Dawn of silicon solar

People have been harnessing renewable energy from the sun, wind, water, and land forever. And even though fossil fuels now dominate the energy picture, the journey of renewable energy is far from over. This slideshow will give you a glimpse of how renewable energy has evolved over the years, where it is now, and some ideas on where it's going. This photo from 1954 depicts an important moment when engineers at Bell Labs in New Jersey unveiled the first practical solar cell made from silicon, which is now the dominant material for solar panels. The basic photo-detector developed for this solar cell led to applications in digital cameras and optical networks.

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Photo by: Bell Labs / Caption by:

Electricity-producing windmill

Windmills for crushing grain or pumping water date back to the Middle Ages and were commonplace in the U.S. in the mid-19th century with many different designs tried. In 1890 Charles Brush developed a wind turbine to generate electricity. Connected to a 12,000-watt dynamo and battery bank, he used it to power his house, which was apparently a very large consumer of energy. This machine, called a turbine rather than a windmill, helped set the stage for development of today's turbines.

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Photo by: Western Reserve Historial Society, Cleveland, Ohio / Caption by:

Wave power of the 19th century

Wave and tidal power is seeing a resurgence in recent years, but the concept was pursued in the U.S. back in the 1870s off the coast of California. Here is a postcard from a "wave motor" experiment off the coast of Santa Cruz from 1898, according to the Western Neighborhoods Project. Incoming water would operate a vertical piston in a tunnel along the side of a cliff, which would pump water into a basin, according to a 1902 Scientific American article. Then the collected water could be run through a standard hydrogenerator. The Santa Cruz wave motor operated for at least four years but other experiments didn't fare as well. The Starr Wave Motor in Los Angeles collapsed after two years in 1909 because of faulty construction of the pier it was on.

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Photo by: Charles Weidner / Caption by:

Solar engine

If you thought concentrating solar rays to make electricity was cutting-edge technology, think again. French engineer Augustin Mouchot patented this solar engine in the 1860s which used the sun's heat to make steam to run an electricity generator. He developed the concentrator because he mistakenly believed that coal would run out in his lifetime. A more famous example of concentrating sunlight in history is the ancient Greek Archimedes who is said to have used mirrors on shore to concentrate sunlight onto invading Roman ships in the Mediterranean to set them on fire.

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Photo by: via Retronaut / Caption by:

Day at the races

Gasoline internal combustion cars eventually were the death of electric and steam-powered vehicles in the early 1900s. But racing cars back in the day didn't always run on gasoline. Ethanol was often used by racing cars, including William K. Vanderbilt's racers such as this Packard Wolf, according to Bill Kovarik, professor of Communication at Radford University.

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Photo by: Vanderbilt Cup Races / Caption by:

Solar water heater

The Climax water heater, first invented in the 1890s, was a turning point for practical solar energy. It is said that during that period one third of the homes in Pasadena, Calif., used solar hot-water heaters to avoid the expense of coal. The solar hot-water industry then thrived in the 1920s building boom in Florida. But then the government froze the use of copper during World War II, which dealt a blow to solar thermal, according to Home Power magazine. Then cheap electricity and new electric hot-water heaters stopped all growth until the 1970s.

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Photo by: via California Solar Center / Caption by:

Jimmy Carter's road not taken

Anyone who lived in the 1970s remembers the oil embargoes that shocked the global economy and made Americans acutely aware of energy. On June 20, 1979, President Jimmy Carter dedicated solar panels on the West Wing of the White House which were used to provide hot water. When he took office, President Ronald Reagan quickly removed the panels in a symbolic move. In addition to disconnecting the panels, the Reagan administration dramatically rolled back funding for renewable energy which had begun during the 1970s as a response to the oil crisis. In 2010, the White House announced it will put solar electric and hot-water panels on the White House but they have not yet been put on.

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Photo by: Jimmy Carter Library / Caption by:

Solar furnace

In the late 1950s, the U.S. government built a "solar furnace" with this 60-foot-high heliostat for military and civilian purposes. By reflecting and concentrating light, it was initially designed to simulate the thermal effects of a nuclear weapon. Then in the 1970s, it was moved to the White Sands Missile Base in New Mexico to evaluate solar energy as a "viable natural resource," according to a 1975 report (PDF).

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Photo by: National Archives / Caption by:

NASA Mod1

Wind turbines have been built for decades but following the oil crisis, there was a push to develop commercially viable and reliable turbines. NASA was one of the technical developers of a new generation of these turbines. Seen here is the Mod1 turbine, built by General Electric, which operated in North Carolina but ultimately suffered from flaws and was dismantled in the early 1980s as funding for the program was cut. According to a history of green technology called "Powering the Dream" by Alexis Madrigal, some U.S. wind companies attempted to leap ahead with radical designs. Meanwhile, companies in Denmark focused on reliability and incremental performance improvements over time, which led to Denmark being a world leader in wind energy.

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Photo by: NASA / Caption by:

Concentrating solar tower

Research for renewable energy did indeed dry up in the 1970s and 1980s, but many of the technologies that got at least a foothold decades ago are finally spreading. A good example is concentrating solar power, which creates heat with mirrors to produce steam and generate electricity in a standard turbine. There are a number of concentrating solar power plants built or being built around the world, including a few planned in the U.S. Pictured here is a demo-scale concentrating solar plant from BrightSource Energy, using a method derived from concentrating solar pioneer Luz Energy in Israel decades ago.

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Photo by: BrightSource Energy / Caption by:

Rooftop thin-film panels

Even with the advance of concentrating solar power, it faces tough price competition from solar photovoltaics, the traditional flat panels that convert sunlight directly into electricity. Seen here are solar panels from First Solar which use thin-film solar cells, another technology which is also lowering prices. Despite the technical advances in solar, the one innovation which has truly caused a jump in residential solar is on the business side. A number of installers now offer solar leases or power purchase agreements, which allow consumers to lower their electricity bills with solar panels without having to buy or own the equipment.

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Photo by: SolarCity / Caption by:

Tidal generator

The Bay of Fundy in Maine has the highest tides in the world, making it ideal for a tidal generator like this one by Ocean Renewable Energy. The potential is significant, but getting energy from waves and tides is very difficult and requires work of lengthy environmental testing and product development. In the U.S., there are several test sites and in Europe, a small number of machines are generating electricity to the grid. In another indicator of the rich history of renewable energy, President Franklin Delano Roosevelt wanted to build a generator near the Bay of Fundy in the 1930s but eventually pulled the plug because of the high cost of the project. For more wave and tidal generators, see this slideshow.

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Photo by: Ocean Renewable Power / Caption by:

Organic waste to biogas

Biomass, often in the form of wood, is the largest source of renewable energy in the U.S. by a significant margin. Incinerators and waste-to-energy plants have been around for decades but one form of biomass that's getting more attention is organic waste, such as yard waste and food. Organic waste can be decomposed using microbes to produce biogas, which is mostly methane, and nutrients for fertilizer. These anaerobic digester tanks pictured here in the municipality of Lidkoping, Sweden, will use waste from the local food industry as its main feedstock to make biogas, which can be used for heating or to generate electricity. Once the plant is completed, operators expect to handle 60,000 metric tons a year of waste and reduce carbon dioxide emissions by more than 14,000 metric tons annually. See related article: Next Wave of recycling? Check your dinner plate

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Photo by: Swedish Biogas International / Caption by:

Concentrating solar photovoltaics

There's another type of solar power that's vying for market share called concentrating photovoltaics. This plant is being constructed in the San Luis Valley in Colorado where these large collectors use mirrors to concentrate sunlight onto very efficient solar cells. Concentrating the light boosts the output but these systems require trackers and can be more complex than regular flat panels.

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Photo by: First Solar / Caption by:

Running on renewables

One of the biggest challenges with renewable energy technologies is scaling up beyond the experimental phase. The U.S. Navy, in its mission to cut its use of fossil fuels for security reasons, is a customer of algae fuels from Solazyme and others. This RCB-X is powered by an alternative-fuel blend of 50 percent algae-based and 50 percent NATO F-76 fuels. Research on algae fuels in the U.S. began back in the 1980s and, like solar and wind, lost funding as oil prices went down. Algae saw a resurgence in the 2000s, but it's still difficult to make algae biofuels at competitive prices with oil.

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Photo by: U.S. Navy photo by Mass Communication Specialist 2nd Class Gregory N. Juday / Caption by:

Sunlight+CO2=fuel

Startup Joule sought to avoid the mistakes of algae companies and took a completely different approach to making fuel. Seen here is a test bioreactor that grows a genetically engineered microorganism called cyanobacteria which produces a hydrocarbon fuel directly. The microbes, which grow in water, are only fed sunlight, nutrients, and CO2 from a power plant or other source. This idea of directly producing fuel from plants, without having to collect and process biomass into fuel, is an area pursued by the ARPA-E agency for breakthrough energy research.

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Photo by: Joule / Caption by:

Jet turbine inspired wind turbine

For the most part, designs for large-scale wind turbines have been consistent for decades. But one company is trying to break the traditional three-blade fan turbine look. Seen here is a model of FloDesign Wind Turbines' wind generator which uses a shroud behind the spinning blades to concentrate the wind. By squeezing the wind through the turbine, it boosts the power output, according to the company. The company tested a full-size prototype on Deer Island in the Boston Harbor as part of a testing process.

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Photo by: Martin LaMonica/CNET / Caption by:

Makani wind wing

Makani Power is pursuing a completely different idea. It's building essentially a tethered wing that spins around in the wind to generate electricity. The idea is to design a wind generator with the ability to capture the stronger winds at high altitudes, perhaps out at sea.

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Photo by: Martin LaMonica/CNET / Caption by:

Storing solar energy

One of the busiest areas of research in renewable energy is in storage, not power generation. SolarReserve has developed a molten-salt storage system that will be used in Nevada to deliver power several hours after the sun has gone down. A field of mirrors, pictured here in an artist's drawing, concentrate sunlight onto a tower to heat up the salt. The hot salt is then converted into steam to run an electricity turbine.

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Photo by: SolarReserve / Caption by:

Grid battery

At the same time, there are dozens if not hundreds of battery companies trying to develop a breakthrough in battery costs and capacity. Here is a conceptual drawing of a grid storage battery from startup Eos Energy Storage. The battery uses a zinc air chemistry and changes in the component design to have reliable performance and very low costs, according to the company. It intends to test a system for easing grid congestion and storing renewable power in the next two years.

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Photo by: Eos Energy / Caption by:

Solar hydrogen generator

A completely different approach to storing renewable energy is with hydrogen. Startup SunCatalytix is developing materials used in electrolyzers, or machines which use a flow of electrical current to split water to generate hydrogen. The hydrogen would then be stored in tanks and used as needed to generate electricity in fuel cells. Pictured here is a solar cell, which when exposed to light, can split water to make hydrogen (and oxygen) directly.

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Photo by: Martin LaMonica/CNET / Caption by:

Offshore wind

The technology for onshore wind turbines is generally well-established and reliable but offshore wind faces years of development before it can be done reliably and cost-effectively. Offshore wind is compelling because there are generally stronger winds than onshore, but the conditions are much more harsh and reliability and construction is more challenging. Seen here are designs from the University of Maine for ballasts to place turbines offshore.

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Photo by: University of Maine / Caption by:

Algae-coated buildings

As people look into the future, more radical schemes have been proposed for reducing the amount of greenhouse gases. One of the geoengineering concepts proposed by the U.K. Institute of Mechanical Engineers is to have algae farms growing in urban buildings. In theory, these urban farms would be able to generate energy on site.

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Photo by: U.K. Institute of Mechanical Engineers / Caption by:

Nuclear fusion

Nuclear fusion, or fusing together two atoms to generate energy, has been touted for decades as the ultimate clean-energy source, but it remains experimental. Seen here is a diagram of a type of nuclear fusion generator pursued by a company called General Fusion. Once a plasma gas is created, the pneumatic pistons would cause a shock wave to induce fusion and the release of heat. That heat would then be converted to steam to generate electricity in a traditional generator. For a longer explanation of fusion, see a related story on nuclear fusion research at MIT.

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Photo by: General Fusion / Caption by:

Hydrogen car

A Daimler photo shows the potential of a fuel cell car powered by renewable energy from wind turbines. The only exhaust from running fuel cell vehicles is water vapor. But to get hydrogen fuel in the first place, today it has to be created using fossil fuels. Many people over the years have pursued this vision of cars or the power grid running on renewable-energy sources, but as history shows, it's quite difficult and takes years of consistent work.

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Photo by: Daimler / Caption by:
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