The Next Generation of Solar Power

Invisible Light, Terrestrial Emissions, and Tiny Antennas

By Justin Williams
Thursday, March 6th, 2014

We all love solar power around here, but this one’s a little different. After reading this, you’ll probably think we've gone a little too speculative.

Time for a quick thought experiment: What if we had a technology that could harvest the Earth’s infrared radiation – kind of like solar power, only we use the Earth as our generator?

The idea probably seems far-fetched, but if top research scientists at Harvard are working on it, you certainly begin to wonder.

The man with the plan is Federico Capasso, the Robert L. Wallace Professor of Applied Physics at Harvard University’s School of Engineering and Applied Sciences (SEAS). Along with his team, they are taking the idea of renewable energy beyond anything we’ve seen.

Renewable energy, in general terms, can be generated any time heat flows from something hot to something cold, and in varying degrees of those two spectra. One such flow of this energy is when the warmth of the Earth is dispersed into outer space, via infrared thermal radiation.

What Professor Capasso’s team is proposing is that electricity can be harvested from the infrared light emitted from Earth into outer space. Simple enough in theory, but to those in the physics field, it's not simple at all.

It should be noted that Federico Capasso is somewhat renowned in his field. The Italian-born applied physicist pioneered the field of band-gap engineering and co-invented the infrared quantum-cascade laser back in 1994.

The promise of his proposal is mind-boggling. What if we really could harness the 100 million gigawatts of infrared heat that we continuously release into outer space?

That would be enough power for all of humanity, for thousands and thousands of years, and it’s continuous – never ending. If we could capture even the tiniest morsel of this energy and use it for power than it would shut down all of the world’s energy woes – for good.

It is a completely untapped source of energy.


The Way it Works

Unlike a traditional solar photovoltaic panel that captures incoming visible light, Capasso and his team want to generate direct current (DC) electric power by capturing infrared emissions that it emits itself. It seems counterintuitive.

The full overview and proposal appears in this week’s issue of Proceedings of the National Academy of Sciences.

In that paper, two types of emissive energy are described; using two designs for a device they call an “emissive energy harvester (EEH)” that would convert infrared radiation into usable power.

The problem right now is that the technology is currently way too expensive to make an affordable harvester, but it lays out plans for how to make such a device work. This has promise.

The two possible devices in the paper are a thermal EEH (analogous to solar thermal power generation) and an optoelectronic EEH (analogous to photovoltaic power generation).

One of these EEH devices would emit much more infrared radiation than it receives, and it is in that imbalance where DC power can be generated.

As for where this would likely take place, a case study the research team conducted looked at how much power could be generated in Lamont, Oklahoma. There lies a facility that measures infrared radiation intensity.

According to IEEE SPECTRUM, the team found that they would get an average of 2.7 Watts from the infrared radiation emitted by a square meter of Oklahoma over 24 hours, which is pretty low for large-scale power generation.

That’s where the case of both EEH devices come into play. Using antennas, they can absorb electromagnetic radiation and convert it into DC electricity. A rectenna as they call it, is a rectifying antenna complete with a diode, where radiation is induced as alternating current (AC) voltage is carried across the antenna to the diode, which would then create the DC electricity.

And Beyond

For years, these nano-sized antenna arrays have been touted as the future of solar energy. They can collect 70 percent of solar radiation, where traditional panels only collect 20. Unfortunately, the fabrication process is extremely difficult.

The Harvard team says that “rectennas” should be easy to make and economical on a large scale. The real challenge is in the diodes; being able to make them work well at the low voltages that would be needed in a harvester. The research suggests some options, but for now they’re still just ideas.

Engineers also have to overcome some technical challenges.

For example, the core electrodes within a rectenna have to be spaced about one nanometer apart. That's 1.0 × 10-7 centimeters. In other words, there are ten million nanometers in a single centimeter.

It's ridiculously tiny.

Researchers at Uconn, however, have devised a potential breakthrough in fabrication known as atomic layer deposition (ALD). The technique was developed by Brian Willis, Uconn's associate professor of chemical and biomolecular engineering. It allows the parts to be spaced appropriately.

Previously, rectennas were built with lithographic processes that couldn't make such a small gap between the two electrodes. The closest scientists could get with this process was 10 nanometers.

So with rectenna technology coming into its own piece by piece, we are slowly approaching a new generation of energy. 

You can call me crazy all you want, but the next age of energy could take place within our lifetime.


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