Feb 28, 2010
While riding my bike along the roads of the Billerica campus of British Petroleum, I stopped for a second to gaze at a stop sign near a guardhouse. The outer edge of the red hexagonal plate was decorated with small light bulbs powered by deep blue solar panels. I was amazed to see photovoltaics popping up on the campus of one of the world’s largest petroleum companies— solar technology had made it into the house of big oil.
Lately there has been a lot of buzz surrounding renewable energy development. President Obama recently delivered a speech at MIT intended to galvanize policymakers, scientists and entrepreneurs into making strides towards using renewable energy sources as an alternative to fossil fuels. The goal of this energy campaign is to leverage the potential economic and political benefits that arise from reducing the long-term US reliance on foreign fossil fuels. The campaign strives to increase the amount of jobs in the US while pursuing the long-term need for an inexhaustible energy source.
The Obama-Biden comprehensive New Energy for America plan intends to help create five million jobs by strategically investing $150 million over the next ten years to encourage private efforts in clean energy1. The plan aims to save more oil within ten years than is currently imported from the Middle East and Venezuela combined. Ambitious predictions state that 10% of US electricity will come from renewable resources by 2012, which will increase to 25% by 20251. While biomass and fuel cells remain viable options for clean technology, photovoltaics are the most attractive form of alternative energy. The allure of being able to harness the inexhaustible energy from the sun seems too good to ignore.
The first modern solar cell emerged in the 1950s, when scientists at Bell Labs engineered silicon semiconductors that could convert six percent of incident light into electricity2,3. While this photo-efficiency might have been perceived as low, it was still useful. Eight years later, 3,600 solar panels were used to power the world’s first communications satellite, Telstar, with 14 watts of electricity. While semiconductor manufacturing became more affordable over the years, the limited applicability of photovoltaics kept their manufacturing cost high. In the 1970s, advances in manufacturing techniques lowered the cost of solar cells. This was in part because photovoltaic use expanded beyond the traditional niche aerospace applications to a broader energy market.
Most photovoltaic cells are made from semiconducting materials, such as silicon. When impingent light strikes a photovoltaic cell, a portion of the photon energy is absorbed within the material. This energy drives electrons to quantum states at energies sufficiently high for them to break loose from their host atom and flow through the material as electric current. The highest recorded energy conversion efficiency is around 40%, which was achieved using a multiple-junction solar cell device; most commercial devices have efficiencies between 12% and 20%3.
The current level of interest in photovoltaic research is obvious. For example, in 2007 the US Department of Energy sponsored 25 next-generation photovoltaic projects4. This research generated a diverse portfolio of novel solar cells that includes advance concentrator cells, thin-film single junction and tandem cells, multi-junction photovoltaic hybrid organic/inorganic cells, plasmonic and dye-sensitized cells. Among these cell types, multi-junction photovoltaics, thin-film solar cells and crystalline silicon cells demonstrate the highest efficiencies5.
Researchers at MIT are embracing the challenge to improve solar cell performance and were awarded 2 out of the 25 photovoltaic projects sponsored by the Department of Energy4. Professor Vladimir Bulovic is using cadmium and lead quantum dots to create a fully transparent solar cell that generates higher voltages than any other cell of its kind. Bulovic’s group stacks multiple layers of colloidal quantum dots between n/p-type metal oxides, and this enables them to finely tune the band-gaps to selectively absorb the highest-energy photons. While the target efficiency for this solid-state device is 15%, this value could become greater if the layers are tuned to absorb the various components of the solar spectrum. The potential environmental concerns of this technology are yet to be addressed and require a better understanding of the issues that can arise from using heavy metals in commercialized devices.
Professor Emanuel Sachs’ MIT lab aims to set a new standard in silicon wafer manufacturing for advanced thin-film single junction solar cells. His "String Ribbon" invention is a ribbon crystal growth process for making low-cost silicon substrates for solar cells. This process effectively doubles the yield of silicon substrates compared to traditional growth processes. This String Ribbon technology is currently commercialized by Evergreen Solar, Inc. of Marlboro, Massachusetts, which now boasts five commercial photovoltaic product lines.
Serial entrepreneurs from the IT sector are also turning to solar energy for opportunities in clean technology ventures. Take for example Sunil Paul, founder and CEO of internet firms such as Brightmail and Freeloader. He has recently become a seed investor in early-stage clean technology companies such as Nanosolar, Advent Solar, Oorja and City Carshare. His story is not unique, and is part of a greater trend in clean technology investment.
Despite the billions of dollars poured into R&D investments for photovoltaics, it is an industry still in its infancy. The photovoltaic industry is still reliant on subsidies and research incentives from individual states and the federal government. According to Photon USA6, an internationally active publishing group devoted to discussions of policies, technology and business related to the growth of solar power in the US, the quantity of electricity generated by solar panels in the US is quite low, with the vast majority of the generation occurring in California. As of 2008, 356 megawatts of energy were delivered from US solar installations, which is enough energy to power around a quarter of a million homes. The government’s support for photovoltaic research and development remains strong; $16.8 billion in stimulus funding is going towards the DOE’s Office of Energy Efficiency and Renewable Energy. Of this, $117 million was appointed to the Solar Energy Technology Program, and $92 million is exclusively marked for photovoltaic research.
The 2010 photovoltaic market growth predictions by several industrial analysts provide additional insight into the status quo and the future of the technology. The most optimistic view comes from Chris Porter of Photon Consulting, who estimates a 2.2 to 3.8 GW photovoltaic energy market share6. A more conservative prediction from Paula Mints of Navigant Consulting says this number is closer to 0.53 GW. Regardless, solar power currently represents less than 0.1% of total energy production, which means that there is still much room for the photovoltaic market to grow6.
Despite the love-hate relationship between fossil fuels and renewables, oil companies also view photovoltaics as a promising technology. BP solar, for instance, spent $70 million on its expansion of US facilities7. Some of the investment was directed towards large-scale domestic solar power infrastructure development. For instance, this year BP Solar will launch their highly successful Certified Installer Program in the US and introduce its new 215-watt black module, which is ideal for residential installations.
All government assistance, research efforts and industrial interest seem to support a stronger photovoltaic presence. Perhaps photovoltaics will emerge from the darkness and shine a bright light on renewable energy as the solution for the world’s energy demand.
- Photon International The Photovoltaic Magazine, 2009 November Issue