WO2011012917A1

WO2011012917A1 - Photovoltaic-cooling-power generator to improve efficiency of photovoltaic power plants

Info

Publication number: WO2011012917A1
Application number: PCT/IB2009/006376
Authority: WO
Inventors: Frank Flechsig; Fridolin Voegeli; Thomas Flechsig
Original assignee: Nanodef Ag
Priority date: 2009-07-27
Filing date: 2009-07-27
Publication date: 2011-02-03

Abstract

The present invention describes a photovoltaic-cooling-power-module. It keeps the photovoltaic cells at low operating temperature by transporting away the unwanted heat generated in the process. This heat transport is done via liquefied gas that drives a turbine and generator and produces additional electricity. The overall electric power generated by this module is about 5-6 times more than in present state-of-the-technology un-cooled photovoltaic modules.

Description

PHOTOVOLTAIC-COOLING-POWER GENERATOR

TO IMPROVE EFFICIENCY OF PHOTOVOLTAIC POWER PLANTS

FIELD OF THE INVENTION

The present invention relates to photovoltaic and solar panel systems that generate electricity and warm water from the sun's irradiation. The invention secures a light-to-current or light-to-heat conversion in an optimized operating point with highest possible efficiency (some 400% over today's highest yields).

BACKGROUND OF THE INVENTION

Modern communities have become more and more aware of our generation's task to apply renewable energy where ever feasible, anyway in the low power applications for domestic lighting, computing, entertainment, communication, heating, cooling, etc.

The free irradiation from the sun, on a bright day in Europe some 1000 W/m2 with good exposition of the collecting panel towards the sun, is a good incentive to save locally quite some expensive electricity or gas that both have been transported from far away power plants, where as every saddle-roof has some 20-40 m2 or more that could be used for a medium-to-high yield exposure. So the goal must be to produce as much electrical and heat energy locally, in order to "save planet earth".

Governments promote and subsidize large and family-home photovoltaic power plants in order to push the technology from the low 14% theoretical conversion efficiency to higher yields, and to encourage industry to build larger and larger production facilities, in order to slash prices by moving into economy of scale.

However the last years have been frustrating for all private and industrial customers and their governmental promoters: No advances in technology, no better applications, only dishonored sales promises and pure fraud by the manufacturers of the systems: They sell us these photovoltaic cells by the Watt they measured and promised us on so-called Standard Test Conditions of 1000 W/m2 light coming in (= rare bright European day with good position of the sun) and 25⁰C working cell temperature; but, in practice, these specifications are not met.

The key problem of the photovoltaic cell is the very thin layer (< 0.2 mm) where the light energy frees electrons from the base material to move away as current. This current is directly proportional to the irradiation (see FIG 1 from a datasheet). At 1000 W/m2 irradiation the 1 m2 cell could deliver some 140 W, e.g. 8 A current and 18 V voltage. However the larger part of the light energy, some 860 W, have not been converted to free electrons, have not been reflected back (the cell still looks black), it has been converted into heat. Within seconds of full irradiation this has heated the thin layer of <0.2 mm to over 120 ⁰C. Internal resistance has heated up, like in a battery. The available voltage drops to half or less; it has a negative temperature coefficient of some -0.5% /⁰C, the power delivered drops to 70 W/m2, so the efficiency on an optimal day is down to 7%.

DESCRIPTION OF PRIOR ART

Many devices have been invented and designed to transport the heat from the panel to the backside outside:

All these applications did not overcome the electro- and thermo-insulating backplane's plastic material and the fact that these metal cooler blocks keep the heat, instead of transporting it away as fast as possible.

And all these schemes eventually do no more work in the heat of sunny Mediterranean cities' rooftops.

SUMMARY OF THE INVENTION

The invention is a Cooling-Voltaic Power Generation System that takes away the heat from the photovoltaic cells generating pressurized gas in a heat exchange module, transports it to a turbine that drives a generator, expands the steam to low pressure and cool temperature until the gas turns liquid again, and recycles it to the inlet of the heat exchange module.

The system includes:

1) a special heat-conducting, electrically insulating and flexible plastic adhesive to fix the back of the photovoltaic cells to the surface of a heat exchanger.

2) a special heat exchanger optimizing the evaporation of the incoming liquid gas into a high volume, high pressure gas leaving the exchanger at the top.

3) a special valve to control temperature stability and pressure build-up in the heat exchanger and collecting tubing.

4) a steam turbine.

5) a generator coupled to the turbine delivering current, e.g. to charge batteries.

6) a collector to keep the cold and liquefied gas, to be pumped back into the lower end of the heat exchanger.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1a-1 b show typical voltage-current curves from a datasheet for multi-crystalline cells.

FIGURE 2 shows the different units in the closed circuit of the Heat to Current conversion. DETAILED DESCRIPTION OF THE INVENTION

Specific numbers dedicated to elements defined with respect to a particular figure will be used consistently in all figures if not mentioned otherwise.

FIG. 1 shows typical voltage-current curves from a datasheet for multi-crystalline cells.

36 standard 6 x 6" cells in serial connection will build a 1 m2 panel discussed above.

Figure 1 a shows clearly that l_max is proportional to the captured irradiation that only on bright days will ever be more then 800 W/m2. It also gives an idea about the accuracy with which to position the panel towards the sun.

Figure 1 b shows how the never considered high temperature of the thin active layer in the cell is cutting down on the available voltage, because of "heated-up" inner resistance. On a really bright day, the layer will heat up to more than 120 ⁰C, heating up the inner resistance and cutting down the available voltage to some 50-60% of STC, making the solar cell again less economically attractive as a stable and reliable power source. It therefore must be the goal of any optimization of the solar panel to reduce this heating up of the active layer, by removing the generated heat as fast as possible.

It would not be surprising to us, if the "guaranteed" but never tested lifetime of more then 20-30 years in optimum irradiation will never be reached and the cell or the surrounding packaging will be destroyed well before.

Figure 2 shows the different units in the closed circuit of the Heat to Current conversion.

The Photovoltaic Cells 1 work at a stabilized inner temperature of some 40 - 45 °C and will deliver about the electric power promised in the data sheet, some 140 - 180 W (instead of some 70 - 90 W with unstabilized temperature) at 1000 W/m2 irradiation.

The Heat Exchanger 2 has to transport away some 70 - 80 % of the generated heat, in order to stabilize the temperature of the Photovoltaic Cells. It is doing this by bringing liquefied Butane or similar gas into the exchanger that will evaporate at the stabilization temperature and will be pressed away towards the Turbine 4 by the high expansion of its volume.

The Turbine 4 with coupled Generator 5 will convert the power of the high-speed volume flow to some 60 - 70 % electrical power. As pressure is reduced, temperature will drop downstream from the turbine exit and a Collector 6 will capture and keep the liquefying gas for the next loop, initiated by the pump bringing it to the inlet of the Heat Exchanger again.

The process shall bring more than 400 W from the photovoltaic- heat-power-module, some 5-6 times the output from an un-cooled module.

Claims

1. A photovoltaic-cooling-power-module, generating electricity from light irradiation in the photo-voltaic process in the semiconductor cells and generating additional electricity from the otherwise unwanted photo-heat in a power-electricity process in a turbine-generator.

2. A photovoltaic-cooling-power-module as in Claim 1 , transporting the unwanted photo-heat from the semiconductor cells, keeping them cool and preventing the negative temperature coefficient of the cell voltage to slash the cell's efficiency.

3. A photovoltaic-cooling-power-module as in Claim 1 , using Butane or similar formulated gas, in a closed loop, in order to stabilize the otherwise increasing operating temperature of the cooled cells at its own, low vaporization temperature.

4. A photovoltaic-cooling-power-process as in Claim 2 and 3, being started and maintained by a self-adjusting valve control loop.

5. A special heat-conducting plastic glue to fix the fragile photovoltaic wafers to the surface of the heat exchanger, insulating the cells electrically but transporting the building-up heat from the cells fast and efficiently to the evaporating gas inside the exchanger.

6. An optimized turbine-generator combination for the high-speed gas flow resulting from the high volume expansion, using magnetic coupling between the gas-inside of the turbine and the air-outside of the generator.