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 are 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 the efficiency of the 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). The biggest drivers of differences are temperature losses and shading – hotter locations will be on the lower end of the range, and cooler locations on the higher end. |