Tag Archives: solar energy

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/

Is Thin-Film Solar Dead?

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When the Chinese energy giant Hanergy decided last week to buy Miasole, a Silicon Valley-based thin-film solar company, at less than a tenth the amount venture capitalists had invested in the firm, it could have been making a savvy move. Though it seems as if thin-film solar panels have no hope of competing with conventional silicon ones under today’s market conditions, the technology might still have a strong future.

In recent years, the price of conventional silicon solar panels has fallen far faster than expected, and once-promising thin-film startups are going bankrupt, delaying manufacturing plans or being bought by Asian companies for pennies on the dollar. (In addition to Hanergy, TFG Radiant, SK Innovation, Taiwan Semiconductor and a few others have bought or taken large stakes in such companies.)

Some analysts think the companies that have been snatching up these bargains know what they’re doing. The poor market conditions that have kept thin-film companies from competing may not last: When demand increases and it comes time to start building solar-panel factories again, the argument goes, the technology might have a significant advantage, because for comparably sized plants, it could cost far less to build a new thin-film factory than a conventional one.

A gigawatt-scale thin-film plant would cost $350 to 450 million, versus $1 billion for a conventional silicon plant, says Travis Bradford, a professor at Columbia University’s school of international and public affairs and president of the Prometheus Institute for Sustainable Development, a nonprofit research firm. (The cost estimates will vary depending on what’s included in the plant. For example, if you add the cost of producing polysilicon, the equivalent to the raw materials that thin-film solar plants use, the capital cost for a silicon plant goes up to $2 billion or more, he says. But most plants buy silicon from large suppliers.)

So far, the companies with the potentially cheapest thin-film technology have built only relatively small factories that cost far more per watt than large ones, and building larger plants doesn’t make sense in the current market. (Solyndra, the failed thin-film company, was building a large plant, but it had notoriously expensive technology, including unusual tube-shaped solar panels. First Solar, by far the most successful thin-film company, has built large plants, but newer types of thin-film technologies may prove cheaper and more efficient.)

Startups can’t afford to wait until market conditions get better. But large companies like Hanergy might be able to bide their time until the market improves and then build a large plant that could compete with conventional silicon. “Hanergy spent $30 million to get Miasole,” Bradford says. “It will take them a few hundred million dollars to eventually build a large factory and launch the technology. But if they’re right, they’ve got assets that will be worth billions of dollars later. That’s the bet they’ve made.”

Waiting for market conditions to turn, however, is a risky strategy. The market is currently flooded with solar panels — current manufacturing capacity is more than enough to satisfy demand, and that’s driven down prices to the point that many manufacturers are selling at a loss. It’s not clear how long it will take for this situation to change.

Timing the construction of new thin-film factories will be difficult. In the meantime, manufacturers of conventional silicon technology continue to lower the cost of their solar panels and improve their efficiency. And there’s no guarantee that new thin-film panels will perform as expected when produced at a large scale — or that cost targets will be met.

One option could be for large companies to develop and build their own solar power plants. That’s the model used by First Solar, and it seems to be the model Hanergy is adopting.

But many analysts remain skeptical that thin film can compete with silicon, given silicon’s overwhelmingly larger scale of production. Thin film may have had a chance once, but it’s taken it too long to reach large-scale production and lower costs, according to Jenny Chase, manager of the Solar Insight Team at Bloomberg New Energy Finance. “That ship has sailed,” she says. She expects that thin-film companies might succeed only in niche markets, such as applications where very lightweight or flexible solar panels are needed.

This article originally published at MIT Technology Review
here

Read more: http://mashable.com/2012/10/10/thin-film-solar-dead/

What Tech Is Next for the Solar Industry?

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Solar panel installations have become increasingly popular, but the solar panel manufacturing industry is in the doldrums because supply far exceeds demand. The poor market may be slowing innovation, but advances continue; judging by the mood this week at the IEEE Photovoltaics Specialists Conference in Tampa, Fla., people in the industry remain optimistic about its long-term prospects.

The technology that’s surprised almost everyone is conventional crystalline silicon. A few years ago, silicon solar panels cost $4 per watt, and Martin Green, professor at the University of New South Wales and one of the leading silicon solar panel researchers, declared that they’d never go below $1 a watt. “Now it’s down to something like $0.50 of watt, and there’s talk of hitting 36 cents per watt,” he says.

The U.S. Department of Energy has set a goal of reaching less than $1 a watt — not just for the solar panels, but for complete, installed systems — by 2020. Green thinks the solar industry will hit that target even sooner than that. If so, that would bring the direct cost of solar power to $0.06 per kilowatt-hour, which is cheaper than the average cost expected for power from new natural gas power plants. (The total cost of solar power, which includes the cost to utilities to compensate for its intermittency, would be higher, though precisely how much higher will depend on how much solar power is on the grid, and other factors.)

All parts of the silicon solar panel industry have been looking for ways to cut costs and improve the power output of solar panels, and that’s led to steady cost reductions. Green points to something as mundane as the pastes used to screen print some of the features on solar panels. Green’s lab built a solar cell in the 1990s that set a record efficiency for silicon solar cells — a record that stands to this day. To achieve that level of efficiency, he had to use expensive lithography techniques to make fine wires for collecting current from the solar cell. But gradual improvements have made it possible to use screen printing to produce ever finer lines. Recent research suggests that screen printing techniques can produce lines as thin as 30 micrometers — about the width of the lines Green used for his record solar cells, but at costs far lower than his lithography techniques.

Green says this and other techniques will make it cheap and practical to replicate the designs of his record solar cell on production lines. Some companies have developed manufacturing techniques for the front metal contacts. Implementing the design of the back electrical contacts is harder, but he expects companies to roll that out next.

Meanwhile, researchers at the National Renewable Energy Laboratory have made flexible solar cells on a new type of glass from Corning called Willow Glass, which is thin and can be rolled up. The type of solar cell they made is the only current challenger to silicon in terms of large-scale production—thin-film cadmium telluride. Right now such solar cells are made in batches (as are silicon solar cells), but the ability to make them on a flexible sheet of glass raises the possibility of continuous roll-to-roll manufacturing (like printing newspapers), which can reduce the cost per watt by increasing production.

One of Green’s former students and colleagues, Jianhua Zhao — cofounder of solar panel manufacturer China Sunergy —announced this week that he is building a pilot manufacturing line for a two-sided solar cell that can absorb light from both the front and back. The basic idea, which isn’t new, is that during some parts of the day, sunlight falls on the land between rows of solar panels in a solar power plant. That light reflects onto the back of the panels and could be harvested to increase the power output. This works particularly well when the solar panels are built on sand, which is highly reflective. Where a one-sided solar panel might generate 340 watts, a two-sided one might generate up to 400 watts. He expects the panels to generate 10% to 20% more electricity over the course of a year.

Such solar panels could be mounted vertically — like a fence — so that one side collects sunlight in the morning, the other in the afternoon. That would make it possible to install the solar panels on very little land; they could serve as noise barriers along highways, for example. Such an arrangement could also be valuable in dusty areas. Many parts of the Middle East might seem to be good places for solar panels, since they get a lot of sunlight, but frequent dust storms decrease the power output. Vertical panels wouldn’t accumulate as much dust, which could help make such systems economical.

Looking even further ahead, Green is betting on silicon, aiming to take advantage of the huge reductions in cost already seen with the technology. He hopes to greatly increase the efficiency of silicon solar panels by combining silicon with one or two other semiconductors, each selected to efficiently convert a part of the solar spectrum that silicon doesn’t convert efficiently. Adding one semiconductor could boost efficiencies from the 20% to 25% range to around 40%. Adding another could make efficiencies as high as 50% feasible, which would cut in half the number of solar panels needed for a given installation. The challenge is to produce good connections between these semiconductors — a task that the arrangement of silicon atoms in crystalline silicon makes quite difficult.

Image courtesy of Chandra Marsono/Flickr

This article originally published at MIT Technology Review
here

Read more: http://mashable.com/2013/06/21/solar-industry-tech/