GB2455753A

GB2455753A - Blind with photovoltaic panels

Info

Publication number: GB2455753A
Application number: GB0724823A
Authority: GB
Inventors: Asim Mumtaz
Original assignee: Enecsys Ltd
Current assignee: Enecsys Ltd
Priority date: 2007-12-20
Filing date: 2007-12-20
Publication date: 2009-06-24
Anticipated expiration: 2027-12-20
Also published as: GB0724823D0; GB2455753B

Abstract

A window blind system, preferably a Venetian or Roman blind, having one or more adjustable shades or slats to provide adjustable shading from sunlight, wherein each adjustable shade has a photovoltaic panel on its surface, the blind having an inverter for converting DC power from the photovoltaic panel to AC power suitable for uses as a mains power supply. A controller may be provided with a light sensor such that the shade is adjusted in response to the level of illumination on the inside of the window. The controller may also be configured to use an "empty room" mode in which the level of power provided by the photovoltaic panel is maximised. The controller may also be used to adjust the angle of the shades in order to track this maximum power configuration. A method of using these blinds is also claimed, as is a carrier, for example a CD or DVD, carrying processor or computer code to implement the method of controlling the blind.

Description

Solar Blinds

FIELD OF THE INVENTION

This invention relates to techniques for incorporating solar photovoltaic devices into a building, in particular using window blinds.

BACKGROUND TO THE INVENTION

Blinds are used to shade the inside of a building from the sun in order to keep the building cool. Many different types of window blind are known, including roller blinds and slat blinds in which the slats may be either horizontal or vertical; venetian blinds are a common form of slat blinds. The slats are typically made of either metal or plastic.

The fact that over 30% of electricity usage is in buildings has pushed for the need for low or even zero carbon buildings. Background prior art falls into two categories, solar powered controllers for blinds, and permanently installed solar blinds, fitted into the fabric of a building. Examples of controllers are described in DE 10015881 and US 5,760,558. A window shutter is described in DE 10028433. A technique for using reflecting mirrors serving as blinds of a building for solar heating is described in JP 57 134665. A photovoltaic roller blind is described in DE 20101298 U; the inventor of this is associated with Syglas GmbH which provides solar blinds for facades for roof mounting, as well as a solar blind product fixed between two sheets of glass to capture as well as offer protection from sunlight. The phototronics unit at ASE GmbII near Munich, Germany manufactures thin-film solar modules such as photovoltaic slats based on amorphous silicon.

Further background prior art can be found in: Sala, M., Grassi, A. and Fusco, P., 1996, "PV covered window blinds as a means of large-scale indoor application of photovoltaic energy", Proceedings of 4th European Conference on Solar Energy in Architecture and Urban Planning, 26-29 March 1996, pp. 617-620 and "A new static concentrator PV module with bifacial cells for integration on facades: the PV VENETIAN store", Alonso J, Diaz V; I lemandez M, Bercero F, Canizo C, Pou I, Mohedano R, Benitez P, Minano J C, Luque, A, Sleckemetz S, Melz A, Ilezel R, Jimeno J C, Gutierrez R, Recart F, Bueno G, Rodriguez V, Hernando F, Sukhostavets V M, Beringov S, Sassoli K, lachetti C, Carotid G, Photovoltaic Specialists Conference, 2002. Conference Record of the Twenty-Ninth IEEE Date: 19-24 May 2002, pages 1584-1587 (a study into PV structures funded by the European Consortium Joule III).

However despite this there remains a need for improved, user-friendly techniques for incorporating solar power generation into a building.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is therefore provided a window blind system, the system comprising a window blind for fitting to the inside of a window and having one or more adjustable shades to provide adjustable shading from sunlight, wherein a said adjustable shade has a photovoltaic surface, the window blind system further comprising an inverter coupled to receive dc power from said photovoltaic surface and to provide an ac mains power supply output for coupling to ac grid mains.

Some preferred embodiments of inverters suitable for use with the above system are described in GB 2439 648, WO 2006/048688 and WO 2007/080429 and our co-pending US applications 11/718,875, 11/718,879 and 11/771,593, all of which are hereby incorporated by reference in their entirety.

In some preferred embodiments the system includes a light sensor and a controller to control the adjustable shade in response to a level of illumination on the inside of the window, for example to balance a desired degree of illumination with power generation -simply maximising power generation will tend to adjust the shade to reduce illumination through the window. Thus preferred embodiments of this system also include a mechanism for controlling the one or more adjustable shades using the controller; this may comprise one or more motors or actuators together with an interface to the controller. In some preferred embodiments the system also has a manual mode which enables manual adjustment, via the controller, of the degree of shading.

Thus in embodiments the controller has a plurality of different modes of operation including at least a first mode in which the controller is configured to control the one or more adjustable shades to achieve a user-selected level of illumination on the inside of the window, and a second mode comprising one or both of a manual mode as described above and an "empty room" mode in which the shade is adjusted to substantially maximise power output from the photovoltaic surface and inverter (which will tend to minimise light through the window). The inverters we have described in our previous patent applications (ihid') are tailored to miniaturisation and thus in some preferred embodiments of the system the inverter is housed in a frame of the window blind.

In preferred embodiments the controller is configured to implement a maximum power point tracking (MPPT) procedure for dc power from the photovoltaic surface. That is the controller is configured to control one or both of voltage and current from the photovoltaic surface such that PV surface operates in the vicinity of a point on its I-V characteristic at which maximum power output is achieved. In embodiments a perturb-and-observe procedure is employed.

The skilled person will appreciate that the window blind system may be employed with any of the previously mentioned window blind types including roller blinds, louvre blinds and slat blinds. In the latter two types of blind each louvre or slat is provided by a said adjustable shade having a photovoltaic surface.

The invention also provides a method of equipping a building with an ac power generation capability using a window blind system as described above. The method comprises providing one or more windows of the building with such a window blind system and using this to provide ac power into an ac grid mains supply of the building.

The invention further provides a method of controlling a window blind system as described above, preferably a multi-mode method of controlling the window blind system including at least one mode which aims to control the one or more adjustable shades to achieve a user-selected level of illumination on the side of the window.

Tne controller, in embodiments, comprises a microprocessor coupled to permanent programme memoiy, for example Flash memory or PROM (programmable read only memory) storing processor control code to implement the above-described procedures and, preferably, an MPT procedure. The microprocessor is also coupled to working memory, an interface to the inverter, and interface to the, in general, plurality of PV elements, a light sensor, a user interface such as a control panel and, optionally, non-volatile storage. As the skilled person will appreciate some communication, for example to the light sensor and/or control panel, may be wireless.

The invention further provides processor control code to implement the above-described system and control procedures, for example on an embedded processor. The code may be provided on a carrier such as a disk, CD-or DVD-ROM, programmed memory such as read-only memory (Firmware), or on a data carrier such as an optical or electrical signal carrier. Code (and/or data) to implement embodiments of the invention may comprise source, object or executable code in a conventional programming language (interpreted or compiled) such as C, or assembly code, code for setting up or controlling an ASIC (Application Specific Integrated Circuit) or FPGA (Field Programmable Gate Array), or code for a hardware description language such as Verilog (Trade Mark) or VhDL (Very high speed integrated circuit Hardware Description Language). As the skilled person will appreciate such code and/or data may be distributed between a plurality of coupled components in communication with one another.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other aspects of the invention will now be further described, by way of example only, with reference to the accompanying figures in which: Figure 1 shows a schematic diagram of an overall configuration of a window blind system according to an embodiment of the invention; Figure 2 shows a slat configuration according to an embodiment of the invention; Figure 3 shows a block diagram of a solar PV blind system according to an embodiment of the invention; Figure 4 shows a flow diagram of a maximum power point tracking (MPPT) procedure for use with embodiments of the invention; and Figure 5 shows a flow diagram of a control procedure for a solar PV blind system according to an embodiment of the invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Broadly speaking we will describe a window blind system for capturing the solar energy falling onto buildings, which can be operated in manual and automated modes, and which allows the generation of energy by solar irradiation for feeding directly into the main utility grid. The window blind may be of any suitable variety including, for example, vertical, roman, roller and the like.

We have developed circuits which enable the use of a low power grid connect inverter (see our previous patent applications, ihid), and these facilitate implementation of a grid-connected solar PV blind, in particular facilitating efficient power transfer from the solar blind into the grid.

Our preferred implementation uses thin film amorphous silicon solar cells attached to the surface of slats of a window blind. However the skilled person will understand that other types of thin film solar cell, for example, polymer-based solar cells, may additionally or alternatively be employed. A typical slat of a window blind is made from a thin metal strip; the solar cells used may, in embodiments, actually form the slat itself and therefore not need an additional support -that is in embodiments the thin metal (or other material) strip may be replaced by a solar cell.

Figures 1 and 2 show an example of an implementation of one embodiment of the system, illustrating blind with horizontal slats, although it will be appreciated that the technique may also be employed with vertical slats, roller blinds, and other shading elements.

In embodimenis the solar cells on the slats are fully laminated to prevent any tampering with a cell. Further, preferably the solar cells have wire connections which are arranged to inhibit tampering with the units (for safety). Preferably these connections are arranged so that they are tolerant to rotation without the breaking connections or shorting, for example using suitable wire and encapsulating or otherwise restricting user access to any connections. I lowever some preferred implementations use one or more end covers of the blind to enclose the region where the solar cells are interconnected, as illustrated in Figure 2. In embodiments the solar cells are connected both in series and parallel with other solar cell slats to create a higher voltage input for the micro-inverter.

Preferably the output of the solar cells slats is directly connected to the micro-inverter.

The voltage, current and power of the blinds will depend on the actual size of the window it is being used in. It is possible to employ modularity such that the same electrical unit may be used independent of the slats configuration. The wires from each solar cell are interconnected along the same side where the physical support to slats is given. The wires which are typically used to adjust the angle of the slats arc connected to an axle which is driven by a DC stepper motor. The stepper motor is controlled by a microcontroller circuit which is in turn sent signal via user input. Preferably there are different modes of operation (described later) and depending on which particular mode of operation is selected the microcontroller will control the system accordingly. A micro-inverter is housed in the upper frame of the solar blind. The micro-inverter circuit connects to series of solar cells, the stepper motor and the utility grid.

To facilitate the operation of the inverter under one mode of operation an internal irradiance sensor is used. This is attached to the user interface. The user the interface allows the solar blind to be controlled and configured. This interface communicates to the solar blind conveying the user settings and irradiance level observed by the sensor.

A block diagram of the overall configuration is given in Figure 3. This shows the blocks used for the electronic implementation of the unit. The bulk of the system is housed in the upper frame of the solar photovoltaic blind. This contains the micro-inverter, microcontroller, stepper motor/driver, transceiver, power supply unit and current sensors. (0

The circuit comprises of a number of sub system control and power blocks. The main block is the micro-inverter which connects the solar cells to the utility. The micro-inverter also has one output which connects to a driver and then the stepper motor. The stepper motor controls the orientation of the slats. One microcontroller unit controls all the operations.

The blind can be operated in three modes of operation. One mode is in a completely manual which allows the user to control the angle of the slats. Once put into position the slats will remain there until manually adjusted or the user changes the mode of operation to automatic. Whichever mode of operation the iriverter is placed into, the unit will attempt to transfer power regardless. When it is transferring power the unit will try to optimise power by using maximum power point tracking. This algorithm is based on a "perturb and observe" method.

There are two other modes of operation for the solar blinds. These are both automatic modes and therefore do not need user involvement. The simplest version is a mode whereby the user is not within the room or does not care about the amount of solar irradiance in the room. This mode of operation is referred to as "empty room" mode. In this mode the solar blinds are controlled to capture maximum power. The control loop does not take into consideration the solar irradiance sensor readings in the room. The slats are orientated to capture maximum power, even if this significantly reduces the solar irradiation with in the room. Other possible implementations may use sensors to optimise the amount of solar irradiance captured. The maximum power point algorithm is shown Figure 4.

The third and more complex mode of operation takes in consideration the required level of solar radiation with in the room. The user can define this level or a default setting may be used. In this mode of operation the reading from the solar irradiance meter is used. This reading is compared to the user required irradiance level. This result is sent to the microcontroller unit. If the reading is below, then the slats are adjusted. The slats are adjusted so as to increase the amount of solar irradiance in the room. If there is too much light then the slats arc moved in the opposite direction. The overall flow diagram is shown in Figure 5.

No doubt many other effective alternatives will occur to the skilled person. It will be understood that the invention is not limited to the described embodiments and encompasses modifications apparent to those skilled in the art lying within the spirit and scope of the claims appended hereto.

Claims

CLAIMS: 1. A window blind system, the system comprising a window blind for filling to the inside of a window and having one or more adjustable shades to provide adjustable shading from sunlight, wherein a said adjustable shade has a photovoltaic surface, the window blind system further comprising an inverter coupled to receive dc power from said photovoltaic surface and to provide an ac mains power supply output for coupling to ac grid mains.
2. A window blind system as claimed in claim 1 further comprising a controller and a light sensor coupled to said controller, said controller being configured to control a said adjustable shade in response to a level of illumination on said inside of said window.
3. A window blind system as claimed in claim 2 wherein said controller is configured to control a said adjustable shade responsive to a user-selected level of illumination on said inside of said window.
4. A window blind system as claimed in claim 2 or 3 wherein said controller has at least two different modes of operation, a first mode in which said controller is configured to control a said adjustable shade in response to a level of illumination on said inside of said window and a second mode comprising either a manual mode in which said adjustable shade is controlled by said controller in response to a user-selected level of shading, and an empty room mode in which a said shade is adjusted to substantially maximise a level of power provided from said photovoltaic surface.
5. A window blind system as claimed in claim 4 wherein said controller has three user-selectable modes of operation, said first mode, said manual mode, and said empty room mode.
6. A window blind system as claimed in any one of claims 2 to 5 wherein said controller is configured to implement maximum power point tracking for said dc power from said photovoltaic surface.
7. A window blind system as claimed in any preceding claim wherein said inverter is housed in a frame of said window blind.
8. A window blind system as claimed in any preceding claim wherein said window blind comprises a slat blind having a plurality of said adjustable shades each comprising a slat of said window blind.
9. A method of equipping a building with an ac power generation capability, the method comprising providing one or more windows of the building with a window blind system as claimed in any preceding claim, and using said window blind system to provide power into an ac grid mains power supply of said building.
10. A method of controlling a window blind system as claimed in any one of claims 2 to 6, the method comprising sensing a level of illumination on said inside of said window and controlling a said adjustable shade in response to said sensing.
II. A method as claimed in claim 10 wherein said controlling comprises controlling ma selected one of at least two different modes of operation, a first mode in which said controller is configured to control a said adjustable shade in response to a level of illumination on said inside of said window and a second mode comprising either a manual mode in which said adjustable shade is controlled by said controller in response to a user-selected level of shading, and an empty room mode is which a said shade is adjusted to substantially maximise a level of power provided from said pholovoltaic surface.
12. A earner carrying processor control code to, when running, implement the method of claim lOor 11. /0