Vast amounts of solar energy radiate to the Earth, but tapping it cost-effectively remains a challenge

Oct 26, 2011 by David L. Chandler

With the world’s energy needs growing rapidly, can zero-carbon energy options be scaled up enough to make a significant difference? How much of a dent can these alternatives make in the world’s total energy usage over the next half-century? As the MIT Energy Initiative approaches its fifth anniversary next month, this five-part series takes a broad view of the likely scalable energy candidates.

The sunlight that reaches Earth every day dwarfs all the planet’s other energy sources. This is clearly sufficient in scale to meet all of mankind’s energy needs — if it can be harnessed and stored in a cost-effective way.

Unfortunately, that’s where the technology lags: Except in certain specific cases, solar energy is still too expensive to compete. But that could change if new technologies can tip the balance of solar economics.

The potential is enormous, says MIT physics professor Washington Taylor, who co-teaches a course on the physics of energy. A total of 173,000 terawatts (trillions of watts) of solar energy strikes the Earth continuously. That’s more than 10,000 times the world’s total energy use. And that energy is completely renewable — at least, for the lifetime of the sun. “It’s finite, but we’re talking billions of years,” Taylor says.

Since solar energy is, at least in theory, sufficient to meet all of humanity’s energy needs, the question becomes: “How big is the engineering challenge to get all our energy from solar?” Taylor says.

Solar thermal systems covering 10 percent of the world’s deserts — about 1.5 percent of the planet’s total land area — could generate about 15 terawatts of energy, given a total efficiency of 2 percent. This amount is roughly equal to the projected growth in worldwide energy demand over the next half-century.

Such grand-scale installations have been seriously proposed. For example, there are suggestions for solar installations in the Sahara, connected to Europe via cables under the Mediterranean, that could meet all of that continent’s electricity needs.

Because solar installations of all types are modular, the experience gained from working with smaller arrays translates directly into what can be expected for much larger applications. “I’m a big fan of large-scale solar thermal,” says Robert Jaffe, the Otto (1939) and Jane Morningstar Professor of Physics. “It may be the only renewable technology that can be deployed at very large scale.”

And we do know how to harness solar energy, even at a colossal scale. “There’s no showstopper, it’s just a matter of price,” says Daniel Nocera, the Henry Dreyfus Professor of Energy at MIT.

Nocera foresees a time when every home could have its own self-contained system: For instance, photovoltaic panels on the roof could run an electrolyzer in the basement, producing hydrogen to feed a fuel cell that generates power. All the necessary ingredients already exist, he says: “I can go on Google right now, and I can put that system together.” Nocera’s own invention, a low-cost system for producing hydrogen from water, could help over the next few years to make such systems cost-competitive.

In principle, we know multiple ways of generating electricity from the sun (direct photovoltaic, or solar thermal energy used to drive a turbine); of storing that energy (in batteries, by pumping water uphill, or by separating water into hydrogen and oxygen using an electrolyzer); and of converting that stored energy into electricity when it’s needed (using fuel cells powered by hydrogen, for example). Some kinds of solar power are already cost-competitive, at least in some settings, and prices have been moving steadily downward.

“Costs have come down very dramatically” for solar power, says Ernest J. Moniz, the Cecil and Ida Green Distinguished Professor of Physics and Engineering Systems and director of the MIT Energy Initiative, “but it’s still not that cheap.” And even as the price of solar panels themselves has dropped, there has been little reduction in the costs associated with installing them.

Like nuclear power, Moniz says, solar is characterized by high initial costs, but very low operating costs. But one significant advantage solar has over nuclear is “you can do it in smaller bites,” rather than needing to build multibillion-dollar plants.

Solar energy is a vibrant research topic, attracting scientists interested in many different approaches. For example, MIT researchers Angela Belcher and Paula Hammond are exploring approaches to solar power that would harness the power of biological organisms to create solar devices; Penny Chisholm and Shuguang Zhen are looking into the possibility of directly harnessing the photosynthesis done by plants or single-celled organisms; and various researchers including Vladimir Bulovic, Michael Strano, Tonio Buonassisi, Jeffrey Grossman and Yang Shao-Horn, among others, are working on ways of improving the efficiency or lowering the costs of solar photovoltaic cells.

Still others are pursuing a variety of approaches to solar thermal energy: using the sun’s heat to power turbines or to heat homes or water. A significant breakthrough in any of these areas could make solar power an economically viable option for the world’s needs. This year, for example, Alexander Slocum and others published a proposal for a solar thermal system that could provide steady, 24/7 baseload power for utility companies, helping to make it cost-competitive with other sources.

Other researchers are studying ways to make effective systems using common, inexpensive materials. For example, cadmium telluride is a very promising material for solar cells. But it turns out that tellurium, one of its ingredients, is “rarer than gold,” Jaffe says. “We need to be able to make solar cells out of common materials, or at least things that are not exquisitely rare,” he adds.


This story is republished courtesy of MIT News (web.mit.edu/newsoffice/), a popular site that covers news about MIT research, innovation and teaching.

Explore further: Shedding light on solar power

More information: Tomorrow: There are many sources that can make a contribution to our energy supply, but likely not at a major scale in the near future.

Part 1. www.physorg.com/news/2011-10-dent.html
Part 2. www.physorg.com/news/2011-10-p… ons-electricity.html
Part 3. www.physorg.com/news/2011-10-v… ar-energy-earth.html

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Jimbaloid
5 / 5 (2) Oct 26, 2011
Thats more than 10,000 times the worlds total energy use
Current energy use. When we can tap all that, we'll find new ways to use it!
ryggesogn2
1 / 5 (6) Oct 26, 2011
According to AGWites, trapping that energy is easy, release more CO2.
CapitalismPrevails
2.3 / 5 (6) Oct 26, 2011
Thats more than 10,000 times the worlds total energy use.


Divide by half to account for day side and night side and you get 5,000. Maybe divide by half again to account for cloud cover so 2,500. If you cover half of all urban areas(1.5% of the earth http://en.wikiped...and_use) you get 37.5. Times average percentage efficiency of solar panels(maybe 16%) and you get 6. So to be conservative I would say we can get 6 times our normal worldwide energy use from the sun every day.
Scottingham
1 / 5 (1) Oct 26, 2011
Can't graphene come in and save the day?
ryggesogn2
1 / 5 (3) Oct 26, 2011
1.66e 17 W at the top of the atm (~1300W/m^2)
Burnerjack
3.3 / 5 (4) Oct 26, 2011
It should be noted that Stirling Cycle engines can utilize ANY temperature DIFFERENCE to generate electrical power. It is possible to engeneer a Stirling system that provides electrical power AND hot water and/or hot air. An added benefit is their silent or nearly silent operation. Where many solar systems fail to live up to expectations is during the Winter, when its needed most. The Stirling systen EXCELS at this time as the cooler ambient temperature actually increases it's effectiveness. It's only drawback is it takes up a larger footprint than we are accustomed to.
The "Thermal exaust can be utilized for Hot water and/or hot air.
Not to shabby for a machine that has only a handful of moving parts!
Burnerjack
not rated yet Oct 26, 2011
It should be noted that an "individual" or distributed power infrastructure is almost guaranteed due to the "NIMBY" effect.
PinkElephant
5 / 5 (2) Oct 26, 2011
Current energy use. When we can tap all that, we'll find new ways to use it!
Conversely, as technology improves so does efficiency. We'll be able to do more with less.
Divide by half to account for day side and night side and you get 5,000
Why? The solar power impacting the planet by definition illuminates only the day side. And as stated in the article, that day-side illumination is equivalent to 10,000x total world power consumption. So, that's one unnecessary division.
Maybe divide by half again to account for cloud cover so 2,500
Why? Not all solar power generators require unobstructed skies. While concentrators suffer under cloud cover, photovoltaics still generate (though not at full load.) And it's doubtful that fully half of Earth's surface is covered by clouds at any given time. Never mind that the main proposal is to situate massive solar farms in *deserts* -- where cloud cover is low by definition. So, another exaggerated reduction factor.
Howhot
5 / 5 (2) Oct 26, 2011
"A total of 173,000 terawatts (trillions of watts) of solar energy strikes the Earth continuously. Thats more than 10,000 times the worlds total energy use. And that energy is completely renewable".

I've seen this statistic in comparison to other source of fuel and what the could provide in the way of man-kind's future energy needs. Oil, Gas, Coal couldn't touch solar and ran out in a 100 years or so. Nuclear was not to good, Hydro-electric, Geothermal, and wind provide renewable resources (wind is second to solar). Bio fuels interestingly enough are not as efficent as solar electric.

Bottom line is Solar is the way to go. I personally think we could really make an impact of solar electric was subsidized to convert roof tops of households and business to grid-solar on a massive scale.
Howhot
5 / 5 (1) Oct 26, 2011
"A total of 173,000 terawatts (trillions of watts) of solar energy strikes the Earth continuously. Thats more than 10,000 times the worlds total energy use. And that energy is completely renewable".

I've seen this statistic in comparison to other source of fuel and what the could provide in the way of man-kind's future energy needs. Oil, Gas, Coal couldn't touch solar and ran out in a 100 years or so. Nuclear was not to good, Hydro-electric, Geothermal, and wind provide renewable resources (wind is second to solar). Bio fuels interestingly enough are not as efficent as solar electric.

Bottom line is Solar is the way to go. I personally think we could really make an impact of solar electric was subsidized to convert roof tops of households and business to grid-solar on a massive scale.

PinkElephant
5 / 5 (1) Oct 26, 2011
Hydro-electric, Geothermal, and wind provide renewable resources (wind is second to solar)
To be clear, let's keep this in perspective: hydroelectric and wind (and to a large extent wave, and thermal gradient, and to a large extent biomass) are also forms of solar energy (just gathered via a different mechanism.) So these don't complement the overall 10,000x factor; they are in fact part of it.

Of course, fossil fuels are mostly concentrated ancient solar energy as well -- just polluting and non-renewable...
antialias_physorg
5 / 5 (3) Oct 27, 2011
Divide by half to account for day side and night side and you get 5,000.

Nope, that is already taken into account. It's 10000.

Maybe divide by half again to account for cloud cover so 2,500.

Nope, that's already taken into account by placing this in desert areas (where cloud cover is less than 1% of the year - and even then output does not drop to zero)

Current energy use. When we can tap all that, we'll find new ways to use it!

E.g. Total energy use in the US, despite a slightly rising population number, has dropped between 2004 and 2008 (only numbers I could find).

To be clear, let's keep this in perspective: hydroelectric and wind...
Depends on what type of powerplant you use. Any type of hydro powerplant that gathers energy from tides is due to the gravitational effect of the Moon (and the Sun)

The point is: The sun provides a lot of power. But there's even more power available (gravity interactions and heat from the Earth's interior)
northern_nuke
4.2 / 5 (5) Oct 27, 2011
Energy storage & transmission are the critical components. Hydrogen generation & storage storage systems in homes represents a technical challenge with real safety and liability issues. Someone has to clean those solar collectors / panels. In the desert washing them presents a problem. Spinning generators provide stability to the grid that is difficult to emulate with solid state switching. Making the distributed generation / smart grid system stable and responsive remains to be demonstrated. Real engineering is replete with challenging picky problems that visionaries seldom seem to understand, let alone estimate.
antialias_physorg
not rated yet Oct 28, 2011
. Someone has to clean those solar collectors / panels.

Have you, ever, seen anyone clean their PV panels on their roof? No? Me neither (and we have some in the family). Funnily enough they produce full output for decades (only slowly degrading due to UV).
CapitalismPrevails
1 / 5 (2) Oct 28, 2011
Antialias, that's probably because you live in an area with little dust. If you live in Arizona were their dry dirt everywhere, you can bet the farm there will be dust blowing around and dirting up solar panels.
Howhot
not rated yet Oct 28, 2011
Real engineering is replete with challenging picky problems that visionaries seldom seem to understand, let alone estimate.

So true. And we are just in the beginnings of the change to a solar powered economy. There will be political blow-back for awhile, but eventually 10-20 years, we will all be solar.

Nerdyguy
2.7 / 5 (3) Oct 28, 2011
"...10-20 years, we will all be solar." - Howhot

Color me...skeptical. I think that number is hopelessly idealistic, politics aside. I see no evidence that the technology is in place. On a personal note, I've heard this exact statement more than once over the last 20 years from a variety of figureheads.

Frankly, I'd prefer that it were, and I do believe it will continue to grow in importance over time, I just think your number is a bit progressive. How about 50-100 years, we will be "heavily" invested in solar?
Eikka
3 / 5 (2) Oct 29, 2011
you can do it in smaller bites, rather than needing to build multibillion-dollar plants.


The main reason to this problem is political, because NIMBY and irrational fear makes it so very hard to build small reactors closer to the demand, or to build any reactors at all.

Tooling up to make nuclear powerplants when you may be allowed to build only one per decade means that it has to be an absolute monstrosity to cover you for the next decade. Most of the early reactors were on the order of couple hundred megawatts, no larger than an average coal plant - but that was when they were still allowed to be built.

It's a circle of fear and failure, because smaller reactors would be inherently safer, up to the point where you could have a meltdown and nothing would come out because the materials are strong enough to hold it all in. But, people oppose reactors, so new reactors have to be made big, which makes them unsafe, which makes people oppose them.
dschlink
5 / 5 (1) Oct 30, 2011
Solar has its place. I put solar heating on a house in 1980. Worked fine, but that was in Tucson, AZ. Solar PV in Portland delivers 85% of the annual output during summer days. The rest of the time, the panels are just very, very expensive rain shelters. If I needed air-conditioning in the summer, solar might make sense; but I don't. I need heat 75% of the year.
ShotmanMaslo
1 / 5 (1) Oct 30, 2011
While some forms of solar (especially concentrated solar thermal with molten salt storage) are certainly perspective, I believe advanced nuclear is the way to go for most of our energy demand (base load). You simply cannot achieve comparable huge energy density (except for hydroelectric power, which is limited by suitable places for a dam), cost and safety per kWh produced, as well as quality of produced electricity and independence on environmental conditions (sun, wind) all at once with any alternative.

http://3.bp.blogspot.com/_VyTCyizqrHs/R9rF7NuGzXI/AAAAAAAAAPw/KcnCX7ly6gw/s1600-h/deathTWH.JPG
ryggesogn2
2.3 / 5 (3) Oct 30, 2011
The US Navy operates dozens of nuclear reactors on ships and subs with crew working and sleeping next to the reactor.
Burying the new sealed reactors under buildings would be a great way to decentralize the power grid and clear the air.
kaasinees
1 / 5 (2) Oct 30, 2011
The US Navy operates dozens of nuclear reactors on ships and subs with crew working and sleeping next to the reactor.
Burying the new sealed reactors under buildings would be a great way to decentralize the power grid and clear the air.


And a nice target for terrorists.
We can power the world longer with fossil fuels than nuclear fuel.
kaasinees
1 / 5 (1) Oct 30, 2011
Solar has its place. I put solar heating on a house in 1980. Worked fine, but that was in Tucson, AZ. Solar PV in Portland delivers 85% of the annual output during summer days. The rest of the time, the panels are just very, very expensive rain shelters. If I needed air-conditioning in the summer, solar might make sense; but I don't. I need heat 75% of the year.

But the panels also last longer because they receive less UV.
Pirouette
3 / 5 (3) Oct 30, 2011
The US Navy operates dozens of nuclear reactors on ships and subs with crew working and sleeping next to the reactor.
Burying the new sealed reactors under buildings would be a great way to decentralize the power grid and clear the air.

Nuclear warships and submarines have the added advantage of mobility, early detection and firepower against possible terrorist threats. They are also able to maintain a permanent cooling system to cool the heat from the reactor.
But burying a reactor underneath a building would depend on the location of the building. If near or on a fault line, that's a recipe for trouble. And it would have to be located in an area with plenty of water and a reservoir big enough to cool the reactor, prevent a meltdown.
On land, a combination of windmill and solar panel, IMO, would be more efficient, with windpower supplementing radiation from the sun.
Pirouette
1 / 5 (2) Oct 30, 2011
Usually, when there's cloud cover, the wind may pick up and turn the "arms" of the windmill, and after the cloud moves off, the windmill and solar panels can work "in tandem" to produce double the amount of electricity usually produced by just one or the other.
Pirouette
1 / 5 (2) Oct 31, 2011
In fact, if the windmills are big enough, say, at least 50 feet off the ground, several solar panels can be inlaid on top of them, most likely above the turbines.
ShotmanMaslo
1 / 5 (1) Oct 31, 2011
And a nice target for terrorists.
We can power the world longer with fossil fuels than nuclear fuel.


Not true, with nuclear, we can power the world for thousands of years, if the reactors were designed for efficiency.
kaasinees
1 / 5 (1) Oct 31, 2011
And a nice target for terrorists.
We can power the world longer with fossil fuels than nuclear fuel.


Not true, with nuclear, we can power the world for thousands of years, if the reactors were designed for efficiency.

Source?
ShotmanMaslo
1 / 5 (1) Oct 31, 2011
And a nice target for terrorists.
We can power the world longer with fossil fuels than nuclear fuel.


Not true, with nuclear, we can power the world for thousands of years, if the reactors were designed for efficiency.

Source?


Current reactors use simple once-through cycle, which exploits only less than 1% of available nuclear fuel energy. Nuclear "waste" still has lots of energy, which can be freed by fast-neutron reactors.
Breeder reactors (which produce more nuclear fuel than they consume) can again multiply our nuclear fuel reserves, especially the thermal breeder (which uses thorium) - LFTR.

http://en.wikiped..._reactor
http://en.wikiped..._reactor
http://en.wikiped..._Reactor
http://en.wikiped..._reactor
rawa1
1 / 5 (3) Oct 31, 2011
"...10-20 years, we will all be solar."
The cold fusion covers all needs of human civilization. The solar energy will become effective only at areas, when don't require concentrated source of energy. We should realize, even the solar energy has many hidden material and environmental costs, which we didn't solve yet - for example connected with recyclation of solar panels and it's very demanding to raw materials.
Nerdyguy
3 / 5 (2) Oct 31, 2011
@rawa1:

If cold fusion were anything beyond sci-fi, perhaps it would be valid to state that it could cover "all needs of human civilization". From that perspective, so could other technologies, like space-based solar collectors. But, none of that exists or is likely to for some time. Cold fusion? Would be nice, but it's not here.

Solar - you're quite correct, there are problems with solar. And this is a point so often forgotten. I think there's a group of people that look at nuclear/coal/oil as "scary, dangerous/anti-environmental" while looking at solar/wind/etc. as "good, green, safe".

Fact is, since our first ancestors discovered fire, every technology and energy source has a cost and presents a tradeoff of one kind or another.
kaasinees
1 / 5 (1) Oct 31, 2011
http://en.wikipedia.org/wiki/Breeder_reactor

Thats nice, they are operational in China in 2014 and 2015.
Maybe we should move to china :O

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