WO2006067350A1

WO2006067350A1 - Method and system for stand-alone electrical supply by means of renewable energy

Info

Publication number: WO2006067350A1
Application number: PCT/FR2005/051099
Authority: WO
Inventors: Didier Marquet; Olivier Foucault; Alain Peraudeau
Original assignee: France Telecom
Priority date: 2004-12-22
Filing date: 2005-12-16
Publication date: 2006-06-29
Also published as: FR2879852A1

Abstract

The invention relates to a method and system for electrical energy supply to a piece of equipment (210), comprising a renewable energy source (220) and a first storage means (230) for storage of the energy produced by the source to provide at least daytime operation. The piece of equipment (210) is designed to operate in variable meteorological conditions comprising at least one long period of high energy production by the renewable energy source (220), which corresponds to an over-production and a period of energy requirement exceeding the capacity of the first storage means. In order to store the excess energy produced during the period of over-production, the renewable energy source (220) is connected to a second storage means (240) when the first storage means (230) has reached a given level of charge. Said excess can subsequently be used on connecting the piece of equipment (210) to the second storage means (240).

Description

Title of the invention

Method and system for autonomous power supply by renewable energy.

Field of the invention

The present invention relates to systems for supplying electrical energy to equipment that require an autonomous power supply means renewable energy such as those located on isolated sites of any electrical network or connected to a non-permanent electrical network

Background of the invention

The supply of electrical energy on isolated site of the electrical network, and by extension in the following text on sites connected to a non-permanent electrical network, involves the use of a primary source of energy which may be fossil origin (oil, gas ...) or so-called renewable origin (wind, sun ...). In most applications, this electrical energy must be available at any time of the day or night, and at any time of the year, summer or winter. This imperative is required especially in the field of telecommunications, where the equipment installed on isolated site must operate 24 hours a day, 365 days a year, with an almost constant consumption.

Therefore, whatever the case, but more particularly in the case of renewable energy sources, it is necessary to associate with this source a storage function, which function is provided essentially by batteries which are most often of technology and design based on lead.

As illustrated in FIG. 1, a conventional solar energy station 100 consists of a set of panels or solar modules composed of photovoltaic cells 120 (energy source), a lead battery 130 (energy storage) and a regulating device 160. In the example under consideration, this station is intended to supply a power supply to a telecommunications equipment 110 such as an antenna or terminal of a mobile telephone network.

Due to its intrinsic characteristics, a high capacity, relatively slow discharge battery (ie several days), which is well adapted to solar sources, can not remain deeply discharged for a long period of time without irreversibly degrading itself and losing of its capacity. It must also not typically discharge more than 15% per 24 hours to limit cycling (fraction of the capacity of the battery that is stored / removed) and ensure a lifetime of several years. This implies an oversizing of its capacity compared to the useful exploitation. It is expected that at least typically 10 days of capacity while 5 could be enough.

The changing weather conditions throughout the year cause some difficulties in the production of energy from a renewable energy source (lack of wind for wind turbines, lack of sun for solar panels ...), which complicates the overall dimensioning of the energy station.

The regulation device 160 serves to control the charging and discharging of the battery. Since a lead battery can not be completely discharged, otherwise it may be damaged, a switch 150 is used to disconnect the load from the equipment 110 in order to protect the battery 130 from a deep and prolonged discharge.

In addition, a lead battery does not deteriorate not only because of deep discharges or excessive cycling, but also because of overcharging. Indeed, when a battery is fully charged, and connected to a source such as solar panels that continue to produce power, there is overload, which has the effect of reducing the service life of this battery by oxidation of the positive grid and to increase the maintenance due to a greater consumption of electrolyte. For this purpose, the regulation device 160 also controls a switch 140 which makes it possible to disconnect the battery 130 from the solar modules 120. In the latter case, the solar modules being disconnected although there is sunshine, the energy producible (energy that would be produced if the panels were connected to a load or a discharged battery) is lost. By way of example, measurements made on an experimental solar station have shown that in winter, the energy produced is equal to the producible energy. Therefore, during this season, we consume the entire production because the battery is more often discharged and the sun is low. Conversely, in summer, the energy production is much higher than the energy actually produced, the battery is often well charged with significant sunlight. So we notice the potentially productive energy that is lost.

Object and summary of the invention

The object of the present invention is to overcome the aforementioned drawbacks and to propose a technical solution that makes it possible to optimize the storage and management of the energy available on an isolated site, despite the very slow variations in the production of the source of energy. energy (eg seasonal variations in pseudo-period solar energy greater than the autonomy of energy storage means (typically a few months) and very large amplitude, (typically more than 50% on this period is achieved by a method of supplying electrical power to an isolated site equipment comprising a renewable energy source and a first storage means for storing the energy produced by said source for a period of time. at least one day operation, the equipment being intended to operate in variable meteorological conditions over a period of several days, including at least one long period of high productivity energy corresponding to an overproduction and a long period of reduced energy production by the renewable energy source corresponding to a need for energy exceeding the capacity of the first storage means, in which process, according to the invention , the renewable energy source is connected to a second storage means when the first means storage has reached a predetermined load level and the equipment is connected to the second storage means when the first storage means has reached a predetermined discharge level.

Thus, the invention proposes to use a second storage means, independent of the first, which is used to store the excess energy produced in a first period of high production and to restore it when the first storage means is empty. in a second period when production is lower. This process therefore makes it possible to adapt the energy storage and the supply of the equipment to the very slow but large fluctuations (seasonal) in the production of the renewable energy source.

According to one aspect of the invention the method may further comprise a step of disconnecting the second storage means of the energy source when it has reached a predetermined load level. This protects the second storage means against overloads.

According to another aspect of the invention the method may further comprise a step of disconnecting the second storage means of the equipment when the latter has reached a predetermined discharge level. This protects the second storage means against deep discharges.

The invention also relates to an electrical power supply system for an isolated site equipment comprising a renewable energy source and a first storage means for storing the energy produced by said source, the equipment being intended for operate under varying conditions including at least one period of high energy production and a period of reduced energy production by the renewable energy source. According to the invention, the system further comprises a second storage means, a first switch disposed between the renewable energy source and the first and second storage means and a second switch disposed between the first and second storage means and equipment. The first and second switches are controlled by a controller to selectively connect the renewable energy source to the first and second storage means and to selectively connect the equipment to the first and second storage means based on the state of charge. first storage means. As for the process described above, this system makes it possible to store the surplus energy usually lost during a period of high energy production and to restore it at the most useful moment, namely during periods of low production during which the first Storage medium can not be recharged enough to provide constant power to the equipment.

According to one embodiment of the invention, the first storage means comprises at least one accumulator such as a nickel-cadmium battery and the second storage means comprises at least one accumulator such as a lead battery.

According to one aspect of the invention, there is provided a means for maintaining a constant charging current between the power source and the battery of the first storage means.

The renewable energy source may be solar modules or equivalent devices that use solar energy to produce electricity.

Brief description of the drawings

Other characteristics and advantages of the invention will emerge from the following description of particular embodiments of the invention, given by way of non-limiting example, with reference to the appended drawings, in which: FIG. 1 is a view schematic of a power supply system according to the prior art;

FIGS. 2A, 2B and 2C are schematic views of one embodiment of an electric power supply system according to the invention; FIG. 3 is a graph showing the influence of the feed system of the invention on the electrical power supply of an isolated site equipment;

FIG. 4 is a schematic view of another embodiment of an electric power supply system according to the invention; FIG. 5 is a curve showing the evolution of the state of charge of the batteries of the system of FIG. 4 during the seasons; and

FIG. 6 is a curve showing the day / night evolution of the state of charge of the batteries of the system of FIG. 4 in summer and in winter.

Detailed description of an embodiment

The present invention is based on the principle of using additional storage means (eg battery) in parallel with the main storage means heretofore used, the charges / discharges of these two storage means being, as described further in detail, controlled by control means according to a method of the invention.

More specifically, the present invention proposes a system and a method of implementing this system which are adapted to these two separate storage means so as to define the principle of "inter-seasonal load" specific to the invention. This principle generally results in operation with short-term charges / discharges for the main storage medium and long-term (inter-seasonal) storage for the secondary storage means, with regulation to protect them as well. against deep discharges or against overloads.

The characteristics of the storage means are different. The first storage means must be very robust to accept many charge and discharge cycles of an amplitude that can typically reach 20% of its capacity.

The second storage means must have a very low self-discharge (internal energy loss) over a long period regardless of the environmental conditions (temperature, humidity, atmospheric pressure, ...) and aging.

The concept of inter-seasonal load is presented in FIGS. 2A to 2C, which represent an electric power supply system 200 comprising solar modules 220 (eg photovoltaic cell panel) as a source of renewable energy in electricity, a first electric battery 230 as the main storage medium, a second 240 electric battery as a way to secondary or long-term storage, a device 210 to power such as an antenna or terminal of a mobile telephone network and a control device 250 which controls two switches 260 and 270, the switch 260 being disposed between the modules 220 and the two batteries 230, 240 while the switch 270 is arranged between the two batteries and the equipment 210. The switches 260 and 270 may be for example well-known devices such as reversing contactors or electromechanical or electronic relays.

The regulating device may be formed of an electronic circuit (not shown) which comprises processing means (eg programmable microcontroller) specifically programmed for regulating the batteries as described below. For this purpose, the circuit further comprises measuring means (eg multimeters) for monitoring the state of charge of each battery and control means (eg command signal generators) for controlling the switches and switches according to predetermined threshold values of charge / discharge of the batteries as explained below.

The system of the invention is here described with a source of renewable solar type electrical energy. However, the system can use other renewable energy sources such as a wind energy installation or a combination of several types of renewable energy sources. Similarly, the long-term storage means used in the example described here is an electric battery. This means could also be a reversible fuel cell with hydrogen storage or a compressed air bottle storage system filled (ie charged) by a compressor powered by the renewable energy source, the restitution of electrical energy. (ie discharge) is done using a compressed air motor and a dynamo. FIG. 2A shows the system 200 in normal operation, that is to say using only the battery 230, the inter-seasonal load not being implemented. In this configuration, the switches 260 and 270 are both controlled by the regulator 250 to be placed on the position A so that the solar modules 220 charge the battery 230 while supplying the equipment 210. Once the battery 230 is recharged, the controller 250 controls the switch 260 to switch to the B position, i.e., on the battery 250 as shown in FIG. 2B. The electrical energy produced by the solar modules 220, previously lost, is switched on the battery 250, which takes charge of the surplus of producible energy. The configuration of the system 200 shown in FIG. 2B corresponds to that used in summer and autumn where the sun is important.

In winter, if the system is properly sized (ie energy production compared to equipment needs) there is no surplus of solar energy. The configuration of the system in winter is then that of Figure 2A. However, during the winter or long periods of lack of sunlight, the battery 230 may discharge into the equipment 210 to the point of being emptied. The regulating device then controls, from a predetermined discharge threshold of the battery 230, the switch 270 so that it switches to position B so as to protect the battery 230 from an excessive discharge as illustrated in FIG. 2C . By switching to this position, the switch 270 connects the battery 240 which has charged during the summer and fall on the equipment that continues to be powered by the latter. As for the battery 230, it is charged with a low electrical energy output from the solar modules 220 until it reaches a predetermined charge level where the switch 260 is re-shifted back to the position B by the regulating device 250. ie, on the battery 240. The regulating device 250 therefore controls the switching of the switches 260 and 270 as a function of the charge and discharge levels of the battery 230. For this purpose, it has measuring means ( not shown) of the charge / discharge level of this battery. The curves shown in FIG. 3 make it possible to compare the operation of an installation with or without an inter-seasonal load, that is to say with or without a secondary battery used as explained above. The fine line curve (series 1) represents the operation of an installation, such as that shown in FIG. 1, without a secondary battery which experiences power cuts (peaks towards 0). The thick line curve (series 2) represents the operation of a installation with secondary battery, as in Figures 2A to 2C, for which there is no power failure.

Regarding the type of battery used in the system of the invention, the use of a second battery 240 reduces the capacity of the main battery 230 to a minimum, that is to say, 3 or 4 days d autonomy, as opposed to usually 8 to 12 days of autonomy (depending on geographical location).

This also results in a lower cost for the main battery, which must normally be robust technology and, therefore, relatively expensive.

Excess energy storage also makes it possible to either reduce the surface area of the solar module panels for the same application, panels which are also expensive, or, for the same surface of solar modules, to provide more average power over the year. (the average power is equivalent to a fairly constant permanent power absorbed by telecommunication equipment).

The overall cost of the station is thus minimized.

Therefore, the main battery 230 is preferably a battery of nickel-cadmium technology and intensive cycling type or solar. Indeed, the fact of dimensioning the autonomy of this battery to 3 or 4 days for example, implies that it will be much sought, undergoing, every day, loads and large discharges

(typical daytime cycling of solar energy), conditions for which nickel-cadmium technology, also insensitive to temperature variations, is in some environments better suited than lead technology.

The secondary battery 240, for its part, is much less stressed so that a conventional stationary lead technology, less expensive than a cycling battery, can be used. This type of battery also has the advantage, important here, to have a low self-discharge. All batteries suffer from self-discharge, but this is the highest for nickel, while it is the lowest for lead, which typically has a self-discharge of only 5% per month and lower. at low temperature, this which is interesting for a winter need. However, we must also choose a technology capable of restoring its capacity.

FIG. 4 illustrates another embodiment of the supply system of the invention which differs from that of FIGS. 2A to 2C in that it allows regulation of the secondary battery so as to protect it against overloads when there is still has too much energy produced in summer and against deep discharges in case of exceptionally bad conditions. The power supply system 300 shown in FIG. 4 comprises solar modules 320, a main battery 330, a secondary battery 340, a device 310 to be powered such as an antenna or terminal of a mobile telephone network and a control device. 350 which controls two switches 360 and 370 (eg inverter contactors or relays), the switch 360 selectively connecting the modules 320 to one of the two batteries 330, 340 while the switch 370 selectively connects one of the two batteries to the second one. In this embodiment, the regulator 350 further controls two switches 380 and 390, such as open contactors (eg relays which open when they are controlled), which are respectively each side of the battery 340 between the two switches 360 and 370. The two switches 380, 390 thus arranged form a device that protects the battery 240 against the discharges and excessive discharges.

Furthermore, as for the main battery 230 described above, the main battery 330 of the system 300 of FIG. 4 is preferably a nickel-cadmium (NiCd) type battery that better withstands the frequent charging / discharging loads than a battery lead. However, a NiCd type battery must, to be 100% charged, absorb 140% of its capacity. For this purpose, when using this type of battery, the system of the invention may further comprise a resistor or an equivalent current limiting electronic device 361 placed in parallel on the switch 360 located between the solar modules 320 and the battery main 330, as shown in Figure 4.

The resistor or the equivalent electronic device 361 allows the battery 330 to finish charging correctly when it is disconnected from the source of electrical power generation in general. 90% of his load. For this purpose, the resistor 361 must be chosen so as to allow charging with a high voltage and a low current determined according to the capacity of the battery. Indeed, for a NiCd battery of capacity C in Ah (ampere (s) -hour (s)), a current of C / 50 to C / 100 in A is needed, in order to provide it with 140% of its capacity. for it to be 100% loaded.

The value R of the resistor 361 is defined by the relation:

_R _ Upv - UbI IbI + Iu

with Upv: Voltage of solar modules UbI: Main battery voltage IbI: Main battery current Iu: Current used by the equipment

For example, when Upv = 36 V (the highest voltage corresponding to the charge regulation of the secondary battery, ie solar panels almost empty), UbI = 28 V (main battery voltage near the end of load), IbI = 1.5 A and Iu = 2.5 A, we have R = 2 Ω. Instead of the resistor 361, it is also possible to use any equivalent means that makes it possible to deliver a specific current such as a direct current source, for example a high-frequency switching MOS circuit.

The various regulation steps that can occur during an inter-seasonal load with the system of FIG. 4 are described. The regulation steps described below are implemented from the control device 350 which controls both the switches 360 and 370 as well as switches 380 and 390.

In the example of FIG. 4, the main battery 330 is a NiCd battery composed of a series of 19 elements or elementary cells of 1.2 V nominal (the real voltage varying from 1 to 1.7 V depending on the load) and which has a capacity of 214 Ah. Secondary battery

340 is a sealed lead battery with a capacity of 400 Ah consisting of 12 elements rated 2 V (the actual voltage varies from 1.9 to 2.5 V). Step 1: Charge the main battery 330.

The main battery 330 is charged by the solar modules 320 up to 90% via the switch 360 in position A. The secondary battery 340 is disconnected. The equipment 310 is powered by the battery 330 at night via the switch 370 in position A.

The end of charge detection of the battery 330 (90%) corresponds to a high voltage threshold of 1.6 V per element thereof, ie 30.4 V.

Step 2: end of charging of the main battery 330 and charging of the secondary battery 340.

At the detection of the high voltage threshold of 30.4 V, the switch 360 switches to the B position, that is to say directs most of the energy flow delivered by the solar modules to the battery 340 which is charge (the switch 390 being closed at rest).

A small part of the power generation is channeled by the resistor 361 to the equipment 310 (via the switch 370 in position A) and to the battery 330, which allows the latter to finish charging correctly (ie with a current of the order of 1 to 2 A).

Step 3: end of charging of the batteries 330 and 340. When the voltage Ub2 of the battery 340 reaches 29 to 30 V, the switch 390 is controlled so that it opens so as to limit the overcharging of the battery 340. Battery 330 continues its low current charging end via resistor 361.

Step 4: Restore the 330 battery.

When it is dark, or when the production of the solar modules is low, the current is delivered to the equipment by the battery 330, which discharges. The voltage of the battery 330 drops, up to the voltage threshold of 27.5 V (1.45 V per element). The switch 360 is then switched back to position A so as to recharge the battery 330 at the return of the day or sufficient sunlight. Step 5: Restore the battery 340.

If the voltage of the battery 340 decreases to a voltage threshold of 27 to 28 V, the switch 390 is no longer actuated, and returns to its rest position (i.e. closed).

Step 6: end of discharge of the battery 330.

When the battery 330 is discharged (10% of remaining capacity, ie UbI = 21 V), the switch 370 is switched to position B. The battery 340 then takes over by supplying the energy required for the equipment 310.

Step 7: End of discharge of the battery 340.

When the battery 340 is discharged by 90%, that is to say Ub2 = 22.8 V (period of very bad weather in winter), the switch 380 opens to protect it from a deep discharge. . The equipment is no longer powered. (Exceptional weather conditions).

Step 8: reconnect the battery 330.

When the battery 330 is sufficiently recharged (UbI = 23.5 to 24 V), the switch 370 is turned back to position A so that the battery 330 supplies the equipment 310 again.

Step 9: reconnect the battery 340

When the battery 340 is sufficiently recharged (Ub2 = 25 to 26 V), the switch 380 is no longer actuated and returns to its idle position (i.e. closed).

Figure 5 shows the average charge states (excluding the daily cycle) during the seasons, batteries 330 and 340. The zone E corresponds to the period of storage in the secondary battery of the surplus of electrical energy produced in summer and zone H to the restitution of this energy by the secondary battery in winter.

Figure 6 shows an example of day / night evolution of the state of batteries 330 and 340 at the end of charge in summer (top graph) and at the end of discharge in winter (bottom graph). In summer, T _E1 corresponds to the disconnection of the main battery

330 solar modules 320 which continues to load via the resistor 361 and at the beginning of charging the secondary battery 340 (switch 360 in position A). T _E2 corresponds to the beginning of the discharge of the battery 330. T _E3 corresponds to the end of charge of the battery 330. T _E4 corresponds to the end of the charge of the battery 340 where the switch 390 is open. In winter, T _H1 corresponds to the moment when the switch 370 is turned to position B to disconnect the main battery 330 from the equipment 310 and supply the latter with the secondary battery 340. T _H2 corresponds to the disconnection of the secondary battery 340 of the equipment 310 to protect it against excessive discharge. The period between T _H2 and T _H3 corresponds to the exceptional disconnection of the two batteries of the equipment until the main battery 330 recharges sufficiently to be reconnected to the equipment (T ₃ ).

According to an alternative embodiment, it is possible to use, in place of the switch 390, a switching charge regulator (maintaining a constant charging voltage of the lead).

According to another variant, between the solar modules 320 and the switch 360, it is possible to insert a search converter of the maximum point of production of the solar modules (MPPT: Maximum Power Point Tracker) which makes it possible to gain 15 to 30% of energy produced. over the year.

At the input of the switch 390, on the battery 340, it is possible to install a backup generator, such as a small wind turbine, to compensate for the self-discharge over long periods and to avoid leaving it deeply discharged for too long. would hurt its life.

Claims

A method of supplying electrical power to equipment (210; 310) comprising a renewable energy source (220; 320) and first storage means (230; 330) for storing energy produced by said source for at least daytime operation, the equipment being adapted to operate under varying conditions and comprising at least one period of high energy production by the renewable energy source (220; 320) and a reduced production period of energy by the renewable energy source (220; 320), these periods respectively corresponding to overproduction and to an energy requirement exceeding the capacity of the first storage means, characterized in that it comprises at least one connection step from the renewable energy source (220; 320) to a second storage means (240; 340) when the first storage means (230; 330) has reached a predetermined load level and a connection step of the eq. uipement (210; 310) to the second storage means (240; 340) when the first storage means (230; 330) has reached a predetermined discharge level.

2. Method according to claim 1, characterized in that it further comprises a step of disconnecting the second storage means (240; 340) of the renewable energy source (220; 320) when said second storage means has reaches a predetermined load level.

3. Method according to claim 1 or 2, characterized in that it further comprises a step of disconnecting the second storage means (240; 340) of the equipment when said second storage means has reached a predetermined discharge level. .

4. Method according to any one of claims 1 to 3, characterized in that the first and second storage means (230, 240, 330, 340) each comprise at least one electric battery.

5. Method according to claim 4, characterized in that there is a means (361) for maintaining a charging current between the renewable energy source (220; 320) and the battery of the first storage means (230; 330). ), when the inverter 260 is in position B.

6. Method according to any one of claims 1 to 5, characterized in that the renewable energy source (220; 320) uses solar energy.

An electric power supply system for isolated site equipment (210; 310) comprising a renewable energy source (220; 320) and a first storage means (230; 330) for storing energy produced by said source, the equipment (210; 310) being adapted to operate under varying conditions including at least one period of high energy production by the renewable energy source (220; 320) and a reduced production period of energy by the renewable energy source (220; 320), characterized in that it further comprises a second storage means (240; 340), a first switch (260; 360) disposed between the renewable energy source and the first and second storage means (230, 240; 330, 340) and a second switch (270; 370) disposed between the first and second storage means (230, 240; 330, 340) and the equipment (210 310), the first and second switches (260, 270, 360, 370) are both controlled by a regulating device (250; 350) for selectively connecting the renewable energy source (220; 320) to the first and second storage means and for selectively connecting the equipment (210; 310) to the first and second storage means (230,240; 330,340). ) as a function of the state of charge of the first storage means (230; 330).

8. System according to claim 7, characterized in that it further comprises a switch (390) disposed between the first switch (360) and the second storage means (340), said first switch being controlled by the control device (350) for disconnecting the second storage means (340) from the source of energy renewable (320) based on a predetermined charge level thereof.

9. System according to claim 7 or 8, characterized in that it further comprises a switch (380) disposed between the second storage means (340) and the second switch (370), said switch being controlled by the control (350) for disconnecting the second storage means (340) from the equipment (310) based on a predetermined discharge level thereof.

10. System according to any one of claims 7 to 9, characterized in that the first and second storage means (230, 240, 330, 340) each comprise at least one electric accumulator.

11. System according to claim 10, characterized in that the first storage means (230; 330) comprises at least one nickel-cadmium battery and in that the second storage means (240; 340) comprises at least one lead battery. .

12. System according to claim 10 or 11, characterized in that it further comprises means (361) for maintaining a charging current between the renewable energy source (320) and the battery of the first storage means (330). ).

13. System according to any one of claims 7 to 12, characterized in that the renewable energy source (220; 320) uses solar energy.