MINI SOLAR ISLANDS FOR HOUSEHOLD NEEDS

Abstract

An improved concentrated solar power collector, includes a frame intended to be mounted rotatable to a stand surface, according to a first axis perpendicular to the stand surface,at least one solar concentrator fixed on the frame at a desired angle determined so that the solar concentrator is oriented at between 20 and 70° with reference to the stand surface and reflect or direct sunlight upwardly toward a heat pipe, connected to a steam network including a steam tank carried by the frame,wherein the frame is able to rotate automatically to provide an azimuth-tracking of the solar concentrator following the azimuth of the sun,wherein the steam tank works with a diffusion absorption cooling machine or a hot water heating arrangement, feeding a warm-water tank and an ice/cold-water tank, the warm-water and ice/cold-water tanks being directly connected to a house.

Description

TECHNICAL FIELD

The present invention relates to the field of exploitation of solar energy. It more specifically concerns a platform allowing optimal collection of solar energy, intended to be used for household needs.

STATE OF THE ART

Solar energy is more and more associated with photovoltaic panels generating electricity. Based on this paradigm, many activities have been launched in a huge effort to deploy this kind of technology. But all these efforts have not been able to solve three principal problems:

• • what happens if there is no sun, at night?
  • how does one address the summer/winter seasonal changes in solar radiation?
  • how are the high costs justified in view of the small energy which can be generated?

On another hand, it can be remarked that nowadays, in the major categories (i.e. households, industry and transport) only about 15% of the total energy is used in the form of electricity. All the rest is thermal energy.

Patent applications PCT/IB2008/002723 and PCT/IB2009/000055 which are expressly incorporated herein by reference, disclose large solar platforms, with a diameter up to several kilometres, intended to exploit solar energy. Such huge installations are preferably implemented in deserts or on seas or lakes, i.e. in large free areas. As a consequence, heat produced in such installations has to be transformed in steam and then in electricity to be carried to inhabited area.

The application US61/119,838 which is expressly incorporated herein by reference discloses a cooling machine, based on a diffusion absorption system, to provide a very efficient cooling.

The present invention aims to propose improved installation adapted to exploit advantageously solar energy in inhabited area.

DESCRIPTION OF THE INVENTION

A first aspect of the invention is illustrated in FIG. 1. It concerns an improved concentrated solar power collector. It comprises a plate able to rotate according to a first axis, said plate being advantageously circular to be easily rotated without modification of its bulk. Several sets of solar concentrators, or reflector panels, are arranged on the plate. Each set comprises a frame, such frame having preferably a rectangular shape, one of its sides being parallel to the plate. According to a first embodiment shown in FIG. 1, each frame is mounted rotatable according to a second axis parallel to the plate. This second axis may coincide with a side of the frame. Each set holds, upwards in its middle, a heat pipe, connected on a first end, to a water supply pipe and, on a second end, to a steam pipe.

Said water supply pipe and said steam pipe are arranged on the frame preferably, in such a manner that the frame is able to rotate according to the second axis, without being disturbed by these pipes. They may comprise a flexible portion in the area of the axis or being connected to a water supply network and to a steam network, by a pipe portion coinciding with the second axis.

For each set, each of the reflector panels is fixed at a desired angle on the frame, so that all of the reflector panels reflect or direct sunlight upwardly toward the heat pipe. This concentrates the reflected solar radiation on the heat pipe and transforms water in steam.

The concentrators of a set can therefore be rotated around two different axes:

• • a first axis is perpendicular to the plate and goes, preferably, through the centre of the plate, and
  • a second axis is comprised in a plane parallel to the plate.

A skilled person can arrange this second axis in different positions. This allows the reflectors to be orientated optimally regarding the incident angle of the solar radiations. Those skilled in the art may consider several actuation means in order to have the frames rotated and provide the second rotation axis. A jack may be used for example, actuating directly on the frames.

It can be remarked that, as shown on FIG. 1, the sets may preferably be arranged in parallel rows. The sets of a row may be arranged on a single frame and share feeding water and steam pipes.

The frames and the plate may be rotated in order to improve the solar radiation collection. Particularly, the orientation of the concentrators on the frame may be chosen and fixed in an optimal manner, according to specific conditions of a place (i.e. geographic latitude). One can also envisage having the frames oriented in a fixed and optimized manner on the plate. The orientation can also be punctually modified, for example, between a summer and a winter positions. The orientation of the frames may also be adapted continuously, according to several tracking methods. One can envisage an azimuth tracking, with an automatic rotation of the plate, following the azimuth of the sun, with the reflector panels arranged horizontally on the frame. One can envisage an elevation tracking, with an automatic rotation of the frames following the elevation of the sun. One can envisage an optimized azimuth tracking, with an automatic rotation of the plate, following the azimuth of the sun, but with an optimized fixed elevation angle. Finally, one can envisage an azimuth/elevation tracking with automatic two axis rotations: of the plate, following the azimuth of the sun, and of the frames following the elevation of the sun.

Thus, the concentrated solar power collector may be fixedly oriented or, according to the tracking parameters to be used, may be able to rotate around 1 or 2 axes. Graphics presented in FIGS. 2-5 show how the method of orientation of the concentrators affects the efficiency of the collector and the irradiated solar energy, for different geographic latitude and for different seasons.

The following abbreviations are used in these graphics:

• • 0° fix: a collector without any tracking,
  • fix: a collector without any tracking, but with an optimized fixed orientation of the reflectors,
  • az tracking: azimuth tracking, as explained above,
  • el tracking: elevation tracking, as explained above,
  • opt. Az. tracking: optimized azimuth tracking, as explained above,
  • az/el tracking: azimuth/elevation tracking, as explained above.

FIG. 6 presents a table illustrating several figures for several technical solutions of the state of the art for exploiting solar energy (i.e. photovoltaic-PV-panels), compared to collector according to the invention. The table shows results obtained for a collector with an optimized fixed orientation of the reflector panels and for a collector with an optimized azimuth tracking.

Graphics and table of FIG. 6 demonstrate that the higher north the geographic position is, the more two effects become apparent:

• • the seasonal differences (winter-summer) become larger,
  • the differences between the tracking methods become larger too.

On the one hand, it can be remarked that the main energy consumption in private households switches from cooling in the south to heating in the north. In the north, peak consumption coincides with the time of minimal solar radiation. In the south, the inverse is true, as peak consumption occurs in summer. The main energy form switches form electricity in the south for air-conditioning to heat supply in the north for heating and for warm-water. Of course, these last remarks concern northern hemisphere and north and south need to be interchanged in the southern hemisphere.

On the other hand, table of FIG. 6 shows that a collector with an optimized azimuth tracking allows obtaining a very good rate of energy per square meter, for a very interesting cost. Compared to a collector with azimuth/elevation tracking, the ratio cost/performance is much more interesting.

Such collectors as described above can be relatively small, with a diameter of 200 meters for the plate. Such dimensions allow this kind of collector to be implemented in inhabited area, or in immediate vicinity of inhabited areas, like illustrated by FIGS. 7 and 8. According to the invention, this kind of collectors, advantageously implemented with an optimized azimuth tracking, can be combined with Diffusion Absorption Cooling Machine (DACM), as described in US61/119,838 application, incorporated herein by reference, and illustrated in FIG. 9. It can also be combined with a hot water heating installation.

With tanks, either for warm-water or for ice/cold-water, connected to the DACM and to a network for feeding to houses, it is possible to provide hot and cold water, either for heating houses of a small city or of a district in winter or for cooling them in summer. These tanks provide cool/heat reserve for days with insufficient irradiation.

Performance provided by collectors described above allows considering the implementation of small sized individual collectors, directly on the roof of houses. Actually, a 3-bedroom apartment of 100 m², using about 100 kWh per square meter and per year, consumes about 10′000 kWh per year, i.e. 27 kWh per day (mean, for the main energy requirements, i.e. warm water and heating or cooling). The daily consumption in winter is about twice the mean, i.e. 55 kWh per day. A collector with an optimized azimuth tracking collects around 3000 Wh/m²/day. That means that only 18 m² of reflectors are needed. This installation can be completed with

• • energy storage of hot water for heating and warm water supply: 88 kWh of energy can be stored in one cubic meter (100° C., 1 atm), and
  • with energy storage of cold water for cooling: 95 kWh of “cold” energy can be stored in an ice-water mixture of one cubic meter (75% ice, 25% water, 0° C., 1 atm).

Such an apartment would need an insulated water storage tank (for 2 days without any sun) which can store 170 kWh, i.e. around 2000 liters for heating and warm water.

Based on this analysis showing that a concentrated solar power collector arranged with an optimized azimuth tracking provides a very advantageous cost/performance, the invention proposes another embodiment illustrated in FIGS. 10 and 11, particularly adapted for household needs. It comprises a frame, supporting at least one solar concentrator. The solar power collector illustrated comprises two solar concentrators. Each of them is built with a reflective foil, arranged with a parabolic shape, in order to reflect sunlight upwardly toward a heat pipe, similar to the heat pipe described above. This solution is very interesting for a low cost concentrated solar power collector to be used in a private area. Moreover, thanks to the shape of the reflective foil, it is possible to arrange the heat pipe very near from the frame. The device is therefore less sensitive to blasts of wind.

As explained previously, the solar concentrators are able to rotate according to an azimuth tracking mode. The reflector panels are oriented on the frame with a fixed and optimized angle while the frame is able to rotate on a stand surface, where the concentrated solar power collector is installed. The optimized angle is chosen so that said reflector panels are oriented at between 20 and 70° with reference to the stand surface, according to local specific conditions.

In order to achieve this rotation of the frame, the embodiment shown in FIGS. 10 and 11 proposes that the frame comprises a circular chassis, equipped with wheels mounted at the periphery of the chassis. The wheels can roll in the bottom of a circular groove arranged on the ground of the stand surface where the collector is installed. In order to guide the chassis, some wheels can be disposed horizontally and cooperate with the sides of the circular groove. A drive motor driving at least some wheels, is preferably arranged on the frame. A skilled person may consider another driving means able to drive the rotation of the frame.

The frame carries preferably any elements necessary to produce and store steam to be used further. More precisely, a steam tank is directly located on the frame and directly connected to the heat pipe. An adapted insulation is arranged between the steam tank and the housing of the collector. This tank provides means to store the heat produced by the reflector panels. In addition, it improves the stability of the concentrated solar power collector, by ballasting the frame. A heat exchanger is directly mounted inside the steam tank and is connected outside by pipes passing through the collector at the centre of its bottom, with reference to its rotation axis. A rotating joint is arranged between the pipes and the collector.

This heat exchanger can simply be connected to a hot water network of a household, or to a DACM cooling machine connected to the concentrated solar power collector.

This embodiment provides a very compact, low cost and high performance concentrated solar power collector that can be easily installed in inhabited areas, especially on flat roofs of houses or buildings. It can be remarked that such a frame can also advantageously be used for supporting photovoltaic panels. These panels can be oriented with an optimized angle and track the azimuth of the sun.

Claims

1-4. (canceled)

5. An improved concentrated solar power collector, comprising a frame intended to be mounted rotatable to a stand surface, according to a first axis perpendicular to the stand surface,at least one solar concentrator fixed on the frame at a desired angle determined so that said solar concentrator is oriented at between 20 and 70° with reference to the stand surface and reflect or direct sunlight upwardly toward a heat pipe, connected to a steam network comprising a steam tank carried by said frame,

6. An improved concentrated solar power collector, comprising a frame intended to be mounted rotatable to a stand surface, according to a first axis perpendicular to the stand surface,at least one solar concentrator fixed on the frame at a desired angle determined so that said solar concentrator is oriented at between 20 and 70° with reference to the stand surface and reflect or direct sunlight upwardly toward a heat pipe, connected to a steam network comprising a steam tank carried by said frame,

7. An improved concentrated solar power collector, comprising a plate able to rotate around a vertical axis, perpendicular to said plate,several sets of solar concentrators, arranged in rows on said plate, each set being arranged on a frame mounted rotatable according to a first axis parallel to the plate,

8. Method of providing a building with warm-water and cold-water, which comprises: arranging the concentrated solar power collector according to claim 5, on the roof of the building, said warm-water and ice/cold-water tanks being located in the building or on the roof of the building and being operatively connected to a network for providing at least this building with warm-water and cold-water.

9. Method of providing a building with warm-water and cold-water, which comprises: arranging the concentrated solar power collector according to claim 6, on the roof of the building, said warm-water and ice/cold-water tanks being located in the building or on the roof of the building and being operatively connected to a network for providing at least this building with warm-water and cold-water.

10. Method of providing a building with warm-water and cold-water, which comprises: arranging the concentrated solar power collector according to claim 7, on the roof of the building, said warm-water and ice/cold-water tanks being located in the building or on the roof of the building and being operatively connected to a network for providing at least this building with warm-water and cold-water.