PV Lab Australia has devised an independent solar panel testing system that gives buyers and installers piece of mind when choosing modules for residential rooftops, writes the company’s co-founder and director, Dr Michelle McCann.
When customers are purchasing solar panels for their roofs, it is expected they will want to know how the modules will perform beforehand. However, for many panels used in residential and small-scale commercial installations in Australia, short-term and long-term performance can be unknown.
Purchasers and installers can look at advertising material and services such as PVOutput – a free service for sharing and comparing PV output data – but what other independent measurements exist for incoming panels in Australia?
To fill the hole, PV Lab Australia has developed independent and individual Model Assessments (iMA), a suite of tests done on a small number of panels to verify an existing product line, and to be used as part of a new product qualification process. It can also be used to differentiate between PV module brands and products.
The iMA process can provide insight into panel power output compared to its nameplate; the quality of the panel build; suitability and safety of the panel; and the likely longevity of the panel.
In Japanese, “ima” means now, and the same is true of iMA – it’s about current panel performance. Let’s take a deeper dive and see some typical findings.
Power performance of a solar panel is stated in watts (W). A typical rating for residential panels is a moving beast, but more than 400W is common. Output is defined as occurring at standard test conditions (STC) and these conditions will rarely be met on your roof so they need to be recreated in a laboratory to check on solar panel output. We do this at PV Lab Australia using a sun simulator, and test according to IEC 61215-2.
In STC tests done during the past decade, we have observed:
Variation within a single shipment is usually 0.5 per cent to two per cent so testing a sample of panels from your shipment will give good insight into the whole lot. You don’t have to test every panel.
High variation can occur within a brand. We have seen up to six per cent variation for different shipments of the same brand. One check won’t cut the mustard so you should be regularly checking on your supplier.
There is high variation (up to eight per cent) between the best and worst performing panels on the market. We have seen 50 per cent underpower performance in extreme cases. Even if you are buying a well-regarded product, you only know the approximate power output.
To assess suitability of modules for use in the Australian market from a safety perspective, iMA includes a wet leakage test. This determines whether parts of the panel that should be electrically live (the cells) have any electrical pathway to parts that should not be live (anything that can be touched). Fortunately, we rarely see new panels fail this test, although there is a good argument they should never fail the wet leakage test.
The iMA includes a basic visual inspection. The purpose of this is to detect any visual defects in the modules that may cause a risk of reliability loss. Visual inspection is defined in IEC 61215-2 by MQT 01. Visual inspection provides a check on both the manufacturer and logistics chain.
On the inside
A good glimpse of module and handling quality can be obtained by electroluminescence imaging, which can identify:
- Microcracks: Cracks in the solar cells that are not visible to the naked eye. It is possible for microcracks to exist in the silicon but the cells to remain electrically connected so that panel’s output is not immediately reduced. But over time, cracks can widen and result in a drop in output power. It is not possible to predict when this will occur.
- Shunts: These may lead to hotspots, which cause a drop in performance. In very extreme cases, they can represent a safety hazard.
- Finger interruptions: These are caused by using a dirty or defective screen in the screen printing step of solar cell production.
- Other issues include mismatched cells and degradation (which is unlikely on new panels).
In our experience in viewing electroluminescence images of panels on the Australian domestic market, we have observed that quality varies between brands and between batches for a single brand. Also, the quality of a given brand can be lower for panels used on the domestic market compared to what is sold to commercial solar farms. Just because the big kids are using it in a multi-hundred megawatt power station, doesn’t mean it will be a quality residential purchase.
Including an assessment of the likely longevity of panels makes for a more comprehensive assessment and, in our experience, provides better differentiation between models. In the iMA, we test panel longevity using the Potential Induced Degradation (PID) test.
While modules used in the residential market may not necessarily experience the high voltages necessary to induce PID, they will be susceptible to degradation and the PID test is an efficient accelerated ageing test.
In a recent study of reputable brands on the Australian market, which we did together with CHOICE, approximately half of the panels exhibited changes after PID. These ranged from the development of shunts and/or obvious cell degradation on panel edges, to outright test failure due to backsheet delamination.
Pricing for an iMA at PV Lab Australia is $2200 for a basic assessment, and $5400 for a comprehensive package.