Solar PV arrays are a common site across Australia and the world, and as the technology becomes cheaper and more accessible they become more common.
Over 3 million PV panels were installed across Australia in 2018. This continues to increase as solar capacity grows at 50% per year, making solar the fastest growing renewable energy generation source.
The incumbent and traditional energy supply modes are well established and management and maintenance of these generation types is well documented.
Fossil fuels formed the backbone of Australia’s centralised electricity grid, however, market forces led by cost are changing the generation landscape.
Renewables now make up over 22% of the grid supply. In addition, micro-grids and stand-alone systems are becoming more prevalent – especially in more remote geographies like Western Australia.
A small-scale solar PV system is commonly defined as +1kW to 99kW, medium-scale as between 100kW and 5MW, and large or utility scale as above 5MW, and can reach over 1GW as seen in the United Arab Emirates.
As systems scale, and particularly those above 1MW, there can be thousands of PV panels, hundreds of inverters, kilometres of wiring, and significant HV infrastructure for grid connection. In short, a large and complex system.
Large scale solar generation investment is usually underpinned by a Power Purchase Agreement (PPA) where the output is sold at a predescribed rate. For the solar asset owner, generating the maximum output is crucial in realising the targeted ROI of the asset.
Any rate of return is first and foremost calculated based on the panel manufacturers’ Standard Test Condition (STC) results. This makes panel performance critical to the entire commercial outcome for the developer or asset owner.
Throughout the commissioning of a solar PV system, a range of defects and issues can create an adverse outcome for the system and its resulting ability to achieve maximum output.
PV panel damage during transport or installation can result in visible and non-visible defects.
In addition, poor connectors, mismatched connectors, damaged wiring, visible and non-visible panel damage and incorrect design parameters can add to output and financial impacts.
The below table provides an illustrative but realistic scenario for an off-grid solar PV array.
Based on a 10MW array
|PPA per kWh||30c|
|Estimated revenue p/year||$5,100,000|
|Example loss as %||5%|
|Resulting revenue p/year||$4,845,000|
|Loss in revenue||$255,000|
The critical element in the scenario above is the 5% loss associated with array output.
Costing over $250,000 per year, 2 things should be understood and rectified:
- What is the cause of the loss, and
- Who is the responsible party?
This is where a considered test regime plays an important role.
Testing to Optimise Performance
Periodic and comparable testing and analysis can protect against both losses and uncertainty around contractual obligations of parties involved in the commissioning and Operations and Maintenance (O&M). In fact, O&M clauses have started being added to PPA’s as their importance is further realised.
A robust suite of testing would likely include:
I-V Curve Tracing
Measuring the output of a solar panel or string of panels, then comparing to the panel manufacturers STC and previous tests.
Aerial Infrared Imaging
Carried out by drone mounted IR cameras, these images once analysed can show panel ‘hotspots’, indicating panel cell or string failures. IR imaging can also be used for HV switchyards, potentially identifying issues without needing to enter the yard.
Ground Flir Radiometric
Handheld or ground infrared can measure all areas of electrical components to assess for any hotspots. Used much like drone IR but employed for items like DC combiner boxes, connectors, AC switchboards and inverters.
Electroluminescence Testing (EL)
EL testing is one the newer tests that has been adapted to be performed onsite where the capture, process and analysis of x-ray like images of solar panels can show what the naked eye cannot see.
Right/below is the result of a severely weather damaged solar panel which had no visible signs of cell damage, only a slightly twisted frame.
With the string voltages pushing towards the HV limit of 1500VDC a good understanding of the dangers of DC electricity must be taken into consideration.
Faults can occur in mismatched connector type, cheap connectors, loose terminals in combiner boxes, insulation damage due to stainless steel cable ties not being installed with the right tools and a variety of other factors.
Battery maintenance plays an important role in any hybrid or off grid systems. Battery energy storage systems affect the efficiency of solar PV systems as excess energy created through the day is stored and dissipated through the night.
Regular discharge testing including voltage and impedance readings are recorded to test the integrity of each cell.
Gloss reflectance meter readings helps determine the reflectance on the panels, measured in Gloss Units (GU), prior to carrying out drone infrared scanning. It allows an initial reading prior to cleaning, and a follow up reading post clean to compare.
Doing this assists with the drone infrared calibration. If there is excessive soiling on the panels, the reflectance of heat may be hiding hot spots.
Asset Safety Monitoring
Installed inverters have some level of protection but often not enough. Solar PV, as any other electrical installation is subjected to moisture, temperature, over-voltage, dust, lightning, rodent or mechanical damage. And all these factors have negative effects on electrical insulation.
As an installation ages, failure of PV modules, breakdown of inverters and deterioration of electrical insulation is inevitable. If left unaddressed, it can lead to unexpected interruption resulting in unplanned downtime, costly repair and as a result loss of revenue.
A Panel Testing Timeline
1. The Manufacturer
By utilising cross border partners, testing can potentially begin at the manufacturers premises. Panel manufacturers state their STC results as part of the supply process. These results can be verified prior to the panels leaving the site.
2. Post Transport
If a batch of panels has left the manufacturer in good condition, there still remains opportunity for damage in the logistics phase. Post transportation testing can verify no adverse effects in transport.
3. Post Installation
Fixing panels to ground mounts or other structures is a predominantly manual task that if not undertaken in a considered manner can result again in panel damage. Sample testing after installation is another insurance level in the supply chain.
4. Ongoing and Periodic Testing
Adverse weather such as hail, cyclones and strong winds can result in panel damage. In addition, abnormal panel deterioration may occur. Periodic testing and documenting can mitigate the risk of poor panel performance, and highlight developing problems.
The above panel testing and analysis procedures aim to insure all parties throughout a build and operations and maintenance phase, with the focus on maximising output and ensuring asset longevity.
The potential losses on a medium or large-scale array can easily justify a robust testing and analysis regime. Any operations and maintenance schedule should involve a testing component. Failure to do so would leave asset owners blind to developing problems, which can take on particular importance in the context of time limited warranties and deteriorating power output.
CPS National, as part of Ampcontrol Group, is well placed to provide a comprehensive range of support services associated with the PV analysis and maintenance requirements of mid to large scale solar, hybrid and storage plants.
Whilst there is a huge amount of focus on the growth and delivery of new renewables projects, the demand for support services to existing installations is growing and emerging, as organisations strive to ensure resilient energy assets that achieve and exceed targeted design through proactive management and maintenance.