13. Photovoltaic System Maintenance

Transcription

1 13. Photovoltaic System Maintenance Paterakis Nikolaos TDK CRETE GR Learning outcomes After studying this chapter, the reader should be able to: Understand the benefits of proper maintenance Discern the main reasons for equipment malfunctions List the basic maintenance parameters Understand why visual inspections are necessary on top of remote monitoring Have a clear view on the recommended number of inspections for each main part of the photovoltaic system List the inspection parameters when checking solar trackers Summary Photovoltaics are investments with at least 20 years of life. They are continuously exposed to weather conditions and natural phenomena. Consequently, it is necessary that the whole equipment is properly maintained. The maintenance of a Ph/P (Photovoltaic Park) is a necessary condition to ensure the uninterrupted and secure operation of the system. Consistent maintenance every six months is recommended by all material and device manufacturers, in order to keep the system running safely over time. Additionally, the consistent maintenance of a Ph/P, as well as the existence of a suitable contract with an expertized and certified company, is generally required by the insurance companies in order to provide a compensation in case of any damage. Introduction Advantages of frequent maintenance 1. Immediate damage/malfunction localization and diagnosis, as well as rapid restoration 2. Avoidance of profit losses (every day and hour without production is an irreplaceable loss) 3. Minimization of the possible technical problems of the equipment, and thus reduction of the economic burden of repairs 4. Minimization of the possibility of an accident to occur 5. Gradual equipment wear and aging

2 Benefits 6. Compliance with all terms and conditions of the current manufacturing warrantees, in order to replace or repair any damaged installed equipment under warranty 7. Technical reports composition for banks and insurance companies, in case of compensation claims due to insured events (e.g. natural disasters, theft, extreme weather conditions) 8. Exporting of useful conclusions and creation of pro-action plans in order to ensure the smooth function of the photovoltaic installation, by processing the periodic reports history on production and maintenance 9. Minimal investor engagement time 10. Ensure proper operation of the photovoltaic installation, aiming to highest possible financial returns on the investment Minimal malfunctions and, consequently, reduction of operating costs Maximal operational performance Extended equipment life by preventive intervention Record of status/function reports Reasons for power outages and malfunctions The photovoltaic systems are always installed outside, thus always exposed to weather conditions. Additionally, they consist of delicate parts, such as inverters and mounting frames. Due to these main two reasons, malfunctions are very likely to appear. Furthermore, grid-connected installations often receive electricity abnormalities from the Electricity Company to which they are connected, which the PV installations are required to absorb and terminate. Permanent power outages A permanent power outage of a photovoltaic system without the simultaneous appearance of a damage, could take place when: The safety fuses of the switchboard are automatically de-activated. In this case they must be re-activated or replaced. A temporary inverter malfunction appears. In this case, it is only necessary to restart the system. Common malfunctions Basic equipment failure (usually on the inverters) could occur due to poor construction, system failure or bad installation, especially when combined with extreme weather/operational conditions Damage to electric circuits by animals, fire or other accidents Communication systems and remote surveillance failure, usually due to the insufficient ventilation of the installation Voltage transformer failure due to safety system dysfunction or unsuitable lubricants Mount links damage that is usually caused by inadequate maintenance or bad construction. Such damages could lead to a partial dismantling of the

3 installation and the destruction of the dismantled panels Maintenance parameters Monitoring Visual inspection Photovoltaic panel Mounts- Trackers Power (electricity) cables Underground power cables Pipes and manholes Inverters Switchboards Lightning/grounding systems Transformer Relay Sensors Alarm, secondary loads and other Infrastructure facilities Vegetation Cleaning Detailed analysis Monitoring Daily By daily monitoring the photovoltaic production, we are able to detect even minor fluctuations, which are usually the harbinger of a greater damage. For example, if we detect a reduced production comparing to older production returns of similar periods, we start the process to identify the reason. It may be something very simple, like dirty photovoltaic panels in need of washing, or something more complicated, like a damaged cell or string. Fig. 1 shows that the production of three inverters (blue, light blue, orange) deviate from the rest. By observing that they come from the same tracker, we can deduct that there is a malfunction of that one tracker. In this case, a visual inspection in the Photovoltaic Park showed that the tracker s sensor was deregulated, resulting to the incorrect positioning of the panels in relation to the sun.

4 Figure 1 - Inverter production in a 80 kw Ph/P Visual inspection Monthly Frequent visits to the Ph/P are mandatory, especially to the ones with trackers. This helps us detect any problems, non-identifiable by monitoring. For example, if a tracker s hydraulic piston presents a minor oil leak and we detect it, the repair cost is much lower than the cost of a destroyed piston. Additionally, by using a thermal camera, we are able to detect panel damages at an initial stage, which have not yet began to appear in our production. Fig. 2 shows a leaking brake piston. At this stage, the damage is fixable and affordable. If had not been detected by visual inspection in time, it could have caused expensive damage.

5 Figure 2 - Leaking hydraulic brake piston Fig. 3 shows the use of a thermal camera to diagnose panel damages. If we do not replace the panel, we will later notice a gradual reduction of our production. Figure 3 - (Left) Thermal picture, damaged panel cells. (Right) The same panel. Photovoltaic panel control Constant The photovoltaic panels are the system s heart. Their daily contact with natural phenomena like rain, dust and animals, impedes their function. This is why diligent visual inspections are necessary. We achieve that by checking the front side of the panel for scratches and discolorations, as well as the back (connection box, cable insulation, Tedlar surface). It is also necessary to check the stability clamps, the aluminium frame bending and the aluminium profile surfaces. In Fig. 4 we can clearly see the dirt that has accumulated on a tracker, resulting to a production reduction by 30%. Figure 4 - Really dirty panel Mounts

6 Due to strong winds and temperature changes that cause material contractionexpansion, it is vital to consistently maintain the mounts. Fixed mounts are more easily to be checked comparing to mounts with trackers, due to lack of moving parts. Check for severe lesions with possible structural consequences Check for superficial damage and oxidation corrective measures Beam curvature check Tracker check and maintenance (as specified by the manufacturer) Every 12 months Construction stability check Check for loose screws Tracker inspection 1. Pins inspection 2. Wind- protection links check 3. Clampers check 4. Panel frames check 5. Panel links check 6. Framework stabilizer check 7. Hydraulic piston brake check 8. Mount stabilizer check 9. Grease application 10. Maximum operational pressure control 11. Reverser pressure control 12. Hydraulic movement/brake pistons inspection 13. Horizontal movement encoder check 14. Lifting piston maximal pressure control 15. Framework tilt encoder check 16. Lifting frame minimal pressure control 17. Descent framework pressure control 18. Descent pressure reduction rate 19. Panel complete movement time control 20. Oil check Figure 5 - Checking all the links of the panel

7 Figure 6 - Checking the tracker s pressure Power Cables Connections check Visual cable check on the mounts Figure 7 - Checking all the connections Underground power cables Thorough cable check for malfunctions Check for excessivee voltage stress

8 Pipes and manholes Visual check of sealed open ends Manhole inspection for water or moisture Inverters Check for external damage Screen check for abnormal displays Cable check for wear and connection loosening Vent filter inspection-replacement (if necessary) Varistor check for delays replacement (if necessary) Switch, regulator and varistor check for damages and abnormal function Safety markings check Grounding continuity check Fuses metal surface lubrication Figure 8 - Checking all inverter connections Switchboards External damage check (scratches, corrosion, bending) Internal damage check (electric arc markings, etc.) Water mold check Connection check (incoming and outgoing cables) Fuses check Fuses metal surface lubrication Automatic switches check for delays Varistor check for delays replacement (if necessary)

9 Check markings on the measuring device Safety markings check Individual measuring of every string's V mpp, I mpp during operation Insulation resistance measurement of each string and field (voltage 1000V with minimal acceptable value 1ΜΩ) Measuring equipment check Grounding continuity check Figure 9 - Switchboard inspection Lightning/ grounding system Every 24 months Surface elements check for damage or corrosion (mount links, etc) Grounding conductors check Grounding resistance measurement Grounding rods check

10 Figure 10 - Checking the grounding system on a switchboard Transformer-Relay Oil level check Oil chemical check Dehumidifier check General transformer control (external damages, air-cleaning, cabling) Oil temperature and pressure control Fan inspection Lighting check Grounding continuity check Switchgear check Measurement systems check Ventilation check and air filter cleaning Door locks inspection Manual arm-disarm system check Every 12 months Oil temperature and pressure control

11 Figure 11 - Medium voltage transformer Sensors Visual inspection of all sensors and cabling Safety alarm, secondary loads, etc. Safety alarm system check, including perimeter lighting UPS system functionality check Fire extinguisher inspection Figure 12 - Wind speed measuring sensor

12 Figure 13 - Safety alarm sensor Infrastructure facilities Perimeter fence and door inspection- repair Vegetation Grass trimming etc Cleaning Every 12 months Panel washing with water and a chemical especially for photovoltaics Bibliography Fragkiadakis, Ioannis. "Photovoltaic systems". Zeta Publications, Preiser, Klaus. "Photovoltaic systems." Handbook of photovoltaic science and engineering (2003). Paterakis Energy ( Mechatron Solar Trackers (