Natural Energy Regulation

By Trevor Arp

At a deep level, all technology, from a car engine to a smartphone, works because it has been engineered to run in an orderly, well-regulated fashion. But nature is rarely neat and orderly. Disorder is natural and unavoidable, and if you make a new technology you must find a way to regulate it against disorder. In the last twenty years, the field of nanotechnology has flourished, producing new microscopic optoelectronics based on quantum physics, such 2D materials and quantum dots, that have the potential to revolutionize technology. But to harness that potential, we must find a way to regulate them. Our research group has uncovered a way to build regulation into a quantum system making it robust against external fluctuations.

Natural regulation

Figure 1: A conceptual diagram of natural regulation showing how introducing a second absorber can reduce fluctuations in output.

The concept behind natural regulation is simple. Figure A shows a basic schematic of how light is turned into power on a quantum level. An absorbing molecule, called molecule a, absorbs a photon of light. This creates an energetic electron, e-, which is transferred to a second molecule, called M, that turns the energy of that electron into power output. But if the power being absorbed, ua, doesn’t exactly match the desired output, um, then the only way to regulate it is to externally turn the whole process off and get um on average. This results in an output which switches between on and off, like that shown in Figure C, which results in large fluctuations.

But there is a way to avoid these fluctuations with no external feedback. Instead of a single absorber, use two absorber molecules a and b, both connected to molecule M, as shown in Figure B. With both connected to it, molecule M will switch between absorbing from a or b. If absorbers a and b are selected such that ua < um < ub and the mechanism to switch between them is tuned correctly, then the output will be far more regulated, as shown in figure D. This requires no external feedback, the regulation is built into the quantum structure of the system. There is a cost, doing this results in less overall power than a single absorber. But a tradeoff between maximum output and regulation is a familiar problem in engineering, any given application will always involve a balance between output and regulation.

The biggest application of natural regulation is solar power. Great strides have been made recently, solar panels are cheaper and more efficient than ever, but regulation is becoming a problem. Clouds and changes in light through the day create fluctuations in the output of a solar farm. Without regulation, this will lead to power outages or dangerous power surges in a power grid that relies on solar power. Regulating conventional solar panels requires inefficient and expensive electronics and control system, wasting power in the process. Newer solar panel concepts harness quantum materials, which could utilize natural regulation. If they did, solar panels could have a near constant output despite fluctuations in light, solving the regulation problem and making it possible to use solar energy efficiently in large sections of the power grid.

This idea is not new, plants figured it out millions of years ago. Plant leaves are solar cells, more effective than any solar panels built by humans, and they have the exact same problem. Without regulation, cloud cover or any kind of fluctuation in the light will cause rapid fluctuations of excess energy inside a living plant cell, damaging it. To overcome this problem, chlorophyll, the chemical that plants use to convert light into energy, has a two-absorber structure very similar to what we described above, giving it natural regulation. Two versions of chlorophyll, chlorophyll a and chlorophyll b work just like the absorbers a and b, regulating the input of solar energy into the plant saving it from dangerous fluctuations. Our research even indicates that plants distinctive green color comes from this regulation, because green is the color that makes chlorophyll most effective at regulation. In fact, our research into natural regulation started by trying to understand how chlorophyll works in plants. It turns out that plants have much to teach us about solar power!