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Thin Film Photovoltaics

      Thin Film Photovoltaics
      from Wikepedia

Many different photovoltaic materials are deposited with various deposition methods on a variety of substrates. Thin-film solar cells are usually categorized according to the photovoltaic material used:

First Solar, Inc. is one of the world’s leading manufacturers of thin film photovoltaic (PV) modules, or solar panels, which can convert sunlight to electricity at competitive prices.  Using cadmium telluride (CdTe) as a semiconductor instead of the more common crystalline silicon, First Solar’s modules are economical and productive in a variety of temperature and light conditions.

Initially appearing as small strips powering hand-held calculators, thin-film PV is now available in very large modules used in sophisticated building-integrated installations and vehicle charging systems.   GBI Research projects thin film production to grow 24% from 2009 levels and to reach 22,214 MW in 2020. “Expectations are that in the long-term, thin-film solar PV technology would surpass dominating conventional solar PV technology, thus enabling the long sought-after grid parity objective.” 

A silicon thin-film cell uses amorphous (a-Si or a-Si:H), protocrystalline, nanocrystalline (nc-Si or nc-Si:H) or black silicon.  Thin-film silicon is opposed to wafer or bulk silicon (monocrystalline or polycrystalline).

The silicon is mainly deposited by chemical vapor deposition, typically plasma-enhanced (PE-CVD), from silane gas and hydrogen gas. Other deposition techniques being investigated include sputtering and hot wire techniques.

The silicon is deposited on glass, plastic or metal which has been coated with a layer of transparent conducting oxide .

A p-i-n structure is usually used, as opposed to an n-i-p structure. This is because the mobility of electrons in a-Si:H is roughly 1 or 2 orders of magnitude larger than that of holes, and thus the collection rate of electrons moving from the p- to n-type contact is better than holes moving from p- to n-type contact. Therefore, the p-type layer should be placed at the top where the light intensity is stronger, so that the majority of the charge carriers crossing the junction would be electrons.

Micromorphous silicon

Micromorphous silicon module technology combines two different types of silicon, amorphous and microcrystalline, in a top and a bottom photovoltaic cell. These two materials are chosen because their different absorption spectrums and easily combined process. Because the two different materials are both Si, they can be manufactured in the same technology, which now is PECVD.

The band gap of a-Si is 1.7 eV and that of c-Si is 1.1 eV, which eventually broaden the spectral acceptance of the micromorph tandem solar cell. The The c-Si layer can help to absorb the energy of red and infrared spectrum and increase the overall efficiency. The best efficiency can be achieved at transition between a-Si and c-Si. Use of protocrystalline silicon for the intrinsic layer has shown to optimize the open-circuit voltage of an a-Si photovoltaic cell.

Solar cell efficiencies

These types of silicon present dangling and twisted bonds, which results in deep defects (energy levels in the bandgap) as well as deformation of the valence and conduction bands (band tails). The solar cells made from these materials tend to have lower energy conversion efficiency than bulk silicon (also called crystalline or wafer silicon), but are also less expensive to produce. The quantum efficiency of thin-film solar cells is also lower due to reduced number of collected charge carriers per incident photon.

Amorphous silicon has a higher bandgap (1.7 eV) than crystalline silicon (c-Si, 1.1 eV), which means it absorbs the visible part of the solar spectrum more strongly than the infrared portion of the spectrum. As nc-Si has about the same bandgap as c-Si, the nc-Si and a-Si can advantageously be combined in thin layers, creating a layered cell called a tandem cell. The top cell in a-Si absorbs the visible light and leaves the infrared part of the spectrum for the bottom cell in nc-Si.

Recently, solutions to overcome the limitations of thin-film silicon have been developed. Light trapping schemes where the incoming light is obliquely coupled into the silicon and the light traverses the film several times enhance the absorption of sunlight in the films. Thermal processing techniques enhance the crystal structure of the silicon and pacify electronic defects.

Thin film photovoltaic panels being installed onto a roof

Thin film solar panels are commercially available for installation onto the roofs of buildings, either applied onto the finished roof, or integrated into the roof covering. The advantage over tradition PV panels is that they are very low in weight, are not subject to wind lifting, and can be walked on with care. The comparable disadvantages are increased cost and reduced efficiency.

A silicon thin film technology is being developed for building integrated photovoltaics (BIPV) in the form of semi-transparent solar cells which can be applied as window glazing. These cells function as window tinting while generating electricity.

Since the invention of the first modern silicon solar cell in 1954, improvements have resulted in modules capable of converting 12 to 18 percent of solar radiation into electricity.

The performance and potential of thin-film materials are high, reaching cell efficiencies of 12–20%; prototype module efficiencies of 7–13%; and production modules in the range of 9%. Future module efficiencies are expected to climb close to the state-of-the-art of today’s best cells, or to about 10–16%.

Annual manufacturing volume in the United States has grown from about 12 megawatts (MW) per year in 2003 to more than 20 MW/yr in 2004; 40–50 MW/yr production levels are expected in 2005 with continued rapid growth in the years after that.

Costs are expected to drop to below $100/m2 in volume production, and could reach even lower levels—well under $50/m2, the DOE/NREL goal for thin films—when fully optimized. At these levels, thin-film modules will cost less than fifty cents per watt to manufacture, opening new markets such as cost-effective distributed power and utility production to thin-film electricity generation.

As crystalline silicon price rose, the production cost of silicon-based solar cell module in 2008 was at some point 4–5 times higher than that of thin film modules. Thin-film producers still enjoy in 2009 price advantage as its production cost is 20% less than that of silicon modules.It is expected that the production cost of thin-film will continue dropping (40% less than silicon), as Chinese producers are now putting more resources into R&D and partnering with manufacturing equipment suppliers.

In recent years, the manufacturers of thin-film solar modules are bringing costs down and gaining in competitive strength through advanced thin film technology. However, the traditional crystalline silicon technologies will not give up their market positions for a few years because they still hold considerable development potential in terms of the cost. Efficiency of thin film solar is considerably lower and thin film solar manufacturing equipment suppliers intend to score costs of below USD 1/W, and Anwell Technologies Limited claimed that they intend to bring it down further to USD 0.5/W.

Those equipment suppliers have been doing R&D for micro-morphous silicon modules since 2008. This technology represents a development based on the thin-film panels made of ordinary amorphous silicon marketed at present that brings higher cell efficiency by depositing an additional absorber layer made of micro crystalline silicon on the amorphous layer.

Some equipment suppliers even claim that there will be machinery in market to manufacture these new modules at $0.70. With such potential of further development of thin film solar technology, the European Photovoltaic Industry Association (EPIA) expects that manufacturing capacities for these technologies will double to over 4GW by 2010 representing a market share of around 20%.
GE announced plans to spend $600 million on a new CdTe solar cell plant and enter this market .

First Solar, the CdTe thin-film manufacturer stated that “at the end of 2007, over 300 MW of First Solar PV modules had been installed worldwide.” Below is a list of several recent installations:

  • Since 16 October 2008, Germany’s largest thin-film pitched roof system, constructed by Riedel Recycling, has been in operation and producing solar power in Moers near Duisburg. Over eleven thousand cadmium telluride modules, from First Solar, deliver a total of 837 kW.
  • First Solar recently completed a 2.4 MW rooftop installation as part of Southern California Edison program to install 250 MW of rooftop solar panels throughout Southern California over by 2013.
  • First Solar announced a 7.5 MW system to be installed in Blythe, CA, where the California Public Utilities Commission has accepted a 12 ¢/kWh power purchase agreement with First Solar (after the application of all incentives).
  • Construction of a 10 MW plant in the Nevada desert began in July 2008. First Solar is partnering with Sempra Generation, which will own and operate the PV power-plant, being built next to their natural gas plant.
  • Stadtwerke Trier (SWT) in Trier, Germany is expected to produce over 9 GWh annually
  • A 40 MW system is being installed by Juwi in Waldpolenz Solar Park, Germany. At the time of its announcement, it was both the largest planned and lowest cost PV system in the world. The price of 3.25 euros translated then (when the euro was equal to US$1.3) to $4.2 per installed watt.
  • 4.8KW of thin film flexible solar panels manufactured by Uni-Solar Ovonic installed on a South Beach hurricane-prone residence in 2008.

Denver-based Conergy Americas and officials at California’s South San Joaquin Irrigation District (SSJID)have installed what is believed to be the world’s first single-axis solar tracking system featuring thin-film photovoltaic cells.

Thin-film photovoltaic cells are included in the TIME‘s Best Inventions of 2008.

First Solar was the first module maker to lower its manufacturing cost below the $1-per-watt threshold, bringing generation cost into the range of power produced by conventional means.  Thin film solar modules have the smallest carbon footprint and fastest energy payback time of current PV technologies.

First Solar manufactures cadmium telluride (CdTe)-based photovoltaic (PV) modules, which produce electricity with a thin CdTe film on glass.[11] The company recently reached an average conversion efficiency of more than 11 percent; For more details on the technology, see cadmium telluride photovoltaics.

First Solar launched production of commercial products in 2002 and reached an annual production of 25 megawatts (MW) in 2005.  At the end of 2009, First Solar had surpassed an annual production rate of one gigawatt (GW)and was the largest PV module manufacturer in the world.  The Company is headquartered in Tempe, Arizona, has manufacturing facilities in Perrysburg, Ohio, Frankfurt (Oder), Germany, and Kulim, Malaysia, and is in the process of building additional manufacturing facilities in the United States and Vietnam.   Additionally, First Solar partnered with natural gas provider Enbridge to build the largest PV solar energy farm in the world,[18] located in Sarnia, Ontario, near the U.S.-Canadian border.

In July 2010, First Solar formed a utility systems business group to address the large-scale PV systems solutions market. While continuing to provide modules sales and turnkey solar projects, as well as engineering, procurement, construction, and operations and maintenance services to its various customer segments, the new unit will support utility customers with an integrated, portfolio-based business model.

Early sales were primarily in Germany because of strong incentives for solar enacted in the German Renewable Energy Sources Act (EEG) of 2000.  Declines and uncertainty in feed-in-tariff subsidies for solar power in European markets, including Germany, France, Italy and Spain, areprompting major PV manufacturers, such as First Solar, to accelerate their expansion into other markets, including the U.S., India and China.

Sales in the U.S. are expected to increase as a result of a number of acquisitions the company has made that provide a development pipeline of utility-scale solar power plants. First Solar is currently responsible for developing more than 40% of U.S. solar farms that had contracts with utilities.

First Solar’s manufacturing cost per watt reached $1.23 in 2007 and $1.08 in 2008. On February 24, 2009, the cost/watt ratio broke the $1 barrier, reaching $0.98 per watt. By the end of2010, its production cost had fallen to $0.75 per watt.

In 2010, the company had 24 production lines with 1,502 megawatts of manufacturing capacity. Each line had a 62.6-megawatt capacity. The first factory was built in Ohio, followed by a four-line manufacturing plant in Frankfurt (Oder), Germany. In April 2007, First Solar announced the construction of an additional manufacturing plant in Kulim Hi-Tech Park, Malaysia, which was expanded to four plants in 2009. In October 2008, First Solar broke ground on an expansion of its Perrysburg, Ohio facility, completed in 2010,which brought First Solar’s global annual production capacity to 1,228 MW.  In 2009, First Solar invested in two additional production plants in Malaysia, consisting of four manufacturing lines each. Additionally, in the summer of 2009, First Solar announced plans to build its fourth production plant in France. In October 2010, First Solar announced it would build two new four-line manufacturing plants, one each in Vietnam and the United States. With the announced expansions, First Solar will nearly double production capacity from 1.4 GW in 2010 to 2.9 GW in 2012, based on current line run rates.

Country↓ 2005 Capacity↓ 2006 Capacity↓ 2007 Capacity↓ 2008 Capacity↓ 2009 Capacity↓ 2010 Capacity↓ 2011 Capacity↓ 2012 Capacity↓
Line capacity 25 MW 33 MW 44 MW 48 MW 53.4 MW 62.6 MW 64.1 MW (est) 64.1 MW (est)
USA 25 MW 99 MW 132 MW 143 MW 160 MW 250 MW 256 MW 512 MW
Germany 176 MW 191 MW 214 MW 250 MW 512 MW 512 MW
Malaysia 382 MW 854 MW 1002 MW 1538 MW 1538 MW
Vietnam 256 MW
Total Capacity 25 MW 100 MW 308 MW 716 MW 1228 MW 1502 MW 2308 MW 2820 MW

(Source: First Solar Financial Report for Quarter 1 2011)

First Solar earned $664.2 million, or $7.68 per share, in fiscal year 2010.[1] but its first quarter profit in 2011 fell by a third, from $172.3 million in first quarter 2010 to $116 million in 2011.  Lower prices and higher costs, as well as uncertainty over European subsidies for renewable energy,  were faulted for the drop in profits.

Historically, the low cost of First Solar’s modules has been the key to its market performance. The use of cadmium telluride instead of silicon has allowed it to achieve a significantly lower price point, especially compared to crystalline-silicon PV which averages $1.85 per watt.  First Solar has indicated that its manufacturing cost has fallen in Q4 2010 to 75 cents per watt. By 2014, it expects to drive down cost per watt to make solar modules to between 52 and 63 cents. The biggest driver of the lower costs is better efficiency.

Below is a partial list of First Solar’s solar installations and development projects:

Europe and North Africa:

  1. Stadtwerke Trier (SWT) in Trier, Germany is one of the world’s largest thin-film solar plants. As of February 2009, it was estimated the facility would produce over 9 GWh per year, which would supply power to more than 2,400 homes each year. Additionally, it is estimated the facility will conserve 100,000 tons of CO2 over 20 years.
  2. Walkdpolenz Solar Park near Leipzig, Germany, is the world’s largest thin-film PV power system in the world. Built and developed by Juwi Group, it has a capacity of 40MW. The facility became fully operational in 2008.
  3. In December 2009 the Lieberose Solar Park, Germany’s biggest conversion land project (126 hectares) on a former military training area, was opened with an output of 53MW. The solar park uses 700,000 solar modules.
  4. For the Sports Stadium Bentegodi, First Solar supplied more than 13,000 thin film modules for a rooftop installation in Verona, Italy.
  5. In March 2010 First Solar was the first pure PV manufacturer to join the Desertec Industrial Initiative (DII).   As an associated partner, First Solar will contribute its considerable PV project expertise to Desertec working groups, demonstrating the potential of PV power plants to provide clean, sustainable, utility-scale energy by harnessing the desert sun.

North America

  1. 10 MW El Dorado Solar Power Plant in Boulder City, NV, developed by Sempra Generation, covering 88 acres. Construction began in July 2008 and the plant is owned and operated by Sempra.[34] In April 2009, it was announced that Sempra and First Solar would construct a 48MW Copper Mountain expansion to the facility. Once the expansion is completed in early 2011, the total facility will be able to power approximately 30,000 homes and displace 50,000 metric tons of CO2 per year.
  2. 21 MW solar plant in Blythe, CA, owned by NRG Energy. It occupies 200 acres, and displaces more than 12,000 metric tons of carbon dioxide emissions per year.
  3. 550 MW solar plant near Desert Center in Riverside County, CA, under two power purchase agreements – one with Pacific Gas and Electric Company (300 MW), and one with Southern California Edison (250 MW) – will provide enough electricity to power approximately 160,000 area homes.
  4. 80 MW solar plant in Sarnia, Ontario, Canada, completed by First Solar and Enbridge Inc. in October 2010. It is the largest operating photovoltaic solar energy facility in the world, and will generate enough energy to power 12,800 homes per year.
  5. 550 MW Topaz Solar Farm in San Luis Obipso County CA, under a power purchase agreement with Pacific Gas and Electric Company.
  6. 30 MW solar plant in Cimarron, New Mexico, sold to Southern Company (NYSE:SO) and Turner Renewable Energy. First Solar developed the project and is providing engineering, procurement and construction (EPC) services. First Solar will also provide operation and maintenance services under a 25-year contract. The facility will supply power to approximately 9,000 homes, or 18,000 residents, and displace more than 45,000 tons of CO2 per year.
  7. 230 MW AV Solar Ranch One solar project, to be built in Los Angeles County, CA, received final environmental permitting approval in January 2011. Construction on the project is scheduled to be completed in 2013.
  8. 290 MW Agua Caliente solar project, which NRG Energy, Inc. has agreed to purchase. Agua Caliente is located in Yuma County, AZ and will be completed by 2014. Once completed, it is expected to be the largest operational photovoltaic (PV) site in the world and will generate electricity with zero air emissions, no water consumption and no waste production. When operating at full capacity, it will provide for more than 225,000 homes and offset the equivalent of 5.5 million metric tons of CO2 over 25 years.
  9. 7.9. 250 MW Silver State South solar project, in partnership with Southern California Edison (SCE), will be built on public land near Primm, NV. The project is expected to begin generating electricity in 2014 and should be fully operational by 2017.

Asia and Australia

  1. 2,000 MW (2GW) solar plant Memorandum of Agreement signed to build solar plant in Ordos City, Inner Mongolia, China.

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