The ancient Romans called it Sol; the Greeks, Helios. Its gods were plentiful in Greece, they worshipped Apollo, the Norse had Freyr, and the Incas paid homage to Inti. Icarus was said to have tried to fly there, but his wings melted long before he arrived. The sun is the star of our solar system and the source of almost all forms of energy on Earth. Plants use sunlight to grow. Wind is generated by temperature differences in the air. Waves form from wind over long stretches of ocean. And the sun’s rays evaporate water from the oceans, which returns as rain and give us hydropower.
Fossil fuel itself is really just stored solar energy, since natural gas, oil and coal are derived from the remains of things that lived long ago. Even the uranium atoms that power our nuclear reactors were created when a sun much larger than ours exploded in a supernova. The sun is a nuclear furnace, the size and strength of which beggars the imagination almost a million miles (1.6 million kilometres) across, with an internal temperature that exceeds 27 million F (15 million C). Even on the surface, it’s still a scorching 9,000 F to 11,000 F (5,000 C to 6,000 C).
Stars are one of the only natural phenomena powerful enough to forge matter itself. Most larger atoms – including those that make up human flesh – are formed by the nuclear might of a sun.
Giant explosions regularly burst outward from the sun’s surface, shooting out fiery tentacles that stretch for millions of miles. Only a tiny fraction of the sun’s energy reaches our planet, in the form of photons. These tiny particles fly through space at the speed of light for a full eight minutes, covering a distance of 93 million miles (150 million kilometres). And they deliver an astounding amount of energy when compared to what we need to power our entire civilization.
According to David Faiman, a professor at Israel’s Ben Gurion University Solar Energy Center, “A square yard of desert absorbs as much energy over a year as you can get out of a barrel of oil.” That’s nothing to sneeze at. And it means that an area of desert the size of tiny Connecticut absorbs enough energy to replace the entire oil output of the OPEC countries8 (that annoying oil cabal). We fight wars over oil, yet the Arizona desert sits peacefully under an American sky. Solar energy that can deliver huge amounts of power is not science fiction. This technology is available today – a fact that’s already been proven by projects the world over.
I remember quite vividly as a child my father gesturing to the expanse of gravel that was our driveway. “Enough sun lands here to power our house, if we could only grab it,” he’d exclaim. We settled for winding black pipe on the roof and attaching it to the pump that heated our pool. It may sound primitive, but the water that jetted out of there was often too hot to touch. We’ve come a long way since then – there are now lots of ways to grab the sun’s energy. Long gone are the days of simple black tubes, or toy-like solar panels that captured just enough energy to power a radio or flashlight.
In the Mojave Desert, fields of reflective troughs and parabolic dishes cover the ground, tracking the desert sun. In Spain, giant mirrors cover the ground for acres, focusing the sun’s rays on a giant tower, generating heat so intense, it melts salt.
In Australia, they plan to construct the world’s largest tower, a “solar chimney.” These solar projects store energy and keep producing electricity well into the night. Germany is well on its way to covering its rooftops with highly efficient solar panels. Europe plans projects in the northern African desert, big enough to power all of the UK. It doesn’t stop there …
Developing large-scale solar energy is even cost-competitive with developing the tar sands of Alberta, Canada, the world’s largest – and dirtiest – oil reserve.
Solar power is big, and tomorrow, it will get even bigger. Literally. We must think big about solar power the way we used to think about securing Gulf oil, saving the world banking system or going to the moon. And thinking big is not just about big projects, but lots of them.
Give a kid a magnifying glass on a sunny day and you’re asking for trouble. From time immemorial, magnifying or concentrating the rays of the sun has served as both boon and bane.
The Chinese first used mirrors to light fires back around 700 BC. In ancient Greece, Archimedes was said to have used soldiers’ shields as a giant mirror, reflecting sunlight onto Roman ships and setting them on fire. While this tale may seem more tall than true, the Greek Navy did confirm some wars back that 60 mirrors could indeed ignite a wooden ship from a distance of 165 feet (50 metres).
Italy was once a solar pioneer (though it’s now fallen behind in the solar race). During construction of the Santa Maria del Fiore cathedral in Florence, mirrors were used to melt copper. And no less a figure than Leonardo da Vinci foresaw the power of concentrated solar, evidenced by drawings in his famous notebooks.
Today, concentrated solar is serious business, commonly generating temperatures hot enough to melt bricks and even salt. The heat captured is used to generate electricity, and with means to store that heat now being developed, the electricity will flow long after the sun goes down.
Are the experts excited about concentrated solar thermal? You bet. “This is just so obvious it’s going to be huge,” says Terry Collins, the Thomas Lord Professor of Chemistry at Carnegie Mellon and director of the university’s Institute for Green Science. “It’s going to completely change the country.”
There are three common ways of concentrating the heat of the sun. This is a stony of the trough, the tower and the dish – with a dash of molten salt.
During the OPEC oil crisis of the 1970s, when Jimmy Carter wore sweaters in the White House to conserve energy and put solar panels on its roof, I had a science teacher who came to class one day with what he called the “solar hot dog cooker.” A hot dog lay skewered inside an open tube, or parabolic trough – a special shape that reflected light from the open top along the same line as the hot dog. It took hours to cook and was more novelty than stove, but my old teacher had the right idea.
Today, an Israeli company called Solei Inc. is building some pretty serious troughs – ones that could vaporize a hot dog. The Mojave Solar Park, expected to be operational by 2011, will be the largest solar thermal electricity plant in the world. Eventually, it will cover nine square miles, and employ 1.2 million mirrors and 317 miles of vacuum tubing. At Solei, they think big. With an estimated cost of $2 billion, the Mojave Solar Park (contracted by Pacific Gas and Electric) can generate 553 megawatts of electricity, or half a medium-sized coal plant – more than enough to power half a million homes.
Existing parabolic fields in the Mojave Desert – at Harper Lake, Kramer Junction and Daggett – have been in operation for years, generating enough power for more than 350,000 homes and reducing California’s annual oil consumption by two million barrels. The Mojave Solar Park is simply the latest, largest and most modern project out there. Add it to the mix, and these parabolic solar farms alone replace over 3.5 million barrels of oil annually.
How does it work? High-tech reflective silver coatings cover the surface of long lines of massive parabolic troughs that are many times taller than the people who built them. Each trough tracks the sun, so that the sunlight reflects onto a tube containing an oil-like fluid, which heats to around 750 F (400 C). The fluid passes through a heat-exchanger that draws heat from the oil and uses that heat to turn water into steam, which in turn powers a turbine.
Andasol One, Europe’s first parabolic trough plant, went online in November 2008 near Granada, Spain. The Spanish have also figured out a way to store the heat produced during the day, in a kind of molten salt mixture. That heat is released at night or when it’s cloudy, almost doubling the amount of time the plant produces power.
Simple – make some heat with a hot dog cooker. Boil some water. Spin a wheel. Or, if you’re really ambitious, add another step: Make some heat. Put some of it into a thermos. When you need it, open the thermos.
The key to efficiency is the reflectivity of the surface coatings, the absorption of the heat-carrying tube, and the tracking of the sun. In other words, bounce lots of photons from the trough onto the tube, where they stick. As coating technologies improve, they will be applied to existing parabolic fields – over the past 10 years, output of the older Mojave Desert plants have increased by 35%.
A big advantage of this type of plant is that there are no hard-to-find materials and no bottlenecks in the supply chain. According to Avi Brenmiller, the CEO of Solel, “The raw materials we are using – glass, metal, cement – are commodities. There are almost no limits to the amount we can use.” What this really means is: We can build as many as we want, and fast. We could cover the desert in these things long before we could get another nuclear plant built or find a new patch of offshore oil.
Ease of large-scale supply applies equally well to the following two processes – the tower and the dish.
Archimedes may or may not have managed to set Roman ships on fire with his soldiers’ shields, but deep in the New Mexico desert sits a facility that takes the science behind his legendary attempt seriously. And they’d have no problem lighting a fire or two.
Sitting next to an abandoned bombing target is the National Solar Thermal Test Facility, run by the US Department of Energy. Eight acres of mirrors (called heliostats) track the sun and aim their beams at a looming concrete tower 200 feet tall. An object placed in the path of that beam of concentrated sunlight would reach temperatures of more than 4,000 F (2,200 C).
How does it work? Tubes inside the tower are filled with molten salt that carries the heat away – much like the oil in the parabolic troughs, but far hotter. And like the troughs, the molten salt heats water, creates steam and turns a turbine.
What a sight – sometimes when there’s dust in the air, the concentrated light is so intense, the air itself seems to glow brightly, and a halo of sorts surrounds the tower. Virtuous power, indeed.
That facility has spawned a number of spin-offs, including two installations in the Mojave Desert that date back to the 1980s and ’90s. Two other spin-offs sit side by side in Spain and produce power for more than 30,000 homes.’ A third project, called Solar Tres, will have 1 5 hours of storage and drive a turbine that can power 17,000 homes. The storage thermos for Solar Tres will hold over 6,000 tons of molten salt. And there’s more coming.
Where is all this going? A solar tower with 12 hours of storage, capable of powering 100,000 homes, would take up 1,000 acres of land. In the US southwest alone, there are millions of acres just sitting empty. A plant like this would cost around $100 million, and with economies of scale would be cost competitive with coal – that’s only $1,000 per powered home.
The Stirling Sun Catcher looks like something designed to scan the skies for signals from extraterrestrials or eavesdrop on the conversations of dodgy military regimes. It’s neither. Instead, this bunch of large parabolic mirrors is the heart of a sunlight engine.
How does it work? The dish works like other concentrating technologies: Large areas of sunlight are focused on a single point, and the heat is used to generate electricity. Instead of heat-transferring liquid, though, the target is the Stirling engine, an external combustion engine that burns sunlight instead of petroleum.
Unlike the internal combustion engine under the hood of your car, which harnesses the power of a controlled explosion inside the engine’s cylinders, the Stirling engine uses heat generated outside the cylinder to heat the expanding gas. The heat here is sunlight. Hence, it is, quite literally, a sunlight engine. The engine drives a turbine, and you know the rest of the story.
What’s great about this technology is its efficiency. Parabolic dish solar power was, until recently, the record-holder for most efficient conversion of sunlight to electricity, at 31%.10 Though it was recently beaten by modern photovoltaic (PV) cells (see the next section), it still holds the record for concentrated solar thermal electrical generation.
Another advantage is that the dishes are modular – you can run just one to power a neighborhood or small building,11 or build a massive field of them, or anything in between.
Stirling Energy Systems (SES) plans some big, utility-sized fields. SES Solar One in the Mojave Desert will be run by Southern California Edison Co., producing power for 500,000 homes to start, and scaling up to just under a million.12 SES Solar Two, in California’s Imperial Valley, will be run by San Diego Gas & Electric and will start by producing enough power for 300,000 homes, again scaling up to close to a million.
These are big fields, capable of powering a small city. Between 12,000 and 36,000 of these SunCatchers, each over 35 feet (11 metres) in diameter, will cover several thousand acres13 of the desert floor. An equal number of Stirling engines will drink that sunlight, converting it to electricity and feeding the grid.
To put this into perspective, these first stabs at big solar are already roughly equivalent to a medium-sized coal plant.
Jimmy Carter put them up, and Ronald Reagan tore them down. Now it looks like the Pope wants in on the action. The roof of Nervi Hall in Vatican City is now covered with 2,400 solar photovoltaic (PV) cells, the Vatican’s vote for solar. The American military, for its part, has weighed in with a field of them at Nellis Air Force Base in Nevada. Solar PV is what most people think of when they think of solar energy – the kind of panels that power our calculators.
How does it work? Electricity is a stream of moving electrons – tiny charged particles that orbit the nucleus of an atom like planets around the sun. Solar PVs are normally made from silicon, with more advanced materials on the way. They’re built so that the incoming photons knock electrons out of their orbit. Those electrons are sucked away by an electromagnetic field, generating an electric current. The record for efficiency – how much of the sun’s energy is converted to electricity was set by researchers at the University of New South Wales, Australia, at 25%.
Later generations of PVs will be able to capture more of that sunlight. Spark Solar of Australia is using multidimensional surface structures designed to capture more wavelengths of light (or energy of photons). New cell designs can convert over 40% of the sunlight to electricity. The next generation of PVs will also be thinner, bendable and incorporated into building structures. One day, the shingles on our rooftops will help to power our homes.
There’s a real treat on the horizon here. Take those high-tech, next-generation solar cells and combine them with a bunch of mirrors or magnifying glasses. Voila – concentrated solar PV! A tiny California-based company called GreenVolts is doing just that. Its device, called the CarouSal, is made up of 172 mirrors that track the sun, magnify its light 625 times, and focus it on a superefficient, next-generation PV cell. Morgan Solar uses an injection-molded Plexiglas optic, instead of a lens, to guide sunlight onto the cell. Morgan’s power could be far cheaper than coal.
Solar PV is promising because enormous amounts of energy can be produced by millions of individual panels, on millions of individual roofs. Power to the people!
Those little projects add up, but you have to give people a reason to do it. Germany is awash in solar PV. In 2007 alone, enough solar PVs were installed on farms and houses throughout the country to power more than 1.2 million homes. Why? Germany provides generous incentives – called feed-in tariffs – to homeowners who install them. Feed-in tariffs pay you for the electricity you produce, and Germany has shown just how effective they can be.
Why are these incentives so effective? In the words of Terry Tamminen, former chief policy advisor to California Governor Arnold Schwarzenegger, the model “turns farms, homes and business into entrepreneurs.” Solar PV lets all of us compete with the utilities.
Stopping at a solar energy store on a camping trip one year, I bought what was touted as a “solar energy shower” – a black plastic bag you filled with lake water and hung in a tree for a few hours. Pricey for a bag and a bit of hosepipe, but it worked.
That’s the basic idea behind the solar collectors that sit on rooftops to provide domestic hot water. Such systems are normally supplemented by another form of heat particularly in northern countries during the winter months – but collectively, they can add up to an awful lot of energy.
How does it work? The most common method is to pump liquid through a black, insulated panel that faces the sun. When the liquid gets warm enough, it’s returned to a heat-exchanger in the hot water tank. Doesn’t sound like much, but remember that the hot water you use starts at around 54 F (12 C), and every degree counts. Even in a notoriously cloudy – and often chilly country like the UK, these systems can provide about half the power required for domestic hot water.
Because these are small systems that anyone can install, the real strength of this energy source is when you add them all together. Back in 2001, there were already almost 72 million square yards (60 million square metres) of these panels installed worldwide.
How much energy pours out of these? It’s hard to say with any precision, but even a conservative estimate would come in at an energy equivalent of more than 28 million barrels of oil a year.14
Commercial-scale systems on hospital and hotel roofs are common, and can provide energy more cheaply than natural gas. Companies like Mondial Energy in Canada are installing arrays of these solar panels at no cost to the building owner, and charging them like a utility.
You can even use the warmed water to heat the building itself. These things are a no brainer.
We all know that heat rises. That’s why our attics are hot and our basements cool. Seems pretty benign as an energy source, but a company in Australia doesn’t think so. The people behind Enviromission think big – big enough to make that rising air a significant source of energy.
Enviromission plans to build the world’s tallest structure – a giant, hollow chimney that will soar 2,600 feet (800 metres) into the sky. Rated at enough power for more than 200,000 homes and costing an estimated $700 million, the chimney would tower over the desert and be surrounded by a 1.5-mile-wide (2.S kilometres) greenhouse canopy, open at the outer perimeter.
How does it work? The sun heats the air in the greenhouse, which fights to get up the chimney. That creates a thermal wind, driving turbines located around the chimney’s base. Thanks to the sheer scale of the structure, the air could reach speeds of close to 30 miles per hour (50 kilometres per hour). It’s possible to operate this sort of structure at night, and this time, the “battery” is warm ground, made black to absorb heat all day and release it at night.
Sound far-fetched? The sheer size of the project is indeed audacious, but the concept has been proven with a successful small-scale pilot plant in Manzanares, Spain. It was a collaboration between the Spanish government and a German civil engineering company, Schlaich Bergermann and Partner. The plant operated for seven years, between 1982 and 1989, and consistently generated around 50 kilowatts of clean energy.
There are advantages to this sort of solar. Aside from the turbines, it’s entirely passive – it just sits there doing its thing. It may only convert 1.3%15 of the sunlight to electricity, but it has a relatively high capacity factor of 40% to 5O%. 16
The key to this technology lies in the cost of building and operating the chimney. If it can be built cheaply enough to compete with other solar technologies (and it looks like it can), it may well spring from the drawing board to a desert near you.
All you have to do is think big. The American southwest can produce solar at much the same level as the northwestern US and Quebec produce hydroelectricity. Australia could stop burning coal in quick order. Even Europe can incorporate huge amounts of solar.
Here’s what thinking big can get you: A group called Trans-Mediterranean Renewable Energy Cooperation (TREC) has developed a plan they call the DESERTEC concept.
The key is to build a transmission “super grid” based on high-efficiency direct current (DC) lines (see Energy Internet page) that connect the North African and Middle Eastern deserts with Europe. Then cover those deserts with solar farms.
The European Commission’s Institute for Energy has confirmed what I alluded to earlier: Just 0.3% of sunlight from these deserts could power all of Europe. That’s an area the size of Massachusetts! Pay the countries sitting on the deserts to put up massive solar farms, each enough to power between 50,000 and 200,000 homes, and feed those megawatts back to Europe.
This is not an idea resting on the loony fringes. British Prime Minister Gordon Brown and French President Nicolas Sarkozy have both expressed support, and the international research team has cooperated with the likes of the German Aerospace Center to make it happen. Plans are already afoot for undersea cables to Sicily and Spain. Costs for the initial lines are in the order of $60 billion.
How big can this get? Scientists working on the project estimate that by 2050, solar farms in North Africa could produce enough power for 100 million homes,” at a total cost of half a trillion dollars. Put a similar amount of money into the American southwest, build an American supergrid, and you’d get similar amounts of power. You might even get more, since the grid doesn’t have to cross a sea. You could even use the power to make hydrogen to run cars and trucks.
Want to think even bigger? According to Solel, solar thermal plants built on just 1% of the surface of the Sahara could provide the entire world’s electricity demands.
lt is often claimed that the only energy solution big enough to satisfy North America’s growing energy appetite is the tar sands in Alberta, Canada. The tar sands are massive deposits of a tar-like substance that is mined, melted and refined. The process is notoriously dirty, not to mention ridiculously expensive. It turns out that large-scale solar energy is highly competitive with the tar sands, and dollar for dollar, we could get the same amount of clean energy from solar as we could from melting all that tar.18
Bottom line? There’s no reason the sun couldn’t fill up to half of our primary energy needs – heat, electricity, even hydrogen for our cars – if we just think big enough. Filling a quarter of all our energy needs is a conservative estimate.
But all solar requires sun, and there’s the rub: It isn’t always shining, and isn’t always near the places that need the power. It also costs a fair bit, but that can be solved with mass production.
Concentrated solar requires lots of hot, direct sunlight, even with a giant thermos to store the energy. So the technology is limited to sunny, desert areas. The American southwest, Spain, the Australian outback, the Sahara, the Middle East – these are all great spots. New York City, London, Paris – not exactly prime solar real estate. The solution is to get the power to the cities that need it. Grid connections are expensive, but they aren’t exactly rocket science.
Solar PV operates on cloudy days, but at reduced output. The energy can generally be stored in batteries, which are always improving, and could include hydrogen production (see Energy Internet page). But solar PV is limited in two other ways. Manufacturing bottlenecks have already appeared, because there are only so many factories capable of producing the wafers. It’s also the most expensive form of solar – costs need to come down significantly. With advanced manufacturing techniques and mass production incentives, these problems can be overcome.
As for solar hot water, that, as I said earlier, is a no-brainer. From Mexico City to Toronto to Paris, it can contribute significant energy by offsetting natural gas or electric heat.
Solar is already fast becoming cost competitive with coal-based production. With economies of scale, lower capital costs and a price attached to emitting carbon, solar is clearly positioned to compete with our dirtiest source of electricity.