WO2017072526A1

WO2017072526A1 - Power generation

Info

Publication number: WO2017072526A1
Application number: PCT/GB2016/053359
Authority: WO
Inventors: David Gordon
Original assignee: Own Energy Ip Ltd
Priority date: 2015-10-28
Filing date: 2016-10-28
Publication date: 2017-05-04
Also published as: GB201519056D0; GB201618283D0; GB2545079A

Abstract

A power generation apparatus (10) comprising a power source (12,14) having a DC output (32, 34);a battery charge controller (24) having an input connected to the DC output of the power source (12,14) and an output connected to a battery (26); a DC load (28) connected to the battery(26); and an inverter (20) comprising an input (38) connected to the DC output (32,34) of the power source (12,14) and an output (40) connected to a mains electricity supply (22), the power generation apparatus (10) further comprising :a controller (16 )adapted to selectively connect the DC output (32,34) of the power source (12,14) to the input of the battery charge controller (24) and the input (38) of the inverter (38).

Description

Title: Power generation

Description:

This invention relates to power generation and in particular to a hybrid, semi-off-grid power generation system that can be used for powering a local load as well as for exporting power to a mains electricity grid.

Micro power generation is a relatively mature technology and involves the use of micro power generators that users can deploy to generate "off grid" power, most often from renewable energy sources. The user can use the power generated off-grid to power an appliance or a premises. However, because micro power generation capacity tends to be variable, it is usual to combine it with a grid connection and a feed-in inverter. Thus, the user can, typically using a feed-in control system:

1 ) where local power generation meets the local demand: use the generated power locally to power a premises; and/or

2) where local power generation exceeds the local demand: use the generated power locally to power a premises and to export surplus power to the grid via a feed-in connection; and/or

3) where local power generation is lower than the local demand: use the generated power locally to power a premises and to import the local power deficit from the grid via a feed- in connection.

So-called "feed-in" arrangements, such as those described above, are commonplace and nowadays quite widely-implemented.

However, micro power generation systems, especially those from renewable energy sources, such as wind or water turbines, photovoltaic cells and the like, typically output micro-generated power as a relatively low, DC voltage, such as 12VDC, 24VDC. In order to export power to the grid, or to connect the micro-generator to a local power distribution system (e.g. the input of a domestic consumer unit), an inverter is required to convert the micro-generator's DC output into mains voltage (e.g. 220VAC, 50Hz).

In such a situation, the inverter typically has a minimum and maximum input power rating and when the power output from the micro-generator falls between these threshold values (i.e. above the minimum power rating and below the maximum power rating), the inverter can operate to convert the micro-generator's DC output into AC power for use locally and/or grid export. However, when the power output from the micro-generator falls outside these threshold values (i.e. below the minimum power rating, or above the maximum power rating), the inverter disconnects the micro-generator's DC output from the inverter's DC input, thereby preventing local use of the micro-generated power and the export of power to the grid. The reasons for this configuration are manifold, but are essentially linked to preventing disruption to the grid supply for other users of the grid (i.e. to prevent draining power from the grid and/or overloading certain part of it with excessive power).

The switching out of micro power generation is generally considered to be undesirable (because it represents a loss of power generation opportunity), but nevertheless unavoidable (to prevent disruption of, or damage to, the grid).

A need therefore exists for an improved and/or an alternative power generation system which addresses and/or overcomes one or more of the above problems. A need also exists for an alternative feed-in arrangement that minimises loss of power generation opportunity. This invention aims to address one or more of the foregoing problems and/or to provide a solution.

Various aspects of the invention are set forth in the appendent claims.

According to one aspect of the invention, there is provided a power generation apparatus comprising a power source having a DC output; a battery charge controller having an input connected to the DC output of the power source and an output connected to a battery; and a DC load connected to the battery; and the apparatus further comprising: an inverter comprising an input connected to the DC output of the power source and an output connected to a mains electricity supply, the power generation apparatus further comprising: a controller adapted to selectively connect the DC output of the power source to the input of the battery charge controller and the input of the inverter.

The or each power source suitably comprises a micro-generator, such as a wind turbine, a water turbine, or a photovoltaic cell.

The power source or sources output a DC electrical voltage, which is used to charge the battery via the battery charge controller. A battery charge sensor is suitably provided for sensing the instantaneous charge state of the battery. Suitably, the battery charge sensor is operatively connected to the battery charge controller to signal when the battery needs recharging and/or when it is fully charged. The battery charge controller suitably comprises a call circuit, operatively connected to the controller and configured such that when the battery is sensed to need recharging, the controller connects the DC output of at least one of the power sources - to recharge the battery via the battery charge controller.

The DC load is connected to the battery and suitably comprises a low-voltage load having a power requirement substantially matching that of the battery. In one example, the load comprises a 12VDC lighting circuit and the battery comprises a 12VDC battery. In another example, the load comprises a 24VDC lighting circuit and the battery comprises a 24VDC battery. The load suitably comprises an LED lighting circuit.

Switch means is suitably provided for selectively connecting and/or disconnecting the load to or from the battery. The switch means may comprise a light-sensitive circuit (e.g. an LDR circuit), a remotely-operated switch, and/or a timer switch.

The inverter comprises an input that can be connected to the DC output of the or each power source by the controller. A power sensing device is suitably provided for sensing the instantaneous power output of the or each power source. In many situations, connecting the power source or sources to the grid, via the feed-in inverter is prohibited where the instantaneous power output of the or each power source falls below a specified lower power limit (for example, when the wind speed falls below 4m/s, in the case of certain micro wind turbines), and/or above a specified upper power limit. The controller is suitably configured to connect the DC input of the feed-in inverter to the or each power source when the sensed power output falls somewhere between the aforesaid lower and upper power limits.

Suitably, the controller is configured to draw power from the DC side of the feed-in inverter in certain situations. Such situations may include, but are not necessarily limited to, the battery charge controller requiring power to recharge the battery, but the sensed power output from the power sources being insufficient to recharge the battery. In such an exemplary situation, the DC side of the feed-in inverter may be connected to the DC input side of the battery charge controller. Thus, the feed-in inverter may comprise a bidirectional inverter, that is to say one that can convert from DC to AC (e.g. during export to the grid) or from AC to DC (e.g. during import from the grid), as required.

The power generation apparatus of the invention may be used in street lighting or other similar installations, such as on powered motorway gantries, illuminated signage and the like.

Embodiments of the invention shall now be described, by way of example only, with reference to the accompanying drawings in which:

Figures 1 , 2 and 3 are schematic system diagrams illustrating one embodiment of a power generation apparatus in accordance with the invention in different modes of operation; and

Figure 4 is a schematic diagram of a semi-off-grid street light in accordance with the invention. Referring to Figures 1 to 3 of the drawings, a power generation apparatus 10 according to the invention is shown in various modes of operation. The power generation apparatus 10 comprises one or more power sources 12, 14, which, in the illustrated embodiment, are a photovoltaic cell 12 and a wind turbine 14, respectively, but it will be appreciated that any type of power source could be connected to the system. Generally, the power generation apparatus 10 also comprises a controller 16, a bidirectional feed-in inverter 20 (connecting the power generation apparatus 10 to a power grid 22), a battery 26 for powering a local load 28 and a battery charge controller 24.

The power sources 12, 14 have DC outputs 32, 34 that are connected to the input of the controller 16 and a power sensing device 18 is interposed between the power sources 12, 14 and the controller 16 to sense the instantaneous power output of the power sources 12, 14. The power sensing device 18 determines whether the power output of the power sources 12, 14 is: below a lower threshold output power; above an upper threshold output power; or between the lower and upper threshold power levels and sends an appropriate control signal 36 to the controller 16.

In Figure 1 , the power generation apparatus 10 is in a normal operating mode, that is to say, with the power sources 12, 14 outputting power at their DC outputs 32, 34 at a level falling somewhere between the lower and upper threshold power levels. In this situation, the controller 16 connects the DC outputs 32, 34 to a DC input side 38 of the feed-in inverter 20, where it is converted to AC and exported to the grid 22, via a grid export connection 40.

A load 28, such as a lighting circuit, is connected to the power generation apparatus 10. In one example, the load 28 comprises one or more 12VDC LEDs used in street lighting. The LEDs are powered by a 12VDC power supply, and can therefore be powered by the battery 26. A switch 30 is provided for switching the load 28 on or off (which, in the example of a street light, may be a light-dependent resistor circuit, which switches the LEDs on at night time and off during the day). The load 28 draws power from the battery 26, and the charge level of the battery 26 is topped-up by the charge controller 24. The instantaneous battery change level is detected by the battery charge controller 24 via a sensing circuit 42, and the battery charge controller 24 can "call" for power (when top-up charging is needed) via a call circuit 44. Thus, as the load 28 draws power, the battery 26 charge level falls, which fall is detected by the sensing circuit 42 and the battery charge controller 24 calls 44 for power and the controller connects the 12VDC outputs 32, 34 of the power source or sources 12, 14 to recharge the battery 26. Once the battery's charge has been sufficiently topped-up, the power sources 12, 14 are disconnected from battery charge controller 24 by a circuit within the controller 16.

The power generation apparatus 10 can operate in this mode when the amount of power being generated by the power sources 12, 14 lies somewhere between the lower and upper threshold power levels mentioned previously. However, when the amount of power being generated by the power sources 12, 14 falls below a lower threshold output power; or rises above an upper threshold output power (as mentioned previously, and as indicated by dashed arrows 32, 34), export of power to the grid is not permitted, and the controller 16 disconnects the feed-in inverter 20 from the power sources 12, 14, as shown in Figure 2.

Even though the amount of power being generated by the power sources 12, 14 is either below the lower threshold output power or above an upper threshold output power (thus preventing power export to the grid 22), the power sources 12, 14 may, nevertheless, still be generating power, which power would otherwise be wasted. In this case, the power generation system uses the power to charge and recharge the battery. Thus, the load 28 can draw power from the battery 26 as and when needed (as indicated by dashed arrow 46) depending on the on/off state of the switch 30. Thus, the load 28 can be operated "off-grid" using only power from the battery 26, which can be recharged as and when needed, by the power sources 12, 14, via the battery charge controller 24, as described above.

Referring now to Figure 3 of the drawings, the power sources 12, 14 have been under- generating for a period time and their power outputs 32, 34 have been insufficient to keep the battery 26 sufficiently charged. The battery charge controller 24 senses this via its battery charge sensor circuit 42 and calls 44 for power from the controller 16. However, due to insufficient power generation by the power sources 12, 14, as sensed by the power sensing device 18, recharging the battery 26 using the power sources 12, 14 is not possible. In this situation, the controller 16 connects the feed-in inverter to the battery charge controller 24, which now draws power 46 from the grid 22, which is inverted to a suitable DC power supply 48 by the feed-in inverter 20, and used to recharge the battery 26 via the batter charge controller 24. Once the battery 26 has fully, or sufficiently, recharged, the battery charge controller 24 stops calling 44 for power, and the controller 16 can disconnect the feed-in inverter 20 and reverts the system 10 to that described above in relation to Figure 2 of the drawings.

It will be noted from the foregoing description that the invention differs from known feed-in power generation systems by virtue of the fact that even though a bidirectional feed-in inverter 20 is provided, as well as a power storage device (in this case, the battery 26); the system 10 is not configured to discharge the battery 26, through the feed-in inverter, to the grid 22. In other words, the battery is used only as a low-voltage (e.g. 12V or 24V) DC power storage device for a locally connected, low- voltage, load, such as a 12V or 24V LED lighting circuit. This configuration obviates the need for large batteries or other devices for storing electrical power, which greatly simplifies the construction and operation of the device, as well as delivering an economic solution. By only needing a relatively small capacity battery, the size of the battery can be made sufficiently small, for example to fit inside a street light support tube or base.

A further distinction of the invention over known power generation systems is that the load is powered only by the battery. Thus, there is no need to install an additional transformer or inverter for powering the load off the mains power supply, which configuration results in avoiding energy losses associated with using, say, a transformer, to power a low-voltage DC load off the mains power supply. In other words, the invention provides a dual power system comprising a DC circuit (i.e. the power source(s), the charge controller, the battery and the load) for powering the load, and a separate AC circuit (i.e. the power source(s), the inverter and the mains connection) for exporting power to the grid. That said, the system can, if necessary, connect the mains connection to the DC circuit, via the inverter, but in this situation, the power flow is only from the grid to the battery, and not from the battery to the grid, as it is known to do.

An example of a street light 60 in accordance with the invention is shown in Figure 4 of the drawings, in which a street light 60 comprises a main support tube 62 affixed to the ground 64 via a hatch-accessible base member 66. The base member 66 houses the battery 26, battery charge controller 16, controller 16 and feed-in inverter 22, and the feed-in inverter 22 is connected to the mains electricity supply 22 (the grid) via a mains connection 44. The connections between the various components are as described previously, and are not indicated in Figure 4 for clarity. Nevertheless, it will be appreciated that the street light 60 has a lamp module 68 housing a low-voltage LED light circuit 28 (being the load described previously). The lamp module 68 has an LDR switch circuit 30 for switching the LED light circuit 28 on or off, as necessary. In certain embodiments of the invention, the switch 30 is centralised, so that rather than switching each street light 60 on or off individually, they are switched in groups (e.g. a street at a time, or a region at a time, or on a timer circuit). The street light 60 additionally comprises a wind turbine 14 and a solar PV panel 12 providing power from renewable energy sources.

Thus, the street light 60 is configured to power its LED lights 28 off the battery 26, which battery is kept charged by the power sources 12, 14. However, when the power sources 12, 14 are unable to maintain the battery 26 charge level, the street light 60 can optionally recharge the battery 26 using mains electricity. Further, when the power sources 12, 14 are able to export power to the grid 22, they do so via the feed-in inverter 22. The street light 60 of Figure 4 therefore provides a hybrid, semi-off- grid lighting solution that is able to export locally-generated power to the grid 22 and/or to power its own LED lighting circuit 28 independently of the grid provided the power sources 12, 14 are generating some power - even if the locally-generated power is insufficient, or too high, to meet the requirements for export.

The invention is not restricted to the details of the foregoing embodiments, which are merely exemplary of the invention. For example, any shapes, sizes, dimensions, capacities, voltages etc. mentioned or implied are exemplary, rather than limiting, notwithstanding that the scope of the invention is set forth in the appendent claims.

Claims

Claims:

A power generation apparatus (10) comprising: a power source (12, 14) having a DC output (32, 34); a battery charge controller (24) having an input connected to the DC output of the power source (12, 14) and an output connected to a battery (26); a DC load (28) connected to the battery (26); and an inverter (20) comprising an input (38) connected to the DC output (32, 34) of the power source (12, 14) and an output (40) connected to a mains electricity supply (22), the power generation apparatus (10) further comprising: a controller (16) adapted to selectively connect the DC output (32, 34) of the power source (12, 14) to the input of the battery charge controller (24) and the input (38) of the inverter (38).

The power generation apparatus (10) of claim 1 , wherein the or each power source (12, 14) comprises a micro-generator.

The power generation apparatus (10) of claim 1 or claim 2, wherein the or each power source (12, 14) comprises any one or more of the group comprising: a wind turbine (14); a water turbine; and a photovoltaic cell (12).

The power generation apparatus (10) of any preceding claim, comprising a battery charge sensor (42) adapted to sense the instantaneous charge state of the battery (26).

5. The power generation apparatus (10) of claim 4, wherein the battery charge sensor (42) is operatively connected to the battery charge controller (24) to signal when the battery (26) needs recharging and/or when it is fully charged.

6. The power generation apparatus (10) of claim 4, wherein the battery charge controller (24) comprises a call circuit operatively connected to the controller (16) and configured to output a "call" signal to the controller (16) when the battery (26) is sensed to need recharging, and wherein upon receipt of the said "call" signal, the controller (16) is adapted to connect the DC output (32, 34) of at least one of the power sources (12, 14) to an input of the battery charge controller (24) to recharge the battery (26).

7. The power generation apparatus (10) of any preceding claim, wherein the load (28) comprises a low-voltage DC load having a power requirement substantially matching the power rating of the battery (26).

8. The power generation apparatus (10) of any preceding claim, wherein the load (10) comprises an LED lighting circuit.

9. The power generation apparatus (10) of any preceding claim, further comprising switch means (30) for selectively connecting and/or disconnecting the load (28) to or from the battery (26), respectively.

10. The power generation apparatus (10) of claim 9, wherein the switch means (30) comprises any one or more of the group comprising: a light-sensitive circuit; an LDR circuit; a remotely- operated switch; and a timer switch.

1 1. The power generation apparatus (10) of any preceding claim, further comprising a power sensing device (18) adapted, in use, to sense the instantaneous power output (32, 34) of the or each power source (12, 14).

12. The power generation apparatus (10) of claim 1 1 , wherein the controller (16) is configured to connect the DC output (32, 34) of the or each power source (12, 14) to the DC input side (38) of the inverter (20) when the sensed instantaneous power output of the or each power source (12, 14) is above a specified lower power limit and below a specified upper power limit, but not otherwise.

1 3. The power generation apparatus (10) of any preceding claim, wherein the inverter (20) comprises a bidirectional inverter.

14. The power generation apparatus (10) of claim 1 3, wherein the controller (16) is adapted to selectively connect the DC side (38) of the inverter (20) to the DC input side of the battery charge controller (24).

1 5. The power generation apparatus of claim 14, wherein the controller (16) is adapted to selectively connect the DC side (38) of the inverter (20) to the DC input side of the battery charge controller (24) when the battery charge controller (24) requires power to recharge the battery (26), but when the power output of the or each power source (12, 14) is insufficient to recharge the battery (26).

16. A street light (60), powered motorway gantry or illuminated sign comprising the power generation apparatus (10) of any preceding claim. The street light (60), powered motorway gantry or illuminated sign of claim 16, comprising a main support tube (64) affixed to the ground (64) via a base member (66) housing any one or more of the battery (26), battery charge controller (24), controller and inverter (20), and wherein the inverter (20) is connected to a mains electricity supply (22) via a mains connection (40).

The street light (60), powered motorway gantry or illuminated sign of claim 16 or claim 17, comprising a lamp module (68) housing a low-voltage LED light circuit (28).

The street light (60), powered motorway gantry or illuminated sign of claim 18, wherein the lamp module (68) comprises a light-sensitive switch (30) adapted, in use, to switch the LED light circuit (28) on at night time and off during the day.

The street light (60), powered motorway gantry or illuminated sign of any of claims 16 to 19 forming a hybrid, semi-off-grid lighting solution that is configured to export locally-generated power to the grid (22) and/or to power its own lighting circuit (28) independently of the grid (22).