Type of losses in Solar PV plant & their % consideration in Simulation Softwares

A.     DC side Losses

1. Module array mismatch losses: Maximum 1% and we have to consider 0.2 to 0.3%. These losses is due to the performance difference in the module parameters. (Example: A same capacity module with the same tilt & irradiance falling on it will show the difference in current band voltage value.

     Suggested Values:

     2% for most modules and systems with long strings

    1% for modules that have tight wattage tolerances

    0% is automatically used on modules with DC optimizers or microinverters

1. Module quality loss:0.2 to 0.3% and it should be less than 1%.this is related to the module manufacturing process and its material chemical composition.
2. LID losses: Light-induced degradation (LID) is a less-well-known phenomenon that impacts a large segment of the crystalline-silicon cell market. In short, it is the degradation that occurs in a solar cell over the first few days after the installation as a result of exposure to sunlight. This can lead to losses of 0.5% - 1.5%.

• To understand the causes of LID, and why certain types of modules are affected, one must first understand two factors that differentiate solar cells: their crystal structure (monocrystalline or multi-crystalline) and their electrical properties (P-type or N-type).
• Crystal structure refers to differences in the structure of a solar cell resulting from how it is produced:
  Monocrystalline - solar cells that are grown using a process (the Czochralski process) that produces a uniform crystal structure that is sliced to make solar cells. These tend to have better electrical properties. They also tend to have somewhat higher oxygen concentrations, which is important for LID.
  Multicrystalline - solar cells that are produced by some form of vapor deposition, which grows silicon onto a substrate. These will have many crystalline sections, which show up as different reflective edges in a solar cell. These are less efficient at producing electricity compared to equivalently-sized monocrystalline cells but are cheaper and faster to produce. They also have less oxygen present in the material.
• Electrical properties refer to properties of silicon wafers (which make up a solar cell) that are needed to create a voltage the difference in the cell when exposed to sunlight:
• P-type: a p-type silicon wafer contains a controlled quantity of impurities, referred to as doping elements, that accept electrons more readily and let a PV module create a voltage difference to produce power under sunlight. Most p-type cells use boron as the doping element, while some others use gallium. Boron plays an important role in LID.
• N-type: these silicon wafers contain impurities that have the opposite effect; they release, rather than accept, electrons. N-type silicon wafers do not exhibit LID.
• LID is typically caused by the formation of boron-oxygen compounds in the silicon wafers that make up the solar cell. This means that monocrystalline solar cells that are p-type with boron will exhibit the most LID, and p-type multi-crystalline cells will also exhibit LID, but to a lesser extent due to a smaller oxygen concentration. The LID process is usually not accounted for in the lab testing of modules, so it won’t be included in the PV module datasheet.

         Suggested Values:

       1.5% for most crystalline solar modules

       0.5% for most multi-crystalline solar modules

       0% for n-type modules,

      3.  Losses due to temperature:8% to 15% as per the site condition.

     4. Soiling Losses: Maximum 3% and depends on the type of soil like loose, hard, soft, etc. and                type of installation like ground-mounted or rooftop.

    5.DC Ohmic Loss: Losses in DC cable from Module to inverter and it should be less than 2% and         it will depend on the size and length of cable.

B.      AC side Losses

1.Inverter efficiency losses:

1.5% but depends on atmospheric temperature and cooling arrangement for the inverter.

These losses can be observed up to 3% if proper ventilation is not available.

2. Transformer losses: It should be maximum of 2% and have two parts:

i. Core loss: Depends on the material.

ii. Copper loss: Depends on current and loading.

3.  AC ohmic losses: Losses due to AC cable voltage drop from the inverter to injection point and depends on the resistance and reactance of AC cable. These should be less than 3% or depends on the Distribution company or utility rules and regulations. These losses depend on reactance and resistance values and length of cable