This company uses thousands of mirrors, AI, and machine learning to unlock the power of the sun.
- What if we could not only harness the power of the sun, but actually use it to run the entire planet?
- Concentrated solar power (CSP) has the potential to do just that — using arrays of revolving mirrors called heliostats, light is reflected into a massive receiver. Thanks to recent advancements in technology, the cost to replicate these Sunlight Refineries™ is dropping. Soon solar energy will be cleaner and cheaper than using fossil fuels, which could mean adoption on a global scale.
- Heliogen, a company founded by Bill Gross and backed by Bill Gates, wants to eliminate all uses of fossil fuels. Using cameras, AI, and machine learning, they are working to make these CSP systems smarter and much more efficient.
This episode is from Hard Reset, a Freethink original series about rebuilding the world from scratch and reimagining everything from first principles.
Catch more Hard Reset episodes on their channel: https://www.freethink.com/shows/hard-reset
How one startup plans to use "death rays" for good instead of evil.
- A new advance in concentrated solar power makes temperatures of 2700° F possible from nothing but sunlight.
- The heat produced can be used to produce electricity, make clean fuels, or power industrial processes.
- Founder Bill Gross sees these plants as part of a grand design to wean the world off oil.
The need for clean, consistent, renewable energy sources has never been more pressing. Rising energy prices threaten to kick-start inflation and slow economic growth. Control of the supply of fossil fuels has caused wars before and may well cause them again. Burning fossil fuels continues to create greenhouse gas emissions, making solving the problem of climate change difficult.
While low-carbon and renewable sources of power are being used more than ever before, none of them are perfect. Solar and wind power are very clean and increasingly inexpensive but have an energy storage problem. The batteries required to store that energy require rare earth metals, which are messy to extract and increasingly in demand. Hydro power is great but can have negative impacts on the river ecosystem. Nuclear is still a tough sell.
If we're going to solve our energy problems, we either need to find a new way to produce a lot of energy or fix the problems with the power sources we have. A renewable energy technology company backed by Bill Gates and founded by serial entrepreneur Bill Gross called Heliogen has a new approach to an existing model that may just accomplish the latter with a giant, extremely precise magnifying glass and some really hot rocks.
Concentrated solar power
The Crescent Dunes Solar Energy Project near Las Vegas, Nevada. This project, while not associated with Heliogen is a typical example of concentrated solar power. DANIEL SLIM/AFP via Getty Images
In Lancaster, California, a mid-sized city in the Mojave Desert, Heliogen has built a miniature version of their planned solar refinery. While concentrated solar power is nothing new — it has been operating commercially since the 1960s and is said to have been used by Archimedes to build a heat ray to burn the Roman fleet — this plant improves on the concept with stunning results.
Essentially a lot of mirrors arranged in a circle reflecting sunlight at an elevated target, concentrated solar power uses the energy in the sun's light to heat that target, which could be water, molten salt, or even something solid, to very high temperatures. (When this heat is used for something other than producing electricity, it is called concentrated solar thermal energy.)
Heliogen's current test refinery has 400 mirrors, known as heliostats, though it is only a tenth the size of what the company is proposing. Even with this reduced number of mirrors, the refinery has produced eye-popping results. Its operation has produced temperatures as high as 1500° C (2732° F). For comparison, most existing, full-sized concentrated solar power plants are able to produce temperatures in the 400° to 500° C range.
Heliogen's advance is made possible by state of the art software. Using AI and a series of cameras, the heliostats are kept on target as much as possible (currently to a twentieth of a degree) through micro-adjustments to their position throughout the day. By keeping the mirrors on target, the greatest amount of sunlight possible is focused on the target, creating more heat than was previously possible.
Concentrated solar power isn't just for electricity
It's important to remember that this is technically a solar thermal system. Unlike solar panels, this project does not use the photovoltaic effect to turn sunlight directly into electricity. This project is about generating heat. This heat can then be used to produce electricity — and the high temperatures involved mean it can do so very efficiently — but it has applications beyond that as well.
Many industries use intense heat in their manufacturing processes, like smelting or cement making, and they often burn fuels to create those high temperatures. Heliogen's refinery is able to produce similar temperatures without burning fuels and could provide the heat for these industries in the future. Additionally, the heat produced is high enough to make hydrogen fuel via electrolysis.
As Gross explained to CNN, "If you can make hydrogen that's green, that's a game-changer. Long term, we want to be the green hydrogen company."
If not used immediately, the heat energy can also be stored in plain old rocks, which can stay hot for days or even up to a week in a properly insulated storage unit. Their energy can then be called upon when needed or possibly even shipped to a location in need of heat. Compared to the difficulties of storing electricity produced from solar, this is child's play.
How can concentrated solar be applied at scale?
Gross hopes to improve the process by reaching the same results with increasingly smaller heliostats. His are already smaller than usual, which would allow them to be mass produced more cheaply than they are today. The hope is that this, along with other refinements to the system, would help lower the cost of energy produced by concentrated solar until it is cheaper than fossil fuel energy.
Currently, energy from concentrated solar power is more expensive than burning fossil fuels but only slightly. Also, compared to large arrays of solar panels, solar refineries are more expensive to build and operate. But costs are expected to decrease, in part because they are much better at energy storage than traditional solar, as discussed earlier. Furthermore, large scale concentrated solar power operations already exist in Spain, the Middle East, and the Southwestern U.S.
Concentrated solar power could radically change manufacturing
Gross's grand vision is to build many refineries all over the world using their heat to power industrial processes. The electricity produced by other refineries would create vast quantities of cheap "HelioFuels," starting with hydrogen. Since hydrogen fuel cells are extremely efficient and can run everything from submarines to laptops, this would be a huge step toward cleaning up the energy supply.
Similar ideas exist and have been used elsewhere to cleanly produce jet fuel, another industrial process that normally requires burning fossil fuels in order to create high temperatures.
The reduction in carbon emissions due to widespread use of concentrated solar could be substantial. Concrete manufacturing alone is responsible for 8 to 10 percent of all global emissions. Nearly 40 percent of those emissions are caused by burning the fossil fuels needed to create heat for the manufacturing process. Quick mental math suggests that if concentrated solar power replaced fossil fuel burning for heat in concrete production alone, global carbon emissions would fall by as much as four percent. For comparison, that is roughly equal to the share of carbon emissions created by France, Italy, the United Kingdom, and Brazil combined.
Although everyone knows that coal-based energy is a thing of the past, declarations about nuclear power plants somehow do not want to enter into force.
No other power-generating device raises as much concern as the nuclear reactor. Because of this, until recently the future of the entire energy sector has been determined by its past.
On the eve of the pandemic, the European energy sector found itself at a crossroads, somewhere between Great Britain, Germany and Poland. Five years ago, across the English Channel, the then Prime Minister David Cameron announced an ambitious program to build 12 new nuclear power plants with a total capacity of 16 GW. While developing renewable energy resources, they would allow the United Kingdom to reduce carbon dioxide emissions from the energy sector to almost zero. Soon after, Cameron came up with the idea of a referendum on leaving the EU – and Brexit reset all long-term British plans. However, the British are already producing electricity in a very sustainable way. Almost 38% comes from renewable sources, about 20% from nuclear power plants, while the remainder is provided by gas-powered plants, the only ones that emit CO2.
Meanwhile in Germany, the aversion towards nuclear energy has been growing for years. Finally, following the Fukushima disaster in March 2011, chancellor Angela Merkel announced that all nuclear power plants would be shut down by 2022. For the first few years, the great Energiewende (energy transformation) plan seemed to be going well. Thanks to subsidies and increased electricity prices for individual customers, the intensive development of wind farms and solar power plants continued. However, no technological solution has been found to overcome the main weakness of renewable energy sources: plants running on renewable sources work on average for 20-30% of the day and remain completely dependent on whether the wind blows or the sun shines. Because of this, they are not able to handle energy peaks. In turn, when a gale comes, suddenly there is a network overload due to excess power. In both these extreme cases, the entire country is at risk of blackout, and the risk of collapsing energy supplies increases significantly when more than 30% is obtained from renewable sources. Safety requires the maintenance of traditional power plants, which due to their flexibility, stabilize the entire system.
In Germany, as subsequent nuclear reactors began to shut down, lignite-fired power plants started to play a key role. Unlike nuclear plants, they devastate the natural environment not only due to CO2 emissions, but also the need to expand opencast mines. A huge wave of criticism from environmentalists and Berlin's goal to lead by example in the fight against global warming have brought an adjustment in strategy. Today, coal-fired power plants are being replaced by gas-fired ones that emit one-third less carbon dioxide. Russia will provide fuel for them via the Nord Stream and Nord Stream 2 gas pipelines. However, withdrawal from the decommissioning of nuclear power plants is now out of the question.
In turn, the development of renewable energy in Poland is suffering, despite the construction of one or more nuclear power plants having been announced two decades ago. Before the pandemic, the government envoy for strategic energy infrastructure Piotr Naimski claimed that by the end of 2045 as many as six nuclear reactors with a total capacity of 6 GW would be built. Although everyone knows that coal-based energy is a thing of the past, declarations about nuclear power plants somehow do not want to enter into force. And this is a very complicated undertaking, during which any disregard of security standards can awaken demons from the past.
A pile of trouble
"In fifteen years, nuclear power will provide electricity too cheap to measure its consumption," the head of the American Atomic Energy Commission, Lewis Strauss, prophesied in 1954. By the end of that decade, energy corporations had overcome technological barriers. "Westinghouse has perfected the PWR reactor, the water-pressure reactor, and GE [General Electric] the BWR reactor, boiling water reactor," explains Daniel Yergin in the The Quest: In Search of Energy. These two types of first generation reactors have spread throughout the world. By 1970, 15 nuclear power plants had launched in 62 countries and the construction of a further 89 had begun. Most of them were located in the US, USSR, UK, France, Japan and West Germany. Three years later, the first oil crisis erupted and it seemed certain that highly developed countries would base their future on nuclear power plants. However, the first problems began to emerge.
The first generation, 1000 MW water-pressure reactor generated as much as 20 tons of radioactive waste annually. Initially, the Americans placed it into metal containers and buried it in the ocean. The Soviets did the same. Protests by environmental organizations led to containers with a guarantee of durability of a thousand years starting to be buried in the Nevada desert – ignoring the fact that the half-life of plutonium-239 is about 24,400 years. In other countries, old mines were used as waste dumps. The French coped with this problem exemplarily by building a plant at La Hague specializing in the recovery of radioactive uranium and plutonium from waste. Later, these elements are enriched and sold to energy companies. During the 1980s, many countries – including Japan, West Germany, Belgium and Switzerland – began to use the services of the French.
In addition to waste, investment costs have become an equally large problem. "Emerging ecological movements, especially anti-nuclear ones, forced additional reviews and changes. It was necessary to thicken the concrete walls, and remove pipeline installations and rework them. Power plants had to be redesigned, even several times during construction," emphasizes Yergin. He writes: "Power plants also became more expensive because of inflation and later, the high interest rates on loans. Instead of six years, construction took ten; it also cost money. The power plants, which were to cost $200million, ultimately cost $2billion." Later, they produced the cheapest electricity on the market, but gigantic expenses had to be included in its price. While the French model handles waste well, investment costs remain the Achilles' heel of nuclear energy to this day, even if they are less important than the media and public fear.
Awaiting the apocalypse
"There is nothing in the laws of nature that stops us from building better nuclear power plants. We are stopped by a deep justified public distrust. The public distrusts the experts because they claimed to be infallible," writes Freeman Dyson, a physicist who participated in the construction of the first reactors, in the book Imagined Worlds. The distrust of nuclear energy emerged gradually. In the 1960s, everyone remembered the fate of Hiroshima and Nagasaki, but the fear of radioactive radiation had not yet paralysed ordinary people. Experts managed to convince Western societies that the nuclear power plant hardly differed from the coal-fired power plant. All it needs is access to a lot more coolant for the reactor, preferably a huge water tank.
The sense of security began to fade not because of a failure, but catastrophic scenarios loved by the press, especially in West Germany. In October 1975, Der Spiegel very vividly presented to readers what would happen if the reactor at a power plant built near Ludwigshafen overheated. "The molten reactor core will penetrate the surrounding protective structures. It will sink into the ground at a speed of two to four meters per hour. The amount of radiation emitted would correspond to the radiation of a thousand bombs such as the one dropped on Hiroshima," the newspaper forecasted, estimating the number of victims at 100,000 killed immediately and about 1.6 million "dying slowly" due to radiation sickness. Such apocalyptic visions interested Hollywood, resulting in the neo-thriller entitled The China Syndrome. In specialist jargon, this name means the severe meltdown of the core components of the reactor.
Lo and behold, two weeks after the film's release, on 28th March 1979, there was a failure at the Three Mile Island nuclear power plant located on an artificial island. Pipes supplying coolant to the reactor burst when the back-up cooling system was disconnected for inspection. The reactor had warmed up, but the safety measures worked. Each reactor is managed using control rods. They are made of alloys that absorb neutrons. Sliding the control rods in between the fuel rods slows down the chain reaction. Pulling them out has the opposite effect. When the reactor overheats, all control rods fall into the core, quenching the reaction.
This happened at Three Mile Island. However, due to the pipes bursting, water poured out onto the reactor jacket and immediately evaporated, forming a mixture of oxygen and hydrogen under the dome of the power block. One spark could have blown up the power plant. The following day, technicians pumped off hazardous, radioactive gases outside. The residents of nearby Harrisburg panicked. About 80,000 people attempted to escape the city in cars. The US energy minister James Schlesinger's assurances that the radiation only increased by around 0.03 rem and would not hurt anyone fell on deaf ears. Those who have seen The China Syndrome knew better. It wasn't until five days later, when President Jimmy Carter personally visited Three Mile Island and in the presence of TV cameras toured the area, that the panic was subjugated. However, the misfortunes of nuclear power plants were only just beginning.
The weakest link
The owners of the plant, the Westinghouse group, largely caused the Three Mile Island disaster. The power plant was built in a rush to make it operational before 30th December 1978, in order for the company to gain a $40 million tax break. After launching the reactor, it turned out that the coolant supply pipes were leaking. At that point, the management ordered temporary sealing of leaks, after which the test of the emergency cooling system was performed, starting with its shutdown. This was done on the assumption that the main pipes would still last a little longer. "The accident was caused by a series of relatively small equipment failures followed by operator error," the head of the commission investigating the causes of the disaster, Admiral Hyman G. Rickover, wrote in his report. Fortunately, none of the Westinghouse executives were so thoughtless as to deactivate the other safeguards. Seven years later, it turned out that even such recklessness is possible.
On the night of 26th April 1986, the management of the Chernobyl power plant began to experiment with manual control of the reactor in block 4. For complete freedom, all automatic security systems were turned off. During the experiments, the stack heated up rapidly, and the control rods blocked by the staff did not automatically quench the chain reaction. Then the pipes supplying water to the cooling system burst. As in Three Mile Island, the water evaporated by the hot reactor turned into hydrogen and oxygen. The explosion of this mixture tore the dome and threw a 500-ton piece of concrete into the air, which a moment later fell into the reactor, breaking it completely. 50 tons of fuel escaped outside and the core melted. Vast areas of northern Ukraine and Belarus became contaminated due to the radioactive cloud. 50,000 residents of the nearby town of Pripyat and surrounding villages were evacuated.
As a result of the disaster, 31 people lost their lives (mainly irradiated firefighters). UNSCEAR (UN Scientific Committee on Effects of Atomic Radiation) found that there were many more casualties: a 2000 report found that of about 600 employees of the power plant and firefighters, 237 were diagnosed with radiation sickness symptoms. Of these, 28 people died. According to the report, epidemiologists have not observed an increase in the incidence of cancer in the most contaminated areas, except for higher than average rates of thyroid cancer. No genetic defects were found in the offspring of irradiated persons.
A quarter of a century later, the 'Chinese syndrome' became Japanese. Two oil crises in the 1970s encouraged the government of Japan to finance the construction of 50 nuclear reactors. They guaranteed energy security for the state. However, haste made them forget about their side effects in a country where earthquakes happen regularly. The Fukushima reactor was built right on the seafront. When massive shocks (9 on the Richter scale) came on 11th March 2011, the security systems functioned properly. The reactors were automatically quenched and the cooling system switched to the emergency power supply. Nothing bad would have happened if it weren't for the sea. Tectonic shocks caused a tsunami wave of 15-metre heights, and the breakwater was only six-metres high. Huge amounts of water flooded the power plant. The power generators went down and the reactor core suddenly stopped being cooled. Then the water evaporated and the hydroxide mixture exploded.
About 10 times less radioactive substance escaped outside than in Chernobyl, and no-one was killed during the event. The first person irradiated as a result of the disaster's aftermath did not die until September 2018. Yet again, however, a wave of fear swept through the entire world.
The sum of fears
The disaster in Fukushima was a strong blow to the nuclear energy sector – which even without it, suffered bad press – and led to public trepidation, even though by the mid-1980s the number of reactors operating worldwide had reached 430 and stopped growing. New ones were still being built in France, Japan, the USSR (later, Russia), South Korea and China, but elsewhere they were gradually dismantled. The only country that had based their entire energy system on nuclear power plants was France, where they produce over 80% of electricity. Finland is also focusing on the development of nuclear energy. Two nuclear power plants currently generate around 30% of the country's energy, and once the third one is built, this will reach 60% (the rest is to come from renewable sources).
Most countries, however, still recognize the nuclear industry as a dead end. The emergence of much better third generation reactors that use less uranium, while reducing the amount of waste, did not change that. Developed by two companies – the French Framatome and the German Siemens – the EPR (European Pressurized Reactor) has a quadruple safety system and reinforcement that can withstand even the impact of an aircraft crash. In turn, the ESBWR (Economic Simplified Boiling Water Reactor) by GE Hitachi, apart from showing similar resistance, requires minimal amounts of coolant and discharges excess heat directly into the atmosphere.
There are more innovative constructions, but they have started to generate interest only recently, thanks to the rapid development of Asian countries, and thus an increase in demand for cheap electricity. A nuclear power plant uses roughly 30-50 tons of uranium per year. At a market price of around $55 per kilogram, a cost of fuel of around $2.5 million a year is very cheap – 100 times cheaper than the cost of fuel for a coal-fired power plant fuel. It is estimated that known uranium deposits will last for about 300 years. At the same time, as with crude oil, this deadline may prove to be much more distant, since no new ones have been sought for years. Therefore, it should not come as a surprise that in April 2019 China presented a plan for the vast expansion of its nuclear energy sector. While today the total capacity of Chinese nuclear power plants is about 42 GW, it will exceed 100 GW in 100 years. Then, the People's Republic of China will overtake the US in this field. South Korea has presented slightly less ambitious goals, announcing an increase in nuclear power by one-third.
And what path will the European Union take? The fight against CO2 emissions determines the direction of its energy policy, and renewable energy sources are a priority. However, to fully base their economy on them, efficient energy storage is necessary – methods capable of accumulating electricity at times of overproduction and releasing it in the absence of sun and wind. Even lithium-ion cells cannot fully cope with this task. Attempts are being made at avoiding the lack of this element by designing self-sufficient buildings that draw energy from solar batteries and heat pumps. However, in the scale of cities and entire countries, large power plants cannot be replaced, and the only ones that do not emit carbon dioxide are nuclear power plants. This fact means that even in Europe, their slow renaissance continues. For now, countries on the outskirts of the EU (Finland, Hungary, Lithuania, the Czech Republic and Slovakia) are modernizing old plants or building new ones. In just one year, the construction of over 60 new reactors began.
Despite public resentment, more investments will begin soon. Right now, fear of the 'China syndrome' is weaker than fear of the effects of global warming and sudden energy shortages and blackouts.
Translated from the Polish by Joanna FigielReprinted with permission of Przekrój. Read the original article.
Utilizing nuclear waste converted to diamonds, this company's batteries will reportedly last thousands of years in some cases.
- Nuclear reactor parts converted to radioactive carbon-14 diamonds produce energy.
- To keep them safe, the carbon-14 diamonds are encased in a second protective diamond layer.
- The company predicts batteries for personal devices could last about nine years.
We have an insatiable need for energy. When we need to operate something that cannot be simply plugged in, power is going to have to come from a battery, and the battle for a better battery is being fought in labs all over the world. Hold that thought for a moment.
Nuclear waste — it's the radioactive detritus from nuclear power plants that no one wants stored near their homes or even transported through their towns. The nasty stuff is toxic, dangerous, it takes thousands of years to fully degrade, and we keep making more of it.
Now a company from California, NDB, believes it can solve both of these problems. They say they've developed a self-powered battery made from nuclear waste that can last 28,000 years, perfect for your future electric vehicle or iPhone 1.6 x 104. Producing its own charge—rather than storing energy created elsewhere—the battery is made from two types of nano-diamonds, rendering it essentially crash-proof if used in cars or other moving objects. The company also says its battery is safe, emitting less radiation than the human body.
NDB has already completed a proof of concept and plans to build its first commercial prototype once its labs have resumed operations post-COVID.
NDB's battery as it might look as a circuit-board component
Image source: NDB
The nuclear waste from which NDB plans to make it batteries are reactor parts that have become radioactive due to exposure to nuclear-plant fuel rods. While not considered high-grade nuclear waste—that would be spent fuel—it's still very toxic, and there's a lot of it in a nuclear generator. According to the International Atomic Energy Agency, the "core of a typical graphite moderated reactor may contain 2000 tonnes of graphite." (A tonne is one metric ton, or about 2,205 lbs.)
The graphite contains the carbon-14 radioisotope, the same radioisotope used by archaeologists for carbon dating. It has a half-life of 5,730 years, eventually transmuting into nitrogen 14, an anti-neutrino, and a beta decay electron, whose charge piqued NDB's interest as a potential means of producing electricity.
NDB purifies the graphite and then turns it into tiny diamonds. Building on existing technology, the company says they've designed their little carbon-14 diamonds to produce a significant amount of power. The diamonds also act as a semiconductor for collecting energy, and as a heat sink that disperses it. They're still radioactive, though, so NDB encases the tiny nuclear power plants within other inexpensive, non-radioactive carbon-12 diamonds. These glittery lab-made shells serve as, well, diamond-hard protection at the same time as they contain the carbon-14 diamonds' radiation.
NDA plans to build batteries in a range of standard—AA, AAA, 18650, and 2170—and custom sizes containing several stacked diamond layers together with a small circuit board and a supercapacitor for collecting, storing, and discharging energy. The end result is a battery, the company says, that will last a very long time.
NDB predicts that if a battery is used in a low-power context, say, as a satellite sensor, it could last 28,000 years. As a vehicle battery, they anticipate a useful life of 90 years, much longer than any single vehicle will last—the company anticipates that one battery could conceivably provide power for one set of wheels after another. For consumer electronics such as phones and tablets, the company expects about nine years of use for a battery.
The company's prospective investor video explains their process in greater detail.
Maybe a very big deal
"Think of it in an iPhone," NDB's Neel Naicker tells New Atlas. "With the same size battery, it would charge your battery from zero to full, five times an hour. Imagine that. Imagine a world where you wouldn't have to charge your battery at all for the day. Now imagine for the week, for the month… How about for decades? That's what we're able to do with this technology."
NDB anticipates having a low-power commercial version on the market in a couple of years, followed by a high-powered version in about five. If all goes as planned, NDB's technology could constitute a major step forward, providing low-cost, long-term energy to the world's electronics and vehicles. The company says, "We can start at the nanoscale and go up to power satellites, locomotives."
The company also expects their batteries to be competitively priced compared to current batteries, including lithium ion, and maybe even cheaper once they're being produced at scale—owners of nuclear waste may even pay the company to take their toxic problem off their hands.
One company's waste becomes another's diamonds.
By leveraging the difference between lit and shadowed areas, a new energy source perfect for wearables is invented.
- Mobile devices used both indoors and out may benefit from a new energy collection system that thrives on mixed and changing lighting conditions.
- Inexpensive new collection cells are said to be twice as efficient as commercial solar cells.
- The system's "shadow effect" would also maker it useful as a sensor for tracking traffic.
For all of its promise, solar energy depends on the capture of light, and the more the better. For residents of sunny climes, that's great, with rooftop collection panels, and solar farms built by utilities in wide open, sunny spaces that can provide power to the rest of us. Now, though, a team of scientists at the National University of Singapore (NUS) has announced success at deriving energy from…shadows.
We've got plenty of them everywhere. "Shadows are omnipresent, and we often take them for granted," says research team leader Tan Swee Ching, who notes how shadows are usually anathema for energy collection. "In conventional photovoltaic or optoelectronic applications where a steady source of light is used to power devices, the presence of shadows is undesirable, since it degrades the performance of devices." His team has come up with something quite different, and Tan claims of their shadow-effect energy generator (SEG) that, "This novel concept of harvesting energy in the presence of shadows is unprecedented."
The research is published in the journal Energy & Environmental Science.
How it works
Image source: Royal Society of Chemistry/NUS
The energy produced by the SEG is generated from the differential between shadowed and lit areas. "In this work," says Tan. "We capitalized on the illumination contrast caused by shadows as an indirect source of power. The contrast in illumination induces a voltage difference between the shadow and illuminated sections, resulting in an electric current."
SEG cells are less expensive to produce than solar cells. Each SEG cell is a thin film of gold on a silicon wafer, and an entire system is a set of four of these cells arrayed on a flexible, transparent plastic film. Experiments suggest the system, in use, is twice as efficient as commercial solar cells.
An SEG cell's shadow effect works best when it is half in light and half in shadow, "as this gives enough area for charge generation and collection respectively," says co-team leader Andrew Wee. When the SEG is entirely in shadow or in light, it doesn't produce a charge.
Gold in them that shadows
To be sure, the amount of energy that NUS researchers have thus far extracted is small, but it's enough to power a digital watch. The researchers envision the SEG system harvesting ambient light to power smart phones and AR glasses that are used both outdoors and indoors. While such devices can run on solar batteries, solar is only replenished outdoors, and the SEG could "scavenge energy from both illumination and shadows associated with low light intensities to maximize the efficiency of energy harvesting," says Tan. It seems clear that we're on the cusp of the era of wearables — AR visionwear, smart fabrics, smart watches, and so on — and so Tan considers the arrival of the SEG "exciting and timely."
The researchers also note an additional application for which the SEG seems a natural: It can function as a self-powered sensor for monitoring moving objects. The shadow caused by a passing object would trigger the SEG sensor, which can then record the event.
Next up for the team is investigating constructing cells using other, less costly materials than gold to make them even less expensive to produce.