Luckily, solar is cheaper than ever, thanks to the falling cost and rising efficiency of photovoltaic (PV) solar panels. But here’s something to consider: figuring out the cost of solar energy is more than just the price tag on the boards and their rated power output. For example, there’s the panels’ lifespan to account for. And then there’s the system’s “solar energy yield” — or how much electricity it will generate over the year.
Solar panels are rated on efficiency and power output under standard laboratory conditions. Of course, your solar energy system needs to be installed in a lab. It’s going outside, where all kinds of things can change its actual solar energy yield. That’s why the Energy Department’s Solar Energy Technologies Office (SETO) funds research into better, more challenging modules that can last longer and generate more electricity in less-than-ideal conditions. Read on to learn about three ways the outside world can conspire to cut into your solar energy yield — and how SETO-funded projects are working on solutions.
MAN, IT’S A HOT ONE
High temperatures reduce the voltage of a solar cell. Conventional rooftop solar modules can lose as much as 30 percent of their electricity output on hot summer days. Researchers at Arizona State University are trying to address this problem by improving the back sheet — or bottom layer — of a solar PV module, which serves as an electrical insulator and protects the module from moisture and other environmental damage. The team hopes to keep solar panels more relaxed and improve performance in hot weather by studying back sheets with different heat-conducting properties.
DIRT DOES HURT
Another way panels lose power is simply that they get dirty. The effects of “soiling” (as it’s known in the solar industry) vary widely by location, but energy yield losses of 10 percent are not uncommon. Research on environmental conditions and panel maintenance procedures could help us better understand how and why panels lose power to dirt, leading to better prediction of soiling from one solar energy system to another and more effective dirt-resistant treatments for PV module glass.
SHADY SITUATIONS
While heat and dirt reduce solar panels’ energy yield pretty straightforwardly, shadows are more complicated. In instances when a faint cloud goes over the solar module, the power levels are reduced. However, sometimes the light is entirely or regularly blocked by a permanent structure — like a utility pole that shades just one part of the module — which can cause “hot spots” that can damage the module over time. The University of Michigan, Ann Arbor, has a clever solution in the works: its “super-cell” design can balance power across the module at the cell level. This lets the unshaded cells keep working usually, increasing the energy yield of the module and even improving its durability.
Increasing energy yield continues to be a fruitful research subject for SETO awardees. SETO has already made considerable advances in solar cell efficiency — including a recent announcement that a new Ohio State University design has the potential to achieve 40 percent efficiency. Increasing energy yield will help drive down the cost of solar power in the real world. Stay tuned for more innovation in this area.