Sunflowers inspire more efficient solar power system

Aug 16, 2012 by Mark Riechers
UW-Madison engineering professor Hongrui Jiang looked to sunflowers to help find more efficient ways to harvest solar energy.

(Phys.org) -- A field of young sunflowers will slowly rotate from east to west during the course of a sunny day, each leaf seeking out as much sunlight as possible as the sun moves across the sky through an adaptation called heliotropism.

It's a clever bit of natural engineering that inspired imitation from a UW-Madison electrical and computer engineer, who has found a way to mimic the passive heliotropism seen in sunflowers for use in the next crop of .

Unlike other "active" solar systems that track the sun's position with GPS and reposition panels with motors, electrical and computer engineering professor Hongrui Jiang's concept leverages the properties of unique materials in concert to create a passive method of re-orienting in the direction of the most direct sunlight.

His design, published Aug. 1 in and recently highlighted in Nature, employs a combination of liquid crystalline elastomer (LCE), which goes through a and contracts in the presence of heat, with carbon nanotubes, which can absorb a wide range of light wavelengths.

"Carbon nanotubes have a very wide range of absorption, all the way to infrared," says Jiang. "That is something we can take advantage of, since it is possible to use sunlight to drive it directly."

This video is not supported by your browser at this time.
Video of a proof-of-concept of Jiang's design in action.

Direct sunlight hits a mirror beneath the solar panel, focused onto one of multiple actuators composed of LCE laced with carbon nanotubes. The carbon nanotubes heat up as they absorb light, and the heat differential between the environment and inside the actuator causes the LCE to shrink.

This causes the entire assembly to bow in the direction of the strongest sunlight. As the sun moves across the sky, the actuators will cool and re-expand, and new ones will shrink, re-positioning the panel over the 180 degrees of sky that the sun covers in the course of the day.

This video is not supported by your browser at this time.
Artificial heliotropism in action.

"The idea is that wherever the sun goes, it will follow," says Jiang.

In Jiang's tests, the system improved the efficiency of solar panels by 10 percent, an enormous increase considering material improvements in the solar panels themselves only net increases of a few percent on average. And a passive system means there are no motors and circuits to eat into increased energy harvest.

"The whole point of solar tracking is to increase the electricity output of the system," says Jiang.

The materials driving Jiang's design have only been available in the past few years, so for now, he and his team are researching ways to refine them for use driving larger solar panels, where the net energy gain from his system will be the greatest.

But eventually, Jiang hopes to see huge industrial solar farms where fields of photovoltaic solar panels shift effortlessly along with the sunflowers that inspired him.

"This is exactly what nature does," says Jiang.

Explore further: Artificial 'beaks' that collect water from fog: A drought solution?

Related Stories

Solar power could get boost from new light absorption design

Nov 02, 2011

Solar power may be on the rise, but solar cells are only as efficient as the amount of sunlight they collect. Under the direction of a new professor at Northwestern University's McCormick School of Engineering and Applied ...

Nanoparticles improve solar collection efficiency

Apr 05, 2011

Using minute graphite particles 1000 times smaller than the width of a human hair, mechanical engineers at Arizona State University hope to boost the efficiency -- and profitability -- of solar power plants.

Willis Tower goes solar

Mar 22, 2011

(PhysOrg.com) -- Do you know the Sears Tower? No, no you don't because for some time now it has been going by the much less famous name of the Willis Tower. While that bit of information may not be news to ...

Device can heat home, save money

Apr 19, 2011

(PhysOrg.com) -- A new polymer-based solar-thermal device is the first to generate power from both heat and visible sunlight – an advance that could shave the cost of heating a home by as much as 40 percent.

Recommended for you

Congress: Safety agency mishandled GM recall

16 hours ago

Both houses of Congress scolded the U.S. highway safety agency Tuesday over its tardy handling of a deadly problem with General Motors cars, questioning whether it is competent to guarantee the safety of ...

Jindal: Obama hasn't done enough to harness energy

Sep 16, 2014

The governor of the state of Louisiana, a possible Republican presidential candidate, said Tuesday that President Barack Obama's administration has become "science deniers," failing to do enough to harness the nation's energy ...

User comments : 5

Adjust slider to filter visible comments by rank

Display comments: newest first

irjsiq
1 / 5 (1) Aug 16, 2012
What mechanism(s)re-orient both Flowers and Panels back to the position of the rising Sun???
PPihkala
1 / 5 (1) Aug 17, 2012
I also wonder what happens when there are clouds passing over the sun? My reasoning goes that when there is cloud coverage, all cells will cool down, turning the panel to night position. Then when clouds pass by, the panel will reorient towards the sun, missing some energy while reorienting. GPS oriented panels always keep the right direction despite the cloud coverage.
antialias_physorg
not rated yet Aug 17, 2012
What mechanism(s)re-orient both Flowers and Panels back to the position of the rising Sun?

The same one. When the sun (or a panel with this meachnism) goes down the heat on both sides even out (making the flower/panel go into a 'neutral' position, which is optimalley right between east and west facing). When the sun risies one side gets heated more and the flower/panel starts turnnig towards the sun.

I also wonder what happens when there are clouds passing over the sun?

Not much since infrared still penetrates somewhat. It's the relative difference of energy that determines the direction - and that relative difference is the same with or without clouds.
then again: Panels output is severly decreased when clouds pass - so: meh.

I think this is a pretty nifty idea as there's nothing to break down/sevice (and some joker can't come along and spoof the GPS signal - which would actually be a neat April-Fools gag)
unknownorgin
not rated yet Aug 19, 2012
Mr jiang's idea is a prime example of why it is a missmatch to use a complex system to do a simple job. Cost and reliability are also benefits of doing things the simple way.
barakn
not rated yet Sep 02, 2012
Can someone explain to me why GPS would be necessary here? A tracking solar panel needs just one thing, a clock/calendar, to know where to point. And I'm not buying the notion that a lot of energy is required to swing a solar array 15 degrees an hour.