The speed of return on investment directly depends on the productivity of SES. Therefore, the issue of service of stations is becoming increasingly important: whether it should be carried out even when everything is working properly, how often to contact service centers, and what actually consists of service work.
Let’s start with the fact that the service regulations are clearly defined by IEC (International Electrotechnical Commission) standards, while the rest of the related work is based only on practical experience. Probably, that is why it is quite common in the Ukrainian reality that the service of industrial SES is no different from the service of a home station – all the same, but adjusted for scale and time. And it would seem that the process of measuring the volt-ampere characteristics of the solar module on a megawatt SES will be no different from similar actions on a home SES of several kW. But it is worth gaining experience in servicing industrial SES from megawatts to five, as this view is wrong. And it’s not just about the tools, software used, training of technical staff, but also about the rules of all steps – from individual preparation of the annual plan to the audit.
If we summarize the experience of manufacturers in the solar industry, we can display statistics of the problems most often faced by SES:
• 34% cables and connections;
• 32% of photomodules;
• 10% inverter equipment;
• 8% other reasons;
• 7% adders and RS;
• 7% of the structure;
• 2% transformers and KTP equipment.
In 2012-2018, the company DuPont did a research on the impact of solar panel defects on station performance. The study analyzed 4 million modules with a total capacity of about a gigawatt, with a lifespan of 0 (new) to 30 years. 23% of the studied modules had some problems.
That is why the inspection of photovoltaic modules, inverters and cable networks is indispensable to ensure the smooth operation of SES. Unfortunately, without exception any manufacturer can have problems. So, service saves you money, because according to our statistics, € 1 invested in the service saves up to € 10 per year.
The key component of service is audit. In our service practice we are guided by IES standards, in particular Photovoltaic (PV) systems, Solar photovoltaic (PV) power supply systems and others. Summarizing all the standards, we have developed our own rules for auditing and servicing both industrial and domestic SES.
The rules of technical operation of power plants and networks in 2019 define two types of FES service: scheduled or preventive maintenance and unscheduled or emergency. From our own experience, we distinguish the following types of service audit: planned, urgent and investment (pre-sale).
Scheduled audit is conducted according to the annual service plan. Its purpose is to analyze the actual state of the station and provide further recommendations. The scheduled audit consists of diagnostics of inverter equipment, inspection of photovoltaic converters and inspection of power equipment and cable networks.
As practice shows, in Ukrainian realities there is often only an emergency audit. That is, service is provided after the problem has arisen. The purpose of an emergency audit is to eliminate urgent problems in certain areas or in certain groups of equipment.
The investment audit is based on the planned service, but at this stage the verification of the project implementation in accordance with the design and estimate documentation is added. In this audit, we create an additional financial model and completely new financial forecasts for the project.
Comprehensive analysis of FES
Now let’s understand what is the analysis of the station, which is present at each stage of the audit:
• Thermal imaging control;
• Visual inspection of equipment and structures;
• Control of live connections;
• Carrying out special measurements (including I – V characteristics of individual modules and strings), inspections and adjustments;
• Checking the serviceability of automation systems.
Currently it is important to test photovoltaic modules with a drone. Unlike manual testing, the drone saves a lot of energy and time. It is important to say that drone testing is the first step in a long set of actions. The result of drone shooting is the construction of an interactive map. How does it work? The drone takes thousands of photos, which are stitched together and, after processing, create an interactive map of your station. It shows all available potential problems in the field, including inverter equipment.
Depending on which software is used, which model of thermal camera, it is necessary to take into account the technical requirements, in particular: the percentage of overlap of each photo, flight trajectory, flight characteristics, etc. Based on the obtained data, the nature of defects, their number, causes, level of criticality and the approximate amount of monetary losses from existing defects are identified.
After receiving the report, there is a visual inspection and local thermal inspection of the surface of the modules. Based on the visual inspection, a second report is created, which confirms or refutes the data taken by the drone. Visual inspection often reveals mechanical damage to the modules, defects in the substrate, problems in the structures, distributing boxes of the modules, and so on. Thermal imaging detects and localizes such problems as shading, non-functioning bypass diodes, local hotspots, etc.
The next step of the inspection is to measure the volt-ampere characteristics of the modules and strings. These measurements reflect the actual state of the modules and the characteristics of the collected strings. We recommend to make the first measurement of volt-ampere characteristics in 2-3 months after the station is put into operation, and then – with a certain frequency to confirm the level of LID-effect and monitor the trend of module performance.
This is followed by an inspection of the inverter equipment, which consists in auditing the contact connections of live parts, reading logs, checking the heat sinks, fans, etc.
The next step is to check the power transmission cables from the power equipment. It includes: thermal inspection, visual inspection of cables (both DC and AC), measuring the insulation resistance of cables, grounding system.
Checking the structures for corrosion and the condition of the joints precedes the final safety check.
If you want to order services from Unisolar, contact us and we will send you a questionnaire, on the basis of which we will be able to offer an individual package of services just for you!