Solar Cell Alternatives: Photovoltaic Foils
Photovoltaic (PV) technology has been on a rollercoaster ride over the past two decades. As an alternative energy solution with attributes that readily compete with fossil fuels, it is now seeing a resurgence in both residential and commercial use. Not only is there greater demand for traditional solar cells over the past few years, R&D efforts have resulted in vast improvements in flexible ethylene tetrafluoroethylene (ETFE) technology.
Here’s a look at the potentially disruptive nature of ETFE on the PV Industry, beginning with recent PV history and trends in PV use today.
A Quick Walk Through PV History
It’s been 70 years since the first solar cells were produced commercially. In the 1950s, Bell Laboratories replaced early solar cells constructed of selenium with silicon and thus, cells capable of powering electrical equipment were born. It would, however, take another 20 years of a looming energy crisis, the sufficient lowering of material costs per watt and federal government initiatives for solar cells to become attractive enough for mass implementation.
By the turn of the century, annual photovoltaic cell global growth rates doubled or, in some cases even tripled. As happens with rapidly growing technology segments, burgeoning investment capital and a multitude of hasty business plans saw a market that was rapidly saturated with high-flying and high-spending solar power companies. Trouble was obvious by 2008, but 2011 is when it became apparent.
For a decade, the double- and triple-digit global growth rates also led to massively over-valued stock prices. Simultaneously, the Chinese government led the charge in state support for the technology, pouring even more investment capital into the technology.
The year 2011, unfortunately, saw both falling demand and a massive oversupply, resulting in a downward spiral in prices and profits. Two major U.S. companies went belly up very publicly, Solyndra, which was backed by the government, and Evergreen.
Unfortunately, a debt crisis in Europe was the proverbial final coffin nail, causing drastic cuts to subsidies for solar power. There was now every reason for projects to wait for prices to back off and for incentives to be available to purchase products, and the market continued to languish for the next six years.
Today’s PV market looks much more optimistic. A recent Frost & Sullivan research report, Global Solar Power Market, 2018 Update, which focuses on solar photovoltaic (PV) technology, predicts that a period of exceptional growth will continue. Recent strong growth is evidenced by an annual installed capacity in 2017 of 101.6 GW, nearly double the 51.4 GW installed in 2015. The key forces behind solar module price reduction include:
- Economies of scale
- Technological advancement
- Increasing automation in production
- Technological advances in battery storage solutions integrated with solar PV systems provide residential, commercial and industrial end-users with the opportunity to reduce peak-period demand by delivering their stored power.
Many research firms and organizations are weighing in with similar optimism:
The global solar PV panel market will exceed $300 million by 2023, according to Allied Market Research.
The cost to install solar has dropped by more than 70 percent since 2010. The Solar Investment Tax Credit provided industry stability and growth since its initial passage in 2006 (Solar Energy Industries Association (SEIA).
The global solar market grew by 26 percent in 2017, with 99 gigawatts of grid-connected PV capacity installed, according to GTM Research. 2018 will be the first-ever triple-digit year for the global solar market, with an anticipated 106 gigawatts of PV coming online. PV continues to compete with (and beat) coal and natural gas.
Bloomberg reports that 3 percent of U.S. commercial roofs will have solar power installations by 2020, while building integrated photovoltaic (BIPV) and building applied photovoltaic (BAPV) markets will double over the next three years.
The future is not without challenges. In early 2018, President Trump issued a 30 percent year-one tariff on solar cells and modules imported in the U.S. The tariffs are slated to decline over a term of four years. China currently produces 60 percent of the world’s solar cells and 71 percent of solar modules, while 25 U.S. companies closed shop in the past six years. GTM Research estimates that the tariffs will cause the U.S. solar market to see a net reduction in installations of around 11 percent as a result.
Traditional vs. Thin Film
|PV Panel Material||Weight||Construction||Production efficiencies||Cost||Light transmission||Transmissibility||Water barrier capabilites||UV discoloration||Long-term durability||Non-reflective option||Breakage||Packaging materials||Shipping costs|
|Traditional 60 Cell||33-47lb||Glass||Good||Low||Excellent||High||Issues if cracked||Excellent||Excellent||n/a||High||Based on fragility||High|
|ETFE||~20 lb/panel||Fluoropolymer frontsheet||Superior||Lower Lifetime||90-95% transparent||Slightly higher||Good to excellent||Excellent||Excellent||Available||Superior||Superior||Substantially lower|
Table 1: A side-by-side comparison of traditional PV and ETFE technology attributes.
There are two types of PV modules: fixed panels, or hard silica and flexible panels. In the past, there was a substantial gap between the two in terms of efficiency. However, ETFE-based flexible panels have narrowed the gap sufficiently to make the technology extremely attractive.
Specifically concerning weight, a typical traditional 20-panel solar array weighs approximately 800 lb.; on top of mounting hardware and equipment, another 500-600 lb. would not be unusual. ETFE solutions could cut that figure by approximately 30-50 percent.
- Self-cleaning: ETFE film features low surface energy and high stain resistance. Dirt is rapidly washed away by rain.
- ETFE features low flammability, stress crack resistance and insulating properties.
- Excellent adhesion to PV module components.
- Increased production speed as there is no glass in the process, eliminating loss due to breakage and handling.
- The lower weight of film versus glass reduces shipping costs and strenuous labor.
It is such advances as ETFE-based solutions that will move PV module technology to rapidly approach grid parity — the point where renewable electricity is equal to or cheaper than grid power.
Grid parity depends on module cost, geographical environment, grid electricity price, insulation and government incentives. Already, California, Arizona and segments of southern Europe are close to grid parity — and may already be there.
Matte Reduces Glare and Imperfections
One ETFE innovation by Saint-Gobain’s VERSIV™ High-Performance Films a matte ETFE-PV option has unique properties. Initially developed for military applications, matte reduces glare and minimizes imperfections. The matte surface provides a visually appealing and uniform outer layer that will be resistant to marking.
Matte ETFE is offered in E2 and E4 grades, with thicknesses from .0015-.004 in. (38 to 100 µm) and widths up to 60 in. (1,524 mm). For the PV market, the film can be C-Treated on one or both sides to facilitate adhesion with other polymer encapsulants, such as
EVA and TPU. Matte can also be incorporated into flexible and rigid photovoltaic panels and devices as a low-glare chemical and water-resistant and UV-stable protective top layer.
There are many considerations when evaluating the optimal properties for the PV module design. These include:
- Knowledge of all of the materials used in the module is important. Understanding and testing construction materials that could impact total performance may be necessary.
- Location of use is important. For example, a matte solution may be critical where glare risk must be curtailed, such as near airports and high-traffic areas.
- Weight considerations involve ensuring that the structural design of the roof or age of the structure has sufficient ability to carry the weight of PV modules.
- Where extreme weather exists, or any condition that could result in PV cell cracks, dead or inactive cell parts will lead to dramatic power loss. An inactive area of 50 percent or more can lead to a power loss of one-third.
Silicon is the second most abundant material on Earth and the most common material used in solar cells, representing approximately 90 percent of the modules on the market. Its inherent lattice pattern provides a structure that efficiently converts light into electricity. Silicon-based solar cells combine high efficiency, low cost, and a long lifetime, with module life expectations of 25 years or more.
The question becomes, can these features be improved on? The answer is yes.
VERSIV™ ETFE Solutions
Saint-Gobain is the world leader in providing the broadest range of thin-film material solutions to the photovoltaic industry. At Saint-Gobain, grid-parity — moving solar-power cost even with that of conventionally generated power — is a major commitment.
Expertise in the innovation and development of high-performance fluoropolymer resins featuring outstanding resistance to chemicals and weathering, low flammability, stress crack resistance, and insulating properties, VERSIV™ High-Performance Films are second-to-none.
ETFE’s unique features and excellent performance characteristics provide the light transmittance, aging resistance, weight advantage, and performance that could enable it to take the place of photovoltaic glass.
This article was produced by IEEE GlobalSpec. Visit the Saint-Gobain Composite Solutions' Engineering360 page on IEEE GlobalSpec.