Embracing the Dark Side: The Science Behind Solar Panels Drawing Energy at Night

It’s common knowledge how solar panels work in the day. An average person on the street will be able to tell you they harvest light from the sun which is then converted into power. Solar enthusiasts will be able to speak more expansively, detailing how photovoltaic cells absorb the sun’s energy, convert it to DC electricity, and then see the solar inverter convert DC electricity to AC electricity for use throughout a home or business. Yet regardless of the general knowledge that exists surrounding solar panel use during the day, their use at night remains a novel—if not totally foreign—idea to most.

But there is progress being made in this area. With real optimism surrounding how solar panels in the future could continue to generate a significant amount of energy during the night in locales with normal-to-high levels of annual daily sunshine hours, and become more effective in the darker winter months. This has widespread implications for solar installations of all kinds, especially for the possibility of a hybrid system being developed that could utilize the current (hereafter called "conventional" solar panels) and this new form of a "night solar panel" (NSPs AKA "anti-solar panels").

Solar Panels at Night Under the Moon

So what’s the science behind solar panels operating at night? And how may they be used alongside conventional solar panels?

HOW NSPs could work

The science behind NSPs is based upon research put forward by Tristan Deppe and Jeremy N. Munday, academics from the University of California Davis.

In their paper Nighttime Photovoltaic Cells: Electrical Power Generation by Optically Coupling with Deep Space, Deppe and Munday point out the current drawback with existing solar technology, namely that it only harvests energy during daylight hours. In turn, that via the use of a concept where the night sky is used as a heat sink and the earth as a heat source, a photovoltaic cell that generates energy at night could be effective. Put simply, while conventional solar panels are cold and the sun is hot, NSPs would essentially invert that concept by emitting radiation via infrared that would then create electron-hole pairs in space thanks to the latter’s cool temperatures.

Although NSPs represent a different operation from how conventional solar panels work, there are still shared elements between the two types. As Professor Munday explained:

A regular solar cell generates power by absorbing sunlight, which causes a voltage to appear across the device and for current to flow. In these new devices, light is instead emitted and the current and voltage go in the opposite direction, but you still generate power. You have to use different materials, but the physics is the same.

While it’s held NSPs would not be as powerful as conventional solar panels, the fact they could work for a longer duration—Munday claims 24 hours a day—offsets that. That they utilize traditional fuel sources for part of their process could be seen as a drawback, but it's theorized they could work via utilizing energy left-over from other existing industrial processes. So hypothetically if NSPs were available for use today, they could serve as a tool for pursuing carbon neutrality (just as they could do if they come online while neutrality is still being pursued).

Munday also contends the panels could be totally green too. As he indicated prior, "while these panels can produce carbon-free power when attached to a waste-free power when attached to waste heat sources, they can also produce carbon-free power by just sitting on your roof, like a solar panel".

At present Munday and his colleagues are in the prototype stage, looking to convert the theory of NSPs into prototypes in a live setting that are functional and give conventional panels a run for their money in performance. It's understood a prototype already developed by Munday did work, but could only generate around 25% of the power a conventional panel could. This is no small achievement, and in turn, it’s expected further research and development could see the gap between conventional and NSPs close further.

It’s reasonable to say we could usually expect a considerable wait before NSPs shift from this stage into being commonplace across the world. But with rapid advances we’re seeing not only in solar power’s technological capabilities but greater government investment and public support for the sector—with the president-elect of the United States Joe Biden has campaigned heavily on a platform promising extensive renewable energy investment—the old presumptions of bygone years should be set aside.

No longer are renewable energy sources seen merely as a "technology of tomorrow" that sees them de-prioritized with major decisions about their use set aside for another day. In this regard, should Munday and his team deliver more promising prototypes, there should be high hopes the ever-increasing support for renewables will help speed up the development cycle. Now, what concrete benefits could NSPs bring once ready for use?

How NSPs could be utilized

Much has been written about the capacity of solar panels to provide a power solution to communities in developing nations where a high rate of annual daily sunshine hours exists. This is right and appropriate given the comparatively low cost of solar, the ease of installation, and the long-term lifespan of an installation. Yet far less has been written about the potential for solar panels to be used at the opposite end of the spectrum.

In remote places with low annual daily sunshine hours—especially during the winter where demands on energy sources increase due to additional needs for lighting, heating, gadgets for entertainment, and so on—there is a dual-challenge of these extra needs being met by energy providers located far away. Put simply, living in a remote area can result in more costly power bills—and these costs add further pressure on the cost of living when other factors like higher transport costs factor in.

It’s necessary to note the possibility of utilizing NSPs in remote areas could also see them met with the same challenges that can hinder the installation of conventional solar panels. Just as it has in Antarctica, the installation of solar panels for use after sunset in certain locales—such as a remote fishing village in Alaska or Greenland—would need to factor in environmental concerns such as the risk of extreme weather or even large wildlife that could damage the panels.

Furthermore, that the technology behind today’s current conventional solar panels is always improving. Not only when it comes to the panels themselves, but other key elements of an installation like batteries. In years to come, we could see the growth in battery capability overlap with the current energy gap that would otherwise be met by NSPs.

Solar Panels and Light Bulbs

Nonetheless, even if such an event does occur it does not diminish the value of NSP tech progressing—for just as each solar installation must essentially be considered on its own merits and what’s ideal for its placement and capacity—so too can it be expected there will be enduring value in the availability of NSPs. A key example of this is the aforementioned communities who have little annual daily sunshine hours, and so would likely benefit far more from the utilization of NSPs that could harvest in months of little-to-no sunshine, versus utilization of battery technology that would not charge in the comparatively rare periods of sunshine to justify the upfront cost of installation, or meet existing energy needs.

The difference is night and day

Solar Magazine: Solar Industry News and Insights

There are high expectations for the ongoing growth of solar energy in 2021. Notwithstanding all the challenges caused by the pandemic in 2020, in the solar sector it was a year where new world records were set, world-leading farms were set up, and nations continued to close in on-grid parity between traditional and renewable sources (with a number having already achieved it before 2020). But just as the sun is undoubtedly shining on solar’s future in the year ahead via the use of conventional panels, so too do NSPs offer an exciting new avenue for the growth of the industry.

NSP’s could provide immense benefits to solar installations right across the world. For existing installations, the introduction of new panels could help harvest additional power at night. For new installations, the opportunity to have a "dual" installation of conventional solar panels with NSPs so as to allow for renewable energy generation 24 hours a day appears promising.

Especially if NSPs take many years to catch up to conventional solar panels in terms of their harvesting capabilities. Should NSPs close this gap faster than expected, then their capacity to generate energy 24 hours a day (in a way that conventional panels cannot) would be a landmark moment. So although we won’t see NSPs in use today or tomorrow certainly we can all look forward to the transformative effect NSP’s would have once upon such time as they shift from potential to actual use across the world.


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