response to signals produced by an electronic clock 287. 
A similar electronic clock 289 and hydraulic control system 291 responsive 
thereto may be utilized to drive the actuators 45 and 47 to adjust the 
relative axes of the pipes 11, 13 and cassegrain mirror system 31, 33 for 
seasonal variations in the direction of the earth's axis relative the 
position of the sun. 
As is well known, the relative movement of the earth and sun is extremely 
predictable and the motor control 285 and hydraulic control 291 will, in 
substantially all instances, effectively direct the axis of the cassegrain 
mirror system 31, 33 to assure that the focused solar energy will be 
applied to the aperture in the shutter 153 and thus to the black body 
cavity. As a backup system, however, optical sensors 293 and 295, shown in 
FIGS. 4 and 9, may be utilized to produce error signals for the hydraulic 
actuator 291 and motor control 285, respectively. If the focused solar 
energy is not centrally located within the small end of the conical tube 
151 used to mount the sensors 293 and 295, an imbalance will occur between 
oppositely located sensor pair 293 or a similar oppositely located pair of 
sensors 295. The oppositely located sensors 293 may thus be used to 
produce a differential error signal for the hydraulic actuator 291, and 
may override the clock signals 289 to adjust for errors produced thereby. 
Similarly, the sensors 295, differentially operated, may produce error 
signals to adjust the motor control system 285 in the event of error 
signals from the clock 287. 
The system thus far described is an extremely efficient solar energy 
conversion apparatus which may be mounted at various locations on the 
surface of the earth through a simple support structure, and which adjusts 
for both diurnal and seasonal variations in the relative position of the 
sun and earth while always maintaining the focal point of the cassegrain 
mirror system 31, 33 at a single location on a stationary cavity 11, 13. 
The maintenance of a stationary cavity such as that shown is extremely 
beneficial, in that no rotating or moving seals are required which would 
increase system expense, since such seals would be required to withstand 
the extreme pressures and temperatures expected in this installation. Thus 
all diurnal motion of the cassegrain mirror system 31, 33 is about a 
single axis, permitting the toroidal lens 15, although located in a 
stationary position, to refract all incident energy along the length of 
the high pressure pipes 11, 13. In addition, the use of direct absorption 
of this solar energy by the transparent or translucent fluid medium itself 
is extremely efficient, no intermediary absorption plate or heat 
exchangers being required for the absorption of energy. By maintaining the 
optical aperture extremely small, no energy is permitted to reradiate from 
the system, since such radiation would require a radiation back toward the 
sun which would violate the first law of thermodynamics. Furthermore, by 
maintaining convection losses at a minimum through a dewar-type 
construction and other insulating techniques, the energy absorption 
efficiency of this system may be maintained at an extremely high level. In 
addition, the system operates as a means of storing the energy thus 
absorbed, both efficiently and without the use of heat exchangers or 
dangerous materials, the inventor having found that the high pressure, 
high temperature working fluid itself may be utilized to store large 
amounts of energy for use during periods of total or partial darkness. 
Since the movable flat mirror 173, 179 effectively varies the size of the 
black body cavity to control the temperature within the cavity, the cavity 
size may be made larger when high levels of solar energy are available. In 
this respect, FIG. 10 shows a temperature sensing probe 297 connected to a 
motor control system 299 used to drive the motor 197 for adjusting the 
position of the flat mirrors 173 and 179. In the morning, when the bulk of 
the stored energy within the pipes 11, 13 has been utilized, the 
temperature within the vessel will be relatively low and the motor control 
system 299, in response to the temperature sensor 297, will have adjusted 
the flat mirrors 173, 179 to a position adjacent the toroidal lens 15. 
During the day, as solar energy is absorbed, if more solar energy is 
absorbed into the fluid within the black body cavity than is required for 
maintaining operation of the turbine 277 and generator 279, the 
temperature sensed by the probe 297 will increase, causing the motor 
control system 299 to move the flat mirrors 173, 179 upstream toward the 
inlet 125 of the pipe 13, increasing the effective size of the black body 
cavity and permitting the storage of this additional available energy. 
As is recognized by those skilled in the art, the manufacture of a large 
primary mirror 31 which may be mounted and rotated using systems such as 
those shown has not heretofore been possible. The present invention 
therefore includes novel techniques and materials for the manufacture of 
the primary mirror 31 to provide an extremely rigid, lightweight structure 
of sufficient optical quality to focus the solar radiation through the 
toroidal lens 15. This is accomplished using the method outlined in FIGS. 
11, 12 and 13. Initially, a large ring 301 may be fabricated by using, for 
example, corrugated cardboard material impregnated with epoxy to make it 
rigid. A sheet of aluminized MYLAR 303 is stretched across one face of the 
ring 301 and attached thereto, as by epoxy. This sheet 303, as viewed in 
FIG. 11, has an aluminum layer on the top and a MYLAR layer for strength 
and corrosion resistance on the underside. This material is presently 
available in mirror-like highly flexible, highly reflective sheets. This 
assembly of the ring 301 and stretched sheet 303 is pressed, as shown by 
the arrows 305, over a large male mold 307 formed as a paraboloid and 
defining the curvature of the primary mirror 31. A cylinder 309 may extend 
from the central axis of the male mold 307 to provide the aperture 41 for 
the completed mirror, and the sheet 303 may be cut to pass over the 
cylindrical form 309. 
When the ring 301 and its attached sheet 303 are pressed down over the male 
mold 307, as shown in FIG. 12, the resilience of the sheet 303 will make 
this sheet conform precisely to the contours of the male mold 307. The 
ring 301 is held depressed, and a layer of epoxy and glass 311 is applied 
to the aluminum backing of the aluminized mylar sheet 301. Cardboard 
honeycomb material 313, with honeycomb axes vertical as viewed in FIG. 12, 
is then placed over the epoxy and glass layer 311 to conform with the 
shape of the male mold 311, and the cardboard 313 is coated with epoxy to 
lend rigidity. A backing layer of epoxy and glass 315 is then applied to 
seal the open ends of the cardboard honeycomb material 313, and may be 
epoxied thereto. A final layer of low density foam material 317 is then 
attached to the epoxy material 315 to complete the assembly. This 
completed assembly is shown in FIG. 13. Each of the layers 311 through 327 
are placed on the sheet 303 to conform with the male mold 307 and are 
epoxied in place in this configuration, resulting in an extremely rigid, 
very lightweight structure. Each of the layers 311 through 317 may be 
apertured to receive the cylindrical extension 309, thus forming the 
central aperture 41 for the primary mirror 31. 
FIG. 14 shows a perspective view, partially cut away, of the primary mirror 
31 with the reflective surface uppermost in this figure. This structure 
includes an aluminum and mylar layer 303, the mylar layer being uppermost, 
and epoxy layer 311 attached to the aluminum of the layer 303 as well as 
the cardboard honeycomb layer 313, a second epoxy layer 315 and the low 
density foam layer 317. It will be appreciated that each layer is bonded 
to the next, forming a lightweight sandwich structure having extremely 
high compression strength. This assembly is surrounded by the original 
epoxy-impregnated cardboard ring 301 which is bonded to each of the 
layers, and this ring 301 may, in turn, be surrounded by and bonded to a 
protective metal ring 319. The ring 319 may be used, through an extension 
bracket 321, to mount the struts 43 used to support the secondary mirror 
31 (FIG. 1). These struts 43 may be made adjustable in length through the 
use of a turnbuckle connection 323, as shown in FIG. 14, permitting the 
axes of the mirrors 31 and 33 to be accurately aligned during installation 
of the system. 
The sun subtends approximately 30 arc minutes at the earth and the optical 
system as described herein is capable of approximately one arc minute of 
optical quality, which will permit a collection of over 90% of the sun's 
energy falling on its aperture. At the same time, the primary mirror 31 is 
relatively inexpensive to manufacture and may be manufactured in extremely 
large sizes. As an example, the primary mirror 31 of the preferred 
embodiment may be 20 meters in diameter while still providing sufficient 
rigidity to maintain the required optical quality, all without excessive 
weight which would interfere with rotation of the system as required by 
the relative motion of the sun and earth. 
The combination of this unique mirror system with the direct solar 
absorption apparatus described in reference to FIGS. 1 through 10 permits 
a relatively low cost, extremely efficient energy absorption and storage 
system which may be effectively mass produced, shipped and installed in 
various locations to supply electrical and thermal energy requirements to 
replace the utilization of fossil fuels. The high efficiency and energy 
storage of the present system makes it far more practical than prior art 
solar energy conversion systems which have been developed and provides an 
extremely practical energy source. 
In addition to other changes to the specific structure disclosed which will 
be apparent to those skilled in the art and which permit the practice of 
this invention while deviating only from the details, those skilled in the 
art will realize also that the interior surface of the pipes 11, 13 need 
not be reflective. So long as the energy is transmitted directly to the 
interior of the pipes 11, 13, even highly absorptive walls will 
immediately attain the same temperature as the included fluid such that 
they will reradiate as much energy as they absorb, the net effect being 
that the working fluid directly absorbs radiated energy rather than being 
heated by convection from the container walls.