How Location and Design Affect Solar PV Performance

When you hear about solar in the news, it’s most likely about a large desert solar system that produces enough energy to power a specific number of homes, or a rooftop system in North Carolina or New York that offsets a certain fraction of a business’ energy consumption. By using complex equations, data, and simulation tools, we can determine how many homes that desert system will power, or offset “x” amount of energy for a business.These calculations are part of the energy simulation process. Energy simulation tools are built to accurately predict how much energy a particular solar system will produce in a given year. There are several factors that can impact how much energy a solar array can produce, but they fall into two main categories.

Location, Location, Location

One key factor that will determine how much energy a system can produce is its location. Along with the distance to the equator, weather plays a significant role in determining how much solar energy can be captured in a particular area. The map below depicts how the rainy Pacific Northwest receives the least amount of solar exposure in the year, while arid Southern California and Arizona receive the most per year. Most of the US is typically in between these two extremes.Other weather trends can also play a role. For example, the Northeast has abundant rainfall that naturally cleans panels. However, significant snowfall will reduce the amount of energy captured. California’s sunny skies allows panels to capture more energy, but the energy conversion process is slightly less efficient partly because dust is more likely to cover the panels.

The Importance of Design

Location plays a large role in determining how much energy output an array can receive, but there is plenty of room for system optimization in the design:

• Tilt: The ideal tilt is closest to the latitude of the project. Reducing the tilt slightly will favor production in the summer months, when the panels produce the most energy in the year.
• Orientation: The orientation, or azimuth, of a tilted module is simply the direction it is facing. Optimal azimuth is 180 degrees, or due south.
• Shading: A shaded solar cell will not produce energy. Therefore, it is advantageous to design a system with as little shading as possible, including shade from other panels. Many solar companies use this principle to reduce the tilt of a solar system in favor of adding more modules (typically 10° for a flat roof), because the panels will leave less shade behind them at lower tilts.
• Type of Mounting: Solar panels perform more efficiently with cooler temperatures. Although roof mounted panels can maximize property usage, ground-mounted modules and carports have more air circulation to release heat, so they will produce more energy than panels on a roof.
• DC/AC ratio: Inverters are the device that turns the DC energy that panels produce into the AC energy that your business uses. Because inverters are often expensive, it is common practice in the industry to have higher DC power than AC power. How much energy you lose from this process depends on your location. As you go further south, the higher the DC/AC ratio can be without losing more than 2% of your overall solar energy. Typical values are between 1.1 and 1.35 Watts DC for every 1 Watt AC.
• Electrical Wiring: The system loses a bit of energy as it passes through the wires (typically up to 2% before the inverter and up to 2% after the inverter) due to electrical resistance. Optimizing the electrical wiring for thickness, length, and material is crucial to maximize system performance and ensure safe operation of the system.

Where Do I Go From Here?

Energy simulation tools are very precise, but are often cost-prohibitive for the average consumer. Fortunately, the National Renewable Energy Laboratory (NREL) has a free software called PVWatts that allows anyone to estimate their own simulations. The standard values are based on decades of research from top-level scientists.This brief overview outlines some of the ways that location and design can impact how much solar photovoltaic energy a system can produce, but there are many other factors. PowerFlex has years of experience designing optimal systems for commercial and industrial clients across the country, and we can help you design the best solution for your needs.If you have any questions about the energy simulation process, please feel free to call us at 646-807-4600 or email us at [email protected].