How to buy a very, very large batch of solar panels
By Dr Michelle McCann for ecogeneration magazine 11 July 2020
Dr Michelle McCann takes a deep(ish) dive into module procurement and quality assurance, from specification through to monitoring on the farm.
At first glance, a solar farm looks simple – modules, racking, inverters, poles and wires. Done. The reality, as many will attest, is that it is not a walk in the park to get to the point of mounting modules in arrays. Unseen to the passing observer are development applications, grid connections, heritage approval, power purchase agreements, community consultation and much more that goes on long before a single module is delivered to site.
Then there is the job of module selection and qualification, which is a practiced artform. Modules make up a very large proportion of the initial cost of a solar farm. Once all the paperwork is in place, it is up to the modules (and the wiring and the inverters) to actually generate and transport the power that is available.
The basic points a good procurement process will follow are:
- Start with the specifications for a good product;
- Check the components are produced well in the factory;
- Conduct spot checks on what arrives in the country;
- Keep an eye on things once the farm is up and running and, of course,
- Link all of the above in a tight contract with the manufacturer.
Starting things off with a BoM
A solar panel has a bill of materials, or BoM. It is not widely known that behind a single solar panel model there may be more than thirty different BoMs. This makes practical sense in a factory for a number of reasons, but mainly to ensure continual supply at lowest cost. It is also not widely known that something like half of all solar panels are made under license at another factory entirely. The brand and even the model can be more of a concept than a true differentiator.
The process of certifying modules to IEC 61215 (the design reliability stage) has an allowable failure rate of 30% built into the process. That’s bonkers, and the only sensible response is not to rely on module certification as a means of procuring top end modules. Clever purchasers will look for the certification, of course, but make sure to specify their own BoM.
Once a BoM has been specified, the next step is production witnessing to ensure the manufactured product matches the ordered product. An example could be selection of encapsulant material, which sits either side of the cells (typically EVA). The inspection will cover, for example: ensuring the EVA used is the specified EVA, that storage conditions have been correct (EVA can spoil under the wrong ambient conditions) and lamination parameters are correct (a faster lamination time will increase factory throughput but compromise final product).
A substituted EVA or poor storage/sub-optimal lamination conditions can be identified to some degree with spot checks of the final product, but they will not be obvious to the naked eye, especially in new panels.
Having specified a BoM and conducted factory inspections of the production line, the final step prior to installation of the panels is spot checking in-country (in Australia). A 200MW solar farm will use more than 500,000 solar panels. Thanks to some statistics (see ISO 2859) developed during World War II for testing of, well, anything, we can get a very good handle on what’s going on with this population by testing just 500 panels (less than 0.1% of the total sample). A minimum testing regime for this sample would be to test: 500 panels for STC power output (thus verifying manufacturers stated output); 500 panels for electroluminescence; 50 for wet leakage (a safety concern), and; 13 for potential induced degradation (PID).
The total cost for testing will be much less than 1% of the cost of the materials.
Like any farm, a solar farm will be more productive if the crop is tended regularly. While perhaps more set-and-forget than, say, peaches, we all know solar farms do require at least some maintenance. System output needs to be monitored and performance issues need to be addressed through activities such as cleaning modules, replacing failed parts, etc.
Checks should be made for a number of degradation mechanisms exhibited by solar panels, for example: light induced degradation (LID), potential induced degradation (PID) and light and elevated temperature induced degradation (LeTID). Catching these degradations early has two advantages: if it’s early enough and covered in the contract, there may be recourse to the manufacturer, and; early detection can allow measures to reduce the severity of the problem, particularly in the case of PID.
In summary and next time
Module purchasing needs to be treated seriously. The project with the lowest levelised cost of electricity will be one where the risk for non-performance or underperformance is correctly allocated. This means allocation to the party best able to minimise the risk: in this case; the manufacturer.
Products need to be well specified, checked during production, spot checked on arrival in Australia and monitored throughout their life. These tests need to be agreed up-front between the parties and should be covered in the purchase contract. Any costs for this process will pay for themselves many times over, often even in the first year of farm operation.
Next issue we take a look at how this process can be transferred to the residential market with an aim to putting an end to the practice where we, as a country, are installing massive, distributed solar farms on the rooftops of our houses with very poor quality control.
Dr Michelle McCann is a partner at PV Lab Australia and has worked in solar energy since 1996. Michelle was CEO and a founder of Spark Solar Australia and has twice held a world record for high-efficiency solar cells.