Sunflowers inspire efficient solar power

In August, UW-Madison researcher Hongrui Jiang published his design for solar panels that act like sunflowers, tracking the sun's movement throughout the day. Jiang, a professor in computer and electrical engineering, used nanotechnology to design a system that helps the panels move by reacting to the warmth of the sun's rays, rather than using a motor and global positioning system (GPS) as many solar tracking panels do. Read Jiang's answers to Madison Commons' questions about how the new solar technology works and what else he is doing with nanotechnology.

MC: Why are you interested in solar technology?

HJ: Renewable energy is very important right now because we are running out of fossil fuels. We have to look for other possible sources of energy. Solar energy is very promising because pretty much everywhere has sunlight, not like wind or geothermal, and it lasts forever.

MC: Describe the work you do in patterning solar panel movement after sunflowers.

HJ: The basic idea is solar-tracking. If you can have a solar panel follow the sun during the day, you’ll have more interception of light, and therefore more electricity. The idea is very simple and done by many plants in nature. Sunflower is one example, a buttercup flower is another. The idea is very simple but not easy to realize with solar panels. It is complicated because you have to mimic complex biochemical processes.

MC: Don’t some solar panels already track the sun’s movment?

HJ: In the solar tracking systems available now, most use GPS with motors. They use active mechanical systems to orient towards sun. Active systems are great but their mechanics consume energy themselves. The purpose is to get as much electricity as possible. Our system is passive, it doesn’t consume electricity to drive solar tracking. Also, it is very hard for active systems to realize full range tracking, sunrise to sunset. Ours does.

MC: How does the passive system of solar tracking work?

HJ: Sunlight hits a mirror which projects light onto an actuator holding carbon nanotubes. When the nanotubes warm they contract, causing the panel to shift toward the contracted nanotubes.

MC: Why do you use carbon nanotubes?

We needed a material that would be sensitive enough to respond to natural sunlight, whole spectrum light of all wavelengths. Some materials are responsive to strong light like lasers, but we need the solar panel to be responsive to whatever intensity the sunlight is at. 

MC: You use nanotechnology in your some of your other research. What else do you do on the super tiny nano scale?

HJ: My expertise in the microsystems and microscale optics. I’m working on making a tunable liquid contact lens that adds extra focusing power. When you are getting older the muscle in your eye starts to lose power and it becomes harder and harder for you to see up close so people wear bi- or trifocals. This contact lens autofocuses, basically like the point and shoot cameras that you use. It’s not just a lens, it’s a whole spectrum of gadgets [with] circuits and everything, but it has to be flexible. You need an energy source to provide electricity for the circuits. Right now we’re trying to harvest and store solar energy right in the lens. It’s a very challenging idea and we’re off to a good start.