Argus electrical simulation overview

Overview

The electrical simulation follows directly after the optical simulation in the Argus PV simulation chain. It takes the spectrally and optically corrected GTI per PV cell — the output of the optical simulation — and converts it into electrical power output, tracking losses at every stage from the PV cell level through to the grid connection.

This stage is essential for accurately quantifying the energy that a PV power plant will deliver under real operating conditions. The Argus electrical simulation achieves high fidelity by combining De Soto's single diode model with the cell-level raytracing results from the optical stage, enabling precise simulation of partial shading effects without simplifying assumptions. Inverter performance, DC and AC cabling losses, transformer losses, and auxiliary consumption are all modeled explicitly using component-specific parameters from the PV Components Catalog (PVCC) and the Energy system designer.

The final output of this stage — power delivered to the grid (PVOUT_AC_GRID) — feeds directly into the post-processing stage, where system unavailability and long-term degradation are accounted for.

Processes included in this stage

The following processes are applied sequentially during the electrical simulation:

• Conversion of irradiation to DC electricity (De Soto single diode model, transient thermal correction model, IV curve addition)

• Inverter clipping losses

• Grid power limitation losses

• DC losses (cabling and combiner boxes)

• Inverter DC/AC conversion (MPP calculation, Sandia inverter model)

• Auxiliary losses

• Transformer losses (variable and constant losses models)

• AC losses (low, medium, and high voltage cabling)

Electrical simulation

Conversion of irradiation to DC electricity

The Single diode equivalent circuit model, also known as De Soto's "Five Parameter" model, is used in Solargis Evaluate to simulate the conversion of solar irradiance into electricity within PV cells.

The Single diode model requires five key parameters to describe the current-voltage (IV) curves of PV cells. These parameters are typically acquired at Standard Test Conditions (STC):

• Modified ideality factor

• Diode saturation current

• Light current (photocurrent)

• Series resistance

• Parallel resistance

These parameters, along with the Global tilted irradiance (GTI) and cell temperature, are used to generate the IV curves for each PV cell.

Note: When calculating the IV curves of bifacial PV modules, the bifaciality factor (as specified in the PV components catalog) is applied to the rear-side GTI to account for the decreased efficiency of the PV module’s rear side.

Advantages of the model

The use of the Single diode model in conjunction with raytracing allows for detailed analysis of shading conditions at the level of individual PV cells. This enables precise simulation of the electrical performance of PV modules under various environmental conditions.

Transient thermal correction model

To calculate the cell temperature, we use the Transient thermal correction model to account for the thermal inertia of PV modules by smoothing 1-minute temperature data with a weighted average over the previous 20 minutes. In the case of 15-minute data, only the current and previous time slots are considered. As a result, module temperature changes more gradually, reflecting real-world behavior and improving the accuracy of performance predictions.

IV curve addition

Solargis Evaluate PV simulator calculates the IV curve for each PV cell in the power plant, based on De Soto’s model. The IV curves of the PV cells are then summed together for the submodules, PV modules, and strings, following the power plant electrical layout and electrical circuit physics. The string’s IV curves then enter the next stage of the PV yield simulation.

Using this approach, the performance of each string in the PV power plant is accurately calculated, reflecting the real operating conditions such as partly-shaded PV modules. This means that no assumptions on partial shading performance have to be made, which is sometimes a requirement in other PV yield simulation software.

Inverter clipping losses

Inverter power limitation losses, also known as clipping losses, occur when a PV array generates more DC electricity than the inverter's maximum rated AC output. The inverter then "clips" or discards this excess power, meaning the potential energy that could have been produced is lost.

Grid power limitation losses

PV power plants may have a limit on the power they can inject into the grid, imposed by the grid operator. If the PV arrays produce more power than the grid limit, the inverters will limit the power they take in from the PV arrays to comply with the grid limit.

DC losses

DC losses in the direct current path from PV modules to inverters are a crucial factor in energy yield simulations. These losses occur due to the electrical resistance in the DC cables, and other DC components such as combiner boxes.

Default value used in Solargis Evaluate is 2%.

Inverter DC/AC conversion

An inverter is an electronic device that converts direct current (DC) generated by PV modules into alternating current (AC). The output can be either a one-phase or a three-phase voltage. Simulation of inverters is based on inverter parameters taken from PV Components Catalog.

Note: The energy losses in inverters (including night losses) are specified in the PV Components Catalog, and are applied in the simulation.

In Solargis Evaluate, the inverter conversion calculation consists of two main stages:

• Maximum power point (MPP) calculation: The Maximum power point (MPP) calculation utilizes the IV curve at the inverter input, which is derived from the previous simulation steps.

• DC/AC conversion model: Solargis Evaluate uses the Sandia inverter model which considers operational and environmental conditions in determining the inverter efficiency and its AC output. It also calculates the active and reactive power components, considering the user-specified power factor and inverter capabilities.

Auxiliary losses

Auxiliary losses in an energy system are caused by various equipment that consumes energy, including systems for protection, monitoring, heating or cooling (depending on the climate zone), lighting, module tracking, and other energy-consuming devices.

Note: Auxiliary losses do not include losses in inverters or transformers.

The auxiliary losses can be divided into two categories:

• Constant losses: These are continuous losses measured in watts, and are split into night and day constant losses.

• Proportional losses: These depend on the power produced by the power plant in each moment, and are expressed as watts per kilowatt of installed power.

Default values used in Solargis Evaluate:

Transformer losses

Transformers are essential devices in energy systems, used to change the voltage level from the AC side of inverters to the desired voltage level for connection to the utility grid. In Solargis Evaluate, we utilize our proprietary Transformer model, which can be segregated into two sub-models:

• Variable losses model: Includes iron (no-load, also applied during the night) losses and copper (load) losses.

• Constant losses model: Transformer losses are represented as a percentage reduction of electrical power at the primary side of the transformer.

If the difference between the AC voltage on the inverter output and the grid connection is sufficiently large, Solargis Evaluate considers several transformer stages - inverter and power transformer. In such case, the transformer losses are considered separately for each transformer and AC cable losses are considered in between the transformer stages, all depending on the respective settings.

Default values used in Solargis Evaluate:

Variable losses model

Constant losses model

AC losses

AC losses in an energy system occur in the AC cabling, affecting the transmission of electricity from the inverters to the grid connection point.

In Solargis Evaluate, required AC cable losses are set as a percentage value. This percentage represents the total AC electrical loss across the AC electrical network at reference conditions, typically Standard Test Conditions (STC). The AC losses are applied in several stages (low, medium, and high voltage) depending on the number of transformer stages (inverter and power transformers) in the power plant.

Default values used in Solargis Evaluate:

Further reading

• Improvement and validation of a model for photovoltaic array performance. W. De Soto, S.A. Klein, and W.A. Beckman.

• Transient Weighted Moving-Average Model of Photovoltaic Module Back-Surface Temperature. M. Prilliman, J. S. Stein, D. Riley, G. Tamizhmani