Typical Loss Factors

Loss Factors in HelioScope

This table provides typical values for the loss factors in HelioScope energy simulations, and the high-level drivers of the various losses.

Parameter “Normal” Range Notes
POA Irradiance +1% to +20% Depends on tilt of array; one of the rare numbers that will be positive, i.e. an increase. If negative, means the modules are pointed away from the equator.
Shaded Irradiance 0 to -10% Depends on shading in Design. Will come from three sources: row-to-row, obstructions, and horizon files.
Reflection -1% to -5% Based on reflection of light from shallow angles. Will be larger for lower-tilt arrays, and locations farther from the equator.
Soiling -1% to -5% Defined in the Condition Set. Can be negative (i.e. to add in gains). Also used to account for snow losses. Default is 2% loss.
Output at Irradiance -1% to -5% Accounts for non-linear behavior of module I/V curve under low light (i.e. at 500W/m2, a module is not producing exactly half of rated power). More details available in our  Output at Irradiance help doc.
Output at Temperature -3 to -7% for fixed tilt
-6 to -15% for flush mount
All arrays will have temperature-related losses. Flush-mounted arrays (i.e. residential) don’t get as much ventilation as fixed-tilt array, and therefore run hotter.
Output at Mismatch 0 to -7% Default mismatch assumptions in Condition Set should lead to ~2% mismatch loss. If shading losses, then there will be additional mismatch caused by the shading, approximately equal to the shading losses. If module-level optimization (i.e. microinverters or optimizers), should be zero by default.
Optimizer Output 0 to -2% Accounts for efficiency of DC optimizers, if included in Design. Otherwise will be zero. 
Optimal DC Output 0 to -2% Accounts for DC wiring losses between modules and inverter
Constrained DC Output 0 to -3% Accounts for clipping losses. Typically over-power clipping can be 1-2% in a healthy design, and up to 4-5% in an aggressive design. Under-voltage can also cause more significant losses (10-30%), but should be able to be addressed by improved design (i.e. string size)
Inverter Output -2% to -7% Accounts for efficiency of inverter.
Energy to Grid -0.5% to -3% Accounts for AC losses between inverter and grid connection. 
Total Performance Ratio
68% to 88% Composite of all of the factors above (excluding POA irradiance).  Biggest drivers of differences are temperature losses and shading – hotter locations will be on the lower end of the range, cooler locations on the higher end.