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Solar PV innovation: the new buzz


Joyce Laird

In the first of a series of articles on advances in solar photovoltaic (PV), Joyce Laird looks at how innovation can create a profitable playing field in the solar PV marketplace.

A changing market

The solar market is going through tremendous fundamental changes. The past years of demand for solar power, led by the Germans and the Spanish, stripped the industry of the ability to provide product. Demand created enormous shortage of materials such as silicon, wafers and production capacity – also of talent, knowledge and understanding of how to manufacture solar PV cells and how to install them.

This emerging solar PV market created an interesting dynamic where anybody who could get their hands on materials was enormously powerful. Some companies tied themselves into long-term contracts of huge value. And it was these long-term contracts for materials, services or equipment that became the most important thing needed to participate in the market.

Then things changed. In the last year or so the major markets have been affected by the economic climate, putting construction plans on hold. At the same time Spain, which in 2008 overtook even Germany as the main market for solar PV modules, has gone into freefall as its subsidy programme has been scaled down to take the heat out of the market.

As if that wasn’t enough, the supply of material volume has caught up. Suddenly the ability to supply products has overshot demand. The powerful end of the market which was materials, has suddenly shifted over to the solar PV module makers and systems companies. Where the spot market for silicon was previously as high as US$400 (up to even US$600 per milligram), it is now back down to US$40.

Everyone is moving the focus to improving both the manufacturing process and the end product."
 

In 2006, 2007 and 2008, virtually all major manufacturers were talking about scaling up, and the focus was diverted somewhat from new processes or materials. Nowadays, everyone is moving the focus to improving both the manufacturing processes and the end product. Whether crystalline or thin-film solar PV, everyone is looking for ways to run the lines more efficiently and increase usable cell watts. Some innovations are coming from in-house technology. Some are coming from new concepts in equipment, from the single system level – all the way up to a “factory in a box”.

Leveraging resources

Innovative cost saving can be seen in many different ways. Sharp Solar Energy Solutions Group, for instance is building a large factory for solar thin-film that is sharing infrastructure, land and the supply chain with an equally large factory for flat screen televisions.

“In our case we take the basic technology which is a thin layer of silicon on a piece of glass, and on the right side of the plant it becomes a television set and on the left side we turn it into a thin-film solar module,” Paul Wormser, senior director of Engineering says.

“It is the same material science to get two very different products. This helps reduce total cost. We have the supply chain co-located at the complex because the glass is made there and this reduces cost. Our current thin-film is two layers to capture more of the sunlight. Future thin-film will be three layers to capture more sunlight to become even more efficient.”

That is just one major platform for Sharp in solar. The other is of course crystalline. Wormser says that Sharp is not abandoning one solar technology for the other. Rather he sees them as complimentary technologies for different applications.

“[There is] value in both...our strategy in crystalline is to put crystalline manufacturing plants around the world so that the product is near the point of use. We have a very large plant in Memphis, Tennessee. Our goal for thin-film is to eventually grow a world wide production system. Cur-rently the production is in Japan but it will move beyond Japan as the market picks up the technology.”

Savings through equipment technology

With a strong background in the semiconductor industry, Applied Materials has transferred years of expertise to the solar industry with two end businesses; equipment used in manufacturing the wafering of crystalline solar PV cells, and its SunFab thin-film process – which is an integrated end-to-end manufacturing line.

The company has 6 thin-film customer SunFabs in production with well over 200 MW currently on line. Four are in Europe, one in India and one in Taiwan. These are all solar thin-film lines that use a form factor of 5.7 m2 – which is a 4×-larger format than was ever previously used.

“This increases manufacturing efficiency because with each pass you are moving far more material through the line,” says Jonathan Pickering, vice president, global marketing and development, Solar Group.

“It takes the same time to produce the product whether you are processing one square inch or 5.7 m. It is much more effective to process large form factors. This increases end product yield using the same processing time. You have seen that a lot in the semiconductor industry with large format wafers. It’s the same here. We are at 5.7 m2 and moving toward 9 m.

“For thin-film, we are looking at ways to improve the quality of the materials. For example, to improve the reflective layer at the back, we optimise the optical properties of that material so that more of the light that isn’t absorbed in the first time around – the light that passes through the active layers – is reflected back,” Pickering says.

“We want the TCO to be optimised it so that it gets the right light into the right layer. A lot of research has gone into this, and the two main materials that have been used for the TCO are tin oxide and zinc oxide. We have been working with both to optimise the TCO performance,” he adds.

On the solar crystalline side, cost comes down by reducing the amount of silicon in each solar PV wafer. This is done by using the thinnest possible wire. Pickering says that they are at around 200 microns wafer thickness, and are forecasting next year that they will be down to 150 microns in production. That is a big saving.

Another is reducing the shading. Nearly all sun contact devices have a wire grid on the front. This wire grid produces shading. “You want to make grid lines as thin as possible, but at the same time, you don’t want to lose conductivity. So we are working on some new screen print technologies which enable a higher aspect ratio of these lines. To do this we have acquired an Italian company that manufactures screen printers, pass and sort equipment that was a clear leader in screen printing and metallisation,” Pickering says.

Lamination is another key area that can greatly reduce production cost of solar PV. Robert Bürkle GmbH, of Freuden-stadt Germany is a company that has focused on this equipment area.

Sven Kramer, senior sales engineer, Burkle North America, Inc., NC, says that its multi-opening lamination Ypsator lines greatly reduce factory footprint while increasing throughput. “13 of these lines are already in operation at customer facilities all over the world for the encapsulation of thin-film glass-glass modules. Different encapsulation foils such as PVB or EVA as well as thermoplastic materials can be used,” Kramer says.

For crystalline solar PV modules, lamination takes approximately 20 minutes using a fast cure EVA, then the product goes into the cooling step where the modules are cooled under pressure.

“The difference between thin-film and crystalline is that we split the lamination into two parts; EVA encapsulation always needs cross linking or final curing and that is what we do in the final lamination using hydraulics,” Kramer says. “The advantage of that is that we apply heat from both sides with uniform pressure onto the module. So we have symmetric heating, uniform pressure application on both sides of the cell. For cooling we apply pressure from both sides and cool under pressure down.”

For either technology application, the multiple openings allow several laminators to be replaced with a single machine. This reduces the equipment footprint and associated energy and labour costs. The extreme control of the internal processes provides a uniform end product with a true power reading, increasing quality yield of the solar PV modules.

When companies need to develop better end products, or find a more efficient way to manufacture them, equipment manufacturers/integrators such as Spire Solar, Inc., Bedford, MA are there to help. One of the market areas Spire is currently addressing is complete turnkey factories that can range in solar PV cell production output from 12 MW to 200 MW per year – crystalline or thin-film.

“We are having meetings with large Chinese manufacturers of modules, which are looking to move production to the US,” says Mark Willingham, vice president of marketing. “This is very unusual. Chinese companies rarely leave their country because of the labour advantage. But they see the value of being close to the fastest and biggest growing end user markets in solar, and want to set up plants close to the actual end users.

“We have identified the most advantageous progression through those lines, and we chart this out for our customers, and show them what the cost of the factory is compared to the cost per Watt of the end product they will be producing,” Willingham says. “We don’t think of our turnkey lines as being fully automated or [having] low automation, we look at this as maximum automation for maximum job creation – a fit, a balance. Because goals might be different for different companies.

“Helping customers save the right money is our goal. A good example is that if a company saves US$100,000 in capital investment in equipment purchase, to start up a 50 MW line – which is sort of an average for the industry in end product – in actuality all they are really saving is four one hundredths of a penny per Watt in production. A completely inconsequential amount.

“Whereas if they lose one percent in uptime? They lose one million dollars a year in revenue. So we get back to the basics of don’t be a penny-wise and pound foolish. Save the right money where it counts. If you have a 50 MW plant and it takes you one additional month to get certified, that’s US$9 million in revenue that you will not have received because you can’t sell to this lucrative market without being certified.”

Since the Spire simulator is used by all major US and Canadian energy markets to certify solar PV manufacturing equipment, Willingham says that Spire can work with these agencies to help get its customers certified: “On the other hand, these agencies are also our customers. We make the gauge they use to test everybody’s products,” he says.

Specific solar PV innovations – crystalline

The core competency of SANYO Electric Co, Tokyo, Japan, is manufacturing crystalline solar PV cells.

“What we are doing is doubling our plant capacity once every two years,” says Robert Zerner, business de-velopment executive, Solar Division.

“That allows us to procure materials cheaper and to run at a higher profit margin. And to hold down cost unlike companies that are building factories in China, Sanyo is about to open an US$80 million factory in Salem Oregon, USA. For us that is a lower cost move because the talent is unmatched anywhere in the world, the silicon expertise, and the power to run the plant (which in Oregon is mostly hydro-power) is very cheap”.

Increasing efficiency is the main aim for SANYO. The company recently announced 23% efficiency from their solar PV cells at the R&D level. This was certified by an independent 3rd party:

Some innovations are coming from in-house technology. Some are coming from new concepts in equipment."
 

“The first thing that we did to achieve the high efficiency rate was that we improved the quality of the Heterojunction; the junction between the single crystalline silicon and the amorphous crystalline silicon,” adds Zerner.

“We have a hybrid technology where we combine a little of the single crystalline silicon and the amorphous silicon. We reduced optical absorption. We call this hybrid technology HIT (Heterojunction with Intrinsic Thin layer). A HIT solar cell is composed of a single thin crystalline silicon wafer sandwiched by ultra-thin amorphous silicon layers. We have a HIT solar panel, and HIT solution,” he says.

Suniva, Inc., based in Norcross, GA, USA, has also announced a breakthrough in low cost, high-efficiency crystalline solar PV cells. The company claims to have achieved 18% efficiency in full production, which Brian Ashley, vice president, says is a world record for screen-printed solar PV cells.

Suniva’s ARTisun series solar PV cells are manufactured with optimised metallisation techniques and proprietary process innovations, both of which maintain low cost while extracting the highest efficiencies possible. Suniva produces solar cells which are integrated into high-performance solar modules, available through Suniva and its global customer partners.

Suniva has also just announced the start of production on a second manufacturing line at the Norcross plant. The new 64 MWp line will triple the production capacity of the facility to approximately 100 MWp.

“Our solar cells were used in the first grid-connected power plant built in India. So we have been producing in volume since October 2008, and have produced about 7 or 8 MW already,” Ashley says.

Suniva says it employs the latest innovations in solar PV cell processing techniques to drive leading-edge cell efficiencies at low manufacturing costs. Its proprietary technology and patents represent more than 16 years of silicon PV experience – exclusively licensed from Georgia Tech’s University Center of Excellence in Photovoltaics (UCEP).

“We are in the unique position to have proprietary IP in our solar cell design, we use standard low cost processes to make our cells. That is low cost screen printing . We are able to optimise every layer of the film based on our intellectual property and many years of experience from our expansive R&D team,” Ashley adds.

“By optimising every layer of cell design, you get a little extra, say 2 tenths of a percent out of this layer and 3 tenths from another layer and some from PECVD. You get other boosts from the selection of the type of end formulation of pastes you are using, and the screen design and firing sequence and recipes you develop. And so there is a whole lot to manufacturing solar cells that are secret recipes that need to be developed and optimised by the manufacturer,” Ashley says.

Specific solar PV innovations – thin-film

Oerlikon Solar AG, headquartered in Trubbach, Switzerland is focused on manufacturing equipment for the solar thin-film processing industry.

“We have trademarked our Micromorph technology,” says Chris O’Brien, head of market development in North America. “It is a method of stacking very thin-film silicon layers in a way so that the overall silicon efficiency of the PV module is up to 50% higher than it would be as a single stack of silicon layers. Advancing that technology is one of the company’s core assets. The second thing is a business model that really hadn’t been seen before in the solar industry. That is what I call the ‘factory in a box’ model,” he adds.

Customers can purchase a complete solar PV thin-film manufacturing line from Oerlikon. This is an approach used in the semiconductor industry. O’Brien says that Oerlikon pioneered the construction of that model and since then, other companies have followed.

“This has proven to be a real catalyst to investment in thin-film silicon manufacturing – to bring a lot of new companies into the market of PV manufacturing,” O’Brien says. “We have a variety of customers in our base. Some are very knowledgeable about the industry and some are quite new. Collectively we have contracts for over 600 MW of power generation. Over half of that is in current generation, and the rest is under construction and expected to be operational in 2010.”

To increase solar cell efficiency, Oerlikon has developed a new method as part of the manufacturing process to deposit this TCO: “What it does is greatly increase efficiency. It’s not a great game changer, but it improves, say, a 7% conversion rate in a module to an 8% conversion rate using our process,” O’Brien continues.

“That’s just one example. We continue to make improvements throughout the line and pass these on to our customers. In many cases we have customers we maintain service agreements with so we not only turn over to them a complete factory, we provide ongoing support and upgrades. We help them maintain state of the art facilities.”

Solarion AG Photovoltaics, of Leipzig Germany has been working with the European Space Agency, providing its unique solar thin-film solar technology, but the goal is definitely terrestrial. Stefan Nitzche says that the company’s technology deposits onto 20 cm width plastic foil with linear evaporators, using no functional evaporators. He adds that they are scaling up to deposit on 80 cm – or about 2.5 ft – of the plastic foil.

“We are dealing with the CIGS chips. We changed the factory so instead of using the glass substrate, we are using the flexible substrate. We use a core evaporation process but with an ion beam assisted deposition. That means we are depositing the metals, indium, gallium and copper from the separators but the selenium is by an ion beam source,” Nitzche says.

“The advantages are that we use less materials by using the ion beam instead of the normal selenium wafer that our competitors are using; we have higher material utilisation and we can reduce the deposition temperature – normally, CIGS manufacturing needs temperatures in the range of 500°C, and we can reduce this to 400°C.This is very important because in all PV manufacturing you want to reduce the manufacturing cost and this fits both material and energy cost reduction.”

Another leading edge in thin-film is Solexant’s Nanocrystal Solar Cell, developed at Lawrence Berkeley National Lab. It is the first ultrathin-film solar PV cell incorporating nanocrystals made of high-performance and flexible inorganic materials that are said to dramatically increase solar PV cell efficiency and reduce manufacturing costs.

Based in San Jose, CA,USA, Solexant’s nanocrystal films, made from high-efficiency inorganic materials, are flexible. Until now, low-efficiency organic materials were required to produce low-cost flexible solar thin-films. Due to the flexibility of its films, Solexant can use the low-cost, high-volume “roll-to-roll” production technique, similar to printing ink on paper. This combination of high-efficiency materials and low-cost production allows Solexant to boast one of the lowest-cost-per-watt figures in the business.

“As a savings example on the capital equipment cost we are extremely efficient so capital equipment cost for a 100 MW system will cost less than US$50m, actually closer to US$40m,” reckons Damoder Reddy, president & CEO. “Normal silicon technology is in the US$140-US$150m range. Standard thin-film runs to about US$100m. It is in our proprietary equipment design. We actually build proprietary equipment in-house.”

Looking to the future

Everyone does agree that the downturn in the solar PV market in 2009 is going to reap tremendous benefits in the long run, because it is causing everyone to look at new ways to operate, new equipment, technologies and materials for a more cost-effective plant operation and better end product.

Whether talking about a newly-developed proprietary crystalline step improvement, a breakthrough in thin-film technology, a single system that replaces multiple machines or a ready-made factory installation, it’s all about driving cost down and quality up in solar PV.

Every solar PV cell manufacturer is looking at this. This is very exciting and it will move the industry forward. Everyone is focusing on key issues, and the industry will become more robust because of it. Every time cost goes down by five or ten cents, it opens up a whole new market for solar PV, allowing it to be more and more competitive against other power generation technologies.

Everybody is looking at the growth curves. Solar PV is growing. Right now it’s only about one tenth of our power generation but it can grow 100 fold very rapidly. Holding the cost down is going to be the big driver. Not just in one area but all areas of solar PV.

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