March 12, 2007 4:00 AM PDT

Full steam ahead for Nevada solar project

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Steam heat
Although solar thermal systems and solar photovoltaic (PV) panels both transform energy from the sun into electricity, they work in vastly different manners. PV panels, which have become very popular in the last five years, split photons from the sun into electrons and positive charges from the sun. The electrons are harvested and funneled into the electrical system of a building or the grid. In general, silicon PV panels convert 15 to 22 percent of the light that strikes them into electricity; mixing other materials into the panels can increase efficiency, but also adds cost.

Solar thermal plants are more efficient, said Cohen, with efficiencies ranging from around 20 percent to 40 percent, according to studies, in part because it's easier to extract heat from sunlight than electrons. Solar thermal water heaters--which heat water for commercial and residential buildings--rely on the same principle.

The molten salt vats also give solar thermal systems insurance against cloudy days, something that PV doesn't have. One hundred thousand square feet of molten salt holds enough heat to provide electricity for four hours.

The big drawback is that solar thermal plants can't be installed everywhere. They work best in warm, dry locations, unlike PV panels which even work well in Germany. Shadows from vapor trails and planes can curb their production. And dust is a major problem. To keep it off, a cart festooned with moist brushes that look like they came from a car wash hoses off the mirrors.

As a result, solar thermal mostly gets deployed for power plants, which cost hundreds of millions of dollars and take up hundreds, if not thousands of acres of land. An individual can put a PV system on a private home, but it will cost about $20,000. Until recently, financing for these projects has been nearly impossible to obtain. Security is a potential issue, too. Venture capitalist Vinod Khosla recently said during a panel discussion that a thermal plant occupying three percent of Morocco's land could provide Western Europe with all of its power. Maybe so, said other panelists, but that would also make it a potential target for terrorists, or even a political tool.

Solar One's location was the result of a host of factors, said Cohen. A lake about 18.5 miles away provides water to the station. Additionally, it's only 3 miles from three electrical substations. It costs about $1.5 million per mile to connect to a substation, so distance counts.

Plus, it's about the sunniest place in America.

"You have a site here that for 360 days is almost like today," Cohen said, nodding toward the bright blue sky. "We had to shut down construction three times because it was snowing. We talked to people who lived here, and they said they had never seen snow in their lives here."

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That's note how PV panels work
You stated that photovoltaics "split photons from the sun into electrons and positive charges from the sun." What you're describing here is a Pair-Production event, which only occurs with gamma rays above a 1.022 MeV threshold. This interaction produces a positron-electron pair, each with a rest mass of 0.511 MeV plus a combined kinetic energy equal to the energy of the incident photon in excess of the threshold energy.

Photovoltaic panels work by means of the photoelectric effect. In this interaction photons simply knock electrons off a metal surface when the incident photon energy is greater than the work function of the metal. The photoelectric effect is most prevalent in high-Z materials and low-energy photons with frequencies above the threshold value. Thus, ultraviolet radiation from the sun is ideally suited for this application.
Posted by gatornuke (27 comments )
Reply Link Flag
meant to say "not"
... and it doesn't appear that cnet allows you to revise comments.
Posted by gatornuke (27 comments )
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Wouldnt solar energy heat the planet?
If you're trapping on Earth solar energy that largely would have been reflected back into space... wouldnt large scale use of this technology warm the planet as the energy balance gets out of whack?

We'd probably have to offset that change to planetary albedo somewhere else.
Posted by LuvThatCO2 (187 comments )
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This is no different than a conventional Rankine cycle power plant. It's the same stuff you'll find in a Nuclear, Coal, or oil-fired plant, the only difference is that the heat to make steam comes from the sun... at the outrageously expensive price of 15 c/kWhr, but that's besides the point.
Posted by gatornuke (27 comments )
Link Flag
The heat energy that is trapped is converted to mechanical energy in the steam turbine which is then converted to electrical energy. The heat energy is not dissipated into the atmosphere. The enrgy converted to electricity would most likely be equal to or greater than the energy that would have been reflected back into space had the sunlight hit the surface of the Earth. So it would NOT heat up the Earth. Also this type of power plant would displace a need for a fossil fuel burning plant that releases large quantities of greenhouse gases. The only difference between a solar thermal plant and a coal, gas or a nuclear one is where the heat comes from.
Posted by baike (39 comments )
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Yeah, the same way that...
opening the refrigerator door cools off the room.
Posted by Hardrada (359 comments )
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Prolly not
It's true that you would be storing energy that would have been otherwise reflected, However it's probably way less energy being added to our surroundings then say nuclear energy or burning fossil fuels would release.
Posted by iwarp62 (2 comments )
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Power for Los Vegas?
You mean the city next to the Boulder dam that gets loads of inexpensive hydro-electrical energy?

What kind of numbskull decided that was a place needing more electricity?
Posted by HandGlad2 (91 comments )
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Las Vegas, yes.
Vegas is indeed one of the fastest growing cities in the nation. (Gambling aside, even.) Pretty much the whole country is on the same grid. The juice doesn't have to be consumed in Vegas, it can be used to alleviate the load of power plants that normally supply LA or Phoenix, or anywhere else in the region.

Remember the blackout of the north east in about 2003? The grid is huge.
Posted by qwiji (3 comments )
Link Flag
Probably the same "numbskull" that looked at the power needs of Las Vegas and realized that they were SEVERELY under supplied already with an expectation of power demand to go up 40% in the next 10 years.

The Hoover Dam has a peak power generation of ~2,000MW. Las Vegas has a current peak demand of ~5,600MW, and that demand is expected to hit ~8,000MW by 2015. Even if demand stays constant and Las Vegas were to get 100% of the energy production from the dam it would still be supplying less then half of what they need.
Posted by Hoser McMoose (182 comments )
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Numbskulls that know that only about 24% of the electricity generated at Boulder/Hoover dam is slated for Nevada and the other 76% is distributed all over the Southwest. In fact, Southern California receives more power from the dam than Nevada.
Posted by adlyb1 (123 comments )
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The drawback of renewable energy...
Well, I don't think the designers picked Las Vegas because of where the demand for electricity is... I don't think this "solar power plant" would be very effective if it were located near, let's say, Seattle.

The drawback of generating electricity from the sun is that you need, well, the SUN to be shining...

The only way renewable energy production can ever be practical is for locations "rich" in natural renewable energy (sun, wind, or water) to produce and share their extra energy with other locations, which, thankfully, is accomplish thanks to the power grid...

The size of the modern power grid is such that variations in weather patterns are evened out, and it will always be sunny, windy, and rainy in at least some parts of the area covered by the grid...
Posted by GMonR (9 comments )
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Las Vegas Is A Waste
Las Vegas, a city in the desert that greedily consumes all available water, energy and lives. The desert IS the right place to put a solar energy production facility. It's definately the wrong place for large populations of humans.

The whole South West is a problem. If Global Warming is truly accelerating, the SW will dry up completely. As a resident of MI, I will fight to the death to keep the same money-grabbing multinationals who have lived fat on oil from building pipelines to shunt our Great Lakes South, just so a bunch of STUPID, Gluttenous, Gamblers/Retirees can have their "paradise" in the sun!

Let's face it people. If we truly had the will to put all the resources we now pour into NASA, the D.O.D. and Entertainment into developing a self-supporting green society, we could be completely free of our dependence on non-renewable energy within 10 years or less! Heck, if we pulled our collective heads out of our @$$, we could wipe out hunger, poverty and crime while we were at it!

As long as greed is the primary motivator for human echievement, all we will ultimately achieve is our own destruction. JCW 2007
Posted by westrajc (78 comments )
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If you look at time lapse pictures of said dam, I believe the level of water in Lake Mead behind the dam has dropped significantly since it went on line as a hydro plant. I don't know the time frame, but I believe experts are afraid that in the very near future there will not be enough water to create the necessary head pressure to spin the turbines. The need to replace this power supply will need to be addressed very soon. The transmission lines are already near by (because of the hydro plant) so it's a logical place to start. Cuts down the cost of running new lines from another site to Las Vegas. Just a thought.
Posted by weeze345 (1 comment )
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solar power
is the way to go but you are not thinking outside the box

thirty volt power for houses will be easer to produce with solar

or it the electric company is afraid of electricity theft 60 or 90 volts with a drop down in power to the home to thirty volts

there are benefits to this including safety
with technology to catch up and each house may be able to produce own energy

taboo for electric companies
Posted by willtr2 (1 comment )
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thirty volts ? would any appliances that everyone already owns run at 30 volts? i dont think so. so what then get converters or just'throw away' the appliances and get new 30 v. ones?
Posted by hogi90 (4 comments )
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why 30v? is that what solar panels put out usally or what?
Posted by hogi90 (4 comments )
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LV Hydro-power?
Doesn't Las Vegas get all of it's electricity from the nearby Hoover
Dam Hydro-Power & Colorado River?

Hydro-power is GREEN renewable energy source too.

Green is GREAT & I am all for it, but I am missing something here?

Good idea with vast amount of solar energy in Las Vegas Nevada.
Posted by Llib Setag (951 comments )
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Just becasue they build a power plant some place does not mean the power it genertaes is for that place. California gets a lot of its power from Nevada
Posted by juno_sun (1 comment )
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Photons, electrons, and square feet
"PV panels ... split photons from the sun into electrons and positive charges from the sun."

The photons actually liberate electrons from the material and set them in motion, creating negative and positive charges that then ripple through the material. In other words, electrons are simply pushed along the electrical circuit using the energy provided by the photons. Electrons aren't created.

"One hundred thousand square feet of molten salt holds enough heat to provide electricity for four hours."

I don't understand how much molten salt this is. Should this be cubic feet? Or is there some amount of depth to this 100k square feet to give us an actual volume?
Posted by fastolfe00 (5 comments )
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I think the solar panel connected to water pump to produce electricity was already outdated. Have anyone see a Japanese version of solar power eledtricity? The solar panels was conected to rechargeable battery cell, then connected to the transformer, then to the meter then to the switch panel, strong enough to power the electricity for the house, a commercial complex. The same sesign can be use to power electric cars.
Posted by rolyb (5 comments )
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