Solar photovoltaic systems offer a viable source for generating clean energy by converting solar irradiation into electrical power. It has been estimated through research that marginal shading can reduce the output of the solar modules by as much as 75% ,subject to site conditions.
What are shading losses in a solar energy system?
In a solar module, electricity is generated when solar irradiation falls on the surface of a silicon cell releasing electrons into free motion. These solar cells are connected in series and parallel configurations to form a solar module and obtain appropriate wattage outputs of electricity. If any physical body, causes to project a shadow on any part of the module configuration, the electrical output of the solar module decreases proportionally to the loss in solar irradiation on the module due to the obstruction. This loss of electrical power due to shading is known as shading losses.
What causes shading?
There has been widespread adoption of solar photovoltaic systems in urban power infrastructure by means of rooftop installations in households. The complexity of urban landscape poses the challenge of shading over solar modules in solar power systems. Shading takes place as a result of a variety of reasons such as
How does shading cause power loss in solar system?
As per the concept of current matching, in a electrical circuit the system current is equivalent to the current of the lowest supplying source. Hence in a solar module even if one cell is shaded, the current output of the entire array is effected. If we extrapolate the findings at a power system level, even if a single panel is underperforming, the output of the entire array is affected. Thus shading can significantly undermine the overall performance of a solar system.
In some cases shading can even cause electron concentration at point and create a “Hot Spot” condition rendering the solar module unusable for future application.
How can shading loss be mitigated in Solar Power System?
Shading losses can be mitigated by taking measures both at the solar module and solar system level.
Bypass diodes are devices within a module that effectively “Bypass” shaded regions of the solar module. By doing the current of the module is maintained at the level produced by the unshaded cell strings. This way the power loss is mitigated. Standard solar PV manufacturers, provide bypass diodes to mitigate shading losses.
In solar systems, solar panels are arranged in series configurations called strings, which are parallelly terminated at the inverter. System installers sometimes estimate possibilities of shading and design solar systems such that shaded modules are grouped into separate strings, thereby elevating the overall system output. Generally in rooftop solar systems, the strings nearby potential obstructions like boundary walls, overhanging tree branches etcetera are grouped into a single string, thereby mitigating major power losses due to shading.
Module Level Power Electronics
Module Level Power Electronics are devices connected to individual solar modules to increase power levels during shaded conditions. This is generally achieved by implementing maximum power point tracking at module level. MLPE’s generally include:
- DC optimizers
DC Optimizers try to mitigate the shading problem by using maximum power point tracking (MPPT) technology. In MPPT, the maximum power point of each panel is monitored in real time. The power output is then conditioned at panel level before sending it to the inverter. This helps the inverter process more electricity.
The DC optimizers mounted on the back of each module in an array resulting in an optimized output , regardless of shading, disorientation or damage to solar modules.
Another way to mitigate shading loss is by replacing a single inverter servicing all the panels by microinverters for individual panels. This way each inverter harvest optimum power output.
Shading Loss Mitigated – Using LUBI Solar Modules
Lubi Solar modules are equipped with three bypass diodes connected in reverse bias to effectively mitigate shading losses and destructive effects of hotspot heating. This ensures optimum power output and long operational life for solar modules.
Independent power producers who manage large scale ground mounted plants, additionally employ Module-level Power Electronics (MLPE) to mitigate losses and optimize power output.