Innovation In Solar Technologies
Concentrating solar power (CSP)
Introduction
Each day the news about climate change grows more disheartening, and the most disheartening aspect is that it didn’t have to happen. Energy sources able to supply power for human activities without wrecking the planet and altering its atmosphere have been there all along. Fossil fuels were fairly simple to mine and employ, though, and they were cheap, since Earth gave them up without charging, at least in the short term. It wasn’t rocket science, as they say, to put them to use, although applications have become quite sophisticated and we can now scarcely imagine life without the engines and gadgets based on their exploitation.
Imagining energy generation not based on oil or natural gas is the next great feat of engineering for the human species, however, and the task is well underway. The past year has been a time of strong innovation in solar technology. Almost every day brings reports of research projects or commercial ventures that aim to make the sun’s energy a more common source of power generation. While some of the advances are funded by government agencies, even where this is lacking developers are not waiting. Recent media announcements show scientists, engineers, commercial entrepreneurs, and philanthropists betting their labor, reputations, and financial means that our future will be run on renewable energy, much of it solar. As I read about the work these innovators are doing to move us that direction, I see them alongside political activists, educators, and other visionaries striving to avert the worst climate outcomes. (See “The Chronicle: The Powers” in this issue of CES Musings for more on who is financing these innovations.)
There are three major categories of solar technology.
- Photovoltaic systems (PV) directly convert sunlight to electricity. They generate electricity using naturally-conductive, light-absorbing materials such as silicon. Electrons in these materials are freed by solar energy and can be induced to travel through an electrical circuit, powering electrical devices or sending electricity to the grid.
- Solar heating and cooling systems (SHC) absorb sunlight to generate heat, which they use to provide hot water, space heating, and cooling.
- Concentrating solar power (CSP) technologies use mirrors to concentrate the energy from the sun to drive traditional steam turbines or engines that create electricity. org
This article offers examples of research in PV cells, batteries, wireless solar transmission, and CSP, as these are areas in which the most dramatic breakthroughs in 2015 seem to have taken place.
PHOTOVOLTAIC CELLS (PV)
Photovoltaic cells convert solar light photons into electricity. The PV effect was observed as early as 1839 by Alexandre Edmund Becquerel, and in 1954 Bell Labs introduced the first solar PV device that produced a useable amount of electricity. Today the conductor layer of most commercial solar cells is made from a refined silicon crystal similar to the material in computer chips, and typically the efficiency ratio of these cells for converting sunlight to usable power is about 20 percent. The familiar rigid solar panel consists of multiple solar cells in an integrated group, all oriented in one plane. seia.org
Most PV cell research aims to lower the cost of solar cells or achieve cost savings by increasing their efficiency. Scarcity or availability of components is a consideration, too, and is related not only to cost, but also to practical implementation. Innovations that expect to come into common use must employ commonly available materials.
Another research consideration is improving safety: toxic or flammable materials need to be avoided or reduced wherever possible. Silicon-based solar PV production involves use of many of the same materials as the microelectronics industry and therefore presents many of the same hazards. solarindustrymag.com. Commonly used perovskite solar cells contain the well-known toxin lead–methylammonium lead iodide is the material of choice for such solar cells. There is a very small amount in a solar cell and a slim chance it would leak, but nevertheless the European Union-funded FutureNanoNeeds project is now investigating the health risks and dangers of lead-based perovskite materials. www.materials
PV modules contain substances such as glass, aluminum and semiconductor materials that can be successfully recovered and reused, and recycling of thin-film and silicon modules is already taking place. In the United States, First Solar has developed a process for recycling thin-film modules under the company’s pre-funded module collection and recycling program. renewableenergyfocus.com
Spherical sun power generator
A spherical sun power generator prototype with trade name Beta.ray will produce twice the yield of a conventional solar panel in a much smaller surface area. It comes with a hybrid collector to convert to daily electricity and thermal energy at the same time. Developed by German architect Andre Broessel for his company Rawlemon, the modular collector system charges and stores energy during daylight hours and can even collect energy from the moon at night. The Rawlemon website asserts, “By using a high efficiency Multi-junction cell, we have reduced the cell surface down to 1% compared to the same power output as a conventional silicon cell in optimal conditions. Our system generates twice the yield of a conventional panel. In addition, our smaller cell area has a lower carbon footprint because its production requires fewer precious semiconductor or other building materials.” rawlemon.com Multi-junction cells made from multiple materials will respond to multiple light wavelengths and some of the energy that would otherwise be lost can be captured and converted. Multi-junction cells can only function with concentrator systems.
Improved polymer solar cells
Polymers are a familiar technology seen in such products as polystyrene plastic. When heated, thermoplastic polymer softens and can be converted into semi-finished products like films and sheets. Polymer solar cells have the desirable features of lighter weight and flexibility, but they need extra processing steps and coating technologies that are a technical challenge. Researchers at Iowa State University and Ames Laboratory took flexible, lightweight polymers and added a textured substrate pattern that provided a thin, uniform light-absorbing layer. This textured substrate pattern remains uniformly thin when going up and down the flat-topped ridges, which are less than a millionth of a meter high. With this layer, efficiency improved by 20 percent. The technology is being patented by Iowa State University Research Foundation Inc. Once the technology is patented, it will be licensed to solar cells manufacturers. alternative-energy-polymer-solar-cells/
Ultra-short pulse laser scribing
Flexible thin-film solar cells that can be used as rooftop shingles and tiles, building facades, or the glazing for skylights are a rapidly expanding portion of the solar cell market. Ultra-thin film-type solar cells have now been manufactured which are quite malleable and appropriate for corners and curvilinear structures. The films when assembled into an array are only as efficient as the “microchannels” on the films which help convert the sunlight to electrons needed for power generation. Until now the scribing of the microchannels has been done with the help of a mechanical stylus—an expensive process that results in inexact grooves of uneven depth. Using the ultra-short pulse laser in a process called “cold ablation” (laser beams flashed for only quadrillionths of a second), a team from Purdue University very rapidly inscribed microchannels with exact depths and well-defined outlines without causing any damage to the ultra-thin-film solar cells. The research, funded by National Science Foundation, aims to increase efficiency while significantly reducing cost. purdue.edu
FDT light-harvesting film
Some of the most promising solar cells today use light-harvesting films made from perovskites, a group of materials with the same type of crystal structure as calcium titanium oxide (CaTiO3). Perovskite-based solar cells use expensive “hole-transporting” materials, whose function is to move the positive charges that are generated when light hits the perovskite film. Publishing in Nature Energy, scientists at École Polytechnique Fédérale de Lausanne have now made a molecularly engineered hole-transporting material called FDT. Lead researcher Mohammad Nazeeruddin reports, “By comparison, FDT is easy to synthesize and purify, and its cost is estimated to be a fifth of that for existing materials.” FDT is able to keep the efficiency of the solar cell above 20%. actu.epfl.ch
Tandem perovskite-silicon cells
A number of chemical researchers believe perovskites open the door to a new era of high-efficiency, low-cost solar cells. Perovskites are easily synthesized, and their ability to absorb light in the blue region of the spectrum complements silicon, which absorbs long-wavelength red and near-infrared light. A new tandem solar cell featuring monolithic perovskite and silicon has been reported to produce electricity with efficiency of 18 percent, according to scientists at Helmholtz-Zentrum Berlin and École Polytechnique Fédérale de Lausanne, Switzerland. While this is not the highest solar cell efficiency rating, Professor Bernd Rech of Helmholtz-Zentrum Berlin believes industry will be interested in the potential. He says, “There are many established production facilities for silicon cells. The perovskite layers could considerably increase the efficiency level. To achieve this, the fabrication techniques only need to be supplemented with a few more production steps.” cleantechnica.com/tandem-perovskite-silicon-solar-cell
3D-Printed Solar Energy Trees
Researchers at the VTT Technical Research Centre of Finland have developed some very decorative prototypes of what they are calling “energy harvesting trees,” thanks to advancing solar and 3D printing technologies. The tiny leaves store solar energy and can be used to power small appliances and mobile devices. They flourish indoors and outdoors and can also harvest kinetic energy from wind and temperature changes in the surrounding environment. The tree’s leaves are flexible organic solar cells, each with a separate power converter. The trunks are 3D-printed using wood-based bio-composites. They are mass producible. alternative-energy-news-solar-energy-trees
Ceria for solar fuel production
Because ceria or cerium oxide—the most commonly-found rare-earth metal—has a natural propensity to alternately exhale and inhale oxygen as it heats up or cools down, it is under exploration for use as a means to create fuel. A new prototype formulated by Swiss and US researchers uses a quartz window to focus sunlight through a small cavity on a ceria-filled cylinder. When water and/or carbon dioxide are pumped into the vessel, hydrogen and/or carbon monoxide are created. Hydrogen by itself is used in hydrogen cells, and by mixing hydrogen and carbon monoxide, a synthetic fuel (syngas) can be produced. The resulting fuels are portable and can be used at any time. Researchers expect improved insulation and smaller apertures can increase efficiency to some 19% and make it a commercially workable option. alternative-energy/ceria
BATTERIES AND STORAGE
The greatest technical challenge with producing electricity from renewable sources is their intermittency. Photovoltaic cells can generate power from sunlight, but they must be partnered with some kind of storage mechanism for power to be available at night or in cloudy weather. Grid-connected users of PV-generated power can receive power from the grid when the sun isn’t shining, whether from renewable or non-renewable energy sources. Off-grid users need to store their own surplus power for those times , and utilities require grid-sized batteries or another large-capacity storage medium.
Until recently, batteries for energy storage have been based on lead-acid chemistry that pollutes, has a short life span, and may be unreliable. Lithium was an attractive alternative to lead, since it is the lightest of all metals and has great electrochemical potential. Due to its inherent instability, however, especially during charging, research shifted to a non-metallic lithium battery using lithium ions. batteryuniversity.com Lithium ion is the advanced technology that has been brought into commercial level production at this time, but a variety of battery chemistries are near that stage. As Ellen Williams, director of the US Advanced Research Projects Agency-Energy (ARPA-E) said in February 2016 of work by that agency, battery storage systems are on the verge of transforming America’s electrical grid. theguardian.com
The objective of all this development is to produce cheaper, safer storage for renewable sources with longer operational capacity. Progress continues, including the arrival on the retail market of the first mass-produced, affordable solar home batteries.
Tesla: lithium ion
At its massive factory near a lithium mine in Nevada, Tesla has started producing its lithium-ion Powerwall battery. Powerwall is a home battery that partners with solar panels to provide stored-up power for use at night or during outages. With the battery, a home can achieve a net-zero energy rating; that is, it can produce as much energy as it consumes while still connected to the utility grid for periods of high demand. Each Powerwall has a 7kWh energy storage capacity, and multiple batteries may be installed together to meet greater energy needs. A 10kWh version is also available. Tesla offered its first demonstration home system batteries in 2015, and in 2016 Tesla is busy filling orders from the long waiting list. The selling price to installers is $3,750 for 10kWh and $3,000 for 7kWh, excluding inverter and installation. teslamotors.com
Tesla is also offering a 100kWh battery for utility scale use. According to Tesla they can scale to any size—10,000 Powerpacks would generate 1Gw of electricity. The CEO of Tesla said that 160 million Powerpacks could enable the entire US to transition to renewable energy and 900 million Powerpacks would enable the whole world to make the transition. emirates247.com
Sonnenbatterie: lithium ion
A German company, Sonnenbatterie, also entered the US market in 2015. Sonnenbatterie employs Sony Fortelion lithium-ion batteries for its storage systems and claims they can be used for up to 10,000 charge cycles. The German manufacturer has opened facilities in Los Angeles and Atlanta. cleantechnica.com and sunwindenergy.com
Aquion Energy: aqueous sodium ion
The world’s first battery with Cradle-to-Cradle Material Health certification works on saltwater and other commonly available materials and stores enough solar or wind energy to power a single-family home for eight hours. The size of a dishwasher or small refrigerator, the Aqueous Hybrid Ion (AHI) battery can fit off-grid and microgrid locations. Aquion Energy has fully scaled manufacturing with global distribution channels and installations in many locations including Australia, California, Germany, Hawaii, Malaysia, and the Philippines. aquionenergy.com
Ambri: liquid-metal
The Ambri battery combines two metals that have different weights and melting points, separated with a salt layer. Electric currents heat the metals to as much as 700 degrees Celsius (1,292 degrees Fahrenheit) to pass electrons through the molten salt. In September 2015 Ambri revealed disappointing test results that pushed back commercial deployment indefinitely. The problem is the seals that keep the liquid electrodes enclosed—steel cans that must be hermetically sealed with materials that hold up for many years. Ambri’s manufacturing facility in Cambridge, Massachusetts, is still seeking a solution to its sealant problem. bloomberg.com and technologyreview.com
Seeo: dry lithium
Silicon Valley start-up Seeo is developing a battery using a solid dry polymer for its electrolyte, which is far less flammable than a liquid one. The second-generation version of the battery utilizes lithium for the anode, and a new material that can store more energy for the cathode. Although it has yet to sell its batteries commercially, Seeo has been making batteries on its pilot production line for test purposes for some time. In August 2015 the company was purchased by German auto parts giant Bosch. bloomberg.com and fortune.com
In research: lithium-air
The potential of lithium-air comes from the fact that it uses two very light elements, lithium and oxygen, that react to form the product lithium peroxide. In October 2015 Cambridge University announced in Science a series of modifications that bring lithium-air batteries far closer to mass production, although some big steps still remain. The team used one-atom-thick sheets of graphene to produce a highly porous electrode. A further modification was to replace lithium peroxide with lithium hydroxide (LiOH). iflscience.com
In research: polymer-based redox-flow
In October 2015 a team at the Friedrich Schiller University in Jena, Germany, reported making a redox-flow battery that uses organic polymers and a harmless saline solution. The electrodes of a redox-flow battery are not made of solid materials such as metals or metal salts, but are in a dissolved form. The electrolyte solutions are stored in two tanks, which form the positive and negative terminal of the battery. With the help of pumps the polymer solutions are transferred to an electrochemical cell in which the polymers are electrochemically reduced or oxidized, thereby charging or discharging the battery. sciencedaily.com
In research: thermo-chemical technology
Most current solar conversion utilizes photovoltaic cells to transform light energy into electricity. Researchers at Massachusetts Institute of Technology (MIT) are hopeful of capturing and releasing solar energy by means of thermo-chemical fuel. Thermo-chemical technology traps solar energy and stores it in the form of heat in molecules of chemicals, preserving the heat energy to be converted and used at a later time. The product could, in fact, be called a “rechargeable heat battery.” The first experiments used ruthenium, a chemical that is a rare element with prohibitive cost. The current project has explored the exact working mechanism of ruthenium in order to find another chemical element more easily found in nature or to synthesize the material in the laboratory. alternative-energy/mit
WIRELESS SOLAR TRANSMISSION
Far greater efficiency in converting solar rays into electricity would be achieved if the conversion were done in outer space rather than on the ground. Although determining exact values for energy flows into the Earth system is an area of ongoing climate research, it is safe to say that nearly 30 percent of the solar energy that arrives at the top of the atmosphere is reflected back to space by clouds, atmospheric particles, or bright ground surfaces like sea ice and snow. earthobservatory.nasa.gov
That’s why an event that took place in March 2015 merits headlines. In conjunction with Japan Aerospace Exploration Agency (JAXA), Mitsubishi Heavy Industries, Ltd. (MHI) conducted a successful ground demonstration testing of wireless power transmission. By completing the test, MHI has now verified the viability of long-distance wireless power transmission—technology Japan has been working on since 2008. The new technology will serve at the core of the space-based solar power (SBSP) systems that are expected to be the power generation systems of the future. A solar battery in orbit (36,000 kilometers above Earth) could potentially generate power which would then be transmitted to Earth via microwave without relying on cables. JAXA anticipates this new technology could become a mainstay energy source that will simultaneously solve both environmental and energy issues here on Earth. The goal is to be able to transmit energy from orbiting solar panels by 2030. mhi-global.com and spectrum.ieee.org
The United States studied space-based solar transmission from 1974 until 1980, when the NASA program was discontinued by the incoming administration. In 1999 the NASA Space Solar Power Exploratory Research and Technology program (SERT) was formed and subsequently proposed an inflatable photovoltaic gossamer structure with concentrator lenses or solar heat engines to convert sunlight into electricity. NASA Space Solar Program. In 2012 China proposed space collaboration with India that mentioned space-based solar power, and in March of 2015 the Chinese announced their scientists were “mulling the construction of a solar power station 36,000 kilometers above ground.” If realized, it would be the largest-ever space project. news.xinhuanet.com
CONCENTRATING SOLAR POWER (CSP)
Utility-scale solar plants utilize mirrors to collect sunlight, and they store the collected energy as heat. Like natural gas, coal, and nuclear plants, many CSP systems require access to water for cooling. All require small amounts of water to wash collection and mirror surfaces, but some plants can utilize wet, dry, and hybrid cooling techniques to maximize water conservation. Finally, CSP plants must have access to a power grid to distribute the garnered power. alternative-energy-news.info
The first phase of what will become the largest concentrated solar power (CSP) plant in the world went live in late 2015.
The Moroccan city of Ouarzazate is the site for a complex of four linked solar mega-plants that, alongside hydro and wind, will help provide nearly half of Morocco’s electricity from renewables by 2020. The project is a major step in the country’s ambitions to use its deserts to become energy-independent. When construction is complete, the plant will have capacity to generate 580MW of electricity, enough to power a million homes. The first phase, Noor 1, has a generating capacity of 160MW and utilizes 500,000 crescent-shaped solar mirrors in 800 rows. Each parabolic mirror is 12 meters high and focused on a steel pipeline carrying a synthetic thermal oil heat transfer solution that is warmed to 393 degrees C as it snakes along the trough before coiling into a heat engine. There it is mixed with water to create steam that turns energy-generating turbines. The heat tank contains molten sands that can store heat energy for three hours. The US$9 billion project is justified as cost-effective, since Morocco has been importing 94% of its energy as fossil fuels from abroad. theguardian.com
CONCLUSION
Future energy scenarios depend on many factors. Government leaders, scientists, and energy investors don’t always agree on the best path. At the present time it takes fossil fuel energy to make solar applications, and if we or fail to apply the remaining supplies of oil and gas to their development, generations from now humans may be back where we were before the industrial revolution—living by direct or crudely amplified sunlight.
The pioneers whose work has been described here are committed to giving us alternatives to both the fossil fuel era and to descent into more primitive tools. This article aims to plant a seed of expectation in our minds to enable us to see beyond the age of oil. The technologies now under development point to a time when there will be cleaner, cheaper, safer ways to generate warmth and cooling, supply water, and empower humans with greater-than-human strength for the daily chores.
Good websites for keeping track of new solar technologies are Solar Energy Industries Association seia.org and Alternative Energy News alternative-energy-news.