In the military, every officer and soldier is numbered, and so are usually properly itemized goods in warehouses or animals in farms. Numbering individual people, things and livestock is a means to improve its organization and management, and this is the idea behind an RFID chip in a solar module.
In most countries every individual has a national identity number, or a health service number, which is nothing else than a tag. All data pertaining to that individual including disease and treatment history, results of any pathology tests, is stored in the health service record under that identity number.
The police will keep a record on anything relevant to the individual according to these numbers – where the individual comes from, where he/she lives and how he/ she behaves within society. The same is possible and increasing reality with solar PV modules.
Tagging solar modules: RFID chip background
In the PV industry, nearly all of us have seen or come accross one type of solar module tagging: serial number barcodes.
However, when large numbers of solar modules are installed in a power generation system they will usually all look alike. How will you know which module performed off-spec and which one was repaired by another person when you were off duty?
Going from module to module with a barcode scanner is a tedious and very limited option. As a manager, you would like to know the performance and repair history of each and every individual module. You would like to decide whether to retire a particular module for persistent bad performance.
All this needs numbering. Numbering can be lettered, embossed, or stamped cheaply, but it has been common that you would have to go close to it and then note.
In a large array, such access may not always be possible. Further, manual reading, recording and cross-checking any data takes time, and automated, remote identification and data transfer is preferred. An RFID chip or more commonly referred to as RFID tag – which is basically the whole device containing the RFID chip with data – integrated with a solar module is thus an interesting solution.
What are RFID tags and how do they work?
RFID is the acronym for radio-frequency identification which uses electromagnetic fields to automatically identify, read and track RFID tags integrated with objects, livestock, animals and even human beings.
RFID tags are memory devices on which multiple information is electronically stored on a built-in RFID chip in form of bits and bytes. They come in different sizes, forms and radio frequencies, such as LF (low frequency), HF (high frequency) and UHF (ultra-high frequency) tags.
RFID tags consist of an integrated circuit (RFID chip or simply IC) that stores and processes the data and an antenna for communication with a reading device – the RFID reader or also called RFID interrogator.
RFID is an Automatic Identification and Data Capture (AIDC) technology that employs radio-frequency waves for data communication between an electronic tag – the RFID tag – and the RFID reader. This environment is commonly referred to as RFID system.
The RFID reader sends a signal to the RFID chip which then responses to the signal and transmits the information electronically stored on it.
Once received, the reader can also store the performance ‘health’ data obtained from the modules and then transfer them to a computer with a few key presses.
The data can later be analyzed to predict trends and make maintenance and life cycle decisions. RFID can in this regard also help in warehousing, physical security and tracing of a given module.
There are three main types of RFID tags:
- Passive RFID tags: have no built-in battery and are activated and powered by radio energy waves when communication with an RFID reader is initiated
Active RFID tags: are powered by a built-in battery and periodically transmit signals that are then intercepted and read by an RFID reader
- Battery-Assisted Passive (BAP) RFID tags: are powered by a small built-in battery and are activated when a related RFID reader is nearby
An RFID chip normally carries about 2 kilobytes (KB) of data which is basically enough to store basic data about the product, but not larger data such as images. However, chips in tags such as passive UHF tags can store up to 8KB of data and are particularly used in the aerospace industry.
One type of RFID tags are the simple and more economic license plate tags which contain only a 96- or 128-bit serial number. They are usually short-lived and disposed of with the packing of the product, thus not suitable for PV modules. The data can be read-only or blank tags on which the data can (later) be written.
All aforementioned three tag types correspond with either an active RFID reader that sends signals to the RFID tag and reads the data stored on them, or a passive RFID reader which merely receives data and works only with active tags.
There are four RFID system work combinations which are:
- Active Reader Active Tag (ARAT): this system uses active tags which are activated with a radio signal transmitted from an active reader
- Active Reader Passive Tag (ARPT): an active reader transmits signals to a passive tag, thus activating it and reading its data
- Passive Reader Active Tag (PRAT): a system in which a passive reader receives signals and thus data from active tags
- Fixed Area Readers: in such system, a reader is installed in a fixed location and covers a defined interrogation area, communicating with tags that enter that area
There are both stationary and portable RFID readers and the devices themselves are generally similar to small computers with operating systems and different functions.
Many RFID readers can do much more beyond RFID interrogating and can include functions such as barcode scanner, 2D scanner, digital camera and communicate with computers and portable devices via bluetooth, such as the handheld RFID from Alien as shown below.
Compulsory solar module RFID tagging – developments
Using RFID tags in solar modules is a relatively new development and method to keep track on the origin and technical performance of individual modules, facilitate replacements and in this regard also insurance and warranty handling.
Being a new trend yet unbeknownst to many in the solar industry, international product standards and trade regimes still largely ignore RFID tags.
However a notable exception is India which makes RFID tagging of solar PV modules a prerequisite in order to obtain subsidies or participate in government policy schemes for grid-connected and off-grid solar projects by the government of India.
In order to qualify for project subsidies and participation in such policy schemes, solar PV module producers and distributors and their respective module types and brands must be registered with and approved by the Government of India’s Ministry of New and Renewable Energy (MNRE).
Only MNRE-approved suppliers and module types produced and/ or imported from abroad and installed in India are entitled to participate in such policy schemes and apply for subsidies.
For MNRE-approval, the PV modules must conform to major quality and standards by the IEC and/ or the Bureau of Indian Standards (BIS)– which are IEC-harmonized standards.
In addition to this, the MNRE also requires that all modules must be traceable and identifiable. For this purpose, they must have an RFID tag that shall contain:
- name of the PV module manufacturer
- name of the manufacturer of the solar cells
- month and year of manufacture of both the module and solar cells
- country of origin of both the module and solar cells
- I-V curve data
- peak wattage, Im, Vm and FF for the module
- unique serial number and model number of the module
- related module certification information (certified standard, date of certification, certifying body)
- other relevant and related information
Until 31 March 2013, the RFID tags could be either placed outside the module or inside the module’s laminate, allowing system and plant owners as well as suppliers to add RFID tags on already produced and installed modules.
However, as RFID tags have also weatherability limitations and because ex post adding of RFID tags potentially invites for abuse and addition of non-verifiable data, since 1 April 2013 the RFID tags are required to be laminated inside the module.
Advantages of solar RFID tagging
Implementing a tag with an RFID chip in a solar PV module comes with considerable advantages as compared to the standard tagging with barcodes.
First of all, RFID systems work automatically and the tag’s RFID chip can store many more of information about a PV module than a normal barcode, including manufacturer and primary material supplier information, production data, electrical and mechanical parameters, serial number, certification data, warranty information and many more historical, numeric and procedural data. However, given the limited capacity of an RFID chip, images cannot be stored on them.
RFID tags are unique which provides for better protection against fake data and information, however this does not guarantee they are fully free from malpractices.
While only one barcode can be scanned and read at a time, an RFID reader can read dozens of modules simultaneously and do not require close physical contact and sight between the reader and the tag. Good RFID readers are capable of singulating a specific PV module for quick tracking.
Thus, depending on the frequency type, distances of 100 and more meters as well as objects between the RFID reader and the tag don’t pose a barrier. This saves a considerable amount of time and associated operational and maintenance costs, especially with regards to large PV projects in form of solar farms.
Provided the RFID tags are laminated inside the PV module, unlike those barcode stickers usually found on the back and sometimes on the side, they cannot be removed and in this way don’t disband under real world conditions.
Disadvantages of solar RFID tagging
Nevertheless, RFID tags are generally also subject to and sensitive to the effects from harsh climatic stress forces, such as very high temperatures and moisture.
Some RFID manufacturers have however come with improved RFID tags that are much more resistant against harsh climates.
Overall, RFID tags come at higher cost than barcodes which is a particular concern in a very price competitive industry such as the solar PV industry.
As the chips of RFID tags have limited capacity and thus cannot save images, crucial quality information such as electroluminescence images of the module cannot be be stored.
Similar to barcodes, an RFID chip is not free from foulplay and there are two major issues and concerns:
- feeding of the RFID tag memory with non-genuine information and incorrectly measured data
- since on-site tagging is much more economical than laminating it into the module during production and promoted as such, one can only guess that this is happening on a large scale
How to ensure that the data on an RFID chip are correct?
It is usually the manufacturer that adds the required data to the RFID tag’s built-in chip. Seen the practice and amount of fake flash test and electroluminescence imaging data, RFID chip data may be actually easily be sugarcoated as well.
In India, it was previously allowed to have an external RFID tag used on PV modules to qualify for MNRE approval. As a result RFID tags were sometimes added later on-site at the already installed PV plant. This was done to meet government requirements. It is questionable whether in every case tags with correct information stored on the RFID chip were added.
The most effective way to counter the potential tagging with incorrect supplier, performance and technical data is being present on-site at the PV factory to oversee the data collection and storing. This is also done by solar PV-specialized 3rd party quality assurance and consultancy companies such as Sinovoltaics.
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