Solar Photovoltaic (PV) System Design Basics

Did you know solar power is the world’s fastest-growing energy source? In fact, over the past few years, solar photovoltaic (PV) system design deployment has increased exponentially due to technological advancements and falling costs. However, in order to design and install a solar photovoltaic system, you must first understand the basics.

Here we give you an overview of what’s involved in a PV system design, the components that make up a PV system, and how you can size each component for your specific needs.

So, whether you’re just starting with solar or looking to expand an existing system, read on to gain a solid understanding of the basics of PV system design.

PV System Component Basic Descriptions

PV Modules/Panels
A building’s rooftop is ideal for installing photovoltaic (PV) modules and generating electricity, providing an on-site power source that can help offset utility costs. PV modules are clusters of solar cells that convert sunlight into direct current (DC) electricity.

When connected to a PV system, the modules can provide power to help meet a building’s energy needs. Since PV systems do not produce emissions, they are a clean and environmentally-friendly way to generate electricity.   

Mounting Systems (Racking)

Racking systems are the framework that PV modules are attached to. There are many different racking systems available. The best choice for a particular project will depend on the building owner’s or developer’s specific requirements.

Inverters
Inverters are a vital component of any PV system, which is why building owners and developers in the commercial building industry are increasingly looking to specify inverters that offer the best value for their investment. Inverters convert the DC power, produced by solar panels, into AC power that can be used by building systems. They are typically mounted on a pole or rack near the array and come in various sizes and configurations. Two main types of inverters, micro-inverters and string inverters, are on the market.

Choosing the Right Components

PV Modules/Panels
Choosing the right photovoltaic (PV) modules/panels for a building project is essential to achieving the targeted rating.  Building owners and developers in the commercial building industry are under constant pressure to achieve higher environmental ratings, whether LEED, WELL, or another green building standard. The type of PV module/panel selected can significantly impact a building’s energy performance and, ultimately, its rating. 

There are many factors to consider when choosing the right PV module/panel, including power output, efficiency, cost, warranty, and aesthetics. However, with so many options on the market, it can be challenging to know where to start. An excellent place to begin is by meeting with a PV expert who can help identify the best PV module/panel for your building project.

Mounting Systems (Racking)
After deciding on a target rating, building owners or developers need to decide on the mounting system, or racking, as it’s called in the industry. There are two main types of systems – attached and ballasted.

Attached systems are fastened directly to the roof structure, while ballasted systems rely on weights to keep them in place. Which one is right for your building? It depends on several factors.  Building type, roof type, budget, and aesthetics play a role in the decision-making process.

Ultimately, it’s up to the building owner or developer to choose the racking system that best meets their needs. However, consulting with a solar PV expert is essential before making any final decisions; they can help you weigh all the factors and make sure you choose the right system for your building.

Inverters
Solar power systems typically consist of panels that convert sunlight into electricity, and inverters that convert that electricity into a usable form. There are two main types of inverters – string inverters and micro-inverters. String inverters are the more traditional type of inverter and are often used in large-scale solar power systems.  These systems utilize larger, separate inverters that connect a long string of panels into a single inverter system to convert the DC power generated by the solar panels into AC power that is usable by the building systems.

On the other hand, micro-inverters are a newer technology that is becoming increasingly popular in the commercial building sector. Micro-inverters offer several advantages over string inverters, including more granular monitoring capabilities, enhanced safety, longer warranties, greater flexibility and easier installation, since they are typically integrated into the panel itself.

Interconnection of Components

Photovoltaic (PV) modules and panels are the foundation of any photovoltaic system, both residential and commercial. They are the individual units that convert sunlight into DC electricity, while PV strings are groups of modules wired together.      

PV modules must be connected to a suitable mounting system, also known as racking, to function properly. Racking provides structural support for the module, keeping it in place even in inclement weather. It also helps to ensure that the module is positioned at the correct angle to maximize its exposure to sunlight.

String Inverters
For string inverters, PV modules/panels are connected to combiner boxes through direct current (DC) wiring with voltages typically ranging between 600 and 1,000 volts. The number of strings in a combiner box depends on the inverter’s capacity. In most cases, there are between 2 and 4 strings per box. Each string is then connected to its terminal. This allows the current from each string to be monitored independently.

The terminals are also labeled so that the voltage from each string can be measured. The inverter uses this information to optimize the power output of the system. By monitoring the voltage and current of each string, the inverter can ensure that each string is operating at peak efficiency.

Micro-inverters
The micro-inverter is connected to a photovoltaic system’s solar panel or PV module. This arrangement differs from the more common string inverter approach, in which all of the panels in an array are connected in series and then fed into a single inverter. The main advantage of using micro-inverters is that they can maximize the power output of each individual PV module since each one operates independently.

This can be beneficial when shading or other factors reduce the production of one or more modules in a string inverter system.  In addition, micro-inverters can simplify the installation process and provide greater flexibility in terms of module placement since the inverter is integrated with the panel.

Tie-in to Facility Power System
The string inverter is a larger power inverter tied into the facility power system through upstream and downstream disconnects. Unlike micro-inverters, string inverters are designed to work with a very specific number of solar panels in a string. This makes them ideal for use in large solar installations, where there is a consistent number of solar panels on each string and all panels are oriented the same direction.

On the other hand, micro-inverters are typically either connected or integrated to one solar panel, although some micro-inverters can connect to up to four solar panels. Several micro-inverters are circuited together on 20- to 30-amp, 240 volt, single-phase circuits and connected to a panelboard. The panelboard is then tied into the facility power distribution system, through a transformer if necessary.

Final Word

Solar PV systems have been growing in popularity for businesses and commercial buildings due to the ever-increasing cost of electricity and the decreasing cost of solar panels. When it comes time to design your system, there are a few basics you need to understand. When you are ready to install a solar PV system, call Schnackel Engineers.