In this document
We will explain how to use simulation parameters from Solargis Evaluate to conduct a detailed investigation into PV system performance.
Solargis Evaluate PV simulation proceeds in a series of steps (PV simulation chain), each of which represents a distinct power loss in the conversion process from solar irradiation to the output of the PV power plant. Solargis Evaluate allows you to export the intermediate results from each of the simulation steps.
By examining these simulation parameters you can focus on the detailed performance of your PV system design, isolate the impact of individual loss types (e.g. soiling or inverter clipping), and by analyzing the seasonal or daily cycles, spikes, and anomalies find ways to optimize your design. This is possible thanks to the detailed PV modelling and the 15-minute native time resolution of the simulation data in Solargis Evaluate.
Investigation process
At the start of the investigation, you should determine which step in the power conversion chain you want to focus on. This could typically be a step, where you see significant losses in the Analysis section of Solargis Evaluate. Or you are considering the use of different components in your design and want to compare their performance in detail so you look at the step in which the loss due to the component is calculated (e.g. conversion losses and angular losses for a PV module).
Figure 1: Example loss diagram from Solargis Evaluate - note its interpretation as per this Knowledge Base article
Once you have chosen the simulation step to investigate, you should identify the corresponding input and output parameters, also known as simulation parameters, intermediate parameters, or data export parameters. These are clearly indicated in the Solargis Evaluate PV simulation scheme and detailed in the description of each simulation step in the Knowledge Base article on Solargis Evaluate PV simulation. Additionally, we also list them at the end of this article. Once identified, export these simulation parameters using the data export functionality in Solargis Evaluate.
Next, load the exported data into a suitable data processing software. We recommend Solargis Analyst, as processing 30 years of data with 15-minute resolution exceeds the capacity of Microsoft Excel and may even challenge other tools. In the chosen software, calculate the difference between the input and output parameters of the analyzed simulation step. This calculated time series represents the total losses in the simulation step - e.g. due to soiling, or inverter clipping. Relative losses can also be calculated by normalizing to a suitable quantity. The list of simulation steps with the relevant input and output parameters, and the formula for calculation of relative loss are shown at the end of this article.
Finally, analyze the calculated loss time series. The analysis should aim to uncover patterns, unexpected behavior, or seemingly random spikes to understand the performance of the PV system. It is important to conduct this analysis while considering key factors that influence PV system performance, such as Global tilted irradiation (GTI) or air temperature (TEMP).
Bifacial PV modules
When your PV design uses bifacial PV modules, the optical part of the PV simulation calculates the losses separately for the front and the rear side of the module. In this case, your analysis must be split into the impact on the front and impact on the rear side of the modules, adding more accuracy to the results.
Example analysis
As an example we consider a simple rectangular PV power plant with bifacial PV modules located in Europe, and investigate the near shading losses on the front and rear sides of the PV modules. From Solargis Evaluate we export the following simulation parameters:
GTI_FRONT_HORIZ_SHD,
GTI_REAR_HORIZ_SHD,
GTI_FRONT_NEAR_SHD,
GTI_REAR_NEAR_SHD.
These are the inputs and outputs of the simulation step “3D backward raytracing”, which calculates the near shading losses, as can be seen in the excerpt from the Solargis Evaluate PV simulation scheme shown in Figure 2 below.
Figure 2: Input and output parameters of the 3D backward raytracing step, which calculates the near shading losses, as shown in the Solargis Evaluate PV simulation scheme.
Next, we calculate the near shading losses on the front and rear side of the PV module as:
SHADING_LOSS_FRONT = GTI_FRONT_NEAR_SHD - GTI_FRONT_HORIZ_SHD
SHADING_LOSS_REAR = GTI_REAR_NEAR_SHD - GTI_REAR_HORIZ_SHD
This calculation observes the convention of losses being denoted as negative numbers.
Lastly we plot the losses and the front and rear unshaded GTI for context using Solargis Analyst, as shown in Figure 3. We observe that the majority of shading losses expectedly originate from the rear side of the PV modules. However, the shading losses on the front of the module during winter (Figure 4) are significantly higher than those on the rear. These losses should be interpreted in the context of the GTI without near shading (shown in the bottom plot), which in winter is much higher on that front side than on the rear side of the module.
Using the information from this simple analysis we may want to increase the row spacing of the PV power plant to decrease the shading loss in winter, and reconsider using bifacial PV modules due to the very low irradiation the rear side receives.
Figure 3: Shading losses (top) on the front and rear side of the PV modules; front and rear GTI without near shading (bottom); full year 2017. Screenshot from Solargis Analyst.
Figure 4: Shading losses (top) on the front and rear side of the PV modules; front and rear GTI without near shading (bottom); December 2017. Screenshot from Solargis Analyst.
Figure 5: Unshaded and shaded GTI, and shading losses for the front (top) and rear (bottom) of the PV modules on 9 December 2017. Screenshot from Solargis Analyst.
List of simulation steps, inputs and outputs
The following table lists all the simulation steps in the Solargis Evaluate PV simulation chain, with their respective input and output parameters that can be exported from Solargis Evaluate. Note that in the optical part of the simulation, the simulation parameters are split for the front and rear side of the PV module.
The relative (percentage) loss for any simulation step is calculated using the input and output parameters as: