Why energy density matters — and three ways to maximize it

as much energy for the space as possible

System designs like this squeeze as much energy out of your available space as possible.

In previous generations of solar installations, the primary cost-driver was the electricity-generating modules. But in the past five years, as costs for the modules themselves have fallen, myriad other costs have become far more central to making the economics of projects work.

The increasing financial burden of fixed-cost items like permitting, interconnection and customer acquisition — just to name a few — forces project designers to evaluate closely whether it’s worth paying a premium for the most efficient solutions. When comparing options, engineers need to look at costs over the project’s lifetime, not just the dollars‑per‑peak‑watt cost of respective modules.

Solar installers generally have less space than needed to generate all the electricity used by a building. Even for distributed-generation ground mounts, where the generation is co-located with the load, developers have space limitations. All of this explains why energy density has become an area of concentration for new product development by manufacturers as of late.

Energy Density Explained

I use the term energy density in this case to indicate the amount of energy that can be generated by a PV system per unit area in a year. Energy density is something that system designers can leverage to achieve the best levelized cost of energy (LCOE) for all solar projects today, whether it’s in rural, suburban or urban areas. A more efficient solar panel or more panels squeezed into the same area will produce more kilowatt hours per square foot.

In recent years, the race to maximize energy density has moved into high gear. From May 2016 to December 2016, four companies broke panel efficiency records (Hanwha set a record in June that it topped in December). Researchers in Australia set a new record at more than 35 percent efficiency, and NREL recommitted itself to the race to find new materials for solar cells that could break the theoretical 29-percent maximum efficiency of traditional silicon solar panels.

The most popular candidates to replace traditional silicon cells are perovskite (which are not yet commercially available) and CIGS thin-film cells like those produced by First Solar. Thin-film panels can not only push efficiencies higher, but they have an added well known benefit of half the temperature coefficient of traditional silicon PV cells.

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Three Technologies

But those aren’t the only technologies that can help solar installers produce the best energy density for their clients’ investment. Here are three technologies that will make the most of the space you have, no matter where your project is located:

1) Bifacial solar modules: Bifacial modules capture the sun’s energy on the front and the backs of the panels, significantly increasing the amount of sunlight each module can convert to electricity. This technology is inspiring new thinking on installation, including the idea of installing bifacial modules at unusual orientations, like west-facing vertically, which exposes both sides to sunlight at the same time. The technology is still evolving, but for roof-space-intensive projects, I believe bifacial modules hold a lot of promise.

2) Creative racking solutions: When space is sparse, creativity is crucial. For example, when Standard Solar won a DC Department of General Services (DC DGS) contract to install solar arrays on 30 buildings in the densely populated Washington, D.C., area, the engineering team realized quickly that we had to figure out how to maximize the energy density on such tight roofs. The solution, as it turned out, was a high-density racking solution — double-sided with limited row spacing — that allowed us to pack more panels into the same space. As a result, the project was able to realize more kilowatts on each roof because the racking systems allowed an array design that was as aggressive as possible to produce a higher power output from the space.

3) MLPEs: Module-level power electronics provide high granularity for module power output control, shade tolerance and data monitoring for the asset managers. MLPEs have been mostly relegated to residential applications where significant shading issues are common. However, MPLEs can deliver better yield by reducing losses even when no shade is present. MLPEs also open wider options for array design and placement — an advantage for engineers looking to maximize the power production of any given space.

As the costs of modules continue to plummet and the share of other costs increase as part of the financial calculations involved in a solar project, installers and engineers must perform a detailed cost-benefit analysis of how to increase the amount of power a project can deliver from any given space to maximize project economics.

And as the space for arrays becomes increasingly restricted, engineers and installers will have to use all the equipment and innovation at their disposal to increase energy density — and keep the solar revolution growing.

C.J. Colavito is director of engineering at Standard Solar.

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