This post was sponsored by PV Case.
The main purpose of a solar PV designer is to optimize the PV system configuration to maximize energy yields of the solar array despite available environmental factors that could affect the performance of modules.
This optimization is deeply related to the equivalent capital expenditure costs and variable O&M costs of the PV project which affect the feasibility of the solar power plant. Therefore, it is crucial that the solar PV engineer uses a simulation software like PVcase that considers critical design parameters to obtain the most realistic, lower cost and highest performance solution.
PV Layout Disposition
The PV layout disposition is the first design factor that the solar engineer must determine. For both large commercial and utility scale projects, the designer needs to select components with specific dimensions and technical specs such as voltage and electrical current values at the maximum power point, efficiency, area, and other electrical properties.
These specs determine how the PV array and string configurations can be sized. While designing the PV array, the solar engineer must consider obstructions that could be located within the PV area and size the system to take advantage of the maximum space available while avoiding obstructions.
Moreover, the solar designer must also consider safety regulations in many countries that establish minimum distances or pitch between frames to serve as pathways for firefighters and minimum operation and maintenance space.
PVcase allows you to design your project in a 3D environment. This ability enables you to take under consideration many of these obstacles, make sure you address them properly, and avoid miscalculations that are inevitable when designing in a 2D environment using a Google Maps terrain model.
You’re also able to accurately size pitch distances between frames that comply with local PV regulations and optimize available area use considering obstructions by using an automatic array sizing tool.
Wiring and String Optimization
Wiring is one of the most important factors that must be considered in any utility-scale or large commercial scale PV project. Cabling is strictly related to two main design factors in PV projects: Ohmic losses and voltage drop.
Power losses associated with Ohm’s law are expressed in the form of heat and they are deeply related to the wire gauge selected for the PV system and the electrical current that flows through the cables.
These transmission losses are present on both DC (between modules, combiner boxes and the inverter) and AC sides of the PV system (output of the inverter to the power transformer and substation). The PV designer must select the right PVwire or RHW-2 wire gauges to minimize these losses while optimizing costs as well, as a higher cable gauge will demand more costs.
Accurately estimating and optimizing the cabling length is also one of the most important duties of the PV designer. Reducing cabling length between combiner boxes, strings and inverters also reduces the voltage drop across the PV array. Ideal estimations establish that the total voltage drop should be less than 1.5%.
Using the accurate automatic sizing tool of PVcase you are able to determine the shortest path between components and calculate the exact amount of cable length required to develop a large-scale PV project, leading to accurate estimations on voltage drop losses.
Temperature influence on module
Environmental conditions also have an important effect on solar energy yields. The voltage output of the PV module varies according to ambient temperature values and has a deep influence in the power output of the entire PV array. If the temperature in the module increases, then the output voltage drops, while if temperature decreases, then the voltage increases.
The solar designer must have accurate and historical ambient temperature values of the location to estimate the maximum and minimum MPP voltage range of the PV array.
This range must match the permissible MPP voltage range of the inverter. Minimum starting voltage and maximum allowed voltage of the inverter must also be verified according to the open circuit voltage of the PV array. The ratings at which both power and voltage vary in the module are determined by the temperature coefficients which must also be considered when selecting a module.
Manual calculations can be made to estimate these factors, but useful software applications like PVsyst also allow you to quickly and accurately verify these elements. Thermal losses are also one of the greatest loss factors in any PV system and PVsyst allows to model these parameters to consider PV losses due to convection.
You can export your project in PVcase to .DAE and import the file into PVsyst.
Shading Losses
Shading losses must also be considered in the PV design. Utility-scale projects generally have less near-shading losses than small commercial and residential PV systems since utility projects are developed in wide opened areas.
However, near-shadings caused by trees, buildings or any other object must be evaluated. Moreover, far-shading losses associated with mountains, clouds, and any other object located far away from the PV array also decrease annual energy outputs of the PV system.
Modeling the PV array in 3D according to topographical layouts and representing the exact environment of the solar power plant in PVcase, allows the designer to estimate shading losses by exporting the accurate 3D model to a specialized software as PVsyst for shading calculations.
Orientation and Tilt Angle Optimization
Solar energy harvesting is linked to the ability of accurately estimating the position in which the module must be placed to receive the more intense and lasting solar radiation available in the location across the year.
For this, the solar designer must decide the right tilt angle of PV modules that must match between a range of latitude values for the location and that is referred to the vertical position of the modules. Meanwhile, the orientation or horizontal position of the modules is linked to the optimum azimuth angle of the PV array. For places located above the Equator, the ideal azimuth angle is located 0° towards South, while places located below the Equator should be placed pointing North for optimum yield extraction.
Utility-scale projects tend to be located in wide opened spaces where no restrictions related to azimuth angle are present. However, depending on the location (generally on template climate locations), there may be a range of optimum tilt angles that could allow the PV array to extract more energy from the Sun. Here it is important for the solar designer to consider implementing a single-axis tracker system that allows the PV array to follow the position of the Sun across the day.
PVcase allows you to accurately size a PV system that includes single-axis trackers with their own piling in the design.
We have reviewed some of the most critical parameters that must be considered when designing PV systems.
However, there are many other factors that are integrated into a PV system design. Irradiance model data selection, soiling, mismatch losses, degradation, unavailability, light-induced degradation (LID), selection of components, performance ratios (PR), DC/AC ratios and new factors like potential induced degradation (PID) especially in utility-scale projects. Financial models and local policy schemes for solar power plants are also decisive elements to determine the feasibility of PV projects.
Using software tools like PVcase and PVsyst allow solar designers to accurately size utility or large-scale commercial projects in a fast way. Presenting your project proposals with these tools give you a better chance to obtain better results and therefore win proposals.
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