The big stuff

There is no fundamental technical reason why PV modules are the size and shape that they are. Many different sizes and shapes have been used over time, from the very small solar cells in electronic devices and concentrating photovoltaic applications to the enormous, wing-like panels adorning spacecraft.

For most residential, commercial and utility-scale applications, the crystalline silicon (c-Si) industry has settled on 156 mm square cells arrayed in 60- or sometimes 72-cell modules, to end up with 1 x 1.65 meters as standard dimensions. These weigh 18-22 kilograms, with glass-glass modules weighing slightly more. This is light enough to be carried by a single worker, though often two workers will carry modules.

And when larger c-Si modules are made, the sizes grow by 12 cells – a number determined by bypass diodes, which makes the format fairly standard across manufacturers.

But unlike c-Si, thin film modules have no such limitations. They can and have been made in many sizes. The two largest thin film companies – First Solar and Solar Frontier – have for decades produced PV modules that are smaller than standard c-Si format. Solar Frontier, the CIGS market leader, makes a 0.98 x 1.26 meter module, roughly the same width, but much shorter than a standard 60-cell c-Si module.

And for 40 years, First Solar has made .6 x 1.20 meter modules – smaller in both dimensions than standard c-Si PV modules, with only a third of the surface area and thus much lower watt ratings.

Thinking big
Seven years ago, at a presentation to the 2010 Intersolar North America trade show, the CEO of a tool maker presented his vision for the future of thin film solar. Since-retired Spire Founder and CEO Roger Little called for the thin film industry to move to much larger modules, proposing 934-watt “breeder” modules, which would cost less than half as much as four 230-watt modules.

This was a fairly radical idea. Glass-glass thin film modules of that size would be harder to ship, and even harder to install. Furthermore, there were issues with scaling some of the tools to the larger formats of glass. However, Little seemed to feel that the idea had legs, and that his company could do it. He proposed to begin making a new turnkey production line for “kilowatt-scale” modules in the fall of 2010, so that his breeder modules could be on the market in 2011.

If Spire did ever produce these lines, they do not appear to have gotten very far. A crushing over-supply of PV modules beginning in the second half of 2011 resulted in many thin film bankruptcies, which greatly thinned the ranks of companies and approaches – as well as leading to a dramatic three-plus year hiatus in most equipment orders.

As an equipment company without big backing, Spire struggled for years and eventually sold off part of the business. Roger Little retired at the beginning of 2014, and little was heard from major manufacturers about the idea. That is, until 2016.

In the Spring of 2016, First Solar gave a big announcement at this legacy manufacturing facility in Ohio, unveiling two new module designs. The first was a hybrid “module” comprised of three of the company’s 60 cm x 120 cm Series 4 modules on dual steel rails, with a single point of interconnection, dubbed its Series 5.

The second was a massive sheet of two layers of glass, 1.2 x 2 meters, darkened with a layer of cadmium telluride thin film PV. This was the Series 6, which would be made in new factories while the company shifted its current factories to Series 5 production.

These were big changes for the world’s largest thin film solar maker, and many in the industry waited for the roll-out of Series 5. It never came. Instead, in November, the company announced that it was again shifting strategy – it would eliminate the Series 5 and move directly to Series 6 by re-tooling its existing factories.

Balance of system edge
Series 6, like other large-format thin film modules, is a big improvement in balance of systems costs from smaller modules. While the new, two square meter, 35 kilogram Series 6 will require two workers to lift it, the module also has a significantly higher capacity rating in a single module with a single electrical interconnection than either the Series 4 or crystalline silicon modules.

“You are lifting 420 watts per lift, versus 340 watts for a best-in class 72-cell crystalline silicon module,” explains Lou Trippel, First Solar’s VP of product management. “At the end of the day this bears itself out in installed watts per hour.” He estimates that the Series 6 will result in installation labor savings in the neighborhood of 10% versus 72-cell c-Si PV modules.

Additionally, unlike First Solar’s previous Series 1-4 modules, the Series 6 will fit on standard racking and tracking solutions designed for crystalline silicon modules, as it has roughly the same vertical dimensions as a standard 72-cell module.

This means that the Series 6, despite its weight, will not impose significant additional loads on most racking and tracking systems. The reason is that the greatest stress on such systems come from wind and snow loads. This is a function of the sail area, and as most racking and tracking systems use a central shaft or beam, these loads are proportionate to the length of the module.

Weight is still a consideration for the workers who will lift these modules. At 35 kg, the Series 6 is substantially heavier than a standard 72-cell c-Si PV module. First Solar has had experience installing the modules at its test site in Mesa, Arizona, and has additionally tested the workers who install the modules. The company says that so far the weight is working out fine, but notes that the final validation will come when these modules are deployed in large volumes.

Given the sheer size of the dual-glass module, it’s a surprise that it doesn’t weigh more. However, despite moving to larger sheets of glass, First Solar has significantly reduced the glass thickness to 2.8 mm on the front side and 2.2 mm on the back. It has done so by introducing a metal frame on the outside of the Series 6, a radical departure from decades of frameless modules.

And despite the additional size and weight, First Solar says that there are few of the sorts of complications that were predicted with Little’s “breeder” modules. “We are not seeing a whole lot that is fundamentally going to change from a big picture logistics standpoint,” notes Trippel.

In the factory
However, the larger driver for First Solar to move to the Series 6 may not be what happens in the field, but the factory. First Solar says that the move to wider sheets of glass will allow it to reduce module costs per watt by 40% versus its current Series 4 production. And while the company stopped releasing cost per watt figures more than a year ago, First Solar estimated a capital expenditure cost of $0.30 per watt to manufacture its Series 6 in its existing factories in its Q4 2016 earnings presentation.

Most of this is expected to be in capital expenditure for tools, and it has been observed by both First Solar and tool makers that the move to larger formats drives greater economic efficiency over the long run. Von Ardenne, a vacuum coating tool supplier that is working with First Solar, notes that with larger formats there is not a one-to-one relationship between capital expenditures and the capacities that can be achieved.

“The increase in capacity is more than proportional to capital expenditure when moving to larger formats,” Von Ardenne VP of Thin Film Photovoltaics Thomas Böcke told pv magazine.

This applies not only across entire lines, but as far as tools and components of tools go. Von Ardenne notes that the overhang of sputter targets remains the same for larger formats, the thin-film material can be used more efficiently, and that many costs such as those related to the control systems and drives are the same, even as vacuum chambers get bigger.

“In general, the vacuum system, power system and media, there are far less increases compared to the capacity that the tool is moving. The increasing of the chamber is also not linear to the increase in capacity,” explains Böcke.

Going big
Given the highly compelling economics of larger formats, it may come as a surprise that many thin film solar producers have not already jumped to larger formats. However, tool makers say that some of the technical developments that enabled First Solar’s larger format are relatively recent.

“Typically, modules for CIGS or CdTel based cells are smaller in size as achievable for (silicon) wafer based modules due to certain historical and technical reasons, such as the cell interconnection,” stated Von Ardenne in a paper on coating equipment for large-area thin-film PV.

Von Ardenne also notes that in the move to larger formats, thin film solar is building on progress in other industries. “The thin-film PV Industry is adopting learning curves typically seen in comparable thin-film technologies such as flat panel display or glass coating to drive down CapEx for thin film modules,” hints the company’s paper.

This includes Von Ardenne’s experience in supplying tools for coating architectural glass, where glass sheets of 3.3 meters by more than 7 meters are possible. As such, Von Ardenne is highly familiar with the challenges of large-area coating. The company notes that some customers in thin-film PV have coating process, which need temperatures of over 300 degrees Celsius, which means care must be taken in the handling of the glass, including the design of the process area and transport system.

“Many people are thinking that the heating is the challenge, but the cooling down is also the challenge,” notes Von Ardenne’s Thomas Böcke.

Big cash
The challenge of moving to larger formats is not only technical, but financial as well. While it is expected to be far more economical over the long run, Series 6 comes with a big up-front price tag. First Solar will invest upwards of a billion dollars re-tooling its factories to produce Series 6, including $500 million for tools in 2017 alone.

Given the amount of money on the line, First Solar is making sure to minimize other risks and other changes, and the company’s statements to pv magazine echo what it has said on quarterly calls. “We are not reinventing the core technology behind series 6, but increasing the form factor,” stated First Solar CEO Mark Widmar on the company’s Q4 2016 results call.

Von Ardenne says the high level of capital expenditure required is why so few companies shift form factors. “You decide for format very early in the timeline for your overall business plan, and you have to stay with that,” explains Böcke.

Böcke says that many thin film makers were happy to work with smaller formats, which made it easier to work on other technical improvements. “The focus for a long time in the thin film was to go for efficiency in the modules and also to have high throughput,” he says.

The future of large format thin film

But despite the big up-front payment, First Solar is not the only thin film company to take on large format modules. MiaSole currently makes very large flexible CIGS panels, and various makers of rigid glass-glass amorphous silicon modules have done large formats in the past – though none at anywhere near the scale of what First Solar is planning.

Other thin film companies are currently looking at larger formats, including for rigid glass-glass modules. In a previous interview, in the March 2017 edition of pv magazine Manz Automation CEO Dieter Manz said that larger formats are “on our roadmap”, noting that copper indium gallium diselenide (CIGS) thin-film modules could be “three times” the size they are now.

This is particularly notable given the company’s recent collaboration with Shenhua and Shanghai Electric, under which Manz will supply €263 million worth of thin-film tools to the two Chinese companies and enter into a joint venture for production in China. “This couldn’t be achieved without a big, strong partner, because you have to redesign all of the machines,” explained Dieter Manz. “And you need a partner to help finance this.”

Similar to Von Ardenne’s experience with glass coating, Manz’s confidence comes from its work with liquid crystal display (LCD) screens. “If you look at what we did in LCD industry in terms of the scaling of substrates, for me it is no question that we do the same in thin film technology,” states Manz.

Von Ardenne notes that the thin film industry is far from homogenous in its approach to format. “Everybody has his own idea how to move forward, which requires a flexible approach from tool makers,” notes Böcke. Solar Frontier, the second-largest thin film maker, has told pv magazine that it has no plans to move to a larger format.

However, If First Solar is able to reach its cost reduction targets, it will be a tremendous achievement. This could enable the company to out-price low-cost Chinese crystalline silicon module makers, and will be a high watermark for thin film PV.

And while it is too soon to say if there is a larger industry trend, given its position in the industry, what First Solar is doing is being watched closely. “If First Solar is successful, other market players will follow that,” predicts Von Ardenne’s Böcke.

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