Note: Descriptions are shown in the official language in which they were submitted.
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A panel-shaped, hybrid photovoltaic/thermal device.
The invention relates to a panel-shaped, hybrid
photovoltaic/thermal device comprising panel-shaped photovoltaic means
for converting solar energy into electric energy, which photovoltaic means
are mounted on panel-shaped absorption means for converting solar energy
into thermal energy, which absorption means are provided with one or more
flow channels for the purpose of delivering thermal energy during operation
to a fluid flowing therein.
A device of this type is known from Patent Abstracts
of Japan, vol. 008, no. 104 (M-296) JP 59 015766 A.
In practice, hybrid photovoltaic/thermal devices are
generally used in combination with an electric subsystem for delivering
electric energy generated by the photovoltaic means to an electric
installation, and with a thermal subsystem for the storage of the thermal
energy delivered by the absorption means. The thermal subsystem may, for
example, comprise a boiler or the like for heating water.
Hybrid photovoltaic/thermal devices are used both for
household and for industrial purposes, and they are also referred to as
hybrid solar collectors.
For use on a large scale, optimization both as regards
the electric and thermal efficiency of a hybrid photovoltaic/thermal device
and the cost of production are necessary. Furthermore, the device must
operate reliably.
From the International patent publication WO 95/0273
a panel-shaped hybrid photovoltaic device is known comprising a structure
which is relatively complicated and costly for production on a large scale.
The absorption means and the photovoltaic means are mounted separately
in a housing, whereby the interior of the housing must be void of air.
This makes the known device less suitable for use in the open air, for
example on a rooftop, because in that case the risk of the vacuum being
broken as a result of damage to the housing is considerable.
Said vacuousness requirement has also its repercussions
on the construction, which must be sufficiently strong mechanically in
order to be able to withstand temperature gradients therein whilst
maintaining the vacuum, in order to provide a reliable operation for a
prolonged period of time.
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In the panel-shaped hybrid photovoltaic device known
from Patent Abstracts of Japan as referred above, the absorption means
comprise a heat conductive construction of a high-molecular plastic. This
construction is a compromise between the generated electric energy and
the thermal energy on the one hand and the weight and the cost of the panel
on the other hand, with the balance being in favour of the latter. Due
to the relatively poor heat conduction capabilities of the plastic
absorption means and the higher average working temperature that inevitably
results therefrom, this construction does not exhibit an optimum electric
efficiency. Since electric energy is valued more than thermal energy in
practi ce, i n vi ew of i is greater converti bi 1 i ty i nto other forms of
energy,
it is not possible with this known construction to provide an economically
exploitable hybrid photovoltaic/thermal device as aimed at by the
invention.
From US patent no. 4,700,013 a rather complicated hybrid
photovoltaic/-thermal device is known, having a linear array of high
current solar cells which are thermally anchored with an alumina loaded
silicone to a copper substrate. The system requires a sunlight or solar
ray concentrator, such as a Fresnel lens concentrator, a lens for focusing
the solar rays on the solar cells, such as a cylindrical piano-concave
lens, and a selective transmitting heat-mirror.
The selective transmitting heat-mirror has a special
profile which closely matches the Quantum Efficiency times Solar Flux
profi 1 a of the photovol tai c sol ar cel 1 s so that essenti al ly onl y the
sol ar
energy that can be converted to electricity by the photovoltaic cells
reaches the cells, and excessive heating thereof is effectively prevented.
US patent no. 4,587,376 relates to a panel-shaped hybrid
photovoltaic/thermal device which is particularly constructed for the use
of photovoltaic cells of an amorphous silicon material. Also in this case
it is not possible, due to the relatively low efficiency of said cells,
to provide an exploitable system which is capable to a sufficient degree
of meeting the electricity requirements of an average household. Without
constructional alterations to the device it is not possible to substitute
the cells of amorphous silicon for photovoltaic cells of monocrystalline
and multicrystalline silicon, whose efficiency is typically twice as high
as that of cells of amorphous silicon.
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German patent appl i cati on DE 38 31 631 di scl oses a sol ar
collector system having heat absorption means comprising a coolant in a
hermetically sealed housing. The volume of the coolant and its thermal
properties are designed to store heat during a period of maximum sunlight
radiation, to avoid excessive heating of the solar cells. This solar
collector system does not provide for heat transfer to a thermal subsystem
and, accordingly, is not a hybrid photovoltaic/thermal device in accordance
with the present invention.
It is an object of the invention to provide a hybrid
photovoltaic/thermal device which is of mechanically simple and reliable
construction, which exhibits an optimized thermal and electric efficiency,
adapted to the varying climatological conditions that occur at different
geographic positions all around the globe, and which is as much as possible
made of reliable, preferably generally commercially available components.
The hybrid photovoltaic/thermal device according to
the invention is characterized in that
- the photovoltaic means have a laminated structure,
comprising at least two sunlight transmissive layers of an electrically
insulating material, having there between electrically interconnected
photovoltaic cells of the crystalline type, for example of silicon,
- the absorption means are made of a metal absorption
plate, and
- the laminated photovoltaic means and the absorption
means have been provided as an integral unit with the interposition of
a plastic material having bonding properties and heat transfer properties,
such as a metal oxide-containing epoxy or a synthetic glue comprising metal
particles dispersed therein.
The invention has succeeded in providing a hybrid
photovoltaic/thermal device which operates satisfactorily, that is, in
terms of electric and thermal efficiency, which is reliable and which is
economically sound as regards cost and exploitation, by combining
components which are actually known per se.
The invention is based on the insight that, in order
to optimize the electric efficiency, an excellent heat conduction must
be realised, both in a direction perpendicularly to the panel, in this
case the direction of incidence of solar energy, and laterally in the
direction of the flow channels of the panel. After all, the efficiency
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of a photovoltaic cell decreases as the temperature increases.
The constructionally and thermally integrated device
according to the invention exhibits a better lateral heat conduction than
the known panels, a better protection against weather influences and an
optimum electricity generating efficiency, due to the fact that the
construction is suitable for the application of photovoltaic cells of
monocrystalline and multicrystalline silicon material or similar types.
The use of a laminated photovoltaic panel provides
adequate protection against weather influences and thermal stresses, as
well as the required electric insulation from the metal-containing
interposed bonding plastic. Plastics, such as a metal oxide-containing
epoxy or a glue comprising metal particles dispersed therein for obtaining
desired thermal conduction properties having thermal, elastic and bonding
properties which are suitable for the purpose of the present invention
are available in practice. Suitable metals are, for example, so-called
copper shavings. The glueing-together results in a robust construction
whose economic life is sufficiently long for household use, without any
further requirements being made as regards vacuousness and the like. The
use of "deformable" plastic material furthermore offers the advantage of
a wide range of options as regards the shape and the material of the
absorption means and the photovoltaic means, whilst retaining the desired
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thermal characteristics of the construction.
The plastic may thereby consist of an adhesive layer
which extends either over the adjacent surfaces of the photovoltaic means
and the absorption means, or only over selected positions, for example
under the photovoltaic cells.
The laminar photovoltaic means as used in the invention
preferably comprise two layers of a plastic material, between which the
cells are disposed, whereby the layer by means of which the laminate is
affixed to the absorption means, via the interposed layer of plastic
material, typically has a thickness in the order of 0.5 mm or less. In
order to obtain an optimum protection against weather influences, it is
preferred in accordance with the invention to use a construction wherein
the laminated photovoltaic cells are mounted on a sunlight transmissive
carri er made of gl ass, whi ch forms the outer 1 ayer onto whi ch the sunl i
ght
incidences. The laminates may be manufactured separately at suitable
production facilities, possibly tailored to the radiation conditions that
prevail in the country where the device is to be used.
Although the photovoltaic means and the absorption means
of the construction according to the invention may in principle have any
desired shape, it has become apparent in practice that a flat or slightly
curved panel-shaped construction is preferred for rooftop or wall mounting.
In the case of a panel-shaped construction, one or more
flow channels may be provided by a space present between the absorption
means and the fluid-tight panel-shaped means, for example a glass plate,
which are spaced therefrom by some distance.
In yet another embodiment of the invention, the flow
channels are provided by pipes or tubes or the like, which are in thermal
contact with the absorption means. These pipes or tubes may be integral
with the material of the absorption means, or be separately attached to
an absorption plate, for example by welding or glueing.
The integral construction according to the invention
furthermore makes it possible to use additional absorption means for the
purpose of further increasing the electric and thermal efficiency without
taking additional, complicated constructional measures.
In an embodiment of the invention, the above aspect
has been realised in that further absorption means are spaced from the
laminated photovoltaic means and the absorption means by some distance,
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in such a manner that the absorption means in question are positioned
opposite each other, with a space being formed therebetween.
Preferably, a thermally insulating, sunlight trans-
missive fluid, such as ambient air, is present in the space between the
absorption means.
This measure makes it possible to achieve a reduction
of the operating temperature of the photovoltaic means, and consequently
a higher electric and thermal efficiency, because two thermally separated
heat exchange sections are obtained, with the photovoltaic means being
positioned in the so-called "cold" section. One and the same fluid can
flow through the respective sections, starting with the cold section.
In yet another embodiment of the invention, a fluid-
tight, sunlight transmissive panel, for example of glass, is disposed
opposite the photovoltaic means, spaced from the laminated photovoltaic
means by some distance. The arrangement is thereby such that a space is
formed between the panel and the photovoltaic means for containing therein-
a sunlight transmissive fluid, for example water, during operation.
Yet another enhancement of the electric efficiency is
aimed at in an embodiment of the invention wherein the sunlight
transmissive panel comprises means for concentrating sunlight in the
direction of the photovoltaic means. These solar concentrating means may
consist of adjacently disposed semicylindrical elements of a sunlight
transmissive material, in such a manner that the concave sides of the
elements are positioned opposite the photovoltaic means. These elements,
together wi th the water, for exampl e, that i s present between the el ements
and the photovoltaic means; in particular concentrate diffuse sunlight,
which is prevalent in a country such as the Netherlands, for example.
The laminated photovoltaic means and absorption means
formed as a single unit according to the invention make it readily possible
to realise all embodiments in a box-shaped housing without any
constructionally complicated supporting structures and the like being
required. It should be kept in mind thereby that the high temperature
gradients that may occur during use of a device make special demands on
the construction, which demands become more exacting as the complexity
of the construction increases.
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In a preferred embodiment of the invention, invertor
means, which are electrically connected with the laminar photovoltaic
means, are integrated in the laminar photovoltaic means for the purpose
of converting the generated direct current energy into alternating current
energy and delivering it to the output terminals of the photovoltaic/
thermal device. Those skilled in the art will appreciate that this makes
it possible to use a very simple, modular construction, wherein several
hybrid photovoltaic/thermal devices according to the invention can be
combined to form a single device of desired dimensions for converting solar
energy.
By providing the invertor means with a so-called
"maximum power point tracker", the total electric efficiency of a
combination of hybrid photovoltaic/thermal devices according to the
invention operating at different temperature levels simultaneously, can
be h i gher than i n the case of one i nvertor bei ng used for the enti re
system.
Preferably, the invertor means are integrated in the
laminate structure in such a manner that the thermal energy generated
thereby during operation is delivered to the absorption means. This makes
it possible to keep the operating temperature of the invertor means low,
and the heat which is generated by the invertor means is added in a
positive manner to the thermal energy being delivered by the absorption
means.
The i nventi on wi 11 be descri bed i n more detai 1 hereafter
by means of embodiments of hybrid photovoltaic/thermal devices as
illustrated in drawings.
Figure 1 shows a schematic, sectional view of a part
of a preferred embodiment of a hybrid photovoltaic/thermal device according
to the invention.
Figure 2 shows a smai 1 er-seal e, schemati c, perspecti ve
view of the device of Figure 1, which comprises an essentially rectangular
housing.
Figure 3 shows a schematic, sectional view of a part
of another embodiment of a hybrid photovoltaic/thermal device according
to the invention.
Figure 4 shows a schematic, sectional view of a part
of yet another embodiment of a hybrid photovoltaic/thermal device according
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to the invention.
Figure 5 shows a schematic, sectional view of a part
of yet another embodiment of a hybrid photovoltaic/thermal device according
to the invention.
Figure 6 shows a schematic, sectional view of a part
of yet another embodiment of a hybrid photovoltaic/thermal device according
to the invention.
Figure 7 shows a schematic, perspective view of the
device of Figure 6, which comprises an essentially rectangular housing.
Figure 8 shows a schematic, simplified plan view of
amorphous photovoltaic means.
Figure 9 shows a schematic, sectional view of the
photovoltaic means of Figure 8.
Figure 10 shows a schematic, simplified side view of
crystalline photovoltaic means intended for use in the device according
to the invention.
Figure 11 shows a schematic view of a possible electric
connection of photovoltaic cells in the form of a laminate for use in the
device according to the invention.
Figure 1 shows a schematic sectional view, not to a
large scale, of a part of a panel-shaped hybrid photovoltaic/thermal device
according to a preferred embodiment of the invention, which is indicated
as a whole by numeral 1.
The device comprises a photovoltaic laminate 2
consi sti ng of photovol tai c cel 1 s 3 of a crystal l i ne s i 1 i con
materi al , whi ch
are mounted on a panel-shaped, sunl i ght transmi ssi ve carri er 4, for
exampl a
in the form of a glass plate. The photovoltaic cells 3 are affixed to the
carrier with interspaces between them by means of a sunlight transmissive
foi 1 or envel ope 5 made up of two el ectri cal 1 y i nsul ati ng 1 ayers of
pl asti c
material, for example hot adhesive material. The layers have a thickness
typically in the order of 0.5 mm or less, at least as regards the layer
with which the laminate 2 adjoins absorption plate 7.
The device 1 furthermore includes absorption means 6
shaped as a metal absorption plate 7, with tubes or pipes 8, which are
in thermal contact with the absorption plate 7, being present on one side
of the absorption plate 7. The figure shows only one tube or pipe 8. Those
skilled in the art will appreciate, however, that several tubes or pipes
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8 may be attached to the absorption plate 7, for example by means of a
soldered connection or a weld 9.
In accordance with the invention, the photovoltaic means
2 and the absorption means 6 are joined to form an integral unit by means
of an interposed bonding and heat conducting layer of plastic material
10. Sai d 1 ayer 10 may extend over the enti re area of the photovol tai c cel
1 s
3 or over a part thereof, for example only in the free areas between the
photovoltaic cells 3. It has become apparent that a synthetic glue of a
metal oxide-containing epoxy is very suitable for use in the invention.
The 1 ayer 10 may al so consi st of a gl ue whi ch contai ns
metal particles dispersed therein so as to improve its heat transfer
properties. The use of this "deformable" plastic, which provides a good
connection between the photovoltaic means 2 and the absorption means 6,
results in excellent heat transfer characteristics of the assembly ll.
The photovoltaic means 2 and the absorption means 6
which have been joined to form a single assembly 11 in this manner, are
supported with tubes or pipes 8 on an insulating layer 12, for example
a layer of glass wool, polyurethane foam and the like.
In most practical applications, a solar transmissive
cover pl ate 13, for exampl a a gl ass pl ate, i s di sposed opposi to and
spaced
from the photovol tai c means 2 . A thermal ly i nsul ati ng, sol ar transmi
ssi ve
fluid, for example ambient air, is present in the space 14 between the
cover plate 13 and the carrier 4.
Fi gure 2 i s a perspect i ve vi ew of the dev i ce 1 accordi ng
to Figure 1 disposed in an approximately rectangular housing 15, wherein
the device comprises an inlet 16 and an outlet 17 for fluid 18, such as
water, which flows through tubes or pipes 8 during use. The figure
furthermore schematically shows electric terminals 19 for delivering
electric energy generated by the photovoltaic means.
Those skilled in the art will appreciate, that device
1 is characterized by a very simple, robust and reliable construction.
The photovoltaic means 2 and the absorption means 6 can each be optimally
constructed in advance, tailored to specific requirements, after which
they can be glued together to form a single unit 11 in accordance with
the i nventi on . In th i s manner, i t i s poss i bl a to provi de a
constructi onal l y
simple, optimized and economically advantageous hybrid photovoltaic/thermal
device according to the invention: The operation of the device 1 is
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essentially as follows.
Sunlight or solar rays incident on the cover plate 13
reach the photovol tai c cel 1 s 3 v i a the carri er 4, wh i ch photovol tai
c cel 1 s
3 convert the energy of the incident sunlight into electric energy. The
exact operation of the photovoltaic cells is not relevant for a correct
understanding of the present invention. An explanation of the operation
of photovoltaic cells can be found in the book "Solar Cells" by M. Green.
Thermal radiation from the photovoltaic means 2 is
bl ocked by the gl ass pl ate 13, because i t i s opaque to i nfrared radi ati
on .
Also convection losses to the outside ambient air are suppressed by the
gl ass pl ate 13 . The gl ass pl ate 13 transmi is as much sunl i ght as possi
bl e,
of course, which sunlight is absorbed by the photovoltaic panel 2 and
absorption plate 7 and delivered in the form of thermal energy to fluid
18, for example water, which flows through the tubes or pipes 8.
The el ectri c energy generated by the photovol tai c means
2 is available on terminals 19. The water in the tubes or pipes 8, which
is heated via the absorption plate 7, circulates via the inlet 16 and the
outlet 17 in a forced or in a natural manner during operation, and it
generally passes through a heat storage vessel or container, for example
a boiler (not shown) which is known per se. The stored heat may be used
for heating bath and shower water, for example, or for heating purposes,
for example via a central heating system. Also other applications are
conceivable, of course.
Figure 3 is a sectional view, not to scale, of another
embodiment of a hybrid photovoltaic/thermal device according to the
invention, which is indicated as a whole by reference numeral 20. In this
figure, like elements or elements performing the same function as in the
embodiment according to Figure 1 are indicated by the same reference
numerals, and they will not be explained further.
A fl uid-tight 1 ayer or pl ate 21 i s di sposed on the
insulating layer 12 instead of the tubes or pipes 8 of the first embodiment
according to Figure 1, and the photovoltaic means 2 and the absorption
means 6 according to the invention, which form a single unit 7, are spaced
therefrom by some distance. Between the plate 21 and the absorption plate
7 is a space 22, which makes up a flow channel for a fluid such as water,
to which the absorption means 6 deliver their heat during use. Although
this is not shown in the figure, it will be apparent that space 21 is
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provided with inlet and outlet means for said fluid. See Figure 2.
Furthermore, stiffening elements (not shown), for example in the form of
partitions, may be disposed in the space 21 in the direction of flow of
the fluid.
Also in this case it applies that it is possible to
bui 1 d up a rel ati vely simpl a devi ce wi th the i ntegrated photovol tai c
means
2 and the absorption means 6 according to the invention, without using
complicated mechanical constructions. This is possible because the assembly
11, or its component parts, and plate 21, insulating layer 12 and cover
plate 13 can be mounted in the walls of a housing 15 in a simple manner.
See Fi gure 2. The pl ate 21 i s preferably made of a materi al whi ch i s
sufficiently strong for the purpose of the invention.
Figure 4 shows yet another embodiment, not to scale,
of the hybrid photovoltaic/thermal device according to the invention, which
is indicated as a whole by reference numeral 25. Also in this case it
applies that like elements or elements which perform a similar function
as described above are indicated by the same reference numerals.
This embodiment is based on the embodiment of Figure
3, wherein a fluid-tight, sunlight transmissive panel 23 is furthermore
disposed parallel to the carrier, spaced therefrom by some distance, in
such a manner that a space 24 i s formed between the panel 23 and the
carrier 4.
The spaces 22 and 24 now form two fl ow channel s, whereby
a fluid, for example water, can flow through both channels jointly or
through each channel separately. As regards space 24 it applies that the
fluid must be a sunlight transmissive fluid.
Arrows 26 indicate a possible direction of flow of fluid
i n the two spaces 22 and 24, whereby col d water, for exampl e, enters space
24 and exits space 25 as hot water, also in this case via suitable inlet
and outlet means (see Figure 2), of course.
Those skilled in the art will appreciate that a fluid-
tight, sunlight transmissive panel 23 as illustrated in Figure 4 can also
be used with the device of Figure 1. In the illustrated embodiment, the
photovoltaic cells 3 are by way of example disposed between two carriers
4, that is, in the form of a sandwich structure.
Yet another embodiment of a hybrid photovoltaic/thermal
device according to the invention, which is indicated as a whole by
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reference numeral 30, is shown, not to scale, in Figure 5. Again it applies
that like elements or elements having like functions as described above
are indicated by the same reference numerals.
In this embodiment, two separate absorption sections
are provided. A first section comprising the photovoltaic means 2, the
absorption means 6 and the plastic material 10 joined to form a single
assembly 11, and a second section comprising a flow channel 22, which is
made up of a fluid-tight layer or plate 21 provided on the insulating layer
12, with absorption means in the form of a further absorption plate 27
being spaced therefrom. As is shown in Figure 5, the assembly 11 is present
between the cover plate 13 and a further absorption plate 27, in such a
manner that a sunlight transmissive, thermally insulating space 28 is
formed between the two absorption sections, which space is filled with
a sunlight transmissive, thermally insulating fluid, such as air.
In this embodiment, the photovoltaic cells 3 are mounted
on the carrier 4 with interspaces which are dimensioned such that
sufficient sunlight can find its way from the cover plate 13, via the
assembly 11, to the further absorption plate 27. To this end, plastic
material 10 extends substantially under the photovoltaic cells 3, whilst
also absorption plate 29 of the absorption means 6 transmits sunlight in
the interspaces between the photovoltaic cells 3. A perforated absorption
pl ate 29 or the 1 i ke may be used for thi s purpose. In the case of a
transparent plastic material 10, said plastic material may extend over
the entire area between the photovoltaic means 2 and the perforated
absorption plate 29, of course.
Space 28 provides thermal insulation between the
photovoltaic means 2 of the assembly 11 and the second absorption section
made up of flow channel 22.
When a fluid 18 flows through tubes or pipes 8, the
photovoltaic cells 3 can be cooled separately, which has a positive effect
on the electric efficiency. The thermal conversion mainly takes place in
the second absorption section comprising the further absorption plate 27.
Fluid 18 may first flow through tubes or pipes 8 and subsequently through
the flow channel 22, if desired. That is, fluid 18 flows through the
absorption means 6 of the assembly 11 in cold condition.
Those skilled in the art will appreciate, that in this
embodiment a flow channel 24 may be formed above the assembly 11 as well,
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as is shown in Figure 4. Furthermore, the second absorption section may
be realized via an absorption plate fitted with tubes or pipes, as has
been described with reference to Figure 1.
It is also possible to use a combination of a bonding
plastic material 10 and mechanical clamping means 31, of course. Mechanical
clamping means 31 which are suitable for the purpose of the invention are
known per se in practice, and they do not require any further explanation
to those skilled in the art.
The advantage of this embodiment, which may also be
indicated by the term "double absorption", is that the operating
temperature of the photovoltaic means 2 can be lower than is the case in
the embodiments according to Figures 1, 3 and 4, because generated heat
is delivered to the fluid 18. In practice this means that this enables
a higher electric efficiency of the photovoltaic means than in the above
described embodiments.
Figure 6 is a sectional view, not to scale, of yet
another embodiment of the i nventi on, whi ch i s i ndi Gated as a whol a by
reference numeral 35.
Beneath the cover plate 13 are means 32 for
concentrating incident solar light on the cover plate 13 in the direction
of the photovoltaic cells 3.
In the illustrated embodiment, means 32 consist of
interconnected semicylindrical elements 33 of a sunlight transmissive
material, whose concave sides are disposed opposite the photovoltaic cells
3. The photovoltaic cells 3 are dimensioned such that they extend, with
spaces between them, in the longitudinal direction of and substantially
under the elements 33, all this as schematically illustrated in Figure
7.
The cover plate 13 and the means 33 may be separate
components, but they may also form a single unit. A thermally insulating
transparent fluid, for example ambient air, is present in the spaces 34
between the convex sides of the means 33 and the cover plate 13. Although
Figure 6 shows the embodiment of the absorption means 6 comprising tubes
or pipes 8, it will be appreciated that a construction comprising a flow
channel 22 as shown in Figure 3 is also possible in this embodiment. Also
in this case no significant constructional efforts are required.
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The absorpti on means 6 to be used i n the i nvent i on
preferably consist of a metal, such as steel plate, which may be provided
with an additional heat-absorbing coating, for example a heat-absorbing
paint.
The photovoltaic means 2 comprise photo-converters which
are sui tabl a for converti ng sol ar energy or sunl i ght i nto el ectri c
energy,
which photo-converters, also called solar cells, are of monocrystalline
or multicrystalline silicon, or comparable types. Suitable cells are,
for example, the 100 x 100 mmz or 125 x 125 mm2 n-type on p-type multi-
crystalline silicon solar cells which are marketed by Shell Solar Energy
B.U.
Figure 8 shows the typical structure of an amorphous
silicon cell 41, a cross-sectional view of which is shown in Figure 9.
The cell 41 comprises a stack made up of a solar
transmissive upper layer 36, generally glass, a transparent upper electric
contact 37, amorphous si 1 i con 38, a 1 ower el ectri c contact 39 and a
carri er
40.
As is shown in Figures 8 and 9, the amorphous silicon
cell comprises a thin structure which is built up of strips.
Figure 10 is a sectional view of a simplified structure
of a crystalline photovoltaic cell 42, which consists of a stack which
is made up of a first n-type silicon layer 43, a second p-type silicon
layer 44, a p-n transition 45 formed between the two layers, electric
contacts 46 provided on the layer 43, and an electric contact 47 provided
on the layer 44.
Generally, the electric efficiency of the cells of
crystal 1 i ne s i 1 i con i s twi ce as h i gh as that of cel 1 s of
amorphous s i 1 i con
(14% against 7%, respectively). For the purpose of the invention, the
crystalline cells are advantageous. However, it is noted that the use of
cells of amorphous silicon is possible with the double-channel embodiments
as shown in Figures 4 and 5.
Figure 11 shows a possible electric connection of
photovoltaic cells 42 to form photovoltaic means 2 for use in the
invention. The cells 42 are connected in series via electric conductors
50, thus providing electric terminals 48 and 49.
In a preferred embodiment of the invention, the
terminals 48, 49 are connected to invertor means 51, which comprise
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terminals 52, 53. The invertor means 51 convert the direct current energy
that i s generated by the cel l s 42 into al ternating current energy.
Invertor
means which are suitable for this purpose are known per se in practice,
and they do not require any further explanation.
It is preferred to use invertor means 51 which are
provided with a so-called "maximum power point tracker", by means of which
the total electric energy delivered by electrically interconnected
photovoltaic means 2, which operate at different temperatures, is higher
than that of photovoltaic means 2 which are interconnected without the
use of such a "maximum power point tracker". A description of such a
maximum power point tracker can be found in the literature on electronic
power conversion, so that it need not be explained in more detail herein.
The invertor means 51 are preferably integrated with
photovoltaic means 2 to form a laminate, whereby the heat generated by
the invertor means 51 is preferably delivered to the absorption means 6,
which has a positive effect on the thermal efficiency of the device.
For practical use, for example for household
applications, a plurality of hybrid photovoltaic/thermal devices or modules
can be combi ned i n one common hous i ng 15 to form a s i ngl a convertor dev
i ce
or solar collector.
Although the invention has been described in the above
by means of a number of embodiments, it will be appreciated by those
skilled in the art that the novel and inventive concept is not limited
to said embodiments.
