Solar Panels of the Future
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The year is 2050. The day is sunny and hot, and the lounge chair you’ve spread yourself on has been warming in the rising sun all morning. Leaning into its back, you bring your face up to the sky. Closing your eyes, you feel the sun lighting up your face so brightly you can see it under your eyelids. You rest here, knowing that when the afternoon heat becomes too much you can retreat into a wonderfully air-conditioned living room, and so can everyone else in the city. Even at the height of a summer’s day when we all demand the most from our energy grids, your home and your neighbors’ home and their neighbors’ homes are powered by a field of solar panels soaking up the sun, just like you.
We’re still far from this goal, and the key to getting there is to make our solar panels more efficient. Solar panels are already remarkable at transforming the sun’s light into electricity, and scientists are struggling to find additional efficiency gains that are worth the investment to implement at a large scale. But given the amount of energy that we plan to source from the sun by 2050, and the little amount of time we have until then, solar panels simply need to use more of the light that the sun gives us. If nothing changes, we’d need to cover the equivalent of 8 Seattles worth of land with solar panels per year, for the next 25 years, to meet the goals laid out by the Department of Energy’s Solar Futures Study.1
We need to somehow make solar more efficient without changing much about the panels themselves. As if that isn’t enough, whatever solution we find can’t increase the price of the panel above the cost of other non-renewable utilities, which would set solar back about a decade in technological advancements.
This is a complex problem, but the solution is simpler than you might think. While solar panels are great at converting the light that they collect into usable energy, the materials they’re made of are quite limited in the kind of light that they can absorb.
To explain this, recall future you lounging in the sun. Sitting in its warmth, you are interacting with sunlight on a cellular level. In a very literal sense, you are soaking up the sun: your cells are absorbing small portions of a broad range of energies whose scale is far larger than just the light we can see and feel. As you stretch yourself across a lounge chair, trying to collect the sun’s warmth on your skin, your cells do the same. They drink in a portion of the light it offers, even overindulging, a damage you’ll only see once you’ve flicked one eye open and think,
Darn, I forgot to sunscreen again.
But everything else, the rest of the light that made it all the way to your porch, has passed right through you doing nothing at all.
Just like you, there are significant portions of sunlight that solar panels can’t absorb. If we could harness this wasted light, we could dramatically increase the efficiency of every kind of solar panel made today.
There are many strategies that scientists use to make solar panels produce more power from the light they absorb; but harnessing light that the panels would normally waste is one of the most important challenges we face in making them more efficient.
In the past two decades, we’ve engineered materials that absorb this wasted light, converting it into usable light that’s released to the solar panel. This process is called upconversion, and the materials that do it function in a system of two components. The first component captures light that passed through the solar panel, gaining energy from what it collected. The second component receives the energy gained from the first, using it to release its own light in a region of energy that the panel can absorb. Together, the two work as helpers for the solar panel, allowing it to absorb more sunlight than before.
But there is a catch. In the past, the first component of upconversion materials required rare earth metals, like platinum. These metals, while excellent at doing their job for upconversion, are extremely expensive and historically exploitative to workers that source them. With all these hurdles, our new goal is to be able to find materials that can serve as upconverters while being cheap and environmentally friendly.
Recently, a new class of entirely organic materials were able to accomplish this without depending on precious metals! They can be made by the truckload in a similar way that we make indigo dyes to dye your jeans blue. When paired with a compatible second component, they form an upconversion system with the potential to allow solar panels to use more sunlight. In a future where we can depend on solar to power our lives, upconversion will be the workhorse ensuring that we make the most of the sun’s energy.
References:
SETO, NREL. Solar Futures Study (2021)
Cecily Rosenbaum is a graduate student in Physical Chemistry in the University of Washington's Department of Chemistry. Her research focuses on identifying materials that can capture the light that solar panels can't, and use it to produce light that can be used by the panels.