Energy storage device for a photovoltaic system, and method for operating an energy storage device of a photovoltaic system

Abstract

An energy storage device for a photovoltaic system includes: at least one first energy store which has a first cycle stability; at least one second energy store which has a second cycle stability, the first cycle stability being higher than the second cycle stability; and a control device which is designed to discharge the first energy store in a first operating mode and to discharge the second energy store in a second operating mode.

Claims

1. An energy storage device for a photovoltaic system, comprising: at least one first energy store which has a first cycle stability; at least one second energy store which has a second cycle stability, wherein the first cycle stability is higher than the second cycle stability; and a control device configured to discharge the first energy store in a first operating mode and to discharge the second energy store in a second operating mode, wherein the control device has a first connection for the first energy store and a second connection for the second energy store, the first connection and the second connection being separate from one another, wherein the control device is coupled to the first and second energy stores in order to enable electrical power from the first energy store and the second energy store to flow through the control device, wherein: the control device is directly coupled to electric consumers that consume electrical power, the control device is coupled to the photovoltaic system, the photovoltaic system generating electrical current from solar energy, the first energy store is configured as a lithium-iron phosphate accumulator, the second energy store is configured as a lead accumulator, and the second operating mode is an operating mode in which: the first energy store and the second energy store are not chargeable by the photovoltaic system on account of the photovoltaic system having ceased to generate the electrical current, a delay occurs between a time at which the photovoltaic system ceases to generate the electrical current and a time at which the second energy store begins to be discharged from a fully charged state, during the delay the first energy store is discharged until a time at which a state of charge of the first energy store is discharged to a predefined lower limiting value, and the time at which the state of charge of the first energy store is discharged to the predefined lower limiting value coincides with the time at which the second energy store begins to be discharged from a fully charged state.

2. The energy storage device as recited in claim 1, wherein the first operating mode is an operating mode in which the first energy store and the second energy store are chargeable by the photovoltaic system.

3. The energy storage device as recited in claim 1, wherein the second operating mode is an operating mode in which the first energy store has a low state of charge.

4. The energy storage device as recited in claim 1, wherein the second operating mode is an operating mode in which there is an increased energy demand by consumers coupled to the first energy store and to the second energy store.

5. The energy storage device as recited in claim 1, wherein the first energy store and the second energy store are configured as electrical accumulators of the same type.

6. The energy storage device as recited in claim 1, wherein the control device is designed in such a way that for a correct connection, only a plug which corresponds to the connection fits into the connection.

7. The energy storage device as recited in claim 6, wherein the plug fits into the connection due to a shape of the plug fitting into the connection.

8. A control device for an energy storage device, wherein the energy storage device includes at least one first energy store which has a first cycle stability and at least one second energy store which has a second cycle stability, the first cycle stability being higher than the second cycle stability, the control device comprising: a first connection for connecting to the at least one first energy store which has the first cycle stability; a second connection for connecting to the at least one second energy store which has the second cycle stability; and a control element configured to discharge the first energy store in a first operating mode and to discharge the second energy store in a second operating mode, wherein the control element connects to the first energy store via the first connection and connects to the second energy store via the second connection, the first connection and the second connection being separate from one another, wherein the control device is coupled to the first and second energy stores in order to enable electrical power from the first energy store and the second energy store to flow through the control device, wherein: the control device is directly coupled to electric consumers that consume electrical power, the control device is coupled to a photovoltaic system that generates electrical current from solar energy, the first energy store is configured as a lithium-iron phosphate accumulator, the second energy store is configured as a lead accumulator, and the second operating mode is an operating mode in which: the first energy store and the second energy store are not chargeable by the photovoltaic system on account of the photovoltaic system having ceased to generate the electrical current, a delay occurs between a time at which the photovoltaic system ceases to generate the electrical current and a time at which the second energy store begins to be discharged from a fully charged state, during the delay the first energy store is discharged until a time at which a state of charge of the first energy store is discharged to a predefined lower limiting value, and the time at which the state of charge of the first energy store is discharged to the predefined lower limiting value coincides with the time at which the second energy store begins to be discharged from a fully charged state.

9. The control device as recited in claim 8, further comprising: a human-machine interface configured to enable a user to input user data for establishing at least one of the first and second operating modes.

10. A method for operating an energy storage device of a photovoltaic system, the energy storage device having a first energy store which has a first cycle stability and a second energy store which has a second cycle stability, the first cycle stability being higher than the second cycle stability, the method comprising: selectively establishing one of a first operating mode or a second operating mode; discharging the first energy store in the first operating mode; and discharging the second energy store in the second operating mode, wherein a control device has a first connection for the first energy store and a second connection for the second energy store, the first connection and the second connection being separate from one another, wherein the control device is coupled to the first and second energy stores in order to enable electrical power from the first energy store and the second energy store to flow through the control device, wherein: the control device is directly coupled to electric consumers that consume electrical power, the control device is coupled to the photovoltaic system, the photovoltaic system generating electrical current from solar energy, the first energy store is configured as a lithium-iron phosphate accumulator, the second energy store is configured as a lead accumulator, and the second operating mode is an operating mode in which: the first energy store and the second energy store are not chargeable by the photovoltaic system on account of the photovoltaic system having ceased to generate the electrical current, a delay occurs between a time at which the photovoltaic system ceases to generate the electrical current and a time at which the second energy store begins to be discharged from a fully charged state, during the delay the first energy store is discharged until a time at which a state of charge of the first energy store is discharged to a predefined lower limiting value, and the time at which the state of charge of the first energy store is discharged to the predefined lower limiting value coincides with the time at which the second energy store begins to be discharged from a fully charged state.

11. The method as recited in claim 10, wherein the second energy store in the first operating mode is charged to a state of charge greater than 80% of nominal capacity of the second energy store.

12. The method as recited in claim 10, wherein the second energy store in the first operating mode is charged to a state of charge in the range of 50%-70% of nominal capacity of the second energy store.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic block diagram of an energy storage device according to a first specific embodiment of the present invention.

(2) FIG. 2 shows a schematic power diagram as a function of time of a first energy store and of a second energy store according to one specific embodiment of the present invention.

(3) FIG. 3 shows a schematic power diagram as a function of time of a first energy store and of a second energy store according to one specific embodiment of the present invention.

(4) FIG. 4 shows a schematic flow chart of one specific embodiment of the method for operating an energy storage device.

DETAILED DESCRIPTION OF THE INVENTION

(5) Unless stated otherwise, identical or functionally equivalent elements and devices are provided with the same reference numerals in all of the figures.

(6) FIG. 1 shows a schematic block diagram of an energy storage device 1 according to a first specific embodiment of the present invention. Energy storage device 1 has a first energy store 2 which has a first cycle stability, and a second energy store 3 which has a second cycle stability. The first cycle stability of first energy store 2 is higher than the cycle stability of second energy store 3. Energy stores 2 and 3 may be designed as lead accumulators or as lithium-ion accumulators, for example.

(7) First energy store 2 and second energy store 3 are electrically coupled to a control device 4. The control device preferably has a separate connection for energy stores having a high cycle stability, and a separate connection for energy stores having a low cycle stability. This connection may, for example, be designed in such a way that for a correct connection, only a plug which corresponds to the connection fits into the connection, for example due to a certain shape. In addition to having a control element 8, control device 4 has a human-machine interface 9 which is designed for inputting user data for establishing the first and/or the second operating mode, described below.

(8) In addition, a system 6 which recovers energy from regenerative sources is coupled to control device 4. For example, a photovoltaic system 6 which generates electrical current from solar energy is coupled to control device 4. In addition, electrical consumers 5 which consume electrical power are coupled to control device 4. Photovoltaic system 6 generates electrical current which may be delivered directly to electrical consumers 5, and/or used for charging first energy store 2 and/or second energy store 3. In addition, control device 4 is coupled to a public power grid 7.

(9) FIG. 2 shows a schematic power diagram as a function of time of a first energy store 2 and of a second energy store 3 according to one specific embodiment of the present invention. In addition, a power diagram of a photovoltaic system 6 is shown for illustrating the mode of operation of energy storage device 1.

(10) The power diagram of the photovoltaic system is illustrated at the top, the vertical axis representing the power of the photovoltaic system and the horizontal axis representing time.

(11) The power diagram of first energy store 2 is illustrated in the middle of FIG. 2, and the power diagram of second energy store 3 is illustrated at the bottom of FIG. 2. The vertical axis of the power diagrams of the energy stores represents the state of charge (SOC) of the energy stores.

(12) It is apparent that first energy store 2 is charged and discharged while photovoltaic system 6 is generating current. For example, first energy store 2 is discharged by consumers 5 which are directly coupled to control device 4. This consumption is also referred to as internal consumption. It is also possible for the first energy store to feed energy into a public power grid 7.

(13) It is also apparent that second energy store 3 is charged while photovoltaic system 6 is generating current. However, second energy store 3 is not discharged. This state is, for example, the first operating mode, in which only first energy store 2 is discharged.

(14) Beginning at the point in time at which photovoltaic system 6 no longer generates current, since, for example, the sun is no longer shining or the weather conditions do not allow this, first energy store 2 and/or second energy store 3 is/are discharged.

(15) Control device 4 recognizes with the aid of sensors that photovoltaic system 6 is no longer generating current, and then enables first energy store 2 and second energy store 3 so that they may be discharged. This state is the second operating mode, for example.

(16) FIG. 3 shows a schematic power diagram as a function of time of a first energy store 2 and of a second energy store 3 according to one specific embodiment of the present invention. The same as in FIG. 2, FIG. 3 illustrates a power diagram of a photovoltaic system at the top. It is apparent that first energy store 2 is charged and discharged. Second energy store 3 has already been fully charged, for example with energy from the photovoltaic system and/or a public power grid. First energy store 2 is discharged as soon as photovoltaic system 6 is no longer generating current.

(17) When the state of charge of second energy store 3 reaches a predefined lower limiting value, second energy store 3 is enabled and discharged. The service life of energy storage device 1 may be significantly increased in this way. In addition, the installation costs may be kept low, since an energy store having a low cycle stability results in lower costs.

(18) FIG. 4 shows a schematic flow chart of one specific embodiment of a method for operating an energy storage device 1. It is established in step S1 whether the energy storage device should be operated in the first operating mode or in the second operating mode. Energy storage device 1 is then operated either in the first operating mode or in the second operating mode.

(19) Although the present invention has been described above with reference to preferred exemplary embodiments, it is not limited thereto, and may be modified in numerous ways. In particular, the present invention may be changed or modified in various ways without departing from the core of the present invention.