By Dr Dino Ponnampalam
The solar industry has grown steadily since the 1960s, and quite rapidly in the last two decades, reaching a point that has made the use of solar technology considerably valuable when it comes to the drive to generate clean electricity. In countries that receive a lot of solar irradiation, using this source makes economic and environmental sense and furthermore, offers solar-rich countries the prospect of energy security.
However, for solar technology to become a truly fundamental component of a country’s energy mix the technology must be inexpensive and the technology must be efficient at converting incoming insolation into usable electricity. Currently, and in spite of falling solar module prices, the technology remains costly, which prevents widespread adoption.
In addition, the electrical efficiency rate is neither very high nor very low; the higher the rate at which sunlight is converted into electricity the better, for this feature increases the attractiveness of utilizing solar energy technology.
Thankfully, the prognosis is good for the solar industry: developments are being made on what seems a monthly basis that are advancing the industry to the point where costs are falling even further and the efficiency rates are increasing. And in the case of Twin Creeks Technologies, a solar technology start-up based in San Jose, California (USA), the improvement on offer in the form of Hyperion 3 has allowed for costs to drop by 50%, which is a significant development.
The Use of Silicon in Solar Cells
Silicon is the central component of first generation solar cells, and to a certain extent, second-generation solar cells as well. Progress has been made in moving from crystalline silicon-based solar cells to non-silicon solar cells, and even amorphous silicon-based solar cells. This shift focuses on reducing costs by reducing the amount of material used or by even eliminating the use of silicon altogether.
An example of solar cells with reduced material and even solar cells without the use of silicon can be found in what is termed thin film solar cells. Examples of these thin film solar cells - second-generation with respect to traditional silicon solar cells - include cadmium telluride (CdTe) thin films and copper indium gallium selenide (CIGS) thin films.
These solar cells have gained a strong following due to their lower costs and flexible nature. In fact, this flexible feature allows for a wider range of application, such as integration into building façades. This offers the dual prospect of generating electricity from sunlight (the original purpose) and maintaining seamless architectural lines on a commercial or residential building project.
However, the conventional crystalline silicon-based solar cells remain the workhorse of the industry. These bulky solar panels mainly feature as rooftop installations or as ground-based installations for projects with ample land available. As such, finding ways to reduce the manufacturing costs would be of great benefit to an industry that is ripe for further (and hopefully rapid) expansion.
Efficiency Improvements vs. Manufacturing Cost Reductions
Developments in the solar industry usually involve improvements to the efficiency rate or cost reductions for the solar manufacturers. In terms of the electrical efficiency rate, conventional first-generation solar cells are rated at around 20% and second-generation thin films are rated at around 15%. Generally, the ratings for solar modules (the final end-product used for installation) are a few percentage points lower. While this efficiency rate is acceptable for the solar industry, research is continually being carried out in order to improve this rate to make solar technology more appealing to the general public.
On the other hand, the manufacturing side, process techniques and technologies are depended on to find cost savings; this too has a desirable effect on the public, in making solar technology cheaper for installation by affecting not only the manufacturing costs but also the balance-of-system costs. In this regard, the cost-saving measure created by Twin Creeks Technologies will surely assist the solar industry in propelling forward.
Hyperion 3: A Game-Changer for the Solar Industry
A combination of reasons has led to the recent glut in solar cell inventories, with a knock-on effect of depressed prices. This has affected solar cell manufacturers worldwide, with the larger ones desperately finding cost savings in other areas to offset this negative change. Smaller manufacturers have experienced greater pain, with some even forced to shut down operations.
From time to time, events conspire so as to produce a ‘game changer’. This usually involves some technology that really changes the face of the industry. Currently, the game changer from Twin Creeks Technologies is called Hyperion 3. Figure 1 is a photograph of Hyperion 3, and Figure 2 is a photograph showing how the silicon wafers are arranged for the implantation process.
Figure 1: Photograph of Hyperion 3, showing the silicon wafer loading docks. Credit: Twin Creek Technologies.
Figure 2: Photograph showing the loading docks for each silicon wafer prior to proton implantation and cleaving. Credit: Twin Creeks Technologies.
In the manufacture of conventional first-generation solar cells, crystalline silicon is first purified in an arc oven. Following this, the silicon is dipped into melted polycrystalline solution, allowing for a single pure crystal to silicon to be created. This silicon ingot, with an average thickness of 600 micrometers (μm, or microns) is then sliced and diced to form wafers with an average thickness of 200 microns. The wafers are then treated and modified to eventually form an encapsulated solar cell, ready for the market and for consumers.
The manufacturing process in its current form is costly and involves a considerable amount of waste, especially at the ingot slicing stage. By developing techniques to minimize this loss, cost savings could be realized.
By using the Hyperion 3 manufacturing system from Twin Creeks Technologies, solar wafers with an average thickness of 20 microns can be manufactured. To offer a sense of comparison, the average thickness of human hair is about 40 microns, so these silicon wafers are roughly half the thickness of human hair. Figure 3 is an illustration of the average wafer thicknesses for the different silicon wafers.
Figure 3: An illustration comparing the silicon wafer thickness for a regular silicon wafer (top), a typical solar wafer (middle), and a wafer produced using Hyperion 3 (bottom). Credit: Twin Creeks Technologies
The sophisticated, patented, and elegant manufacturing technique of Hyperion 3 involves reducing the thickness of the solar wafer to incredibly small proportions. By doing so, these ultra-thin solar wafers (one-tenth the conventional size of solar wafers) allow manufacturers to reduce their manufacturing costs by 50%, offering solar manufacturers with an opportunity to produce industry-standard solar cells and modules with less material.
Proton-Induced Exfoliation: Refining Manufacturing Further
The Hyperion manufacturing system is based on a phenomenon known as proton-induced exfoliation (PIE). This technique involves the use of high-energy protons (basically, hydrogen ions) that are embedded onto substrate wafers such as silicon. While silicon is the substrate of choice due to its use in first generation solar cells, other substrates could also be utilized.
In PIE, using high voltages, high-energy protons are rooted into the silicon substrate without changing the innate properties of the substrate. Upon heating, these high-energy protons raise a very thin and uniformed substrate layer (called the lamina layer) higher. The next step involves mechanical cleaving. The thin, uniformed layer of substrate is then sliced. This lamina layer is then used for solar cell wafer processing, which goes on to form solar modules.
Due to the ultra-thin dimensions of each lamina layer, the silicon substrate can be reused with the entire process of embedding and cleaving being repeated until the substrate is used up. This patented technique allows Twin Creek technologies to produce up to fourteen laminae from a single silicon wafer, and in terms of producing solar cells, Twin Creeks Technologies managed to manufacture ten solar cells from a single silicon wafer. Figure 4 is an illustration of the process of proton embedding and laminar cleaving.
Figure 4: An illustration showing the two-stage process of Proton-Induced Exfoliation (PIE). The first stage involves high-energy protons being embedded into the substrate, and the second stage involves a heat treatment that raises the thin laminar layer for cleaving. The remaining substrate is then reused. Credit: Twin Creeks Technologies.
The Advantages of Hyperion 3 in Solar Cell / Module Production
As each silicon wafer cleaved using Hyperion 3 is only 20 microns thick, the immediate benefit comes from the cost-savings achieved from using less material. This in turn allows manufacturers to better protect themselves from the daily price fluctuations of silicon, which is the most expensive component cost in a solar cell / module. In addition, by using Hyperion 3, the proton-inducing equipment makes redundant the use of other pieces of machinery such as saws and furnaces.
This has helped to further reduce costs during the manufacturing process: from current manufacturing prices of US$0.80 Watts peak (Wp), Hyperion 3-produced solar cells can be manufactured for US$0.40 Wp. When one considers that solar prices are at present around US$0.97 Wp, installing Hyperion 3 to manufacture flexible solar cells with higher efficiency rates will allow manufacturers to increase their profits without affecting their output quality or pricing.
By using less material, ultra-thin silicon solar cells are produced. In normal circumstances, the breakage rate would be quite high. However, these thin solar cells are incredibly flexible and rival those of the second-generation solar cells. As these layers are ultra-thin and flexible, the other components found in finished solar cells / modules are also reduced in volume. For example, less silver paste would be required, which is a substantial cost saving in itself.
A major benefit of producing these ultra-thin, strong, and flexible solar cells and solar modules using Hyperion 3 concerns the efficiency rate aspect. With conventional silicon solar cells possessing efficiency rates of around 20% (for solar cells) and around 15% (for solar modules), the possibility of now using flexible first-generation solar cell efficiency rates with second-generation solar cell characteristics is an exciting one. With Hyperion 3 being production-ready, solar cells can now be produced that are low cost and fairly efficient, with the added feature that allows for solar cells and modules to be integrated into the fabric of buildings and rooftops.
Another benefit would be the crossover applications. Hyperion 3 is suitable for silicon, but this manufacturing process would work equally well with any substrate. With research into solar cell technology evolving into third and fourth generation models, Hyperion 3 could easily be used to produce ultra-thin versions of these solar cells. This would offer controls on solar cells that are predicted to have enhanced efficiency rates.
Future Scope for Hyperion 3
By producing ultra-thin solar cells with only minor modification required making them ready for installation (addition of back contact, and then encapsulation), Twin Creeks Technologies, through the use of Hyperion 3, has provided the tool in which the solar industry could embark on its second period of rapid expansion. As this company is a capital equipment company, all solar cell and solar module manufacturers will find this to be an asset to their existing manufacturing capabilities.
As Asia is home to numerous solar cell manufacturers who are ranked high globally, such manufacturing capabilities will be advantageous as they can reduce manufacturing costs while still maintaining manufacturing output. Accordingly, solar cell manufacturers such as Gintech Energy Corporation, Neo Solar Power Corporation, Suntech Power, Trina Solar, Motech Solar, and Taiwan Semiconductor Manufacturing Company (TSMC) will find that the advances offered by Hyperion 3 deserve greater attention.
By lowering costs and maintaining high efficiency ratings, the solar industry can expand and help insolation-rich countries establish solar energy as a substantial component of the energy mix. This will reduce the dependence on polluting and finite fossil fuels while accelerating the transition to a clean energy future. To summarize: demonstrable reduced manufacturing costs, better solar cell and solar module efficiency ratings, and a sunny future. Clearly, Hyperion 3 is much more than just hype.