Patent Application
20090283135
1. Field of the Invention
The present intention relates to an apparatus for powering an electric load with a low voltage power source. More specifically, the present intention relates to powering an electric load with a power source that generates a voltage that is much lower than the voltage required by electric load. The apparatus increases the voltage to the work point of the electric load, without significant losses in electrical energy.
2. Description of the Related Art
Due to the high cost of fossil fuel and the concern about global warming caused by the production of carbon dioxide in the combustion of fossil fuels, there is a growing interest in power sources that operate on renewable energy. Examples include photovoltaic cells, thermovoltaic cells, hydrogen fuel cells, biofuels cells, and the like.
Many of these power sources produce electrical power at a low voltage, often on the order of one Volt or less. Photovoltaic cells for example provide a voltage of 0.35 to 0.65 V, typically about 0.45 V. For most applications, the electrical power needs to be provided at a much higher voltage, for example 12V direct current, or 110 or 230 volts AC. One reason is that, for a certain amount of electrical energy, the current is inversely related to the voltage, making it impractical to transport low voltage electrical energy over long distances. The high current requires very thick cables, and is associated with a high risk of overheating and fire.
It is therefore customary to provide an assembly in which a significant number of low voltage power sources are connected in series, so as to provide a suitably higher voltage at the terminals of the assembly. For a plurality of low voltage power sources connected in series, the performance of the assembly is governed by the weakest link in the chain. Such an assembly will only optimally perform if all of the individual units provide identical performance. In practice, this is never the case. For example, the performance of enzymes in a biofuel cell differs from cells to cell. Photovoltaic cells in an assembly may differ in electric output. A manufacturing tolerance of 5% is common, which means that even cells receiving identical amounts of solar radiation may have different outputs of electric energy. In addition, cells within an assembly may receive different amounts of solar radiation, for example as result of a shadow or debris covering some of the cells. Such events may reduce the output of an assembly of photovoltaic cells connected in series by 30 to 70%. To some extent this loss may be reduced by incorporating bypass diodes, so that poorly performing cells may be bypassed.
For this reason, there are always weaker cells in an assembly of cells connected in series. These weaker cells drag down the performance of the assembly, because they act as loads on the system rather than as contributors to its performance.
It is an object of the present intention to raise the voltage of a low voltage power source to the required voltage of an electric load without the disadvantages of existing systems.
The present intention relates to an apparatus for powering an electric load with a low voltage power source, said apparatus comprising:
wherein V1+Vp=V2.
Examples of the low voltage power source include photovoltaic cells, thermovoltaic cells, hydrogen fuel cells and biofuel cells.
Examples of accumulators of electric energy for use in the apparatus of the present intention include flywheels, capacitors, and chemical batteries.
The present intention relates to an apparatus for powering an electric load with a low-voltage power source, said apparatus comprising:
The low voltage power source for use in the apparatus of the present intention may be any power source producing a voltage Vp that is lower than the voltage required to power the electric load. The low voltage power source may be powered by a fossil fuel, or by a non-fossil fuel, preferably by a renewable energy source. Preferred examples include photovoltaic cells, thermovoltaic cells, hydrogen fuel cells, and biofuel cells.
The invention will be further illustrated for embodiments of the apparatus in which the low voltage power source comprises at least one photovoltaic cell. It will be understood that the principles illustrated by these embodiments can be applied to any other low voltage power source.
Shown in
Photovoltaic power source 2 is connected in series with a first accumulator of electric energy 3. The second accumulator of electric energy 4 is connected parallel to the first accumulator of electric energy 3. Preferably, the first accumulator 3 and the second accumulator 4 are of equal design, but it will be understood that the apparatus will function properly if the two accumulators are of different design.
The first accumulator 3 provides a first voltage V1. The photovoltaic power source 2 provides an output voltage Vp. The voltage over the second accumulator 4 is given by the equation:
V2=V1+Vp (1)
It will be understood that in practice the value of V2 may be slightly lower than the value provided by equation (1), due to losses in the circuit, in particular when further components are added to the circuit as exemplified in embodiments discussed herein below.
Terminals 5 and 6 are provided for connecting an external electric load, which is to be powered by apparatus 1. When no external load is connected to terminals 5 and 6, electric power generated by photovoltaic power source 2 is used to charge the second accumulator 4. When a load is connected to terminals 5 and 6 that draws less power than is generated by power source 2, any excess power is used to charge accumulator 4. When the external load connected to terminals 5 and 6 consumes more power than is being generated by power source 2, additional power is provided to the load by accumulator 4.
The accumulators to 3 and 4 may be any type of device capable of storing electrical energy. Examples include traditional forms, such as batteries and capacitors, and non-traditional forms such as flywheels provided with electrical generators.
The term “battery” as used herein means a device capable of converting electrical energy into chemical energy, and of converting chemical energy to electrical energy. This type of battery is also referred to as secondary battery or rechargeable battery. Examples include lead-acid batteries, for example wet batteries, gel batteries and absorbent glass mat batteries; lithium ion batteries; lithium ion polymer batteries; NaS batteries; nickel-iron batteries; nickel-metal hydride batteries; nickel-cadmium batteries; nickel-zinc batteries; and molten salt batteries.
Examples of capacitors that may be used as accumulators of electric energy include conventional capacitors (metal film capacitors; mica capacitors; paper capacitors; glass capacitors; and ceramic capacitors); electrolytic capacitors; and in particular the so-called super capacitors.
Super capacitors, sometimes also referred to as ultra capacitors, may be made from carbon aerogel, carbon nano-tubes, or highly porous electrode materials. They are known for their extremely high capacity, and are being evaluated as alternatives to rechargeable batteries. Particularly preferred are ceramic ultra capacitors with a barium-titanate dielectric, which have a high specific energy.
In a preferred embodiment controller 7 is capable of monitoring and controlling the respective charge conditions of accumulators 3 and 4. For example, if accumulator 4 is fully charged, and power source 2 produces more power than is required by a load connected to terminals 5 and 6, controller 7 will divert electric energy to charge accumulator 3.
When the demand of a load connected to terminals 5 and 6 exceeds the power production of power source 2, controller 8 may draw power from accumulator 9. This embodiment is particularly suitable for supplying power to a load having rapidly fluctuating power needs. Rapid changes in power needs can be accommodated by accumulator 9, in particular if actuator 9 is a capacitor. Accumulators 3 and 4, which may be chemical batteries, are more suitable for responding to fluctuations in power needs that are longer lasting.
The embodiment of
The embodiment of
It will be clear from the foregoing that the apparatus of the present invention is capable of providing a voltage to and electric load that is much higher than the voltage generated by the low voltage power source. For this reason, it is not necessary for the low voltage power source to be connected to other such power sources in series. In a preferred embodiment, the apparatus comprises a plurality of photovoltaic cells grouped in a matrix of parallel connected units. Photovoltaic cells may conveniently be connected in parallel by mounting the cells on a unitary sheet of conducting material. Preferably the unitary sheet of conducting material is made of a metal. Preferred metals are those that have a high conductivity for both electricity and heat, and are suitably corrosion resistant. Examples of suitable metals include copper, nickel, aluminum, gold, and alloys thereof. Although gold is preferred in terms of conductivity and corrosion resistance, its price is prohibitive for many applications. Therefore in many cases copper is the preferred metal for use in the unitary sheet.
Mounting photovoltaic cells conductively onto a unitary metal sheet offers a number of advantages. First of all, it obviates the need for wire connections between the corresponding electrodes of the individual photovoltaic cells, which reduces the complexity and cost of the manufacture of a photovoltaic cell assembly. In addition, because the cells are connected in parallel, there is no need for bypass diodes as are often included in photovoltaic cell grids that have the cells connected in series. Yet another advantage is improved dissipation of heat through the unitary sheet of conducting material. In use, photovoltaic cells generate heat as a byproduct. This is undesirable, because the effectiveness of photovoltaic cells goes down as the temperature of the cells goes up. Having the cells mounted on a metal sheet makes it possible to provide cooling by thermally connecting the conducting material to a cooling medium. This may conveniently be accomplished by providing a cooling coil to the surface of the sheet opposite to the surface to which the photovoltaic cells are mounted. The cooling coil may be connected to a heat pump, so that the temperature of the photovoltaic cells may be kept at or near its optimum. The heat energy may be recovered from the cooling medium and may be used for heating purposes, for example for heating a water supply.
As mentioned hereinabove, it is advantageous to maximize the number of photovoltaic cells that are connected in parallel, and minimize same the number of photovoltaic cells that are connected in series. This reduces the need for bypass diodes. Accordingly, the low voltage power source preferably contains fewer than two bypass diodes for every 10 photovoltaic cells present in the low voltage power source, and preferably the low voltage power source is free of bypass diodes.
Another advantage of connecting the photovoltaic cells in parallel is that a small number of photovoltaic cells, each having a large surface area, may be used. In a preferred embodiment, the apparatus comprises a low voltage power source which comprises at least one photovoltaic cell having the surface area of more than 400 square cm, preferably more than 600 square cm, still more preferably more than 1,000 square cm.
As mentioned earlier, it is not necessary for the low-voltage power source to provide an output voltage Vp sufficient to power the external electric load. It is therefore possible to provide a low voltage power source having an output voltage of less than 20 volts, preferably less than 10 volts, and more preferably less than 5 volts. Likewise, the external voltage Ve provided to be electric load is such that Ve is at least two times Vp, preferably at least ten times Vp, and more preferably at least 100 times Vp.
Hot fuel cells expand when in use, which causes problems when the cells are connected in series. Exotic materials have been proposed to limit this thermal expansion, so that fuel cells may be placed closely together. The present invention allows fuel cells to be connected in parallel, so that they do not need to be placed closely together, and thermal expansion does not cause problems.
It will be clear that the external load can be any load, or a combination of electric loads. For example, it may be a single light source, such as a light emitting diode, or it may be the combination of electric loads as may be present in a home or a building. A particularly attractive use of the apparatus of the present invention is connecting it to a power grid. This requires that the apparatus be connected to a converter for converting electric energy generated by the apparatus to an alternating current at a voltage compatible with that of the grid. This arrangement makes it possible to sell power to the grid when the apparatus produces more power than is needed for internal use, and to supplement the power with power from the grid at times that the demand is greater than the amount of power produced by the apparatus.
Thus, the invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art.
| Number | Date | Country | Kind |
|---|---|---|---|
| 07101312.2 | Jan 2007 | EP | regional |
This application is a continuation of international application no. PCT/EP2008/051066, filed on Jan. 29, 2008, and claims priority from European patent application number 07101312.2 filed on Jan. 29, 2007. The contents of these application are hereby incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/EP2008/051066 | Jan 2008 | US |
| Child | 12511217 | US |
