Cabling solar installations for maximum efficiency
The way that cables are laid out in a solar power plant can affect its performance and return on investment. Here’s how.
27 Dec, 21
Spain’s renewable energy sector has been growing rapidly and the country has installed around 3.8GW of solar photovoltaic (PV) capacity in 2021, up slightly from 3.5GW in 2020, according to the latest EU Market Outlook from industry association SolarPower Europe.
Nearly 3GW was realised from power purchase agreement (PPA) based systems “out of a gigantic pipeline under development in Spain'', according to the report. “This makes the Southern European country probably the world’s largest market for subsidy-free solar, but it also demonstrates that grid constraints can be a major burden for rapid deployment of large solar volumes.”
The rapid growth of renewable energy is presenting challenges for the power grid in maintaining stability.
To get the most out of a solar installation in Spain, you should consider that the way photovoltaic solar cables are wired affects the performance of an installation as well as the ease of access for monitoring and repair of the system. You want to reduce cable lengths as much as is practical to reduce energy losses and find the best position for convenient maintenance.
There are different ways to wire solar panels effectively, whether in parallel or in a series. Using a string inverter rather than a central inverter also affects the way that panels are wired.
With solar panel wiring affecting the electricity output of the system, choosing the right configuration is essential to maximizing your return on investment. Let’s look at the different types of cables as well as the cabling structures suitable for large-scale solar plants.
Types of solar PV cabling
Medium-voltage (MV) cables interconnect power stations at the site and deliver power to the local substation. The correct configuration of these cables is essential, as they carry large volumes of energy from the solar plant to the grid. For that reason, it is important to design their routing to facilitate easy maintenance and reduce costly downtime.
Low-voltage (LV) cables connect collector elements with the power station. They need to be installed in a way that they avoid passing below structures, as this would reduce their accessibility for maintenance.
These cables connect strings, or groups, of modules to the LV collector element. This requires straightforward routing, as the cables go in the air and are connected directly to the LV collector element.
What are the best ways to configure these cables for the most efficient power generation?
Grouping cable structures
MV structures are grouped in squares to reduce their length, limiting energy losses and cable costs as they send electricity to the same medium voltage power stations. The power stations are also located as centrally as possible to reduce cable length.
LV structures send power to the same collector element, whether a string box, string inverter or other equipment. As with MV structures, they are typically grouped in squares. But there are other considerations that could require a slightly different configuration. For example, some systems – such as grounding conductors or direct current (DC) bus voltage conductors—will use rectangular groups so that structures from different rows are not connected together.
After creating the groups, the LV equipment is positioned to reduce the length of the cables that connect strings with these elements, find the best location for maintenance—such as near roads—and reduce the volume of trenches.
Solar modules are connected either in a series or in parallel. The number of panels connected together in an installation depends on several factors, such as the space available for the power plant, the size and type of solar panel used, and the type of inverter in the system—whether a string or central inverter.
Connecting solar panels in series increases the voltage of the solar array while maintaining the same amperage. Solar systems require a certain voltage for the inverter to work correctly, so this is key. Connecting solar panels in parallel increases the amperage but maintains the same voltage, enabling the use of more panels without exceeding the inverter’s voltage limits or its amperage limitations.
In a PV plant using a string inverter, a certain number of modules are connected to each other to create a single string that is then connected to the collector element. With a central inverter, the longer cables connect to the central unit, which converts more power.
String inverters are smaller than central inverters, so more are used in each energy system. As each row of panels connects to a single inverter, the cables can be shorter. Central inverters are often used in large utility-scale systems as fewer units are required, saving on equipment costs and enabling centralized control.
Whether a solar PV system uses a string or central inverter, the way the modules are grouped depends on several considerations, including reducing shading losses, limiting the length of cables and complying with the manufacturers’ specifications. Reducing shading is crucial, as the less the system is shaded the more electricity it can generate. And manufacturers often design systems so that the cable to connect one module to another requires modules to be grouped together in a specific way.
Curious on how pvDesign performs the electrical calculation through the PV plant? Take a look at our Electrical equipment and power cables methodology, a document that covers the criteria of each of the electrical cabling standards available in the software.
Choose RatedPower to design your solar energy system
The layout of cabling in a solar PV system can have a direct impact on the amount of electricity it sends to the grid and in turn the project’s return on investment.
If you are designing a solar plant project, Rated Power’s pvDesign software can help you automate the design to create the most efficient structure. Contact us today to find out more.
What you should do now
Whenever you’re ready, here are 4 ways we can help you grow your solar business and reduce LCOE of your PV plants.
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