PV System Losses

Manufacturers quote the efficiency of a PV System at STC conditions, i.e. at 1000 W/m2, however, due to parasitic resistances the efficiency is not constant as the intensity of solar irradiance changes. This is referred to as Irradiance loss

Irradiation losses seem to be rising from spaces in between two consecutive rows due to which solar radiation will be not be collected by solar cells. This is also referred to as Linear Shading Losses’.

The efficiency of a photovoltaic cell/module changes as the intensity of incident irradiance decreases and these changes are referred to as low irradiance losses. Usually, the efficiency drops in a nonlinear way as the irradiance decreases and solar simulator measurements are utilized to determine the actual reduction in efficiency.

While using the short circuit current enables a more precise determination of the module performance as a function of irradiance it does not allow information on the absolute efficiency to be obtained. Examination of the low irradiance losses will be calculated by using

Where ηef is the normalized efficiency of a module when the incident irradiance in the plane of the array is Gt . The ratio of decrease in performance is equal to one minus the result of the equation.

Module Quality Losses

The Module quality loss is a parameter that expresses your own confidence to the real module’s performance, by respect to the manufacturer’s specifications.

This loss refers to positive and negative Wp tolerances of modules. One of the purposes of power tolerance is to estimate how much electrical power a solar panel can produce. For example, a power tolerance of -10% / +10% on a 330-watt peak (Wp) panel tells you the panel could produce 297 W to 363 W under STC conditions.

Following cases shall be considered while choosing the right solar modules:

1) If both tolerances are present means positive and negative(i.e+-5Wp) then this will add loss in the system so that generation becomes less.

2) If only positive tolerances will be present then generation will be more so gain of max up to +0.4%.

Module Array Mismatch Losses

Losses due to “mismatch” are related to the fact that the real modules in the array do not rigorously present the same I/V characteristics. Each PV device (e.g., cell, module, string) in operation will have a maximum power point for the ambient operating conditions of incident irradiance and device temperature. Even at the same irradiance and temperature, seemingly identical devices will not have the same maximum power point because of small manufacturing differences. However, when interconnected in series and parallel to form a DC array, series strings of PV devices all must carry the same current and parallel strings must operate at the same voltage measured at the point of common connection. 

More on module mismatch has been covered in this article.

Inverter Loss during operation: 

This loss is completely dependent on the type or make of the inverter. While selecting inverters through efficiency we can know the loss figure.

Array Wiring losses

The wiring ohmic resistance induces losses ( R · I² ) between the power available from the modules and that at the terminals of the array. These losses can be characterised by parameter, R (Resistance) 

DC wiring loss: 

This loss is due to cables selection, representing the loss on the DC side in between module to the inverter through DC cables. This shall not be more than 2%@STC, superior solar designing while selecting the right size of DC cables can be reduced further up to 1% depending on the shape of land and contract also.

AC Wiring Losses

The AC wiring losses may simply be defined by the distance between the inverter and the injection point.

Auxiliary losses

As the name implies auxiliary means various loads are present in the solar plant which will take power for running at day time as well as night time. This loss shall be in between 0.7% to 1% depends on the size of the plant.

All of the derating factors can be multiplied together to come up with a single derating factor.

0.95 × 0.92 × 0.98 × 0.995 × 0.98 × 0.99 × 0.95 × 0.98 × 1.0 × 1.0 = 0.77

When all of the derating factors above are multiplied together, the system derate value will be 0.77, which means that the PV system will keep 77 percent of the energy or in other words lose 23% of the energy.