PV PLANT CHECK SERVICE

The check-up service is offered to owners and conductors of photovoltaic plants. 

The check-up is fundamental because the power of the photovoltaic plants  varies instantaneously according to different meteorological variables; it is therefore impossible to determine whether the functioning of the plant is correct or incorrect, based only on the production data. 

The checks are therefore aimed at identifying any failure, malfunction or potentially harmful situation with the maximum timeliness, so as to intervene and keep the systems constantly in maximum performance.

The activities are carried out by experienced graduates technicians, who make use of certified and calibrated instrumentation. Each activity performed in the field is completed with a desk phase and with the issuance of a survey report.

The report has these purposes: 

• report on the precise condition of the plant 
• guide the maintenance phase in order to solve problems 
• support potential claims towards technology suppliers 
• compile a probative document in the event of any contentious 

The service comprehends the following activities, which may be executed integrally or modulated based on  the requests: 

1. performance of thermographic survey on the plants components 
   
   
2. performance of functional tests through the measurement of the curve I-V on photovoltaic modules that show thermographic anomaly and on a sample of installed modules, in order to determine wether the functioning is within the expected tolerances or whether there is a need to invoke the manufacturer’s performance guarantee
   
   
3. measurement of the PR, that is the efficiency of energy conversion through portable instrumentation with measurements of DC/ AC efficiency  conversion and the efficiency of solar modules.

KEYPOINTS OF THE PLANT CHECK SERVICE 

The activities are carried out by qualified and trained personnel.

The instrumentation used is equipped with all the necessary certifications and has, at the time of use, a valid calibration. In particular, the specifications for the implementation of the various activities are as follows:

• thermographic survey carried out as per UNI 10824-1 and ASTM E1934 regulations. Surveys are carried out in irradiance condition > 600 W/mq; the results are treated in such a way as to highlight the types of defects that may be encountered and their rapid localization on site. The elements under investigation are:
  – Modules
  – Inverters
  
  
• measurement of characteristics I-V of the modules that show anomalies and following comparison with values of the list in the flash test as per IEC/EN 60891. The tests are carried out with portable instrumentation in irradiance condition IEC/EN 60891. The committee must grant the assistance of the O&M Contractor of the plant to ALENS’s personnel in order to carry out this test.
  
  
• measurement of the PR and conversion efficiency: the verification of the energy yield is carried out with portable instrumentation according to the M.D. 19/02/2007 and the CEI Guide 82-25 in order to determine energy production produced by photovoltaic modules and by the inverter, and to verify that they are above certain reference thresholds. 

OUTPUT SYNTHESIS AND THERMOGRAPHIC REPORT

The thermographic report presents a list of detailed anomalies observed with the thermal imaging camera. 

Information are gathered in synoptic prospects that immediately return the condition of the plant. Here we show an example of a few prospects, from a real cluster of plants:

Deficiency statistics 

ACCURATE TEST OF ANOMALIES 

Note that for each anomaly all position information (layout reference), serial number and type of anomaly/defect are reported. 

EXAMPLE OF WHOLE INACTIVE CELLS SUBSTRING 

SN: 201106117851

Position: 7° sail; 4° high panel from east 

Deficiency: substring of warmer cells (ΔT= 3-5°C). Highlight on a light overheating on the juncture box of the panel due to the power dissolved by the bypass diode in conduction.

EXAMPLE OF DEFICIENCY ON THE SINGLE CELL 

SN: 201010121193

Position: 26° sail; 22° high panel from west

Deficiency: warmer single cell. Thermal anomaly connected to drops for “mismatching” in the cell. The defective cell is forced into reverse polarization by heat dissipating part of the power generated by the remaining cells.

Notes: the areas of the panel with thermal anomalies were examined using the temperature profile reported in the margin of the thermogram. The cold areas visible in the thermograms represent the supporting structures of the FTV generator.

OUTPUT SYNTHESIS AND PRESENTATION REPORT

The presentation report shows the result of the accomplished survey of the performance: 

• of the whole plant (instantaneous PR on the singles inverter)
• on the residual performance of the individual modules, which must be aligned with that guaranteed by the manufacturer (depending on the guarantee on performance decay)

VERIFICATION PLANT PERFORMANCE  

The energy efficiency of photovoltaic generators is verified in accordance with the requirements of M.D. 19/02/2007 and of the CEI Guide 82-25 and s.m.i..

The verification is carried out in the presence of an irradiance on the modules plan higher than 600 W/m2.

The output consists of a table that shows, in addition to other quantities, the value of the instantaneous PR of each subfield associated with an inverter or inverter drawer. 

If the PR is under 80%, there is a problem regarding the subcamp which must be examined.  

MODULES PERFORMANCE TEST  (CURVES I-V)

These checks are carried out on a sample of photovoltaic modules thanks to a special tool.

For each panel examined the power values measured under the test conditions, translated into STC conditions according to IEC/EN 60891, are compared with the nominal data declared by the manufacturer.

In particular, each manufacturer offers a guarantee on the performance of the modules for a period of 25 years. Typically the modules are guaranteed for a decay of 10% of the nominal power in the first 10-12 years and 20% per year.

Thanks to this verification it is possible to measure accurately the current-voltage characteristic of the module bringing it back to standard conditions and compare it with the expected decay. If the difference between actual and expected decay is greater than the guaranteed one, it is necessary to deepen the causes and the opening of the warranty claim with the module manufacturer.

Below is an example of a sample of real modules. It should be noted that for the determination of the variance, acceptable if less than 10%, the modules under investigation have peak power of 230Wp.

*In order to determine the temperature of the module, the ECT function (Equivalent Cell Temperature) has been used, according to the regulation CEI EN 60904-5.

CONCLUSION AND CHECK PLANS 

In order to carry out these tests, it is not necessary to disable the plants. 

Test reports are intended to clearly indicate where action should be taken to restore optimal operating conditions.

It must be considered that, for the way a photovoltaic system is made, a problem of under-performance on a module affects the entire string, which means it leads to under-performing also the other 15-19 modules electrically connected to it. 

For more complex problems or for different needs, the services described can be complemented by other custom checks, such as:

• verification of the correct functioning  and maintenance in calibration margins of field measuring instruments, from which continuous measurements are provided historical data for the calculation of contractual PR and/or other performance parameters, in particular solarimeters (or pyrometers) and the local temperature sensors of the modules.
  
  
• annual PR calculation based on historical data given by the monitoring system, with a report that states the results of the calculation, the consumption made and the conformity or non-conformity to the contractual conditions communicated (EPC o O&M). 
  
  
• visual investigation according to CEI 82-25 on the condition of the plants and their ancillary works with identification of any anomalies or criticality found.
  
  
• isolation measurement.
  
  
• analysis of PID phenomenon (potential induced degradation) for incorrect installation or planning.

The recommended frequency of verification shall be annual. It is possible to structure and agree multi-year monitoring plans with considerable advantage for the Customer.