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LID vs PID: What’s degrading your solar panels?

PV modules may experience one or both of two forms of degradation: Potential Induced Degradation (PID) and Light Induced Degradation (LID). PID refers to degradation induced by high voltages. On the other hand, LID refers to degradation that occurs due to sunlight.

LID – Light Induced Degradation

PV modules experience degradation naturally without it being owing to the flow of electrons across p-n junctions within the module. Modules experience power loss rates of approximately 3% within the first year of usage. Thereafter, a phenomenon known as power stabilization is said to occur, which refers to lower levels of power loss in subsequent years of usage at rates typically around 0.8%. This indicates that the rates of degradation are most prominent initially. LID of a PV module refers to the power loss and other loss of performance of crystalline p-type boron doped silicon solar cells after the first few hours upon exposure to sunlight. LID typically varies between 1-3%. The degradation of cells by sunlight is highly dependent on the quality of the wafer manufactured and is the result of a defect known as “boron oxygen complex”. This defect occurs owing to oxygen being trapped in the silicon as part of the “Czochralski process” during manufacture.

PID – Potential Induced Degradation

The second form of degradation PID caused by voltages as high as 1000 V and above together with high temperatures and humidity. Furthermore, the accumulation of dirt and the degradation of glass can catalyse the process owing to the release of sodium ions. Modules that have experienced such degradation generally contain some black cells that are non-functional and found near the frame. This occurs due to a large flow of electrons through such cells, due to the differential in voltage across the pane.
The IEC standard 62804 created to assess the capability of PV modules to withstand high voltages and not experience any degradation as a result. The proposed method involves the subjection of PV modules to a DC voltage bias of magnitude of 1000 V at a humidity of 85% rH and a temperature of 60 ºC, for a period of 96 hours. The graph shows the Pmpp/W rating (Pmpp is the panel maximum power) together with the pictures of the panel exhibiting Electroluminescence before and after the test

Solar panel PID stress test graph [Source: http://sinovoltaics.com/quality-control/pid-lid-devastating-phenomena-pv-plants/]

It can be seen from the above graphic that the PV experienced a power loss of around 25% over the course of the PID test. As per the IEC standard 60924, for the module to meet the required standard, this measurement must not exceed 5%. It may be argued that there is variability across PV modules. However, the said standard has been decided based on tests on a large number of various PV panels.

Implications

PID and LID are two different sources of degradation of cells in PV panels and are therefore ratings pertaining to these phenomena should be carefully considered. Although the phenomena may be well known among installers of such panels, ratings are often neglected and thus affect the long-term life of the PV panel. This is particularly important for the purpose of making accurate forecasts pertaining to energy generation. In the absence of PID and LID being considered, the panel will incorrectly be thought to be performing lower than its rated efficiency. Sophisticated measurement tools allow for such metrics to be recalculated based on deviations of real performance from predicted performance.

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Solar efficiency: are defective panels hurting your bottom line?

The solar industry is booming, yet plant operators are being affected by underperforming panels. To earn a profit in this global, dynamic market, solar farm managers must answer an important question: how can you ensure your solar array is working well?
Normally, Operations and Maintenance (O&M) teams periodically check performance, usually by analyzing the graphs on the monitoring solution and sampling a portion of your plant’s panels. But this can be expensive, and won’t give you a detailed account of all your panels. If unsampled panels are defective, or something goes wrong outside of testing, your profits start to shrink. And expired warranties only makes things worse.
At Raycatch, we believe there’s a better way.
DeepSolar from Raycatch gives you daily diagnostics on all your solar panels. Using sophisticated AI technology, DeepSolar tells you where defective panels are and what’s wrong with them. We’ll then work with you to create a recovery strategy that aligns with your business goals – either helping you claim under warranty, repair faults, or replace panels and strings.
DeepSolar could grow your revenue 2-7%, as well as saving you 12-20% on O&M costs. Already, we’ve helped one of our clients replace 20% of their panels absolutely free. Optimising your solar plant ensures your getting value for money, but more importantly, helps maximise profit in an industry working hard to make the world a better place.
Due to the fast growing of solar energy installations in the world, the operators need to maximise the output of their panels, or risk underperforming. An inefficient solar farm reduces returns on investment, endangers market share, and restricts expansion. It’s crystal clear that understanding solar efficiency is vital – the question is, how successful has your monitoring strategy been?
Operations and Maintenance (O&M) teams can only do so much with limited budgets. How often do you run I-V tests on your panels and strings? Once, maybe twice per year? Plus a diagnostic if output drops significantly?
Given the pressure to keep costs low, it’s unsurprising that O&M teams test just a few times a year, and in many cases, only test a sample of components. We’ve seen testing of 1-5 MW solar farms using samples of just 20-100 panels. There’s a global shortage of solar engineering talent, and consequently, labour costs are high.
But what if you could do daily diagnostic tests on all your panels, automatically, for a fraction of the cost of O&M testing? What if you could use this information to repair or replace defective panels – even strings – before they impact performance? That’s exactly what DeepSolar does.
DeepSolar conducts daily diagnostic testing on your entire solar array without the need for extra hardware or staff. We gather plant performance data from your sensors, combine it with metadata, and normalise it for temperature, irradiance, dust, pollen, shading, and other sources of “noise”. This gives us virtual I-V curves that are as robust as those taken under laboratory conditions. We then correlate the data with physical and electrical models and process the results through our AI algorithm to give a full diagnostic report of your array’s performance.
Light induced degradation (LID) is an inevitable consequence of the technology most solar farms employ, and potential induced degradation (PID) can also be an issue in some installations (you are welcome to read about it in our next blog). But neither LID nor PID should affect your bottom line. Frequent, regular monitoring and fast remediation ensure your panels are working at their best, all year round.
We can pinpoint defects to an individual string, saving hours of diagnostic testing, and determine how much lost power you could restore, and how to recover it in the most economical way. We diagnose exactly what kind of fault the panel is experiencing, whether it’s sun exposure, poor coatings, or microcracks, and help you prioritise which problems need dealt with first to meet your plant’s targets.
The solar industry is rife with players, and to get ahead, your panels need to be at the top of their game. That means understanding, on a deeper level, how well your panels are performing all the time.
To discuss how DeepSolar can improve the efficiency of your solar array, please get in touch.

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Advanced Solar Data: Is It Really Music To Our Ears?

We recently revisited a fascinating study by researchers from Imperial College London and Queen Mary University of London, who discovered that solar-electric power conversion accomplished by photovoltaic devices is enhanced by acoustic vibrations. In layman’s terms, music improves solar energy outputs. Yes, music.
Published in 2013, the study highlights something that remains relevant to this day: how can we keep track of the multitude of parameters affecting performance? Is data becoming too “big” for effective analysis?

Preferring Pop to Classical
To produce effective energy yield, solar plants are required to monitor and analyze vast amounts of data. PV panels and devices are influenced by weather, temperature, dust and wind. But they are also impacted by hundreds of other, lesser known parameters, who also interact and impact one another.
Let’s take acoustic vibrations as an example. According to the research, these impact types of solar cells and significantly increase PV device efficiency. The researchers even found that solar cells performed better when subjected to high-pitched pop music, compared to low-key classical music.
The research also suggests that PV applications could benefit from proximity to devices emitting high ambient vibrations such as motor vehicles, rooftops with active AC units and more. This leads to a legitimate question: Assuming a solar plant can’t do it all, how does it decide what methods to adopt, and which to abandon?

More Data, More Potential
In today’s world, solar plant owners have access to game-changing tools that can help them analyze more data, make better decisions and become more effective. Yet in order to do so, they must adopt a sophisticated mindset and be open to research and technology that move at breakneck speed. While data capacity is indeed getting bigger, and its scope is hard to comprehend, we see this as an advantage.
It is up to everyone invested in the solar power ecosystem to stay updated on current research and methodologies that can create better energy yield. It is up to us to share our accumulated knowledge with one another. As demonstrated by four London researchers in 2013, some important discoveries hide right under our nose. Or ears.

To download and read the original study, click here.

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