|Publication number||US20080190413 A1|
|Application number||US 12/028,517|
|Publication date||Aug 14, 2008|
|Filing date||Feb 8, 2008|
|Priority date||Feb 12, 2007|
|Also published as||EP2118582A1, WO2008098283A1|
|Publication number||028517, 12028517, US 2008/0190413 A1, US 2008/190413 A1, US 20080190413 A1, US 20080190413A1, US 2008190413 A1, US 2008190413A1, US-A1-20080190413, US-A1-2008190413, US2008/0190413A1, US2008/190413A1, US20080190413 A1, US20080190413A1, US2008190413 A1, US2008190413A1|
|Inventors||Gregory Martin Grochola|
|Original Assignee||Solexus Pty Ltd.|
|Export Citation||BiBTeX, EndNote, RefMan|
|Referenced by (7), Classifications (21), Legal Events (1)|
|External Links: USPTO, USPTO Assignment, Espacenet|
The present application claims priority from Australian Provisional Patent Application No 2007900662 filed on 12 Feb. 2007, and Australian Provisional Patent Application No 2007901492 filed on 21 Mar. 2007, the contents of which are incorporated herein by reference.
The present invention relates to the use of solar collectors to collect energy in the form of heat from solar radiation for uses such as space heating and hot water supply for residential, commercial or industrial buildings.
Presently, there is growing concern about the global warming effects caused by the burning of fossil fuels, such as for example in fueling space heaters and domestic hot water systems. The increasing environmental costs associated with such effects are expected to force governments around the world to eventually introduce taxes on the burning of fossil fuels or carbon trading schemes, both of which would increase the cost associated with the burning of fossil fuels.
The use of incident solar radiation for the above mentioned applications is an obvious and fitting alternative to burning fossil fuels and yet presently, such systems are not used extensively. Glass/metal solar hot water system have found some use, but yet even these systems are mostly subsidized by government rebates due to their high up-front costs. The average pay-back time for such systems can be 5 to 10 years and yet glass/metal collectors have an average lifetime of only around 15 years. Needless to say the recent spike in metal prices has not help the economic viability of such systems, since they make extensive use of copper and aluminum.
There have been numerous efforts to use plastic in the production of solar collectors due to lower material costs, yet for a variety of reasons plastic collectors have not been widely commercially produced or are not commercially competitive with glass/metal. These are mainly due to well known limitations of plastic when used for glazing and especially absorbers. The main limitation concerns the exposure of absorber components, or other structural components of the collector to extreme temperatures under stagnant conditions, where the collector is exposed to full sun conditions and where the internal cooling fluid does not flow. Inner stagnant temperature can easily reach upwards of 160° C. for flat solar collectors which have selective surface coatings to maximize absorption while minimizing heat loss. Panel exposure to stagnant conditions is common and can take place during installation or pump, controller or value failure and can easily cause catastrophic damage to plastic collectors or severely limit the collector's life time. This can mandate the use of performance plastics for absorbers and associated components which can withstand these high temperatures but unfortunately such performance plastics are much more costly.
There have been many attempts at limiting stagnant temperatures in plastic solar collectors. The simplest of these allow significant heat loss from the top face of the panel through the use of non-selective coatings for the absorber and glazing or the outright lack of a glazing cover as in pool type solar collector, or the lack of underside insulation. Unfortunately, all of these limit the efficiencies of such solar panels and hence limit their use specifically in winter. More sophisticated passive methods include the use of materials which change their transmission of light as a function of temperature, but these have not found use as solar collector components. Many active control methods can and have been envisaged, such as for example ventilation systems or the mechanical turning of reflector components so that the sun is rejected back out into the atmosphere instead of onto the designated absorber. Such strategies have the obvious disadvantage of using complex moving parts and associated monitoring and controller systems which are prone to high maintenance costs and eventual failure.
The present invention provides a low profile solar collector, for collecting solar energy as heat, while limiting possible peak stagnant temperatures in the collector in summer months, comprising:
(a) a plurality of reflective elements, having respectively first and second edges, the reflective elements being arranged in a fixed offset parallel array, to form a staircase of upwardly facing reflective surfaces in use;
(b) an absorber element having an exposed surface located between each pair of reflective elements the exposed surface being located substantially between the first edge of one of the adjacent pair of reflective elements and the second edge of the other of the pair of reflective elements, and the exposed surfaces being disposed at an angle to each of the reflective elements to thereby form a fixed parallel array of exposed surfaces of the absorber elements; and
(c) a transparent top cover extending over the reflective and absorber elements;
such that in use the reflective elements are oriented in a first generally horizontal orientation with incident sunlight passing through the top cover and falling directly onto the exposed surface of each absorber element and/or onto a reflector adjacent to an exposed surface of one of the absorber elements and from which it may be reflected onto the respective exposed surface.
Typically the collector panel will be mounted on a flat supporting structure, such as a roof, preferably facing the solar noon sun, where the roof has a pitch p, such that the upper edges of the absorber elements describe a line at an angle p to the horizontal (see
The solar collector will preferably include a housing of which the top cover forms part, such that the housing encompasses the array of reflectors and absorber elements.
The sun exposed surface area of the absorber elements (which are not necessarily flat) are preferably angled such that a normal of the sun exposed surface area (or average normal if the sun exposed surface is not flat) makes a larger incident angle with the solar noon sun radiation in midsummer than in midwinter or mid spring/autumn (see
The reflective elements may be made from materials including, (but not limited to) polished sheet metal which can be placed on or attached to the connecting absorber elements, polycarbonate mirror which can be attached to the glazing or absorber elements, a layer of vacuuming chroming or plating deposited directly on certain areas of the absorber elements, particularly if those areas are substantially flat, or by the addition of a thin sheet of reflective plastic like aluminized MylarŪ to the absorber element areas, whereby an aperture is defined between each adjacent pair of reflective elements, the aperture being defined by the first edge of one of the pair of elements and the second edge of the other of the pair of elements.
Preferably, the exposed absorber element surface is blackened and hence has a high solar absorptivity.
Embodiments of the solar collector panel may include one or more transparent top covers which may be formed of a polymer material or glass. Preferably the material is a low cost material, such as a low cost sheet of transparent polymer material or a low cost glass. The top cover material is preferably clear but may partially or completely block ultra violet light transmission. The solar collector may include a plurality of top covers separated by sealed air gaps to reduce heat transfer through the top covers.
In embodiments of the solar collector the fixed parallel array of absorber elements are of an elongate rectangular shape and run the length of one horizontal dimension of the collector. When the solar collector is mounted in an in use position, the orientation of the solar collector is preferably such that these plastic absorber elements extend in a substantially East-West direction. The plastic absorber structure can be manufactured as a single piece, containing these joined absorber elements, or can alternatively be manufactured as separate absorber elements and then arranged or connected in the parallel array.
The fixed parallel array of rectangular reflective elements may be substantially of elongate rectangular shape and also run the length of a horizontal dimension of the collector (the same horizontal dimension as the plastic absorber elements). Therefore again the reflective elements will preferably extend in a substantially East-West direction in use, where reflective elements and absorber elements are arranged to alternate in the assembly; with the reflective elements forming a substantially step-like appearance as viewed in the direction down the pitch of the roof with the reflective elements forming the treads and the absorber elements forming the risers of the steps.
In one embodiment the collector may be mounted such that the lengths of the absorber and reflector elements are at a slight angle to the horizontal in the range of 1°-5°.
Preferably the long edge of one reflector and the long edge of a second reflector form an elongated planar rectangular aperture through which an absorber area or face is exposed to direct and reflected solar insolation, and where this exposed area or face is preferably flat and preferably coincides with the planar rectangular aperture and hence can protrude slightly forward of or be slightly behind the planar rectangular aperture. The planar rectangular aperture and the exposed area or face is also preferably tilted downward toward the horizon at an angle so that the direct midsummer solar noon sun strikes the area or face (or penetrates the rectangular aperture) with a large incident angle, while the direct midwinter or midspring/autumn (equinox) solar noon sun strikes the area or face at a smaller incident angle;
Each sun exposed surface area or face has in front of it (as viewed down the pitch of the roof or supporting structure) a corresponding reflector which is preferably fixed at a small angle, r rotated toward or away from the corresponding sun exposed surface area, the purpose of the corresponding reflector is to reflect winter solar insolation onto the corresponding sun exposed surface area of the absorber element;
The angle, r of each such corresponding reflector is dependent on a roof pitch, p (assuming the collector panel is mounted parallel to the pitch of a roof) and the latitude at the place of installation. The angle r for a particular roof pitch and latitude may be in a range having limits defined by Equation 1 and Equation 2 below. The values r and p are preferably chosen such that the majority of the winter solar radiation impinging upon the reflective elements is reflected upon the corresponding sun exposed surface area, for the purposes of concentrating wintertime radiation, while rejecting back out into the atmosphere all of, or some portion of the summer solar radiation, for the purposes of limiting summertime stagnant temperatures.
The absorber structure has at least one fluid channel underneath the sun exposed surfaces in thermal communication with the exposed surface of the absorber elements and optionally underneath the reflector areas. These channels may run the length of the panel (parallel with the adjacent edges of the reflectors and absorber elements) or alternatively they may run perpendicularly to the reflectors (up the pitch of the roof) or at any angle. Preferably each absorber element has at least one internal fluid carrying channel extending underneath the exposed surface thereof and—in thermal communication with the exposed surface to carry heat away to be stored or otherwise used. These channels can also run the length of the panel (parallel with the reflective elements and absorber elements) or alternatively perpendicular to the reflective elements or at any such angle.
When the fluid carrying channels are such that they also run underneath the reflector areas then it may be advantageous in certain situations to additionally allow significant thermal communication between the reflector areas and the fluid carrying channels below such that any residual heat on the reflector areas may is also transferred to the fluid.
The collector includes an inlet passage to introduce the heat transfer fluid into the collector panel and the fluid channels and an outlet passage to drain the heat transfer fluid from the channels and the collector panel.
Preferably the absorber element (incorporating the fluid channels) is to be formed out of a polymer material such as for example a plastic material.
The plastic absorber elements may be UV stabilized and/or painted or treated with a selective coating on the sun exposed surface areas or left untreated. The absorber elements may also have a thin surface selective film attached to the sun exposed surface areas. The glazing may also be UV stabilized and made to block UV radiation and may also be treated with a non-reflective or selective coating.
In one preferred embodiment, the top glazing cover and the absorber assembly are connected by sliding engagements comprising an undercut channel and a co-operating ribbed projection having a complementary cross sectional shape to that of the channel. In this arrangement, each absorber element includes one half of the engagement namely one of the projection or the channel and an adjacent surface of the top glazing cover is provided with the respective co-operating part which forms the other half of the engagement. Preferably each absorber element will include an undercut channel and the adjacent surfaces of the top glazing cover are provided with the respective co-operating ribbed projections.
Preferred embodiments may also include a bottom cover connected to the absorber assembly by sliding engagements similarly comprising an undercut channel and a co-operating ribbed projection having a complementary cross sectional shape to that of the channel. In this arrangement, each absorber element again includes one half of the engagement namely one of the projection or the channel and an adjacent surface of the bottom cover is provided with the respective co-operating part which forms the other half of the engagement. Preferably each absorber element will include an undercut channel and the adjacent surfaces of the bottom cover are provided with the respective co-operating ribbed projections.
The absorber elements of the solar collector may have a midsummer solar noon sun acceptance aperture (see
The reflective elements may also reduce heat loss from the absorber element fluid channel or channels which can run substantially underneath the reflective areas. To this end the reflectors may be made from a material with a very low emissivity.
The possible angles of the stepped reflective elements are determined by the pitch of the roof and the latitude of the place of installation and may be, for any particular pitch and latitude, in the range of values between those given by the equations 1 & 2 below:
Where r is the angle of the reflective element, w is the angle of the solar noon midwinter sun at the particular place of installation and p is the pitch of the roof (see
Equation 1 gives the lower limit for the reflector angle for systems which are substantially winter only collectors and which may need to be installed on roofs which are oriented slightly off solar noon (i.e. which need to maximize the capture of lower winter sun angles). Such applications do not require substantial summertime collection.
Equation 2 gives the upper limit for the reflector angles where maximum heat collection takes place near the Spring and Autumn equinox points. However, the embodiment still entails significant summertime rejection and hence protection against summertime stagnant temperatures. Reflector angles near the upper range correspond to installation conditions where a substantial amount of heat is still required in the summertime, such as for domestic hot water systems only.
The preferred reflector angle for installations where the collector faces the solar noon sun is that angle where the midwinter solar noon sun hits the outer edge of the reflector and is reflected to the top edge of the absorber face. The equation for this value of r is:
Embodiments of the solar collector may make use of surface selective coatings and insulation underneath the absorber structure while still maintaining summer time stagnant temperatures below destructive levels such that the use of inexpensive non-performance plastics is acceptable.
Where a solar collector covers a substantial part of the solar noon facing roof it may also help to lower roof cavity temperatures and hence internal house temperatures in summer by providing a good form of reflective and non-reflective insulation on the roof.
A preferred solar collector may collect more energy in winter or a relatively constant supply of heat energy in the four seasons and it may thereby avoid overheating of storage tank water and hence avoid the need for an active heat preventative provision in the summer. Such solar collectors may also provide a flatter heat collection curve throughout the day, eliminating sharp collection peaks especially in the summer months.
Although some plastics may be less robust materials, a plastic collector may still provide a longer lasting collector. Such collectors, for example, may not suffer from problems including internal corrosion or clogging with deposits from use of hard water, or damaged due to freezing of water inside inflexible metal piping, as do metal collectors. Because the top glazing cover may need periodic replacement solar collectors may have a provision for the easy replacement of this plastic cover which substantially covers the entire collector and which blocks a substantial amount of UV radiation.
Solar collectors may be sufficiently light that a slim-line roof supported collector may take advantage of a typical roof as an existing flat supporting structure and hence to obviate the need for any extensive internal or external collector supporting or stiffening structures. Such a collector might use a minimum of materials in construction resulting in a lower cost of production.
Embodiments of a solar collector will now be described, by way of example, with reference to the accompanying drawings in which:
The preferred solar collector 11 is a low profile panel which absorbs solar energy and converts it to heat. A passive or non-mechanical method is used for limiting peak stagnant temperatures in the collector in the summer months such that low cost materials may be employed which could otherwise potentially be destroyed if the peak stagnant temperature was not limited.
The collector panel 11 is substantially flat and has major components such as absorber elements 10 and top glazing cover formed of plastic or other low cost materials.
The preferred solar collector is proposed to be mounted on a flat supporting structure, such as a roof, having a pitch of up to 60° but preferably between 10° and 50° measured from the horizontal. The solar collector 11 is preferably mounted to face the direction of the solar noon sun (i.e. due North in the Southern Hemisphere or due South in the Northern Hemisphere), but may be mounted at a small angle to one side of the direction of the solar noon sun without significant loss of efficiency.
Cross-sectional drawings of the structures of various embodiments are shown by way of example in
At least one transparent (clear) plastic glazing top cover 14 is located over the absorber structure 28 to retain heat and protect the absorber structure.
The long edges of pairs of adjacent reflectors form an elongated planar rectangular aperture through or within which an absorber area or face 21 of an absorber element 10 is exposed to direct and reflected solar insolation. This exposed area or face 21 is preferably flat and preferably coincides with the planar rectangular aperture and hence can protrude slightly forward of or be slightly behind the planar rectangular aperture. As seen in
The angle, r of the reflective elements is dependent on the roof pitch, p (refer again to
While the solar collector can be adapted to a variety of heat absorber technologies, in the preferred embodiment each absorber element has at least one inner fluid carrying channel 22 to which heat is transferred and carried away to be stored, and where these channels run underneath the sun exposed absorber areas 10 and can also optionally run underneath the reflective areas (see
Proposed embodiments of the solar collector at first may seem counterintuitive since the collector efficiency is deliberately limited during the best solar collecting season namely, summer, while nearly all previous solutions seek to increase efficiencies for every season. Furthermore, with the present collector nearly twice the panel area is needed to collect the same amount of energy over an entire year as a standard flat solar panel will collect over a year, hence this may also seem counterintuitive. For the present solar collector it must be realized that firstly, for typical situations the need for hot water in wintertime is much greater than the need in summertime and hence if we had a large enough panel installation to supply sufficient wintertime hot water (for domestic heating and the hot water service) then we would have much more than enough hot water in summer and hence we can easily sacrifice summertime efficiency without approaching or dropping under the maximum summer hot water requirement. Secondly, it must be realized that a typical hot water solar flat panel installation today takes up much less roof area than is available, and hence a typical roof area can accommodate a much larger panel. Thirdly, most prior art units focus on maximizing heat collected per square meter, while it must be realized that the sun's energy per square meter is of course free, and while the available roof area (or supporting structure) for a typical house/building is generally already existent and of a size that could accommodate larger collectors that commonly in use today. Therefore there is no significant extra cost associated with supporting a larger panel or more panels, hence the design of the present solar collector focuses on cost per unit of heat collected, making up the shortfall in heat collection over the entire year by increasing the area of the collector. By employing a much cheaper method of construction for the solar collector, this approach makes possible a significantly lower cost per unit of heat.
Preferred collector arrangements of this type can potentially produce a solar panel with a midsummer solar noon sun acceptance aperture (refer to
Hence, it becomes possible to produce a passive solar panel of this type with the dual benefit of preventing overheating in the summertime while concentrating wintertime insolation. While the proposed panel does significantly concentrate wintertime insolation and hence could run into winter time stagnant temperature issues, it must be realized that for the majority of places on earth, the wintertime temperatures are much lower than summertime temperatures and the winter sun's radiation is lower in the sky and as such has more atmosphere to go through and hence is of a lower concentration than the summer's sun, and thirdly for the envisaged typical installation (for a roof pitch around 25-35°) the winter's sun strikes the entire collector at a higher incident angle than during other seasons. As such this collector for the first time allows the use of glazing (or double glazing) with effective surface selective coatings and very good underside insulation in combination with the use of inexpensive non-performance plastics in the majority of the structure without any concerns over summertime stagnant temperatures. This has the potential to provide a solar panel which is very efficient in the wintertime while purposefully being less efficient during summer, at a much lower cost than traditional flat plate collectors.
Using the principles outlined above it becomes possible to construct a solar collector which can collect more energy in winter or a relatively constant supply of heat energy in the four seasons. As an added advantage the collector may avoid overheating of storage tank water and hence the need for an active heat preventative provision in the summer, and thereby potentially lowering total system costs.
It also becomes possible to provide a flatter heat collection curve throughout the day, eliminating sharp collection peaks especially in the summer months when this is a more commonly a problem.
The panel may also be constructed to serve the purpose of providing a good form of reflective and non-reflective insulation on the roof and hence help to lower roof cavity temperatures and hence internal house temperatures in the summer, where the solar collector covers a substantial part of the solar noon facing roof.
By use of plastic components it also becomes possible to construct a collector panel which is cheaper and much longer lasting and which does not corrode or internally clog with deposits from use of hard water, or become damaged due to freezing of water inside inflexible metal piping as do metal collectors. Toward this end it is likely that the top glazing cover may need periodic replacement. For this reason it is proposed to make provision in preferred embodiments for the easy replacement of this plastic cover, which substantially covers the entire collector and which can block a substantial amount of UV radiation.
By constructing a slim-line roof supported panel it may also be possible for the collector to take advantage of a typical roof as an existing flat supporting structure and hence to obviate the need for any extensive internal or external collector supporting or stiffening structures and as such to provide a collector which uses a minimum of materials in construction and which substantially lowers the cost of the collector and its installation.
If the fluid medium consists of air, then the air can run preferably through the parallel arrangement of substantially east-west running channels 22 and the channels 43 in front of the sun exposed surface absorber areas 21. Initially the air can enter the collector through the first channels 43 in front of the absorber face/reflector structure, then through the absorber sun exposed face 21 (which is in this instance is porous to air) and then through the second set of channels 22 underneath the heat absorbing surfaces in the same direction as the incoming air and exiting on the opposite side of the collector. Alternatively, air can enter at the bottom of the collector, but in the front section of the absorber/reflector structure, again moving through the absorber sun exposed face 21 (which is porous to air) and exit out of the collector from the underneath absorber/reflector structure at the top of the collector.
The examples of solar collector panels illustrated in
It will be appreciated by persons skilled in the art that numerous variations, combinations and/or modifications may be made to the invention as shown in the specific embodiments without departing from the spirit or scope of the invention as broadly described. The present embodiments are, therefore, to be considered in all respects as illustrative and not restrictive.
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|U.S. Classification||126/623, 126/634, 126/684|
|International Classification||F24J2/10, F24J2/50|
|Cooperative Classification||F24J2/202, F24J2/4621, F24J2/50, Y02B10/20, F24J2002/1014, F24J2/16, Y02E10/44, F24J2/51, F24J2002/503, F24J2/0488|
|European Classification||F24J2/20C, F24J2/04F, F24J2/46B20, F24J2/50, F24J2/51, F24J2/16|
|Feb 23, 2008||AS||Assignment|
Owner name: SOLEXUS PTY LTD, AUSTRALIA
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNOR:GROCHOLA, GREGORY MARTIN;REEL/FRAME:020549/0005
Effective date: 20080206