JMU AFV Lab Blog

This article was on the Science Daily Website this morning. If this coating can be produced economically, it shows promise to make solar electricity generation much more attractive. Not only does it make solar cells more efficient, improving their efficiency from absorbing “…67.4 percent of sunlight shone upon it…” at present to absorbing “…96.21 percent of sunlight shone upon it…” after application of the coating, it also makes solar cells equally efficient regardless of the angle of the sun’s rays.  From the article:   “…his antireflective coating absorbs sunlight evenly and equally from all angles. This means that a stationary solar panel treated with the coating would absorb 96.21 percent of sunlight no matter the position of the sun in the sky….” If this is indeed true (The article doesn’t mention any independent verifications of its claims. I hope this isn’t just “grant fishing.”) then solar panels can be installed on roofs in the same plane as the roof. This avoids installing the extra superstructure needed to align panels to the optimum angle to take best advantage of the sun and the attendant unsightliness of such structures.  Go to http://www.sciencedaily.com/releases/2008/11/081103130924.htm to read all the details.

Solar Power Game-changer: ‘Near Perfect’ Absorption Of Sunlight, From All Angles

A new antireflective coating developed by researchers at Rensselaer could help to overcome two major hurdles blocking the progress and wider use of solar power. The nanoengineered coating, pictured here, boosts the amount of sunlight captured by solar panels and allows those panels to absorb the entire spectrum of sunlight from any angle, regardless of the sun’s position in the sky. (Credit: Rensselaer/Shawn Lin)

ScienceDaily (Nov. 4, 2008) — Researchers at Rensselaer Polytechnic Institute have discovered and demonstrated a new method for overcoming two major hurdles facing solar energy. By developing a new antireflective coating that boosts the amount of sunlight captured by solar panels and allows those panels to absorb the entire solar spectrum from nearly any angle, the research team has moved academia and industry closer to realizing high-efficiency, cost-effective solar power.

“To get maximum efficiency when converting solar power into electricity, you want a solar panel that can absorb nearly every single photon of light, regardless of the sun’s position in the sky,” said Shawn-Yu Lin, professor of physics at Rensselaer and a member of the university’s Future Chips Constellation, who led the research project.  “Our new antireflective coating makes this possible.”

An untreated silicon solar cell only absorbs 67.4 percent of sunlight shone upon it — meaning that nearly one-third of that sunlight is reflected away and thus unharvestable. From an economic and efficiency perspective, this unharvested light is wasted potential and a major barrier hampering the proliferation and widespread adoption of solar power.

After a silicon surface was treated with Lin’s new nanoengineered reflective coating, however, the material absorbed 96.21 percent of sunlight shone upon it — meaning that only 3.79 percent of the sunlight was reflected and unharvested. This huge gain in absorption was consistent across the entire spectrum of sunlight, from UV to visible light and infrared, and moves solar power a significant step forward toward economic viability.

Lin’s new coating also successfully tackles the tricky challenge of angles.

Most surfaces and coatings are designed to absorb light — i.e., be antireflective — and transmit light — i.e., allow the light to pass through it — from a specific range of angles. Eyeglass lenses, for example, will absorb and transmit quite a bit of light from a light source directly in front of them, but those same lenses would absorb and transmit considerably less light if the light source were off to the side or on the wearer’s periphery.

This same is true of conventional solar panels, which is why some industrial solar arrays are mechanized to slowly move throughout the day so their panels are perfectly aligned with the sun’s position in the sky. Without this automated movement, the panels would not be optimally positioned and would therefore absorb less sunlight. The tradeoff for this increased efficiency, however, is the energy needed to power the automation system, the cost of upkeeping this system, and the possibility of errors or misalignment.

Lin’s discovery could antiquate these automated solar arrays, as his antireflective coating absorbs sunlight evenly and equally from all angles. This means that a stationary solar panel treated with the coating would absorb 96.21 percent of sunlight no matter the position of the sun in the sky. So along with significantly better absorption of sunlight, Lin’s discovery could also enable a new generation of stationary, more cost-efficient solar arrays….

Source: http://www.sciencedaily.com/releases/2008/11/081103130924.htm

This item was in a Forbes.com newsletter I get. It reports on a fascinating new idea in solar electric power generation. It’s one of those classically “elegant” solutions that seem so simple and obvious that one wanders why no one thought of it before. Go to http://www.forbes.com/technology/forbes/2008/1117/058.html?partner=technology_newsletter to read the full article. They simply make huge balloons that have the form of segments of rotated parabolas, with a thin reflective coating on one half and a clear film on the other half. At the focal point of the reflective rotated parabola, which is inside the balloon, they situate a solar cell array. For a video that explains the concept much better than I can, go to http://www.youtube.com/watch?v=kROgE4Jdm-k . This looks like something we could duplicate and study in the AFV Lab.

Solar Bubbles

Kerry A. Dolan 10.29.08, 6:00 PM ET
Forbes Magazine dated November 17, 2008

Here’s an audacious bet: Cheap plastic balloons with solar cells inside can solve the world’s energy problem.

Behind a warehouse workshop in Livermore, Calif., an 8-foot shiny plastic balloon soaks up the abundant late September sun. Its shape reflects so much heat to its middle that you can’t leave your hand on it or you’ll burn. Insert a round plate covered with solar cells into the balloon and you may have the next idea in renewable power.

Eric Cummings, the brainy scientist who dreamed up the balloon idea, dismisses flat solar panels as expensive to install and difficult to deploy. The curvature of his balloon concentrates more sunlight onto fewer photovoltaic cells. He envisions vast farms of his 1-kilowatt balloons strung on wires and producing gigawatts of power.

Cummings has no deals yet with a utility, but his company, Cool Earth Solar, raised $21 million from Quercus Trust, a Los Angeles private equity firm, and other investors to build a 1.5 megawatt installation in California’s Central Valley. Construction of a test project in a field of brown weeds across the street from its offices is just beginning. “This is scalable in a way that dwarfs other options,” he boasts. “The goal is to be the 100% solution” to the energy crisis.

Cool Earth Chief Executive Robert Lamkin, who previously oversaw the development and construction of power plants at Calpine and managed plants at Mirant, says rather boldly that next year the company will have its costs down to $1 per watt, installed—at which point it can compete with natural gas and beat other kinds of solar technologies. Typical photovoltaic panels on rooftops cost up to $8 per watt installed. Solar thermal power, which concentrates heat to make steam, is aiming for $4 per watt. (These costs are all in terms of peak watts. Nights and clouds included, solar’s average cost per watt is four times as much.)

Whether solar balloons are viable has yet to be proved. “It’s definitely a nice idea, but this doesn’t appear to be a game changer,” says Daniel Kammen, a professor in the Energy & Resources Group at UC, Berkeley. Kammen says far bigger balloons up in the jet streamwould generate more electricity. Says Christopher Porter of Photon Consulting in Boston, “Relative to other solar, we’re not particularly excited about concentrated photovoltaics as a broad technology group.”

Cummings, 41, is undeterred. He has a doctorate in aeronautics and quantum chemistry from the California Institute of Technology—and a record of solving challenging problems. At the Department of Energy’s Sandia National Laboratories in Livermore, Cummings solved a 150-year-old electromechanical design problem in three months, pioneering a method to quickly and simply separate molecules.

Concentrating the reflected light into a receiver produces 300 to 400 times as much electricity out of each solar cell as a system without a concentrator, the company claims. A water-cooled jacket on the back side of the receiver keeps it from overheating. The balloon can add or bleed air to maintain its shape.

Cool Earth’s balloons can last five years but are so cheap it plans to replace them once a year. Or more frequently. It has yet to test against BB guns.

I came across this interesting article in Renewable Energy World.com’s blog this morning. The concept is new to me, and I’m fascinated by it. It seems to be quite an elegant concept.  It’s not terribly economic at this point in time, as the article itself says: Estimates for the cost of electricity produced range from €0.05 per kilowatt-hour (kWh) up to €0.25 [US $0.07 to 0.34 per kWh], depending on the cost of land and the financing scenario. However, it is carbon neutral and there is very little maintenance after the initial investment, (keeping the membrane repaired and the turbine/generator serviced and maintained.)  I wasn’t very far into reading the article before I wondered:  Why wouldn’t this work better using some portion of the top half of one of Buckminster Fuller’s Geodesic Domes?  Go to http://www.renewableenergyworld.com/rea/news/story?id=53742 to read more about this concept. The article is too long to include all of it here.

Solar Updraft Towers: Variations and Research
by Tom Bosschaert
Rotterdam, the Netherlands [RenewableEnergyWorld.com]

Aerial Photo of Solar Updraft Tower

The idea of using solar radiation to generate air convection that can subsequently be converted to an energy source has been around since the start of the 20th century, when a Spanish Colonel called Isidoro Cabanyes proposed it in a scientific magazine. Solar Updraft towers, also called solar wind or solar chimney plants, provide a very simple method for renewable electricity generation, with a constant and reliable output. Other renewable energy sources such as wind turbines and solar arrays suffer from high diurnal and seasonal fluctuations, or unpredictable patterns of output.

Due to the large initial investment required, unfamiliarity with the system and the solar updraft tower’s relatively low capture efficiency, only one prototype was ever built, in the 1980’s in Spain. This prototype however, performed above and beyond expectations, and continued to operate for almost 7 years after its designed life span of 3.

The solar updraft tower has been left on the shelf due to its perceived low efficiency, which is to a large degree undeserved. Most studies on this elegant and simple renewable energy producer consider the land occupied by the tower and its collector as one of the largest resource inputs required for this process. However, Except Architecture & Consultancy is investigating the possibility of more creative applications of the system, which would combine the tower with other land uses.

The Classic Solar Updraft Tower Scenario

The small experimental solar updraft tower plant, built in Manzanares, Spain in 1982 by Schlaich Bergermann, can be considered the classic example of the system. The design calls for a large, unused plot of land to house a collector between 500 m and 10 km in diameter, with a centrally located chimney ranging from 100 m to 1 km in height. The collector is a transparent membrane suspended several meters off the ground, which can be made of glass or a strong transparent polymer. (See pilot plant image left, as well as lead image, above.)

Sunlight penetrates this membrane, and the solar radiation is converted to heat upon hitting the ground. The air underneath the membrane quickly increases in temperature due to the greenhouse effect and flows towards the chimney, which, through the stack effect, becomes the lowest point of pressure in the system. This continuous airflow spins a turbine located at the base of the chimney. The nighttime difference in temperature between the ground and the air allows this effect to continue. Thermal storage devices can be used to smooth out the differences in intensity between night and day temperature differentials. As with other solar technologies, a higher latitude placement translates into a lower energy output. (See Figure 1, below.)

Schematic of Solar Updraft Tower

Figure 1: Classic Solar Updraft Tower Diagram…

To read the rest of the article, go to: http://www.renewableenergyworld.com/rea/news/story?id=53742