Tag Archives: solar cells

How to Double the Power of Solar Panels

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In an attempt to further drop the cost of solar power, Bandgap Engineering, a startup in Woburn, Mass., is developing a nanowire-based solar cell that could eventually generate twice as much power as conventional solar cells.

That’s a long-term project, but meanwhile the company is about to start selling a simpler version of the technology, using silicon nanowires that can improve the performance and lower the cost of conventional silicon solar cells. Bandgap says its nanowires, which can be built using existing manufacturing tools, boost the power output of solar cells by increasing the amount of light the cells can absorb.

Right now most solar-panel manufacturers aren’t building new factories because the market for their product is glutted. But if market conditions improve and manufacturers do start building, they’ll be able to introduce larger changes to production lines. In that case the Bandgap technology could make it possible to change solar cells more significantly.

For example, by increasing light absorption, it could allow manufacturers to use far thinner wafers of silicon, reducing the largest part of a solar cell’s cost. It could also enable manufacturers to use copper wires instead of more expensive silver wires to collect charge from the solar panels.

These changes could lead to solar panels that convert more than 20% of the energy in sunlight into electricity (compared with about 15% for most solar cells now) yet cost only $1 per watt to produce and install, says Richard Chleboski, Bandgap’s CEO. (Solar installations cost a few dollars per watt now, depending on their size and type.) Over the operating lifetime of the system, costs would come to $0.06-0.10 per kilowatt-hour.

That’s still higher than the current cost of natural-gas power in the United States, which is about $0.04 per kilowatt-hour. But it’s low enough to secure solar power a substantial market in many parts of the world where energy costs can be higher, or in certain niche markets in the United States.

Meanwhile, Bandgap is pursuing technology that could someday improve efficiency enough to allow solar power to compete widely with fossil fuels. Double the efficiency of solar cells without greatly increasing manufacturing costs, and you substantially lower the cost per watt of solar panels and halve the cost of installation — currently the biggest expense in solar power — by making it possible to get the same amount of power out of half as many cells.

Both the cells Bandgap is about to introduce and the cells it hopes to produce in the long term are based on the idea of minimizing the energy loss that typically occurs when light passes through a solar cell unabsorbed or when certain wavelengths of light are absorbed but don’t have enough energy to dislodge electrons to create electricity. (That energy is wasted as heat.) In a conventional solar cell, at least two-thirds of the energy in sunlight is wasted — usually much more.

The company’s existing technology makes use of the fact that when light encounters the nanowires, it’s refracted in a way that causes it to bounce around in the solar cell rather than simply moving through it or bouncing off it. That increases its chances of being absorbed.

But what Bandgap ultimately wants to do is to change the way light is converted to electricity inside the cell. If the nanowires can be made uniformly enough, and if they can be formed in such a way that their atoms line up along certain planes, the tiny structures could change the electronic properties of silicon.

These changes could allow solar cells to generate electricity from low-energy light that normally produces only heat, says Marcie Black, the company’s founder and chief technology officer. It does this in part by providing a way to combine energy from more than one photon of low-energy light.

The technology could take many years to develop. For one thing, it requires very precise control over the properties of each of millions of nanowires. Also, the techniques needed to make the solar cells might not be cheap or reliable enough to produce them on a large scale. But such solar cells could theoretically convert 60% of the energy in sunlight into electricity. That will be hard to achieve in practice, so the company is aiming at a more modest 38% efficiency, which is still more than twice that of typical silicon solar cells made now.

Researchers are taking several other approaches to producing very high-efficiency solar cells, such as using quantum dots or combining several kinds of materials.

The nanowire technology could be simpler, however. “In theory, the approach has many potential advantages, but you’ve got to get it to work,” says Andrew Norman, a senior researcher at the National Renewable Energy Laboratory in Golden, Colo.

Bandgap hasn’t yet built solar cells using the approach it hopes to pursue in the long term, but it’s made indirect measurements showing that its nanowires can change the electronic properties of silicon. “This is still in the research phase,” Black says. “We’re being very honest with investors — there’s still a lot of work to do.”

This article originally published at MIT Technology Review
here

Read more: http://mashable.com/2012/10/17/double-power-solar-panels/

Double-Decker Solar Cells Capture More Sunlight

Swiss engineers have demonstrated tandem solar cells layered so they can catch more of the solar spectrum, providing a route to cheaper and more efficient solar power. The cells are not yet ready for commercial applications, but could mark a major step forwards for renewable energy.

Traditional solar cells present engineers with a fundamental problem. The colors in sunlight are photons of different energies,but individual cells can only extract the same amount of energy from each photon, leaving designers with a choice. One path involves collecting high-energy photons and missing out on the majority of the Sun’s photons whose energy is too low. The alternative is to harvest a larger portion of the spectrum, but only get a small amount of energy from each photon, so that much of the potential of higher energy photons is wasted.

This problem can be resolved by placing different types of cells on top of each other, with the top layer catching high-energy photons while letting those of lower energy through to be captured by another cell below. Multi-junction cells that stack four layers upon each other have achieved 46 percent efficiency,but at prices notviable for most circumstances. An alternative path is to split sunlight with a prism so that each cell gets the light for which it is most suited.

Professor Ayodhya Tiwariis co-leader of a team at Empa-Swiss Federal Laboratories who have announcedin Nature Communicationsaproof of conceptfor a way to make the top cell cheaply enough for widespread use, while still letting most of the unused light through.

Tiwari’s version uses the new wondermaterialperovskitefor the top cell, with copper indium gallium diselenide below. Perovskite is a naturally occurring mineral that can also be manufactured for energy-collecting purposes. Although still not as efficient as the best solar cells, progress in perovskite materialhas happened far more rapidlythan any other solar material ever tried.

While most solar cells, perovskites included,require high-temperature manufacturing, greatly adding to the cost, Tiwari created the top layer at 50C (122F), opening up the possibility of very cheap mass production.

The test cells used perovskite crystals to collect 14.2 percent of the energy in sunlight, while letting 72 percent through. The cell below captured another 6.3 percent. The total efficiency of 20.5 percent is similar to the best commercial cells and nothing exceptional by laboratory standards. However, Tiwari claimed in a statementthat 30 percent efficiency is in sight for the cells made this way.”What we have achieved now is just the beginning,” he said.”We will have to overcome many obstacles before reaching this ambitious goal.”

Higher efficiency, even at the same price per watt, would makesolar energy more attractivewhere space is limited (such as the roofsof electric cars)and reduces the costs of installation and associated infrastructure.

Perovskite cells currently lack the durabilityof silicon crystals though, particularly when exposed to water, and this remains the biggest obstacle to their widespread use.

Read more: http://www.iflscience.com/physics/double-decker-solar-cells-capture-more-sunlight-0

These Robots Install Solar Panels

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As the price of solar panels has plummeted, the amount of solar power being generated worldwide is soaring. Yet solar still accounts for less than 2% of the world’s total electricity capacity.

Each square meter of solar panel generates around 145 watts of electrical power, enough to turn on just two or three light bulbs. That means you’d have to cover the National Mall in Washington, D.C. five or six times over to match the peak capacity of a large fossil-fuel power plant. What’s more, every one of those panels needs to be installed by hand.

Now companies such as PV Kraftwerker and Gehrlicher in Germany are developing mobile robots that can automatically install ground-mounted solar panels day and night, in all sorts of weather. PV Kraftwerker’s robot is designed to assemble power-plant-grade solar panels, which are four times the size of the ones you’d see on a home.

The main idea is to save money on labor, which accounts for a growing fraction of the cost of solar power as panels get cheaper. According to PV Kraftwerker, a construction firm specializing in solar parks, installations that used to require 35 workers can now be done with just three workers in an eighth the time.

For a 14-megawatt solar plant, the company estimates, it might cost about $2 million to install the panels manually. Using the robot could cut that cost by nearly half. The company says that the robot, which lists for $900,000, could pay for itself in less than a year of steady use.

Robotic help could be a plus given Germany’s ambitious plans to get a third of its electricity from renewable sources within eight years and 80% by 2050 (see: The Great German Energy Experiment). Germany led the world in solar installations in 2011, putting up panels capable of generating around 7.5 gigawatts and covering an estimated 50 square kilometers of ground and rooftops.

PV Kraftwerker built its robot from off-the-shelf Japanese components. The machinery consists of a robotic arm mounted on an all-terrain vehicle with tanklike tracks. Suction cups grip the glass face of the solar panels and the arm swings them into place, guided by cameras that give the robot a three-dimensional view of the scene.

The robot’s limitations give a glimpse of how hard it’s going to be to completely automate the installation process. Much solar power in Germany is generated by rooftop arrays, but the shape and orientation of roofs is too varied for robots to handle. Even for small solar farms and those using ordinary-size panels, human workers are both faster and cheaper than the robot, says Markus Gattenlöhner, head of marketing at PV Kraftwerker.

Christian Hoepfner, a scientific director at the Fraunhofer Center for Sustainable Energy Systems (see: Redesigning Solar Power), agrees that the role of robots will be limited.

“But I can see the beauty of it for large, ground-mounted installations,” he says. “When you think of huge fields covered with identical panels, you think, ‘Why not have a robot do it?’ As the size of installations increases, it’s unavoidable.”

So far, the PV Kraftwerker robot can only do one thing: lay panels on a metal frame that humans have already installed. Two people walking along beside the robot screw the panels to the frame and make electrical connections.

Yet robotic installation may become more common as other components get adapted to automation. PV Kraftwerker and other companies are also developing robots that, guided by GPS, can pound poles into the ground and then mount panels on them, eliminating the need for workers to install frames. Newer solar modules can be snapped or glued into position instead of being screwed in. Special plugs could even allow robots to make the electrical connections (see: New Solar Panel Designs Make Installation Cheaper).

Robots like these could be useful in bringing electricity to inhospitable environments. The Japanese government commissioned PV Kraftwerker to develop a version of its robot that could install a solar power plant largely on its own in radioactive areas near the site of the Fukushima nuclear-plant disaster. Gattenlöhner says Japan wants the robot within six months.

Image courtesy of Gehrlicher Solar AG

This article originally published at MIT Technology Review
here

Read more: http://mashable.com/2012/07/25/robots-solar-panels/