Aurora's system loss diagram is a breakdown of system losses, showing exactly how much energy is lost at every stage of a design.
Irradiance
This category shows the losses in irradiance on the modules in a design. It covers environmental losses as well as losses due to suboptimal tilt and orientation.
Irradiance at optimal tilt/orientation
This is the “input” to the loss diagram; it is the maximum annual irradiance that could fall on the modules if they were tilted and oriented optimally for the location.
Tilt/orientation
This is the first loss in the diagram; it represents how much of the potential irradiance is not captured by the solar panels due to the way they are oriented and tilted. Designs with flush modules in a flat rooftop, for example, may show a higher percentage loss than designs with modules tilted by 20-30°, depending on the location of the site.
Shade
This is the loss of irradiance caused by shading. Trees, obstructions, walls/roofs, and other modules can cast shade on an array and reduce the overall irradiance. Aurora’s integrated shading engine computes these losses directly and quantifies them here; if you run a simulation with the shading engine disabled, the loss you see here will be whatever shade derate you provide in the system loss settings.
Soiling
This is the loss due to soiling (dirt, sand, etc.) on the modules. The soiling loss that is applied is equal to the value given in the system loss settings (or values, if given monthly).
Snow
This is the loss in irradiance due to snow covering the modules. The snow loss that is applied is equal to the value given in the system loss settings (or values, if given monthly).
Incidence angle modifier
The angle of the irradiance on a solar panel is typically not perfectly normal to the panel, meaning the light comes in at some angle. The loss given here represent the optical losses in transmission of the light through the module covers. Aurora’s model is based on Snell’s and Bougher’s physical laws; more can be read about it here.
DC
This category breaks down all the losses in DC energy, or in other words, all electrical losses that occur on the input side of the inverters.
Energy after PV conversion
This is the “input” to this category; it represents how much energy a design could produce given the incident irradiance (the last value in the ‘Irradiance’ section of the loss diagram), the efficiency of the modules, and the area of the modules: E = S × Σ(ηA) , where S is the irradiance in kWh/m2, η is the maximum module efficiency (usually at STC), A is the area of the module in m2, and Σ represents the sum of ηA for all modules in the design.
Environmental conditions
This is the first loss in the DC category, representing the energy lost due to the modules operating at varying irradiance and temperature conditions throughout the year. Aurora performs a full circuit simulation of the design, adjusting the equivalent circuit parameters of each module (or cell string for submodule simulation) according to the irradiance and temperature on a module at a given hour (more information the model we apply can be found here). Because the panels are not operating at STC over the course of the year, the energy produced will be lower than the “energy after PV conversion” described above.
Module nameplate rating
This is the same as the module nameplate rating loss in the system loss settings, representing the loss due to inaccurate specification of the STC rating of a module. It is sometimes referred to as “power tolerance;” most modern solar panels have a positive power tolerance, meaning it is uncommon that a 300 W module you purchase will output less than 300 W (but it could output slightly more).
Light-induced degradation
This is the same as the light-induced degradation (LID) loss in the system loss settings, representing a phenomenon wherein the electrical characteristics of crystalline silicon solar cells change upon exposure to light. LID only occurs within the first few hours of the panels being exposed to light, but because the effect can change the power output of a module relative to its STC rating, it is typically modeled as a fixed loss factor.
Connections
This is the loss due to internal wiring and soldering inside solar panels. The internal connections add electrical resistance to the circuit, which results in power loss.
Mismatch
Two modules of the same type from the same manufacturer are not perfectly identical; manufacturing variation leads to small variation in the electrical parameters of the modules. This loss represents these manufacturing variations. It is not applied for designs using microinverters or DC optimizers, because these module level power electronics isolate the modules from one another.
DC wiring
This is the loss due to the wiring that connects solar panels together in strings. The cabling adds electrical resistance to the circuit, which results in power loss.
AC
This category includes all losses that occur on the output side of the inverter.
DC/AC conversion
The first loss in this category is due to the efficiencies of the inverters in the design. No inverter operates at 100% efficiency, meaning the energy at the output (AC) side is never as large as the energy at the input (DC) side. Most inverters have an efficiency of 96-98%, but that value varies with input DC power and voltage. Because Aurora is capable of modeling the full efficiency curve of inverters with available test data, the loss shown in the diagram can help indicate whether an array is properly sized for the inverter. For example, the DC/AC conversion loss may be very large if the DC system size is less than 30% of the inverter’s nameplate rating.
Inverter clipping
In some cases, a solar array may output more energy than the inverter is capable of converting to AC; when this occurs, the inverter “clips” the output power to its nameplate rating. The loss shown here represents how much DC energy is clipped throughout the year. The amount of energy lost to inverter clipping is also noted in the ‘Simulation warnings’ section. If inverter clipping is not enabled in a simulation the loss will be displayed as 0%.
Other
The losses in this category are all applied to the AC energy, but are not explicit AC derates. They are miscellaneous losses that could affect the annual energy production of the system.
Age
This is the loss due to module weathering over time. It is the same as the age loss specified in the system loss settings.
System availability
This represents the loss in available energy due to the system being taken offline for maintenance or due to grid outages. It is the same as the system availability loss specified in the system loss settings. Other This is any other loss you wish to account for; it has no specific origin. It is the same as the other loss specified in the system loss settings.