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Description  |
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FIELD OF THE INVENTION
The invention relates to apparatuses for focusing by reflection and using
solar energy, of the type which comprise outer reflectors and inner
back-reflectors arranged according to an invariable geometry and
symmetrically distributed with respect to an axis; means adapted to keep
this axis directed towards the sun during daylight hours; and heat
collecting means located along said axis in a position such that they
receive the solar rays reflected by the reflectors and back-reflectors.
By "reflectors" is meant reflecting surfaces oriented so as to receive
directly incident solar rays and by "back-reflectors" reflecting surfaces
oriented so as to receive the solar rays already reflected by the
reflectors and send them back after a further reflection.
BACKGROUND OF THE INVENTION
Apparatuses of the type outlined in the foregoing are already known. Thus
U.S. Pat. No. 3,295,512 (Thomas J. McCusker) describes an apparatus which
comprises a single conical reflector inside which a column of parabolic
back-reflectors is arranged. The assembly of this apparatus is such that
each incident solar ray is reflected first inwards by the conical
reflector, then outwards by one of the parabolic back-reflectors and again
inwards by the conical reflector, which focuses the solar rays, which have
thus undergone triple reflection, on to heat collecting means whose centre
coincides with that of the base (or input surface) of the conical
reflector.
One of the drawbacks of this known apparatus is that its parabolic
back-reflectors are difficult to construct with a satisfactory geometrical
shape.
Another drawback is that the heat-collecting means are situated at a
position which is difficult to reach, and constitute an impassible
obstacle for the incident solar rays. The space available is therefore
insufficient to house, inside the conical reflector, the heat-collecting
means and their connections with the outside of the apparatus, if it is
desired to limit to a reasonable value the central fraction of the conical
reflector which is rendered unusable by the presence of these collecting
means.
A third drawback resides in the fact that the solar rays all undergo triple
reflection which considerably reduces the energy efficiency of the
apparatus.
SUMMARY OF THE INVENTION
It is an object of the invention to provide an apparatus of the type
concerned which eliminates the above-mentioned drawbacks or at least
reduces them.
To this end, the apparatus for focusing by reflection and using solar
energy is characterised, according to the invention, essentially in that
all its reflectors and back-reflectors have a rectilinear aspect in
section through any plane passing through its axis and are arranged so
that the heat-collecting means are positioned beyond their assembly, in
the input direction of the incident solar rays, and in that the reflectors
are grouped so as to form a practically continuous surface whose general
appearance is that of a truncated cone or pyramid but whose section
through said plane is a broken line whilst the back-reflectors are
staggered axially and radially so that the solar rays reflected directly
by the reflectors and reflected a second time by the back-reflectors can
reach the collecting means without being intercepted by another reflector
or back-reflector.
The reflectors and back-reflectors can each have a frustoconic shape or
polyhedral truncated pyramid shape. If their shape is frustoconic, the
axis of the apparatus constitutes their axis of revolution and they can
easily each be formed by bending over a jig, from a flat sheet of metal or
of reflecting plastics material. If their shape is polyhedral, they can be
constituted by the juxtaposition of flat facets. In this case, if each of
the reflectors and back-reflectors comprises an even number of facets, the
axis of the apparatus constitutes an axis of symmetry for the reflectors
and back-reflectors; if it comprises an odd number n of facets, the latter
are derived from one another by rotation, around said axis, through an
angle equal to 360.degree./n or to a multiple of this angle.
In a preferred embodiment, at least one back-reflector situated in the
vicinity of the input plane of the assembly of reflectors acts not only on
one of its surfaces as a back-reflector for the solar rays already
reflected directly by reflectors, but also by its other surface as a
reflector to reflect directly the solar rays close to the axis of the
apparatus, to another back-reflector closer still to the axis.
Considering that the reflectors and back-reflectors of the apparatus
according to the invention are formed of furstoconic surfaces or of flat
facets, it is possible to manufacture them easily by means of flat sheets
of metal or of reflecting plastics material which it suffices to bend in
the case of frustoconic surfaces or to assemble side by side, notably by
welding or glueing, in the case of polyhedral surfaces. Since the
collecting means are placed beyond the assembly of reflectors and back
reflectors, it is possible to give them the desired volume without risking
intercepting useful solar rays and, consequently, reducing the efficiency
of the apparatus. Considering lastly that the solar rays only undergo two
reflections before reaching the collecting means, the energy losses by
reflection are relatively low, which contributes also to increasing the
overall efficiency of the apparatus.
Preferably, the truncated conical or pyramidal surface along which the
reflectors are grouped has a half angle at the apex of the order of
40.degree. and the section of each reflector through a plane passing
through the axis of the apparatus forms with this axis an angle comprised
between 35.degree. and 50.degree..
By graphical methods or by calculation, in particular by means of a
computer, it is easy, with the aid of the rules given above, to determine
the angles, the dimensions and the mutual positioning of the reflectors
and back-reflectors. However, it has been proved by experimental methods
that the particular embodiment which is illustrated in the accompanying
drawings gives particularly advantageous results.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 of these drawings, shows in perspective an apparatus according to
the invention with polyhedral reflectors and back-reflectors.
FIG. 2 shows in perspective, a modification of a portion of the apparatus
of FIG. 1, with frustoconic reflectors and back-reflectors.
FIGS. 3 and 4 show, in plan, respectively the assembly of reflectors and
back-reflectors of the apparatus of FIG. 1 and that of the apparatus of
FIG. 2.
FIG. 5 shows, in section through a plane passing through the axis of the
apparatus, the assembly of reflectors and back-reflectors, as well as the
path of incident and reflected rays.
FIGS. 6 to 8 show, by sections similar to that of FIG. 5, how the various
reflectors and back-reflectors are located and dimensioned.
FIG. 9, lastly, shows the diagram of a heating installation comprising
several apparatuses similar to that of FIGS. 1 to 8.
PREFERRED EMBODIMENTS OF THE INVENTION
In the preferred embodiment which is shown in the accompanying drawings,
the apparatus comprises nine reflectors denoted respectively by 1,2. . 8
and 9 and eight back-reflectors denoted respectively by 1c, 2c . . . 7c
and 8c; these reflectors and back-reflectors are distributed symmetrically
around an axis O--O', in an invariable geometry.
The apparatus comprises in addition means adapted to maintain
automatically, during daylight hours, the axis O--O' directed towards the
sun. Such means are well known, for example, for orienting astronomical
telescopes and will hence not be described here in detail. As is shown in
FIG. 1, these means can rotate the movable mechanism 10 comprising
reflectors and back-reflectors, as indicated by the arrows f, around a
shaft 11 and adjust also the inclination of this shaft as indicated by the
arrows F. The angle of inclination of the shaft 11 is determined according
to the latitude of the site where the apparatus is located and the height
of the sun according to the periodic cycles whilst the apparent diurnal
motion of the sun is followed by the rotation of the mechanism around the
shaft 11.
The apparatus also comprises heat-collecting means situated along the axis
O--O' at a position such that they receive the solar rays reflected by the
reflectors 1 to 9 and back-reflectors 1c to 8c. These heat collecting
means can be constituted by a collector 12 (FIG. 5) closed and heat
insulated, forming a black box. The collected energy can be used directly
as radiant energy or converted into another form of energy, for example
electric or thermal, which will be used for domestic or industrial
purposes.
By way of indication, there is shown in FIG. 9 a central heating
installation which comprises in series three apparatuses with a movable
mechanism 10 and collector 12 each of which is identical with that of FIG.
1 or with that of FIG. 1 as modified by FIG. 2. A primary
heat-transmitting fluid circuit 13 passes through the collectors 12 where
it takes up the captured solar heat and transmits it to a heat accumulator
14. A secondary fluid circuit 15 can be established between the
accumulator 14 and a secondary accumulator 16. Lastly, a hot water central
heating circuit 17, of which only a radiator 18 is shown, takes up the
heat in accumulator 16 to transmit it to radiators such as 18. The circuit
17 can also serve for heating water in a container 19 for distribution in
residential premises for the usual purposes (kitchen, bathroom, etc.).
As is shown in FIGS. 1 and 3, the reflectors 1 to 9 and the back-reflectors
1c to 8c can have a truncated pyramidal shape and can be constituted from
juxtaposed flat facets. In the embodiment shown in FIGS. 1 to 3, each
reflector and back-reflector comprises eight facets but it is possible to
adopt a different number, even or odd, according to the circumstances. As
shown in FIGS. 2 and 4, the reflectors 1 to 9 and the back-reflectors 1c
to 8c can also have a truncated conical shape.
According to the invention, each of the reflectors 1 to 9 and
back-reflectors 1c to 8c has a rectilinear aspect in section through any
plane passing through axis O--O', as emerges notably from FIGS. 6 to 8
which correspond to the planes of section OX of FIGS. 3 and 4. In FIG. 3,
the plane OX passes through the middle of the side of each facet of a
series of polyhedral reflectors and back-reflectors. In FIG. 4, the plane
OX has any orientation since the axis O--O' constitutes an axis of
revolution for the assembly of reflectors and back-reflectors.
Moreover, the reflectors and back-reflectors are arranged so that the heat
collecting means are positioned beyond their assembly, in the input
direction of the incident solar rays. This is shown in particular by FIG.
5 where the incident rays arrive vertically, from above to below, and
where the collecting means or collector 12 are situated lower than the
last reflector 9 and the last back-reflector 8c.
In addition, the reflectors are grouped so as to form a practically
continuous surface whose general appearance is that of a truncated pyramid
(FIGS. 1 and 3) or a cone (FIGS. 2 and 4) but whose section through a
plane OX passing through the axis O--O' is a broken line (see FIGS. 5 to
8).
Lastly, the back-reflectors 1c to 8c are staggered axially and radially so
that the solar rays reflected directly by the reflectors and reflected a
second time by the back-reflectors can arrive at the collecting means or
collector 12 without being intercepted by another reflector or
back-reflector as shown in FIG. 5.
FIGS. 6 to 8 show the preferred embodiment of the invention and illustrate
the method enabling the various reflectors and back-reflectors to be
dimensioned and positioned.
One commences by drawing a rectangle ABCD of which one side BD coincides
with the axis O--O' of the apparatus and of which the half diagonals BG
and GD form an angle of 75.degree. with one another, G being the centre of
the rectangle ABDC.
Then, as regards the reflectors, inside th angle AGC, one traces
succesively (see FIG. 6) angles whose values are indicated below and whose
sides cut the small side AC of the rectangle at a', b', c'. . . . j'.
AGa' = 6.degree.45'
a'Gb' =11.degree.10'
b'Gc' = 8.degree.50'
c'Gd' = 9.degree.40'
d'Ge' = 9.degree.40'
e'Gf' = 5.degree.5'
f'Gg' = 7.degree.25'
g'Gh' = 5.degree.25'
h'Gi' = 2.degree.35'
i'Gj' = 5.degree.35'
j'Gc = 2.degree.50'.
From points a', b'. . . j', parallels to the large sides AB or CD of the
rectangle are then traced, these parallels being denoted by a'a", b'b". .
. j'j" in FIG. 6. Lastly, on these parallels a'a", b'b". . . j'j", one
traces the angles whose values are indicated below, so that their sides
non-parallel to the large sides AB or CD of the rectangle pass, for the
first angle, through the point A; for the second angle, through the point
a constituting the apex of the preceding angle and so on up to point h.
Aaa' = 47.degree.20'
abb' = 45.degree.30'
bcc' = 40.degree.30'
cdd' = 51.degree.35'
dee' = 55.degree.40'
eff' = 53.degree.
fgg' = 49.degree.
ghh' = 50.degree.30'.
The point i is the intersection of the line i'i" with a perpendicular to
this line brought from the point h. Lastly, one obtains the point j at the
intersection with j'j" of a line passing through the point i and making
with j'j" an angle of 47.degree.15'.
One thus obtains an assembly of reflectors whose section through a plane
passing through the axis O--O' is constituted by the broken line Aa
(reflector 1), ab (reflector 2), bc (reflector 3), cd (reflector 4), de
(reflector 5), ef (reflector 6), fg (reflector 7) and gh (reflector 8).
The reflector 9, whose edges are defined by the points i and j is
separated from the assembly of the preceding ones by the distance hi. It
is observed that the reflectors 1 to 9 are grouped practically along a
surface of a truncated cone or pyramid whose half angle a the apex, that
is to say the angle formed by the lines AA' and O--O' in FIG. 6, is equal
to 39.degree.10'. In other words, the angle AA'C, which is the complement
of the preceding one, is equal to 50.degree.50'.
Another method for positioning the points a, b, . . . i and j has been
shown in FIG. 7. Let E be the middle of the side AB and I be the middle of
the side AC.
From the point I taken as apex, one traces successively the angles whose
values are indicated below:
AIa = 14.degree.20'
aIb = 33.degree.45'
bIc = 24.degree.10'
cId = 16.degree.15'.
In the same way, from the point C taken as apex, one traces successively
the angles whose values are indicated below:
ACb = 19.degree.25'
i bCc = 12.degree.25'
cCd = 11.degree.5'
dCe = 11.degree.25'
eCf = 6.degree.15'
fCg = 9.degree.10'
gCh = 6.degree.50'
hCi = 2.degree.40'
iCj = 7.degree.30'
jCD = 3.degree.15'.
lastly, from the point E taken as apex, one traces successively the angles
whose values are indicated below:
AEa = 11.degree.15'
aEb = 23.degree.
bEc = 20.degree.45'
cEd = 15.degree.20'
dEe = 10.degree.10'
eEf = 4.degree.45'
fEg = 5.degree.20'
gEh = 4.degree.45'
hEj = 4.degree.15'.
The point a is at the intersection of the half-lines Ia
and Ea; the point b at the intersection of the half-lines Ib, Cb
and Eb; the point c at the intersection of the half-lines Ic, Cc
and Ec; the point d at the intersection of the half-lines Id, Cd
and Ed; the point e at the intersection of the half-lines Ce and
Ee; the point f at the intersection of the half-lines Cf and Ef;
the point g at the intersection of the half-lines Cg and Eg;
the point h at the intersection of the half-lines Ch and Eh;
the point i practically at the intersection of the half-lines Ci and Eh;
and finally the point j at the intersection of the half-lines Cj and Ej.
Similar methods enable the location of the back-reflectors 1c . . . 8c.
These methods are a little more delicate than for the reflectors
considering that the back-reflectors are staggered both radially and
axially.
Let us call r, k, l, m, n, o, p and q the lower edges of the
back-reflectors 1c, 2c, . . . 8c, respectively. The point k also
constitutes the upper edge of the back-reflector 3c. Let us call r.sub.1,
k.sub.1, m.sub.1, n.sub.1, o.sub.1, p.sub.1, q.sub.1 the upper edges of
the back-reflectors 1c, 2c, 4c, 5c, 6c, 7c and 8c, respectively.
From the point J, the middle of the side BD, taken as apex, we trace the
following angles (FIG. 8):
bjl = 10.degree.15'
lJk = 7.degree.55'
kJk.sub.1 = 11.degree.5'
k.sub.1 Jm = 6.degree.50'
mJm.sub.1 = 11.degree.30'
m.sub.1 Jn.sub.1 = 39.degree.30'
n.sub.1 Jn = 31.degree.50'
nJp.sub.1 = 2.degree.10'
p.sub.1 Jq.sub.1 = 6.degree.50'
q.sub.1 Jo = 21.degree.25'
oJp = 0.degree.45'
pJq = 2.degree.45'
qJD = 27.degree.10'.
from the point B taken as apex, the angles traced are
OBr = 1.degree.
and
rBr.sub.1 = 23.degree..
From the point E taken as apex, one traces, upwards, the angles
BEr = 13.degree.30'
and
rEr.sub.1 = 4.degree.40'
as well as, downwards, the angles
BEk = 6.degree.15'
kEl = 4.degree.
lEm.sub.1 = 9.degree.10'
m.sub.1 Em = 9.degree.25'
mEn = 16.degree.
nEn.sub.1 = 10.degree.15'
n.sub.1 Eo.sub.1 = 10.degree.25'
o.sub.1 EF = 14.degree.30'.
from the point G taken as apex, one traces on the one hand the angles
FGq.sub.1 = 28.degree.25'
q.sub.1 Gp.sub.1 = 5.degree.40'.
From the point F taken as apex, one traces the angles
GFn.sub.1 = 23.degree.10' = GFo.sub.1
n.sub.1 Fp.sub.1 = 17.degree.35'
p.sub.1 Fo = 28.degree.25'
oFp = 7.degree.35'
pFq = 8.degree.25'
qFD = 4.degree.40'.
the back-reflector 1c is defined by its edge r, the intersection of the
half-lines Er and Br, and by its edge r.sub.1, the intersection of
Br.sub.1 with Er.sub.1.
The back-reflector 2c is defined by its edge k, the intersection of the
half-lines Ek and Jk, and by its edge k.sub.1, the intersection of the
side AB with the half-line JK.sub.1.
The back-reflector 3c is defined by its edge k, common with the
back-reflector 2c, and by its edge l, the intersection of the half-lines
El and Jl.
The back-reflector 4c is defined by its edge m, the intersection of the
half-lines Em and Jm, and by its edge m.sub.1, the intersection of the
half-lines Em.sub.1 and Jm.sub.1.
The back-reflector 5c is defined by its edge n, the intersection of the
half-lines En and Jn, and by its edge n.sub.1, the intersection of the
half-lines En.sub.1 and Fn.sub.1.
The back-reflector 6c is defined by its edge o, the intersection of the
half-lines Fo and Jo, and by its edge o.sub.1, the intersection of the
half-lines Eo.sub.1 and Fo.sub.1.
The back-reflector 7c is defined by its edge p, the intersection of the
half-lines Fp and Jp, and by its edge p.sub.1, the intersection of the
half-lines Fp.sub.1 and Jp.sub.1.
Lastly, the back-reflector 8c is defined by its edge q, the intersection of
the half-lines Fq and Jq, and by its edge q.sub.1, the intersection of the
half-lines Gq.sub.1 and Jq.sub.1.
To avoid any error, two methods of checking are provided. The first relates
to the ordinate (side parallel to the axis O--O') of the lower edges of
the majority of the back-reflectors. From the point G taken as apex, one
traces successively the angles whose values are indicated below and of
which the sides cut the small side BD of the rectangle ABDC at k', l'. .
p', q' (FIG. 6):
BGk' =3.degree.15'
k'Gl' = 3.degree.5'
1'Gm' = 11.degree.30'
m'Gn' = 30.degree.5'
n'Go' = 15.degree.35'
o'Gp' = 5.degree.
p'Gq' = 4.degree.
q'GD = 2.degree.30'.
if one traces, through the points k', l'. . . p', q', parallels k"k', l"l',
. . . p"p', q"q' to the side AB, these parallels must pass respectively
through the lower edges k, l, . . . p, q of the back-reflectors 2c, 3c . .
. 7c, 8c.
The second method of checking relates of the angles of inclination of the
back-reflectors with respect to the parallels r'r", k'k", l'l". . . q'q".
These angles must be equal, respectively to
21.degree.30' for the back-reflector 1c
22.degree.40' for the back-reflector 2c
33.degree.30' for the back-reflector 3c
33.degree.40' for the back-reflector 4c
33.degree.20' for the back-reflector 5c
33.degree.20' for the back-reflector 6c
26.degree.10' for the back-reflector 7c
24.degree.35' for the back-reflector 8c.
An apparatus is thus obtained in which the solar rays are reflected in the
manner indicated in FIG. 5.
The rays received by the reflectors 1,2 and 3 are reflected to the
back-reflector 4c; the rays received by the reflector 4 are reflected to
the back-reflector 5c; the rays received by the reflectors 5,6 and 7 are
reflected to the back-reflector 6c; the rays received by the reflectors 8
and 9 are reflected respectively to the back-reflectors 7c and 8c.
The rays which are intercepted by the back of the back-reflector 4c are
reflected by the latter to the back-reflectors 2c and 3c. Lastly, the
major part of the rays intercepted by the back of the back-reflector 2c
are reflected by the latter to the back-reflector 1c.
Finally, and except for a small central zone, all the rays are reflected by
the back-reflectors, after only two reflections, to the collecting means
12. Since the later are located beyond the reflectors and back-reflectors
in the direction of arrival of the incident rays, it is possible to give
them optimal shape and volume without risk of impeding the propagation of
the useful solar rays and thus reducing the energy efficiency of the
installation.
The reflectors and back-reflectors are preferably constructed of steel
sheet which has been subjected to surface treatment to give it the desired
reflecting power.
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