PVSYST Losses & Some Remedies


We all are well aware about the functioning of the PvSyst software. We generally use this to simulate the generation of solar PV plants at various locations. For that we have to consider some losses also and in this article we will get some information about the various losses which need to be considered while preparing PvSyst file and also how to optimize these losses:

1. Near Shading: This is basically shading loss due to lesser inter row distances (pitch) of two consecutive solar module rows, as per pvsyst this can further categorize into two subcategories:
a. Irradiance losses: Due to lesser space, in between two consecutive rows some amount of irradiance in the morning and evening will not collected by solar cells so termed as irradiance loss formerly called "Linear shading losses”.

b. Electrical losses: How you form the strings on structures whether I or U, based on that "according to string" minimal amount of loss present in the system.

Depend on the tilt of the structures this can be max up to 2.5%.

2. IAM factor on global: The incidence effect (the designated term is IAM, for "Incidence Angle Modifier") corresponds to the decrease of the irradiance really reaching the PV cells's surface, with respect to irradiance under normal incidence, due to reflexions increasing with the incidence angle. This will be calculated by Pvsyst itself as this is module dependent. Done many pvsyst simulation and found this shall not be more than 3%.

3. Soiling loss factor: We have no measurement device which can measure the soil/dust/bird dropping at site, generally considered as max up to 2% but can be further reduced up to 0.5% if we can reduce the time cycle for module cleaning.

4. PV loss due to irradiance level & PV loss due to temperature: Both the losses are dependent on .PAN file of module manufacturer and also completely dependent on the site meteo data, shall be calculated by pvsyst internal simulation.

5. Module quality loss: This loss refers positive and negative Wp tolerances of modules. Following cases shall be considered while choosing solar modules:

a. If both tolerances are present means positive and negative(i.e+-5Wp) then this will add loss in the system so that generation become less.
b. If only positive tolerances will be present then generation will be more so gain of max up to +0.4%.

6. LID - Light induced degradation: LID occurs when oxygen impurities in the silicon wafers react with the doped (p type) boron or gallium in the first few hours/weeks of illumination of cell. The effect can reduce cell efficiency from 2 to 4% right of the bat. Better to get the confirmation from module manufacturer for first year degradation of solar modules so as to LID loss.

7. Module array mismatch loss: Mismatch losses are function of production electrical uniformity and binning thereof. If module comes with bin class then surely this will be less say 1% otherwise more if electrical characteristics(Current/Voltage) are different in comparison with each other modules.

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

9. Inverter Loss during operation: This loss completely dependent on the .OND file of inverter manufacturer. While selecting inverters through efficiency we can know the loss figure.

10. Auxiliary losses: As the name implies auxiliary means various loads are present in 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% depend on the size of the plant.

11. System unavailability: During O&M contract this loss shall be finalized based on mutual understanding in between client and O&M company, this loss shall be in between 0.5% to 1% depend on the size of the plant.

12. AC ohmic loss: Representing the loss on AC side in between inverter to evacuation through AC cables. This shall not be more than 0.5% at full load.

13. External transfo loss: Basically this loss refers to inverter transformer loss, max considered up to 1.1%.

By Amit Upadhyay. Amit is a solar energy enthusiast and is currently Deputy Manager-Design & Engineering at Mahindra Susten.