Options to increase energy density for solar PV arrays

Finding new ways to boost the energy density of a solar PV array remains a top priority for engineers and manufacturers. Without constant technological upgrades, conventional solar panels hit an efficiency ceiling, limiting the total amount of power produced. Energy density is the key to increasing power, so researchers have been heightening the efficiency of solar panels by optimizing manufacturing techniques and incorporating higher quality materials during production.

Two innovations crucial to increasing energy density have been the development of bifacial modules and smart solar systems.

What is energy density?

Since solar panels present a two-dimensional profile, sunlight shining down on a single surface can only produce so much energy - energy is limited by the size restriction of the space. As noted by The Energy Collective, a rigorous calculation to measure energy density would be watts (or electrical output) per unit of square meter (W/m2). Further, the angle of the sun, the time of the year and other factors such as shading, also play a role in how much sunlight solar panels can absorb.

Using this metric, MIT reported in its 2015 study "Future of Solar Energy" that using solely solar power to generate 100 percent of estimated U.S. electricity demand by 2050 would require approximately 33,000 square kilometers of land spread out evenly across the country. This might sound like a lot of space, but to put things into perspective, the source also noted that golf courses in the U.S. currently span roughly 10,000 sq-km of land.

While energy density creates a fundamental physical limit on how much energy a solar panel can extract on a given area of land, there are ways to increase this number. The more efficient a solar panel is, the better the energy density.

Bifacial module

Conventional methods for converting sunlight into energy rely on a single surface, like your traditional solar panel. However, as opposed to solar panels that can only absorb sunlight from one profile, bifacial modules soak up photons from two directions. This two-sided design allows the bifacial module to absorb direct sunlight from the front while the back receives scattered and reflected light. With the ability to capture more sunlight from more directions, bifacial modules have the potential to generate as much as 25 percent more energy than traditional modules.

Solar PV projects with high albedo - the proportion of the incident light or radiation that is reflected by a surface - and surrounding reflections are ideal for these bifacial cells in the dual glass modules. This includes flat-roof commercial or industrial spaces, carports, ground-mounted utility-scale arrays or building-integrated PV. Floating solar applications and snowy areas with high incidence of reflected light make for especially good spots to deploy bifacial modules. Certain agricultural operations and greenhouses can also take advantage of the bifacial modules' ability to capture more sunlight.

This dual-sided sunlight absorption allows for a greater variety of tilt and installation options as well, which opens the door to installing solar arrays in places that might not otherwise be suitable. In addition, bifacial modules enable more “productive time” from solar system by activating the inverters earlier in the morning till later in the afternoon. Thus, the total energy generated is higher vs. standard modules for the same installation footprint.

With access to a two-sided module, solar PV arrays can increase the energy density, which, in turn, allows for higher power generation per square meter. This reduces levelized cost of electricity (LCOE), providing a faster return on investment (ROI) for the system.

Smart modules

In addition to bifacial modules, smart solar PV systems can also boost energy density.

With conventional solar panels, when a single panel experiences shading, it will negatively impact the performance of the entire string and drag down the energy output of the entire system. To avoid this problem, intelligent solar solutions allow each module to operate independently of the rest of the string, allowing the unshaded panels to operate at maximum power despite shading on some panels.

Smart solar PV systems also allow installers to utilize uneven string lengths and multiple panel orientations/tilts, providing greater design flexibility and allowing installers to fit more modules on a rooftop or array. They also allow for more panels on a single string, reducing the number of strings required per system. This leads to significantly higher energy density and lower balance of system costs. In addition, smart modules reduce LCOE for a home solar system, which speeds up the ROI.

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