Solar heating panels

A solar heating panel is constructed from a kit of parts which essentially comprises a number of absorber plate sections, each of which has on one edge an outwardly-facing concave part-cylindrical portion, the concave surface of which has a radius of curvature equal to the radius of curvature of the outside circumferential surface of the tubes which will carry the water to be heated through the panel. In the embodiment described, the part-cylindrical portions on the absorber plate sections are clamped with their concave surfaces in heat-conducting contact with the outer surfaces of the tubes by spring clips which are readily snapped over the convex surfaces of adjacent absorber plate sections. The heat-conducting contact between the concave surfaces on the part-cylindrical portions of the absorber plates and the outer surfaces of the tubes may be either an intimate surface contact between essentially smooth surfaces, or it may be a contact through a film of a heat-conductive paste which ensures a substantial exclusion of air or moisture from between the two curved surfaces.

SUMMARY OF THE INVENTION 
This invention relates to solar heating panels. 
Solar heating panels are panels which are exposed to receive radiation 
either directly or indirectly (by diffusion) from the sun and which 
convert the received radiation into heat which is taken from the panel by 
a liquid which flows through it. Many types of solar heating panel are 
already known and in general such solar heating panels are relatively 
bulky panels which are difficult to transport. It is an object of the 
present invention to provide a solar heating panel which may be 
transported as a package of relatively convenient size, and may also be 
readily assembled on site. 
According to the present invention there is provided a solar heating panel 
which includes a plurality of absorber plate sections each having at one 
edge an outwardly-facing concave part-cylindrical portion, and the 
part-cylindrical portions on adjacent absorber plate sections being 
clamped with their concave surfaces in heat-conducting contact with the 
outer cylindrical surface of a cylindrical tube for carrying a liquid to 
be heated. 
The heat-conducting contact between the concave surfaces of the 
part-cylindrical portions and the outer cylindrical surfaces of the 
associated tubes may be an intimate surface contact between two 
essentially smooth surfaces. Alternatively, however, the heat-conducting 
contact may be a contact through a thin film (for example 25 microns in 
thickness or less) of a heat-conductive paste which is pressed into full 
contact with the concave surfaces of the part-cylindrical portions and the 
outer cylindrical surfaces of the associated tubes. 
The heat-conducting contact which is provided in accordance with the 
present invention is a close proximity between the outwardly-facing 
concave surface of the part-cylindrical portion and the outer cylindrical 
surface of the tube with a substantial exclusion of moisture, air or any 
other gas from between the said surfaces. Most advantageously, the 
exclusion of gas from between the two surfaces is achieved by the presence 
of the heat-conductive paste which is applied to the two surfaces before 
these are brought together, surplus heat-conductive paste being squeezed 
from between the two surfaces as they are clamped together thereby 
ensuring a substantially total exclusion of gas or moisture which would 
otherwise have caused a reduction in the flow of heat between the two 
surfaces over the area occupied by the gas or moisture. 
The heat-conductive paste is preferably a compound similar to the 
heat-transfer compounds (otherwise known as heat sink compounds) which are 
used for promoting the dissipation of heat from electric circuit 
components. 
In order to achieve the most advantageous arrangement for efficient heat 
conduction from the absorber plate sections to the cylindrical tubes, the 
part-cylindrical portions of the plate sections preferably have 
substantially semi-cylindrical concave surfaces. 
More specifically in accordance with the present invention therefore there 
is provided a solar heating panel comprising a plurality of cylindrical 
tubes for carrying a liquid to be heated and an absorber plate for 
absorbing solar radiation falling thereon, the absorber plate including a 
plurality of plate sections each having at one edge an outwardly-facing 
concave substantially semi-cylindrical portion, the concave surface of the 
semi-cylindrical portion having the same radius of curvature as the outer 
circumferential surface of one of the cylindrical tubes, and spring clip 
means for engaging the convex outer surfaces of the semi-cylindrical 
portions on two adjacent plate sections and thereby clamping a cylindrical 
tube with its outer surface in heat-conducting contact with the concave 
surfaces of said semi-cylindrical portions. 
When it is stated that the plate sections have outwardly-facing concave 
substantially semi-cylindrical portions it is to be understood that, while 
the concave surfaces of these portions conform exactly to part of a 
cylindrical surface, they should extend over a fraction less than half the 
surface of a cylinder in order that the clamping means may provide a tight 
fit between the concave surfaces on the absorber plate sections and the 
outer surfaces of the cylindrical tubes so that good heat-conducting 
contact is obtained. Nevertheless substantially complete circumferential 
contact between the concave surfaces of two semi-cylindrical portions and 
the outer surface of the cylindrical tube is obtained over essentially the 
whole length of the cylindrical tube embraced by adjacent absorber plate 
sections. 
The plate sections may be provided with part-cylindrical portions, 
preferably substantially semi-cylindrical portions, on opposed parallel 
edges of at least the sections which form the central part of the absorber 
plate. In such a case the absorber plate should either not be mounted in a 
surrounding frame, or, if mounted in a surrounding frame, the absorber 
plate should be so positioned within the frame as to allow for both 
lateral and longitudinal expansion of the absorber plate within the frame. 
However, it is preferred that one absorber plate section shall have a 
part-cylindrical, preferably semi-cylindrical, portion on only one edge, 
and that an opposite edge of the plate section which is parallel to the 
said one edge shall face towards the said one edge thereby defining a 
channel in the plate section within which channel a similar opposite edge 
of another adjacent plate section is slidingly engaged in a manner which 
interlocks the said opposite edges but permits expansion of the plate 
sections relative to one another. 
It will be appreciated that, in order that the opposite edges of two plate 
sections may interlock in sliding engagement with one another, the 
engaging portions of the opposite edges on the two plate sections must be 
differently shaped. Accordingly the solar heating panel comprises two 
kinds of plate section. 
Conveniently the adjacent plate sections are clamped in heat-conducting 
contact with the respective tubes by a plurality of spring clips each of 
which additionally engages one of a plurality of T-bars extending across 
that dimension of the panel which is perpendicular to the longitudinal 
direction of the cylindrical tubes. The securing of the adjacent plate 
sections to a plurality of T-bars provides for a rigidity in the assembly 
of the cylindrical tubes and the absorber plate which enables the solar 
heating panel to be formed without a mounting frame. 
However, in the preferred embodiment of the present invention which will be 
described, the solar heating panel is formed with a surrounding frame to 
which are secured a plurality of spring plates into which the T-bars are 
mounted. 
A solar heating panel in accordance with the present invention which is 
capable of being readily assembled on site is particularly suitable for 
domestic installations for providing space heat and domestic hot water. 
Advantageously in a solar heating panel in accordance with the present 
invention for such domestic use there are provided tubular elbow portions 
for linking the ends of adjacent cylindrical tubes in such manner that the 
liquid to be heated is caused to pass successively through all the tubes 
of the panel. 
In accordance with a further aspect of the present invention there is 
provided a kit of parts for use with cylindrical tubes for erection into a 
solar heating panel which comprises a plurality of absorber plate sections 
of similar length and each having on one longitudinal edge an 
outwardly-facing concave substantially semi-cylindrical portion the 
concave surface of which has a radius of curvature equal to the radius of 
curvature of the outer circumferential surface of the said tubes, and each 
having on the opposite longitudinal edge a channel section constituted by 
a portion of the plate section which is folded back so that the edge faces 
the said one edge, and a plurality of spring clips for clamping the 
semi-cylindrical portions on respective pairs of absorber plate sections 
with their concave surfaces in heat-conducting contact with the outer 
cylindrical surfaces of the tubes engaged thereby when a solar heating 
panel is assembled.

DETAILED DESCRIPTION 
Referring to FIGS. 1 to 5 of the accompanying drawings there is shown a 
solar heating panel which includes five cylindrical tubes 1 which may be 
of any suitable conducting material such as copper, stainless steel, glass 
or a corrosion resistant aluminum alloy such as that obtainable from 
Birmetals Ltd. under the name Birmabright BB2. The cylindrical tubes 1 are 
longitudinally disposed in parallel, as shown in FIG. 1, the upper and 
lower tubes 1 shown in FIG. 1 extending beyond the periphery of the solar 
heating panel in order to provide an inlet and an outlet for the liquid 
(usually water) which is to be heated in the panel. By means of connector 
tubes 2 which are connected between the ends of adjacent cylindrical tubes 
1 by elbows 3, as shown in FIG. 1, water may be circulated successively 
through all the cylindrical tubes 1 so that it receives a substantial 
increase in temperature before emerging from the panel. Circulation of 
water for a substantial time within the panel to maximize heat absorption 
is particularly desirable in a solar heating panel designed for domestic 
use. 
The absorber plate in the solar heating panel in accordance with the 
present invention is comprised of a plurality of absorber plate sections 4 
and 5 which are best illustrated in FIG. 5 of the accompanying drawings. 
The absorber plate sections 4 and 5 are similar to one another in that 
each has at one edge a substantially semi-cylindrical portion 26. An 
opposite edge portion 28 of absorber plate section 4 which includes an 
edge of that plate section which is parallel to the edge of the plate 
section on the substantially semi-cylindrical portion 26 is shaped by 
folding back a part of the plate section 4 on itself so that a return lip 
is provided defining a downwardly facing channel. By contrast the absorber 
plate section 5 has an opposite edge portion 30 which is shaped so that 
its edge faces back towards the said one edge on the substantially 
semi-cylindrical portion 26 in a manner which defines an upwardly facing 
channel. The channels which are defined by the respective edge portions 28 
and 30 are so dimensioned that the absorber plate sections 4 and 5 may be 
loosely secured to one another by sliding the respective edge portions 28 
and 30 into one another. When so engaged the absorber plate sections 4 and 
5 are interlocked and cannot be readily separated from one another (other 
than by sliding them out of engagement), but as illustrated in FIG. 5, a 
gap between the main bodies of the absorber plate sections 4 and 5 is 
provided to permit expansion of these absorber plate sections as a result 
of increase in temperature when exposed to strong solar radiation. 
The absorber plate sections 4 and 5 are preferably both made from a sheet 
(for example 22 gauge) of a corrosion resistant aluminium alloy such as 
that which is obtainable from Birmetals Ltd. under the name Birmabright 
BB2. This aluminium alloy contains by weight from 1.7% to 2.4% of 
magnesium with small quantities of silicon up to a maximum of 0.5%, 0.5% 
of iron, 0.5% of chromium and manganese together, 0.2% of zinc and 0.1% of 
copper, the balance which is well in excess of 95% being aluminium. The 
absorber plate sections 4 and 5 made from such an aluminium alloy sheet 
are coated with a selective matt black finish 24 on their upper surfaces 
as indicated in FIG. 1 in order that the absorption of solar radiation by 
the absorber plate sections 4 and 5 is maximized. 
It will be observed from FIG. 5 that the absorber plate sections which are 
used at the two lateral extremities of the solar heating panel are 
absorber plate sections 4, that is to say, sections which have the simpler 
edge portion 28. As illustrated in FIG. 1, the absorber plate sections 4 
at the lateral extremities of the solar heating panel have a greater width 
than the absorber plate sections 4 which alternate with absorber plate 
sections 5 in the central part of the solar heating panel. However, more 
advantageously the absorber plate sections 4 at the lateral extremities of 
the solar heating panel have widths similar to the more centrally located 
absorber plate sections 4, thereby simplifying the number of members 
required for assembly of the solar heating panel. 
The solar heating panel which is illustrated in the accompanying drawings 
is assembled within end frame members 6 and side frame members 7 which are 
preferably also made of corrosion resistant aluminium alloy and are 
secured together by angle brackets 8 and screws 18 as shown in FIG. 4 to 
form a rectangular frame as illustrated in FIG. 1. The end frame members 6 
and the side frame members 7 are of similar cross-section as illustrated 
in FIGS. 4 and 5 respectively. 
As shown in FIG. 5 of the accompanying drawings the outwardly-facing 
concave surfaces of the substantially semi-cylindrical portions 26 on the 
respective absorber plate sections 4 and 5 engage the outer cylindrical 
surfaces of the tubes 1. The radius of curvature of the concave surfaces 
of the portions 26 is the same as the radius of curvature of the outer 
surface of the cylindrical tube 1 so that a substantially perfect fit 
between the two surfaces is obtained, and a spring clip 11 is clipped over 
the portions 26 of the respective absorber plate sections 4 and 5 so as to 
clamp these portions to the cylindrical tube 1 and thus retain the concave 
surfaces of the portions 26 and the respective absorber plate sections 4 
and 5 in intimate surface contact with the outer cylindrical surface of 
the tube 1 over substantially the whole of the outer cylindrical tube 1 
along the length of the tube which is embraced by the absorber plate 
sections 4 and 5. In practice there may be a small clearance between the 
portions 26 on the absorber plate sections 4 and 5 at both the top and the 
bottom of their engagement with the cylindrical tubes 1 as seen in FIG. 5, 
but these clearances are kept to a practical minimum in order to maximize 
heat transfer from the absorber plate sections 4 and 5 to the cylindrical 
tubes 1 and the water or other liquid passing through the tubes 1. 
The spring clips 11 which are effective to form the absorber plate of the 
solar heating panel of the present invention from the absorber plate 
sections 4 and 5 by clamping the substantially semi-cylindrical portions 
26 of the absorber plate sections into good heat-conducting contact with 
the outer surfaces of the cylindrical tubes 1, may be simple spring clips 
11 which serve the sole function of clamping the portions 26 to the 
cylindrical tubes 1. However, in the embodiment of the invention which is 
illustrated in FIGS. 1 to 5 of the drawings, the spring clips 11 are 
formed integrally with a lower channel portion 11a (see FIG. 4) which 
enables the spring clips 11 to be slid over the upper horizontal portions 
of T-bar supports 9. Preferably the spring clips 11 are made from 
cadmium-plated steel, and the T-bar supports 9 are made of a corrosion 
resistant aluminium alloy such as the Birmabright BB2. 
The T-bar supports 9 are themselves supported by spring plates 10 from 
which the T-bar supports 9 are insulated by a neoprene seal 14 and a 
neoprene end piece 15 (see FIGS. 5 and 4 respectively). The spring plates 
10 are themselves retained in the side frame members 7 as illustrated in 
FIGS. 1 and 5. The same spring plates 10 are utilized with neoprene side 
seals 13 to locate the edge portions 28 of the absorber plate sections 4 
at the lateral extremities of the solar heating panel. It will be noted 
that the neoprene side seal 13 which supports the absorber plate sections 
4 in the spring plates 10 is of substantially greater thickness than the 
other neoprene members for reducing heat loss from the absorber plate to 
the spring plates 10, and the spring plates 10 themselves occupy only a 
very small proportion of the length of the side frame members 7 so that 
the risk of heat conduction from the absorber plate sections 4 to the 
spring plates 10 and thence to the side frame members 7 is kept to a 
practical minimum. 
Located in dovetailed grooves in the end frame members 6 and the side frame 
members 7 are strips of neoprene beading 12, upon which is supported a 
glass sheet 23 which is the top cover of the solar heating panel. The 
glass sheet 23 is held in position by snap-on plastic beading 19 which, as 
indicated in FIG. 4, is snapped on to a projection 32 on the top of the 
frame member. The inwardly projecting part of the plastic beading 19 
provides a weather seal to the panel, the junctions between the plastic 
beadings 19 being themselves protected by plastic corner trims 20 which 
cover the plastic beadings 19 at the corners. Also a neoprene end seal 16 
is secured to the end frame members 6 and engages the end surface portions 
of the absorber plate sections 4 and 5 in order to cover, and exclude from 
view, the elbows which join the cylindrical tubes 1 to the connector tubes 
2. 
The cylindrical tubes 1 which pass through the end frames 6 are located in 
apertures in the end frames 6 by neoprene grommets 17 (see FIGS. 4 and 5). 
Retained within horizontal feet 34, 35 on the end and side frame members 6 
and 7 is a backing plate 21 which is advantageously a glass reinforced 
plastic plate. The backing plate 21 constitutes the effective base of the 
solar heating panel illustrated in the accompanying drawings and provides 
support for fiberglass wool insulation 22 which fills all the available 
space between the absorber plate comprised of the sections 4 and 5, and 
the backing plate 21. 
In the above description of the embodiment of the invention illustrated in 
FIGS. 1 to 5 of the accompanying drawings it has been stated that the 
concave surfaces of the substantially semi-cylindrical portions 26 on the 
respective absorber plate sections 4 and 5 are in intimate surface contact 
with the outer cylindrical surfaces of the tubes 1 and the intimate 
surface contact results in good thermal conductivity between the absorber 
plate sections 4 and 5 to the tubes 1 and the water flowing through the 
tubes 1. Good thermal conductivity between the substantially 
semi-cylindrical surfaces of the portions 26 and the tubes 1 may also be 
obtained by applying to the semi-cylindrical surfaces of the portions 26 
and the external surfaces of the tubes 1 a heat-conductive paste which is 
stable over the range of operating temperatures of the solar heating 
panel. 
The heat-conductive paste is a grease-like material such as a siloxane 
polymer which includes metal and/or metal oxide in powder form. Siloxane 
polymers are especially suitable as the basis of a heat-conductive paste 
which includes a carrier for metals or metal oxides in powder form because 
siloxane polymers are heat resistant, they will not set unless catalysed 
and they retain their viscosity over a substantial temperature range. 
Siloxane polymers retain a stable state up to temperatures as high as 
200.degree. C. 
A heat-conductive paste which has been found to be suitable for use as a 
heat-conductive film between the surfaces of an absorber plate and 
corresponding surfaces on cylindrical tubes to which heat is to be 
transferred is a siloxane polymer heavily loaded with heat-conductive 
metal oxides, that is to say, a siloxane polymer containing the maximum 
quantities of heat-conductive metal oxides, whilst still retaining its 
essentially viscous state. One heat-conductive paste in accordance with 
this description is the heat transfer compound sold under the trade name 
Dow Corning 340. 
The application of the heat-conductive paste is made to the 
outwardly-facing concave surfaces of the substantially semi-cylindrical 
portions 26 and the outer cylindrical surfaces of the tubes 1 before these 
surfaces are clamped together using the spring clips 11. The clamping 
reduces the heat-conductive paste to a thin film of thickness of the order 
of one to two thousandths of an inch, the surfaces of this film following 
the contours of the outer concave surfaces on the semi-cylindrical 
portions 26 and the outer cylindrical surfaces of the tubes 1. There is 
thus no surface contact between the tubes 1 and the semi-cylindrical 
portions 26, but the continuous film of the heat-conductive paste provides 
thermal conductivity as good as is obtained by maintaining the most 
intimate surface contact between commercially produced smooth surfaces on 
both the semi-cylindrical portions 26 and the tubes 1. Indeed, by 
excluding pockets of air from places where there may be irregularities in 
one or other of the surfaces which are clamped together, the 
heat-conductive paste provides substantially improved thermal conductivity 
between the surfaces in such areas. 
The presence of a thin film, or barrier, (of the order of 25-50 microns in 
thickness) of heat-conductive paste between the outer cylindrical surfaces 
of the tubes 1 and the concave surfaces of the semi-cylindrical portions 
26 enables the tubes 1 and the absorber plate sections 4 and 5 to be made 
of different metals, if desired, without significant deterioration due to 
electrolysis between different metals in the absorber plate and the tubes 
occurring. In particular, the presence of the heat-conductive paste 
enables the tubes 1 to be made of copper, which is highly desirable when 
the solar heating panel is to be used for hot water systems for domestic 
or industrial use. 
The presence of the heat-conductive paste also facilitates linear expansion 
of the semi-cylindrical portions 26 relative to the tubes 1 whilst 
maintaining good heat-conducting contact between the parts. This feature 
is particularly important when the tubes 1 are made from a different 
material from that used in the manufacture of the absorber plate sections 
4 and 5. 
FIG. 6 illustrates an alternative embodiment of the invention which is 
specifically designed for incorporating a heat-conductive paste. The solar 
heating panel of FIG. 6 has a series of absorber plate sections 41 and 42 
which have at their adjacent edges respective outwardly-facing concave 
substantially semi-cylindrical portions 43 and 44. The plate sections 41 
and 42 are assembled so that the concave surfaces of the semi-cylindrical 
portions 43 and 44 substantially surround a cylindrical tube 45, the outer 
surface of which has identical curvature to the concave surfaces of the 
semi-cylindrical portions 43 and 44. The concave surfaces of the 
semi-cylindrical portions 43 and 44, and the outer surface of the 
cylindrical tube 45 have a heat-conductive paste applied to them before 
assembly, and the relationship between the semi-cylindrical portions 43 
and 44 and the cylindrical tube 45 is maintained by a series of pressure 
clips, or spring clips, 46 which are snapped over the outer surfaces of 
the adjacent members 43 and 44 when these are embracing the outer surface 
of the tube 45 through the heat-conductive paste which is thereby reduced 
to a film 47. 
The edges of the plate sections 41 and 42 which include the 
outwardly-facing concave substantially semi-cylindrical portions 43 and 44 
respectively, are formed so that a rebate 48 on the edge of the plate 
section 41 which includes semi-cylindrical portion 43 is engaged by a 
projecting nib 49 on the edge of plate section 42 adjacent to the 
semi-cylindrical portion 44. The engagement of the nib 49 in the rebate 48 
effectively provides a small chamber 50 into which heat-conductive paste 
is squeezed from between the engaging surfaces of the semi-cylindrical 
portions 43 and 44, and the outer surface of the tube 45. The displaced 
heat-conductive compound is thereby prevented from exuding on the surface 
of the absorber plate comprised by the plate sections 41 and 42. 
The film 47 of heat-conductive paste is maintained under pressure so that 
the heat-conductive paste is in contact with the whole of the surfaces of 
the absorber plate sections and the cylindrical tubes, between which 
thermal conduction of heat is desired in operation of the solar heating 
panel. In thus providing thorough contact between the heat-conductive 
paste and the respective surfaces, the paste effectively ensures that 
there is no moisture or air trapped between the surfaces, and improved 
thermal conduction of heat from the absorber plate to the tubes is 
achieved as compared with prior solar heating panels in which tubes are 
soldered into position in channels in absorber plates. 
Conveniently a solar heating panel in accordance with the present invention 
has dimensions of 1300 mm.times.900 mm.times.90 mm, and contains 
cylindrical tubes of 15 mm external diameter. The solar heating panel has 
an effective area of 1 sq. meter and it is found that the use of four such 
panels for a domestic installation having an existing hot water storage 
capacity of the order of 25 to 35 gallons is competitive in terms of 
production of thermal energy with an electric immersion heater. 
Accordingly the use of a system comprising four such panels in accordance 
with the present invention can effect substantial savings in the use of 
electrical energy, particularly during the summer months when up to 90% of 
the daily hot water requirements in the average household may be provided 
from solar energy. 
Although the present invention has been described in conjunction with a 
solar heating panel having five cylindrical tubes 1, the nature of the 
panel which is constructed from absorber plate sections 4 and 5 enables 
panels of different dimensions to be easily assembled from the same basic 
parts. Indeed, it has been found that a solar heating panel assembled from 
absorber plate sections 4 and 5 and having three cylindrical tubes 1 is of 
suitable dimension to fit between the joists in the roof construction of 
many domestic houses. A solar heating panel may thus be installed in the 
roof of such a house (without the necessity for encasing the absorber 
plate sections in side and end frame members) but by simply supporting the 
assembly of absorber plate sections between the joists (with appropriate 
thermal insulation) and immediately behind a roof light entered into the 
roof. 
It will be appreciated therefore that a solar heating panel in accordance 
with the present invention may be extended or reduced in size to meet the 
desired configuration of absorber plate. 
It is envisaged that the solar heating panel in accordance with the present 
invention will be supplied as a kit of parts in a package of much more 
convenient size than the assembled panel itself. While this kit of parts 
may include all the essential parts of the panel in accordance with this 
invention, viz the absorber plate sections 4 and 5, the cylindrical tubes 
1 and the spring clips 11, it is not necessary to include the cylindrical 
tubes 1 since these will be readily available in standard sizes in any 
part of the world to which the kit for assembling the panel may be 
exported. The preferred kit will include the side and end frame members, 
six absorber plate sections 4 and four absorber plate sections 5 having 
part-cylindrical portions so made to fit perfectly around a part of the 
outer circumferential surface of any tube having an outside diameter of 
either 15 mm or 22 mm or 28 mm, spring clips to snap over the portions of 
the absorber plate sections which embrace each tube and secure the perfect 
fit necessary between the absorber plate sections and the heat-conducting 
cylindrical tubes, fibreglass insulation and the necessary sealing and 
insulating members, snap-on plastic beading and angle brackets as 
described with reference to the accompanying drawings. The preferred kit 
of parts may also include a container containing a supply of 
heat-conductive paste. 
This preferred kit of parts can be supplied in a package measuring only 
1400 mm.times.300 mm.times.160 mm and weighing about 13 kilos. The kit is 
capable of being assembled by semi-skilled labour using a local supply of 
the cylindrical tubes 1, the backing plate 21 and the sheet of glass 23 
which constitutes the glazing on the upper surface of the panel. 
However, it is also contemplated that the solar heating panel of the 
present invention may be supplied as a kit of parts containing all the 
members of the panel as hereinbefore described with reference to the 
drawings. 
It will be appreciated that the essence of the present invention resides in 
the concept of a solar heating panel, the absorber plate of which is 
assembled by a method including the steps of taking a first absorber plate 
section having an outwardly-facing concave part-cylindrical portion at one 
edge thereof, the concave surface of the part-cylindrical portion having a 
radius of curvature equal to the radius of curvature of the outer 
circumferential surface of a tube which in operation of the panel will 
carry water to be heated, placing the concave surface of the 
part-cylindrical portion of that absorber plate section in heat-conducting 
contact with part of the outer cylindrical surface of the tube, taking a 
second absorber plate section having a similar part-cylindrical portion to 
the first absorber plate section, placing the concave surface of the 
part-cylindrical portion of the second absorber plate section in 
heat-conducting contact with the outer cylindrical surface of the tube so 
that the part-cylindrical surfaces on the two absorber plate sections 
substantially surround the outer cylindrical surface of the tube, and then 
clamping the two part-cylindrical portions of the two absorber plate 
sections towards one another and against the outer cylindrical surface of 
the tube so that the heat-conductive contact between the concave surfaces 
of the two part-cylindrical portions of the absorber plate sections and 
the outer cylindrical surface of the tube is maintained. 
By utilizing absorber plate sections having edge configurations similar to 
those shown for absorber plate sections 4 and 5 in the accompanying 
drawings, the absorber plate may be readily made of any desired size 
simply by using the appropriate number of absorber plate sections and 
cylindrical tubes. The absorber plate thus made has a built-in ability to 
accommodate thermal expansion where the edges of adjacent absorber plate 
sections 4 and 5 are in sliding engagement with one another. Also the 
absorber plate may be readily utilized with tubes of any material easily 
and economically because the tubes are retained in position by clamping 
and without recourse to any expensive jointing techniques.