Operations & Maintenance (O&M) For Utility Scale PV Solar Plants
Once the PV solar plant has been built, it needs to be efficiently operated and carefully maintained. Compared to other power generating technologies, solar PV power plants have low maintenance and servicing requirements.
However, as International Financial Corporation warns, “proper maintenance of a PV plant is essential to maximise both energy yield and the plant’s useful life. Optimal operations must strike a balance between maximising production and minimising cost”.
Indeed, while solar energy does require almost no maintenance at all as compared to the other generation sources, PV solar plants are investments that are likely to last for 20–25 years or more, and that’s why in order to arrive at an accurate ROI figure, one needs to address the operation and maintenance issues.
Thus, before turning to the actual process and stages of maintenance and operation, one needs to understand the issues involved in the functioning of a PV solar plant. Naturally, they can be divided into the groups according to the plant’s main components.
O&M Issues in PV Solar Energy
1- Natural Degradation
All solar cells naturally degrade over time, regardless of the environment they are in. This is called natural degradation, and is completely normal for all solar cells to experience once in operation. Depending on the material, the rate of degradation can vary. This is important to take into account in budgeting and investment planning.
The following table summarizes the degradation rates of solar panels made of different materials. As is clear from the table, Monocrystalline PV plants are The lowest annual degradation rates.
Natural degradation cannot be prevented, but must be taken into account in the planning process. It can also be covered by warranties. Usually, manufacturing companies that produce solar modules offer warranties if degradation rate exceeds certain amounts, for example, if it is more than 0.8–0.6% depending on the particular firm. The good news is that the higher quality panel, the less natural degradation.
The degradation rate must be weighed against the cost and the utility of particular materials from which the solar models are made. The following chart, provided by Scandia Labs, demonstrates the estimates for Average Utility-Scale Solar PV O&M Costs, by Technology ($/kWAC-yr), including different types of solar panels materials, as well as different types of trackers with which the panels are equipped. Here, again, crystalline silicon stands out, as do conventional solar panels as opposed to concentrating photovoltaics that uses lenses and curved mirrors to focus sunlight on the solar cells.
- CdTe — cadmium telluride;
- CIGS — copper indium gallium selenide;
- c-Si — crystalline silicon;
- SAT — single-axis tracking;
- DAT — dual-axis tracking;
- CPV — concentrating photovoltaics.
2- Grounding & Lighting Protection
PV solar plant is a structure of considerable size, which is why some lightning protection is in order. The first level of such protection is the ground mount system itself, whereby the grounding system redirects the energy from the lightning into the ground and away from the panels. Depending on the foundation, different forms of grounding can be used, as summarized in the following table provided by the Desert Research Institute:
Note that copper conductor may be tinned, and that aluminium is not allowed to be buried into the soil. It is also important to use the same type of metal in both the grounding system and in the protection equipment, so as to avoid corrosion.
Even with a proper grounding system, a PV installation can still be at risk from lightning. Even after the lightning energy has been discharged into the ground, it can still cause a power surge within the solar panels array, which is why a surge protection equipment is in order. In some cases it is not needed, if the grounding system is effective enough to reduce the lightning strike energy.
3- Component Failures (Panels, Inverters,…)
3.1. Panel Cracking
Different components of PV solar plant may fail during the operation. First, panels might crack, even in the new once, if they have been damaged in the manufacturing process. The micro-cracks are not always obvious, and that’s why the new panels must be inspected and a warranty must be secured. The cracks may lead to the failure of panels or losses of optimal efficiency.
3.2. Visual Discoloration
Visual discoloration is another common defect that reduces the amount of sunlight that penetrates into a solar cell. As a result, solar cells are less exposed to solar irradiation, and generate less energy. The reason it leads to loss of efficiency is because different color panels changes the wavelength of light that can be absorbed. As in the case with panel cracking, not much can be done once the panel became discolored, hence the solar panels must be carefully operated and maintained.
Contrary to the common misleading opinion, solar panels are most efficient when they gain maximum solar irradiance, not maximum temperature. Quite the contrary, high temperatures can actually damage solar panels, leading to the emergence of the hot spots. Hot spots occur when a panel is shaded, damaged, or electrically mismatched and decrease power output. Since solar cells are attached in strings, just one hot spot can lead to multiple cells functioning poorly. To solve this problem, all shading should be negated, and electrical connections should be optimized.
3.4 Inverter Failures
Generally, inverter faults are the most common cause of system downtime in PV power plants. Therefore, the scheduled maintenance of inverters should be treated as a centrally important part of the O&M strategy.
3.5. Trackers & Panel Orientations
Panel orientation is an issue for static PV solar systems. It requires due diligence on the consumer’s part to make sure the installer is taking the proper steps necessary to determine an ideal panel orientation. Similarly, tracking systems also require maintenance checks. These checks will be outlined in the manufacturer’s documentation and defined within the warranty conditions. In general, the checks will include inspection for wear and tear on the moving parts, servicing of the motors or actuators, checks on the integrity of the control and power cables, servicing of the gearboxes and ensuring that the levels of lubricating fluids are appropriate. The alignment and positioning of the tracking system should also be checked to ensure that it is functioning optimally. Sensors and controllers should be checked periodically for calibration and alignment.
3.6. Mounting Structure
The module mounting assembly, cable conduits and any other structures built for the solar PV power plant should be checked periodically for mechanical integrity and signs of corrosion. This will include an inspection of support structure foundations for evidence of erosion from water run-off.
4- Weather Conditions (Snow, Wind, Soiling)
Finally, depending on the environmental conditions, the panels must be protected from wind, snow, and soiling (in dusty areas). Regular cleaning and maintenance will be enough in these cases. Top Professional Companies use durable crystalline silicon panels that are built of lead-free, optically transparent, anti-reflective glass, which can withstand the tested shot of an ice ball with 35mm diameter at a speed of 30 m/s. Their serviceable life is up to 25 years, with 10 years of guaranteed performance.
5- Other Issues
Other common unscheduled maintenance requirements include but are not limited to:
- Tightening cable connections that have loosened.
- Replacing blown fuses.
- Repairing lightning damage.
- Repairing equipment damaged by intruders or during module cleaning.
- Rectifying SCADA faults.
- Repairing mounting structure faults.
- Rectifying tracking system faults.