/ Outlook
Outlook for the Next Generation Projects
Which retrofitting solutions can be implemented to boost the energy production of the inspected PV plants?

PI Berlin suggests 5 retrofitting actions to partially mitigate the negative consequences of the findings described in the previous section. The most important actions associated to these retrofitting actions are described below.

Depending on the status of each PV plant, and as long as the future O&M contractor has sufficient personnel and budget, all or only some of the following measures can be applied. In any case, the measures proposed by PI Berlin do not imply huge investments and can be implemented with a reasonable budget.

The measures suggested by PI Berlin must be complemented with a reinforcement of the commercial conditions in the O&M contracts, mainly in regards to (i) the reduction of the reaction times and (ii) the storage of spare parts needed to commit to the said reaction times.

Besides the retrofitting actions needed to increase the energy generation, any necessary improvements to operate the PV plants in a safe environment shall also be carried out. These improvements shall be conducted regardless of how high the estimated performance boost is.

Re-sorting of modules and strings

A re-sorting of the modules shall be conducted in those cases where the present configuration leads to significant mismatch at the inverter level or to low output currents of some strings due to the low performance of individual modules. Modules affected by inactive cell strings and/or heavy cracks with isolated cell sections that induce hotspots, shall be grouped in the same strings. In those cases where the output voltage of low performing strings affects significantly the string voltage, “good” and “bad” strings will be assigned to different MPP trackers. The distinction between good and bad strings and between damaged and not damaged modules can be conducted with a multimeter and an infrared camera respectively. The infrared inspection shall be conducted after cleaning and at irradiation values higher than 800W/m2 at the module plane.

Increasing of the module cleaning frequency

The source of soiling in most of the inspected PV plants is either bird droppings, pollution, debris or a combination of all three. In order to figure out what the optimum cleaning interval is, the output of clean and dirty strings shall be compared for at least 3 months. As soon as the difference in the output leads to a loss of revenue that equals the cleaning costs of the whole plant, a cleaning visit shall be scheduled. This study will be performed separately for the dry and rainy season, as natural cleaning comes into place in the rainy months. Cleaning becomes particularly relevant in those plants where the modules are mounted with very flat angles.

Module replacement

The replacement of the modules should only be carried out if the cost of the components is borne by the manufacturer. This case can only occur (i) if the manufacturer still exists, (ii) if the reasons why the replacement is required are due to product defects or a loss of performance higher than the guaranteed values, and (iii) if the warranties are still active. The manufacturer’s warranties do not cover damages caused by bad handling or improper installation or O&M practices.

Shorten module strings

In situations where the near shadings seriously affect the energy generation of the modules, it is recommended to shorten the strings by reducing the number of modules connected in series. The strings will be grouped by MPPTs at the inverter level to reduce as much as possible the voltage mismatch. DC/DC converters may be necessary at the inverter input in cases where the minimum MPP voltage is not reached under operating conditions.

Increase of the albedo factor

It is recommended to paint in white, cover the ground with white gravel and/or stick reflective materials to the walls and shading objects surrounding the PV modules. These measures aim at increasing the overall albedo factor to 0.5 and thus, the amount of kWh/m2 reaching the PV module surface. Glaring of neighbouring buildings shall be avoided.

Recommendations for stakeholders

The following measures will contribute to reducing the risks and avoiding significant deviations from the assumptions made in the financial model.
Technical report of the project
The Lender must ensure that a descriptive report is presented for each project indicating the selection criteria for PV modules and inverters, the design assumptions and the proposed cleaning methodology.
Bankable modules
The entity requesting the credit must provide evidence of the quality and durability of the PV modules. These evidences should not be limited exclusively to the basic guidelines of the IEC and should be adjusted to the climatic requirements of the region in which they will be installed.
Binding EPC and O&M warranties
The Lender shall request that the EPC and O&M contracts include dedicated sections detailing the warranties for the handover and the plant’s operation.
Yield assessment according to standards
The methodology applied by the Planner for conducting the yield assessment must be validated by the Lender before approval.
Accurate meteorological data sets
The Lender must ensure that the irradiation and temperature values used for the simulation are representative and that all shadings have been taken into account, so that the P50 values ​​used for the financial models are not overestimated.
Validation of the readings
The Lender must request periodic validations of the weather stations to ensure accurate performance metrics.
The following measures will contribute to optimizing the design in terms of LCOE reduction and create a realistic production estimate.
Site assessment
The Planner shall visit the site before conducting the design of the plant and identify the aspects that have a direct impact on the plant’s layout, the external shadings and other input parameters of the simulation.
Shorter strings
The Planner will choose less modules per string in those cases where the near shadings have a significant impact on the energy production. Shading losses higher than 5% shall be avoided.
High amount of MPPTs
The use of inverters with several MPPT shall be considered by the Planner in order to reduce the mismatch caused by shadings.
Reduce self shading
Self-shading between rows shall be kept as low as possible. Lower tilt angles help achieving this goal.
Minimize deviation from South
The PV plants shall not deviate more than 30° from true South. Aligning the PV plant's layout to the orientation of the building is not always the best solution.
Ensure structural integrity
The structural integrity of the roof shall be properly addressed by the Planner in the feasibility study.
The following measures will contribute to maximizing the installation quality and avoiding damages in the components that may affect the performance and durability of the same during project’s lifetime.
Module transport
The module transport and handling of the modules shall be conducted taking into account the manufacturer's guidelines and avoiding mechanical damages in all cases.
Commissioning procedures
The Installer shall be responsible for the commissioning of the PV plant according to the requirements specified in the EPC contract.
Homogeneous tilt angle
A homogeneous tilt angle throughout the system shall be ensured by the Installer to avoid mismatch and unexpected shading losses.
As-built vs. design guidelines
The Installer must ensure that the as-built situation is perfectly aligned with the design guidelines. This is especially relevant for the interrow and near shading losses.
Training programs
In case of lack of experience, the Installer shall be trained prior to the start of the construction phase in order to ensure proper workmanship.
Health & Safety program
The H&S program shall consider project-specific risks for the installation and commissioning phase. Part of the program shall be the proper assessment and reinforcement of the structural integrity of the roof.
The following measures will contribute to maximizing the revenues, ensuring a transparent monitoring of the plant and avoiding unnecessary risks that can actually be transferred to subcontracted companies.
EPC warranties
The Owner must ensure by contract that the PV plant is commissioned before handover according to the industrial best practices. These practices shall include besides all safety tests stated in the IEC 62446, a PR test of at least 5 days and an infrared inspection of 100% of the PV modules, inverters and cables. The reliability of the SCADA system and the weather station shall be evaluated as well.
Pass/fail criteria for the commissioning
The EPC contract shall include dedicated sections describing the pass and fail criteria for handover with its associated penalties. This includes cold and hot commissioning along with the requirements for the as-built documentation.
O&M scope and warranties
The Owner must ensure that the O&M contract includes clear indications of the expected reaction times, intervention plan during corrective maintenance, preventive maintenance plan, spare part management, reporting, contractual availability and SCADA visualization.
Weather station
The Owner must ensure that the PV plant includes a minimum of (i) one irradiation sensor on the tilted plane, (ii) one ambient temperature sensor and (iii) one module temperature sensor. All sensors shall be properly installed according to the manufacturer's requirements. The irradiation sensor shall be calibrated every 2 years, kept clean and installed at the right tilt, in order to ensure an accurate and representative performance monitoring.
Module cleaning
The Owner must ensure in the O&M contracts that the module cleaning frequency is adjusted to the needs of the site.
Defect liability period
The Owner shall negotiate an EPC warranty of at least 2 years.