The photovoltaic (PV) manufacturing process typically requires solar cells to be heated to extremely high temperatures.  Traditional methods for heating involve utilizing conventional electric or infrared furnaces to heat the cells for long periods of time.

The heating process allows for the fabrication of the cells but is very expensive and results in impurities and imperfections in the PV cells.

The National Renewable Energy Laboratory (NREL), the only federal laboratory exclusively dedicated to the research, commercialization and development of renewable energy and energy efficiency technologies, has developed an optical furnace that may change the solar industry.

The optical furnace is able to heat PV cells more effectively at a fraction of the cost of traditional methods, which may result in a higher quality product at a lower cost.

The optical furnace is described in U.S. Patent Number 5,577,157, entitled “Optical Processing Furnace with Quartz Muffle and Diffuser Plate ” (’157 Patent) and U.S. Patent Application Number 2011/0003485, entitled “Optical Cavity Furnace for Semiconductor Wafer Processing” (’485 Application).

Figure 1 of the ’485 Application depicts an embodiment of the optical furnace.  The furnace includes a bank of optical energy sources 12 a-n and reflectors 14 surrounding a transport system 22 enclosed in a cavity 18.

According to both the ’157 Patent and the ’485 Application, it is advantageous if the optical reflectors are made of a diffuse rather than a specular material.  A diffuse reflector is advantageous becuase it ensures the optical energy is reflected evenly within the furnace cavity with a minimum of energy loss.

Figure 2 of the ’157 Patent shows another view of the optical furnace.  The figure shows a bank of optical energy sources 21 above the furnace cavity 7.  The cavity consists of a diffuse reflector box 15, 16, 17, 18 made of quartz, called the quartz box or muffle. 

The figure also depicts a diffuser plate 9.  The diffuser plate is also made of quartz and is placed on top of the quartz muffle in order to protect the muffle from the high energy released by the optical energy sources. 

If the quartz muffle were to be damaged, replacement costs would be very high and the process would be time consuming.  The diffuser plate is designed to be quickly and inexpensively replaced when damage occurs.

According to NREL, their optical furnace can potentially increase PV efficiency by four percentage points (from 16 to 20 percent).  This would represent a major increase in efficiency.

Further, NREL is working in conjunction with AOS, Inc. to produce a manufacturing sized furnace. NREL anticipates this manufacturing furnace will be able to produce 1,200 highly efficient solar cells per hour.  The increase in efficiency and manufacturer-scale production will all occur at a quarter of traditional PV manufacturing costs.

These improvements and reduced costs will hopefully mean better and less expensive PV cells on the market in the near future.

David Gibbs is a contributor to Green Patent Blog.  David is currently in his third and final year at Thomas Jefferson School of Law in San Diego.  He received his undergraduate degree in Geology from the University of California, Berkeley.

A team of researchers at the University of Notre Dame, led by Prashant V. Kamat, has developed a semi-conductive paint that turns surfaces on which it is applied into solar cells.

The solar paint is described in U.S. Patent Application Publication No. 2009/0114273 (’273 Application), entitled “Nanomaterial Scaffolds for Electron Transport”.

Single wall carbon nanotubes (SWCNT) create the scaffold architecture, which allows electrons to move more efficiently than prior art vis-a-vis nanoparticles or quantum dots.

The nanoparticles are coated in titanium dioxide and either cadmium sulfide or cadmium senenide.  The particles are then suspended in a water and alcohol mixure to form a paste.

Figure 1 depicts the improvement made in the ’273 Application (Figure 1B) over the prior art (Figure 1A).  Figures 10A and 10B depict random electron transport versus direct electron transport utilizing the nanotubes described in the ’273 Application.

According to the ’273 Application, because of the SWCNT’s special properties, it can boost the solar paint’s photoconversion efficiency:

The unique electrical and electronic properties, wide electrochemical stability window, and high surface area render SWCNT beneficial as a scaffold to anchor light harvesting assemblies.  In accordance with an embodiment, the electron accepting ability of semiconducting SWCNT thus offers an opportunity to facilitate electron transport and thus increase the photoconversion efficiency of nanostructure semiconductor based solar cells.

See Kamat’s article about the paint, dubbed “Sun-Believable,” here.

The possibilities surrounding an inexpensive and efficient solar paint are clear, as it could be applied on everyday surfaces like fences and homes to generate electricity. This product could be a huge breakthrough for renewable energy production.

See a short video about how solar paint works here.

I previously wrote about the patents for sale as a result of the bankruptcy of Massachusetts PV company Evergreen Solar.

Those patents include U.S. Patents Nos. 6,814,802, 7,022,180 and 7,507,291, each entitled “Method and apparatus for growing multiple crystalline ribbons from a single crucible” (collectively “Ribbon Patents”).

The Ribbon Patents cover Evergreen’s core innovation, a PV manufacturing process known as String Ribbon technology.

In a fascinating development, the U.S. Department of Energy (DOE) wrote a letter to Evergreen demanding that it assign title to the Ribbon Patents to DOE (DOE_Letter):

The Department of Energy (“DOE”) hereby demands that Evergreen Solar Inc. assign title to DOE for the following invention: method and apparatus for growing multiple crystalline ribbons from a single crucible (“the Gemini Method”), including U.S. Patent Nos. 6,814,802; 7,022,180; and 7,507,291 and all other pending U.S. or foreign patent applications and patents that relate or claim priority to any of the foregoing U.S. patents.

The DOE concurrently filed a motion in the Evergreen bankruptcy proceeding to get the court’s permission to obtain title to the Ribbon Patents (DOE_Motion).

According to the DOE letter and motion papers, the research and development that led to the String Ribbon technology was funded at least in part by DOE.  The letter states:

We believe the Gemini Method is a “subject invention” as defined by the Bayh-Dole Act and NREL subcontract ZDO-2-30628 . . . to which Evergreen Solar Inc. was a party.

The motion states that the federally funded research led to the String Ribbon process:

Under the Funding Agreement, Evergreen conducted the Gemini project to develop a method to generate two String Ribbons of silicon simultaneously out of [a] single crucible of molten silicon rather than just one String Ribbon at a time.

Under the Bayh-Dole Act, which governs rights in government-funded technology (see my post on Bayh-Dole here), Evergreen had to disclose to DOE any inventions developed with the federal funding and provide notice to DOE that it elected to retain title to the inventions. 

According to DOE, Evergreen failed to do so for the String Ribbon technology, so DOE can take ownerhsip of the Ribbon Patents.

The invention of the Ribbon Patents enables continuous and concurrent growth of multiple semiconductor ribbons from a single crucible.

Figure 2A, for example, shows a continuous two-ribbon dual growth system (20) including a crucible (21) having a melt (22) of silicon and two pairs of strings (25a, 25b) extending through the crucible. 

Each of the pairs of string (25a, 25b) has a fixed distance between the strings.  Two crystalline ribbons (27a, 27b) of silicon are drawn from the melt (22) as the cooler liquid silicon crystallizes at the tops of the menisci (29a, 29b). 

The pairs of strings (25a, 25b) pass through holes in the bottom of the crucible and become incorporated in and define the edge boundaries of the crystalline ribbons (27a, 27b).

According to the Ribbon Patents, the disclosed methods and apparatus allow for a substantially better rate of production and efficiency and reduce capital, material, and labor costs. 

According to some news reports, Chinese solar manufacturers have shown considerable interest in the auction of Evergreen’s assets.  Apparently, DOE wants to block sale of the String Ribbon technology to foreign companies.

Indeed, DOE’s motion papers argue the court should allow it to maintain its rights in the Ribbon Patents to “prevent foreign entities from gaining control over federally-funded technology and competing with American industry unfairly.”

I will be at Solar Power International in Dallas on Tuesday and Wednesday of this week with my firm, Luce Forward, at Booth No. 2345 in Hall C.

I invite all of my solar friends and colleagues to stop by and say hello.

We’ll be wearing our signature blue polo shirts, and, more importantly, we’ll be providing complimentary bags of our signature freshly made mini-doughnuts.

I would be happy to share my insights on best practices in clean tech patent prosecution and strategy, and I’m always working on the latest solar tech / solar intellectual property stories for publication in this space so I’m interested in hearing your news and exciting things you’re working on.

I hope to see you, and I wish you all an enjoyable and successful conference.