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Thin-Film Solar Modules Offer a Cost-Effective Solution in Utility-Scale Projects

Alternative Power Construction

July 13, 2010

As the interest of using alternative energy sources continues to heat up, harnessing power from the sun has become a popular choice for utilities across the country. While there are many advantages to building solar power plants and embracing this form of energy, these types of construction projects often encounter one tough obstacle — price.

Ever since the advent of the solar industry in the late 1950s and 1960s, crystalline silicon solar cells have been the main workhorse in the business by creating modules used to generate power across the globe. However, the high price of crystalline silicon has made it difficult for utilities and project owners to use these products in large-scale solar farms — leaving manufacturers with the task to deliver a lower-cost solution. Over the last decade, companies have begun to extensively study, develop and produce an alternative to the traditional crystalline silicon modules in the form of thin-film solar cells.

“The problem with that material or technology is that crystalline silicon is pretty expensive to use,” says Mike Hall, CEO of Borrego Solar, a solar electric contractor specializing in commercial and public sector turnkey, grid-connected solar electric systems. “For decades, engineers and physicists have been trying to work out an alternative that uses less or cheaper material and that’s what thin-film is.”

Within thin-film technology, there are three different material types used to create these modules:

• Amorphous Silicon (a-Si):

This technology, which was the first type of thin-film to be extensively developed and manufactured, involves using a non-crystalline version of silicon rather than the traditional crystalline form. Its biggest advantage comes from its cost, as a-Si uses around 1 percent of the amount of silicon that’s usually needed for crystalline silicon cells — producing a much cheaper, thinner film.

Hall mentions that although a-Si thin-film is the type of technology most companies have tried to develop in the past, it has definitely cooled off the last couple of years. Today, some major manufacturers of this type of thin-film are Sharp Electronics, Applied Materials, Uni-Solar and Mitsubishi. Recent developments in the technology have brought about a multi-layer a-Si thin-film capable of reaching 10 percent efficiency, which is good for thin-film modules. For example, the run-of-the-mill, thin-film technology typically weighs in at 6 to 8 percent efficiency and traditional crystalline silicon ranks around 14 to 20 percent efficiency.

• Cadmium Telluride (CdTe):

Cadmium telluride solar cells are an efficient light-absorbing material, ideal for large-scale thin-film module production. CdTe thin-films are higher in efficiency at around 10 percent — making them more efficient than competing thin-film technologies that can be commercially produced.

First Solar is the largest known manufacturer of CdTe thin-film modules. According to First Solar officials, the company has achieved the lowest manufacturing cost per watt in the industry, breaking $1 per watt in 2008. In addition, First Solar will bring total expected capacity to more than 1.3 gigawatts by the end of 2010.

“First Solar has been so successful in thin-film manufacturing, because the company has been able to get the manufacturing cost low and efficiency high,” says Hall. “The cost is lower than any other module product in the world and the modules are more efficient than any other thin-film product around.”

• Copper Indium Gallium Diselenide (CIGS):

This type of thin-film technology, which has been studied for decades, is intended to produce high-efficiency modules at a low cost. Its aim is to deliver a module capable of reaching the same efficiency of crystalline silicon modules, but with a significantly lower price tag. Although CIGS technology has been developed for many years, there have been challenges in commercially producing these cells successfully to compete with traditional modules.

Hall mentions that although the idea behind creating modules from CIGS technology is notable and would be a breakthrough in the thin-film industry, there has been no real commercial success in mass producing these high-efficiency thin-films at a low cost. However, the National Renewable Energy Laboratory (NREL) notes the record high efficiency of CIGS solar cells at 19.2 percent, which is by far the highest compared to other thin-film technologies.

This type of data proves that the innovation is there, but perfecting the production process and cost is another hurdle. Major manufacturers of CIGS modules are MiaSole, Global Solar, NanoSolar and Solyndra.

Reaching the Utilities

As thin-film technologies continue to develop and manufacturers offer more and more products, thin-film modules are becoming a compelling choice for utilities looking to add large-scale projects to their energy portfolios. With a lower price than traditional crystalline silicon modules, thin-film presents utilities with a cost-effective solution to their energy needs.

“Thin-film, with its strong performance and lower installed cost for large-scale systems, is the preferred technology for multi-megawatt, utility-scale projects,” says Paul Wormer, senior director of engineering for Sharp Solar Energy Solutions Group. “Thin-film delivers more megawatt-hours of energy per megawatt of power for the end-user, particularly in hot climates. Lower installed cost and higher production mean lower cost electricity.”

Aside from price, another big advantage of thin-film modules is better thermal performance. One common misconception about solar modules is that they work best in hot climates — this is not the case. In actuality, the hotter the modules become, the less efficient they are. With thin-film modules, the output decreases less than traditional crystalline silicon models; this is especially important when in

extremely warm temperatures.

“A lot of people think that for a solar farm to produce energy, you want it to be really hot, which is not the case,” says Hall. “For solar modules to work efficiently, the sun is good, but heat is bad. Thin-film degrades slower with heat than crystalline silicon does. This makes thin-film a great choice when looking to install modules in very hot desert applications.”

“With a low temperature coefficient for output power — approximately half that of crystalline silicon — thin-film generates greater specific power than its crystalline silicon counterpart in geographic regions where temperatures are high,” adds Wormer. “In warm climates, this translates into as much as 10 percent more kilowatt-hours per kilowatt.”

Low maintenance is another advantage to using thin-film modules. Since contractors wouldn’t typically install a tracker with a thin-film module, maintenance on the tracker and its components would not be required. The bulk of maintenance tasks come from washing the modules when needed, especially after a dusty, dry spell. Preventive maintenance is needed on the power plant’s inverter, which is a common thread across all solar module technologies.

On top of the perks of using thin-film modules for utility-scale projects, there are some disadvantages to consider during the decision process. One important feature to note is efficiency. Since thin-film modules are less efficient than traditional crystalline silicon modules, more of them are needed to obtain the desired power output. Therefore, Hall urges utilities to consider thin-film when land usage is not an issue.

Another disadvantage comes from the price of the balance of system (this includes everything from foundations and mounting structures to the cost of the land) needed for the modules. Although the module itself may be cheaper, a customer will have to pay more for the balance of system since there are more modules in the farm.

Customers will need to do their homework in determining the pricing of the systems and if they are a cost-effective choice.

“Thin-film modules are less efficient and produce less power than traditional crystalline silicon, so you’re going to need more modules and balance of system to get the energy that’s needed,” explains Hall. “These support structures are made out of steel or aluminum, so the more modules you have the more racking you need and the more money you’ll spend. There’s a definite balancing act between cost and efficiency, and if it’s not cheaper in the long run it’s not worth using this type of technology.”

A shift in the cost of materials is also causing concerns. Recently, the cost of silicon has also brought about a challenge in the thin-film market. Over the last 18 months, the price of silicon as a raw material has dropped by as much as 75 percent and caused the price of crystalline silicon modules to drop about 40 percent — making them an option for large-scale projects that may be cost-effective.

“Most thin-film business plans were created to compete with much higher priced crystalline silicon modules, so when prices dropped it’s been hard for those technologies to compete,” says Hall. “This is especially true with amorphous silicon where there was a lot of investment between 2006 and 2008. A lot of these thin-film companies have seen decreases in interest and have been confined to niche places, with the exception of some companies such as First Solar and Sharp.”

Buying Tips

When looking at solar modules for a large-scale project, there are many considerations to make before deciding which one is ideal for purchase. One of the most important factors to take a look at is the balance sheet and background of the manufacturer. This will ensure that you are doing business with a company that has a proven track record of thin-film manufacturing, sales and customer support.

“You’ll definitely want to check out the balance sheet of the manufacturer that you’re considering, because you are making a very large investment with them,” says Hall. “When you’re building a large-scale facility, you can spend $5 to $10 million just on modules alone so you need to buy from a company that can support that.”

In addition to the manufacturer’s balance sheet, you’ll also want to check out the warranty the company offers on its products. Households, businesses and other energy customers will be relying on this power, so making sure that you are building with a module that has after-sale support is a necessity. A typical warranty on thin-film solar modules is for 20 to 25 years.

Degradation is another important issue when dealing with solar modules. The module’s efficiency will degrade over time, especially within the first weeks of its use (initial degradation). Taking this degradation into consideration, most manufacturers will post the module’s power rating after the initial degradation so customers know what to expect from the module.

“When someone is looking to make a large purchase of thin-film modules, it is important for them to look at real data and get comfortable with the degradation that’s already factored in,” says Hall. “This way they will understand what they’re getting out of their purchase and throughout the life of the modules.”

When looking for a cost-effective solution in solar farm construction, using thin-film modules are a good alternative for utilities. With a variety of technologies and manufacturers to choose from, thin-film modules are becoming an efficient choice for those looking to add solar power to their energy portfolio.

Pam Stask is assistant editor of Alternative Power Construction.

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