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.
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.
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.
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.
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.
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
