Sheng X.,University of Illinois at Urbana - Champaign |
Bower C.A.,Semprius |
Bonafede S.,Semprius |
Wilson J.W.,Semprius |
And 10 more authors.
Nature Materials | Year: 2014
Expenses associated with shipping, installation, land, regulatory compliance and on-going maintenance and operations of utility-scale photovoltaics can be significantly reduced by increasing the power conversion efficiency of solar modules through improved materials, device designs and strategies for light management. Single-junction cells have performance constraints defined by their Shockley-Queisser limits. Multi-junction cells can achieve higher efficiencies, but epitaxial and current matching requirements between the single junctions in the devices hinder progress. Mechanical stacking of independent multi-junction cells circumvents these disadvantages. Here we present a fabrication approach for the realization of mechanically assembled multi-junction cells using materials and techniques compatible with large-scale manufacturing. The strategy involves printing-based stacking of microscale solar cells, sol-gel processes for interlayers with advanced optical, electrical and thermal properties, together with unusual packaging techniques, electrical matching networks, and compact ultrahigh-concentration optics. We demonstrate quadruple-junction, four-terminal solar cells with measured efficiencies of 43.9% at concentrations exceeding 1,000 suns, and modules with efficiencies of 36.5%. © 2014 Macmillan Publishers Limited. Source
News Article | February 16, 2011
Solar Junction's solar cell is like a tiny layer cake able to crank out more power per inch than most cells. The 4-year-old company yesterday said it expects to start production of its high-efficiency solar cells by early next year in its home town of San Jose, Calif. It is also awaiting word in the next few months on an $80 million loan from the Department of Energy, which would give it favorable financing to expand its current demonstration plant to produce 250 megawatts worth of cells per year, said co-founder Craig Stauffer. Solar Junction cells are designed to be fitted into concentrating photovoltaic (CPV) solar collectors. Originally used in space, CPV systems concentrate the light hundreds of times using mirrors and lenses onto a small but relatively efficiency solar cell. They are typically mounted on racks to follow the sun in desert areas and are used for installations up to 50 megawatts. The company, which was spun out of Stanford University, last month said that the National Renewable Energy Laboratory certified its cell to operate at 41.4 percent efficiency. For comparison, silicon solar cells are in the range of 15 percent or 20 percent efficient at converting sunlight to electricity. These types of cells, called multijunction cells, achieve those higher conversion rates by using different materials than the traditional silicon cell and multiple semiconductors within a single package. During manufacturing, there are multiple layers of material deposited onto a gallium arsenide substrate, with each layer optimized to convert a different portion of the sunlight's spectrum. "In essence, you have three basic subcell materials that take in some light and pass the rest to the next. They are connected serially inside the device just like battery cells," Stauffer explained. There could be up to 20 layers of material used on each cell which is usually a square of about five millimeters, or just a fraction of an inch. The main customers for these multijunction cells are CPV solar makers such as Amonix and Concentrix Solar in Germany. But even though this technology has been around for years, it still hasn't become as established or widely used for wholesale electricity production as regular flat solar panels. Multijunction cells are more complex and expensive. But Stauffer said that the costs of CPV systems with those cells are getting more attractive due to efficiency gains and higher levels of concentration. CPV solar collectors can now concentrate light 1,000 times, compared to 500 times in the past year or two, he said. Solar Junction expects to stand out from other multijunction suppliers with better reliability in high temperatures and higher efficiency, which Stauffer projects will go over 50 percent in five years as the company adds more layers to capture different wavelengths of light. Updated at 8:20 a.m. PT with correction to unit conversion.
News Article | February 13, 2012
Solar Junction’s mission is to develop and supply the highest-efficiency solar cells enabling significant growth for the CPV market. These cells poses’s the highest efficiency for III-V terrestrial solar cells combined with the highest reliability.
Good companies will always get funded. If that’s your company, it’s important to make sure you have the resources to keep it alive long enough to get funded. Murmurs of a looming downturn in venture capital are pressuring more companies to preemptively begin fundraising, whether or not they have gained sufficient traction to justify their stated valuations. In the race to store dry powder before the checks dry up, too many companies are attempting to raise too much, too early and at too high of a valuation. Unfortunately for these founders, many investors are well aware of market sentiment and are pulling back, waiting for valuations to fall. This is creating a vicious cycle for entrepreneurs that will force many of them to increase dilution, and possibly face the dreaded down round, from which few startups have recovered. Prior years of relatively easy VC money seem to have led to an ecosystem-wide amnesia about the purpose of VC investment. VCs want to see their money go toward accelerated product and technology growth and value-add milestones. VC money is not for early proof of concept — leave that to angel investors, friends and family. As the global economy cools down, it will take an increasingly long time to complete a round. Fortunately, there are a number of sources of non-dilutive capital that entrepreneurs can leverage to keep their companies afloat — if you know where to look. Keep in mind, these sources require planning and foresight, and often are not obtained at a moment’s notice. Below are some options to consider. Government agencies, such as DARPA, ARPA-E, NIH and NSF, are well-known sources of funding for academic research, but they provide startup grants, as well. Many of these funds are earmarked specifically for clinical trials or prototyping and product development, and can provide critical funding to build significant traction and hit major technology and product milestones before seeking the next round of VC money. Other grants will fund the setup of manufacturing processes and reliability testing. Many government grants also come with fringe benefits: When my company, Solar Junction, received funding from the DOE, we were able to access national laboratory resources as part of the program. If your company has licensed technology from a university or laboratory, check to see if the entity has any programs or processes to provide startup grants (as cash or in-kind services) — after all, they want the IP to succeed in going to market. Before accepting grants, be careful about when and where additional technology development occurs. Make sure your IP has been filed or disclosed, or use the funds for engineering and product scale-up to avoid competing ownership claims. For seed-stage companies, consider applying to pitch or business plan competitions. These programs offer prizes ranging from $5,000 to as high as $250,000. Many of them are targeted to promote entrepreneurship in a specific group, whether it’s a university, minority group, emerging sector or geographic region. A small proportion of these competitions also serve as applications to accelerator programs — make sure to read the fine print to see whether the prize money being offered is actual cash and does not take equity; that’s an investment, despite what the marketing states. As the economy continues to slow, federal, regional and local government entities will increase support for job creation activity and allocate increased support for small businesses. Many cities will provide grants to startups that bring jobs to a specific sector. Some of these grants come with requirements that you hire a certain quota of local residents for a set period of time; in many cases, that number is closely aligned with your existing hiring plan. In some cases, this support comes in the form of tax breaks. While it’s not money up front, sometimes that tax return break can end up making a huge difference to your bottom line. Although not free money, small business loans can sometimes be preferable to giving up more equity in the short term. If protecting your team from early dilution wins out over future burn, consider the following options. The Small Business Administration offers startup loans up to $250,000 at some of the lowest interest rates on the market. Special loans exist for minority entrepreneurs, as well. Aciom is another nonprofit lender, providing microloans up to $30,000. “Peer-to-peer” lending platforms have recently emerged as another financing option for small businesses. For the cost of a small origination fee and interest, sites like Prosper and Lending Club allow you to borrow up to $35,000 from complete strangers. Whichever source you choose to pursue, start this outreach and research early, long before you need it. I speak from hard-won experience as a co-founder of Solar Junction, which we led through two cleantech boom and bust cycles before exiting in 2014. While the check sizes might seem small in comparison to the seven-digit-plus rounds that have closed in the last 18 months, it can be a godsend when your team is facing an unexpected cash flow crunch. It’s always easier to get more money when you already have plenty in the bank.
A 30-megawatt solar project changing hands is no longer headline news in today's solar industry, or at GTM. But, when that project is the 30-megawatt Alamosa project -- a power plant that happens to be the world's largest operating concentrated photovoltaic (CPV) installation -- that calls for a mention. Korea Electric Power Corp (Kepco) is going to acquire the PV power plant from Carlyle Group‘s Cogentrix Solar Holdings, according to a statement from the utility, in its first move into the American energy industry. The deal was estimated at $34 million by the The Korea Economic Daily. Cho Hwan-ik, president of Kepco, said, "I am glad to secure a beachhead to move into the U.S. power market. We will keep looking for power generation assets for acquisition including wind power, solar, and other renewable energy plants." He explained in a release, "In accordance with the Paris Climate Change deal, Korea must reduce greenhouse gas emissions by 37 percent by 2030. The best way to do this is acquiring renewable energy power plants overseas." CPV is a troubled solar sub-market with roughly 100 megawatts deployed and $500 million invested over the last 10 years, compared to the tens of billions received by the silicon industry. China's Suncore is still in the CPV business. Amonix had to shut down its Las Vegas production facility in 2012 and has rechristened itself as Arzon Solar, with Amonix founder Vahan Garboushian as CEO. Soitec left the CPV business in 2015. SolFocus shut down in 2013. GreenVolts went out of business in 2012. JDSU quietly exited the CPV cell market after acquiring QuantaSol. Energy Innovations, Soliant, Concentrator Optics, SunPower's C7 and Skyline Solar's low-concentration PV (LCPV) have all passed on. Cogenra moved from LCPV-plus-heat to a solar cell mounting business that got bought by SunPower. Solaria is still building or licensing LCPV and solar windows. Early-stage startups such as Morgan Solar, REhnu and Semprius still believe that CPV's economic riddle can be solved. Former Solar Junction CEO Vijit Sabnis told GTM in a previous interview that no other PV technology has the headroom to improve its efficiency like multi-junction solar cells. Sabnis said he saw 50 percent cell efficiency as achievable in a few years -- which could get DC module efficiencies to greater than 40 percent.