Slashdot Mirror

This made me chuckle: "the oil at a solar thermal plant".

The proliferation of solar thermal power plants is one of the worst-publicized success stories of the modern age. Not that there isn't tons of stuff googlable about it:

http://news.cnet.com/8301-11128_3-20012060-54.html
http://terrainforma.ca/2010/09/20/the-promise-of-thermal-solar-power-activist-and-educator-sheila-watt-cloutier/
http://climateprogress.org/2007/08/30/the-solar-power-you-dont-hear-about/
http://carbon-pros.com/blog1/2009/06/solar_thermal_at_utility_scale.html
http://venturebeat.com/2010/02/22/energy-dept-gives-brightsource-solar-thermal-a-1-4b-boost/
http://www.abengoasolar.es/corp/web/en/index.html
http://www.acciona-na.com/About-Us/Our-Projects/U-S-/Nevada-Solar-One.aspx
http://www.leonardo-energy.org/worlds-largest-solar-thermal-power-plant

This already exists. Among the many links I got from Google when searching for info about DC server power: http://www.leonardo-energy.org/dc-power-distribution-server-farms

I invite you to actually Google the things you are interested in.

High water usage is also a significant problem with Coal and Nuclear power.

The first google result i get is between 1.5 and 46.2 gal/kWh. A typical 500-megawatt coal-fired power plant draws about 8.3 billion litres of water each year.

Now put 700 nuclear plants in the deserts of Nevada. You have enough power for everyone to live at the energy consumption level of the US.

Not quite
From Wikipedia US electricity consuption per capita (2005 figures) works out to 12.8 MWh/year.

Multiply that by 6.5 billion people gives 83.2 billion MWh/year.

The US's 103 nuclear reactors' highest ever output (2004) was 788.5 million MWh.

Put the numbers together and you find you need around 10,900 nuclear reactors working at the average output for a US nuclear power stations.
Were every one of those stations to be the same design as the world's largest nuclear power station (which actually consists of 7 operating units) you'd still need 1150 of the things to match US power consumption rates.

http://www.leonardo-energy.org/drupal/node/809

Article mentions this PDF http://www.netl.doe.gov/ssl/workshop/Report%20led%20November%202002a_1.pdf from the DOE that outlines LED technology Roadmap putting LEDs at the same price of CFL lighting by 2012. Currently, LED technology is already ahead of the roadmap. www.LEDSmagazine.com

Also, in commercial spaces as it stands today. LED actually pays out in the long-term(5-10 years) when you factor in the cost of replacing the bulbs every few years. Even better, there is 0 mercury content in LED. Plus, LED is getting cheaper and cheaper every year when you calculate all the costs involved. Which leads to the idea that LED will pretty much replace 90 percent of lighting by 2012.

You will find that the current rating for 14 AWG cables (you probably wouldn't use anything smaller) is typically 18A. Granted there are some derating factors, but you'd be unlucky to have thermal overload on a 14AWG cable from a 10A fuse.

Dude, if all you worry about is thermal overload and such, you have totally missed the point.

Here is a short example... Assume a 12 volt supply. After all that is what the discussion is all about. Now again lets assume a 100 foot extension cord. Again, no problem. That's 14 AWG wire with a 200 foot round trip. Put a 10 amp load on it so we don't overheat the wire. After all overheating is the worry in your example. Pray tell, how many volts will you get to the load with a 10 Amp draw.. The heat isn't the problem. The voltage drop is the problem.

A loss of 5 volts on a 120 volt line is less than a 5% drop. A 5 volt drop in a 12 volt line is a major brownout of about 40% which is unacceptable even though the 10 amp current in the wire is the same. Feed your 12 volt laptop 12 minus 5 or 7 volts and see how well it does.

Back to the math. That 200 feet of wire has a resistance of .00297 ohms per foot or .594 ohms. At 10 amps, a safe current for a 14 guage wire, the voltage drop is 5.94 volts or just about half if you round off the 5.94 volts to 6. You could safely connect the 100 foot extension cord to a 6 volt deep cycle golf cart battery and put a dead short on the end and not overheat the wire, or blow a 15 amp fuse. The current draw would be just over 10 amps.

At 12 volts a shorted 100 foot 14 AWG extension cord would be 12 / 0.594 or only 20.2 amps. Needless to say you would never consider using a 100 foot extension cord for an 18 amp load as you would only deliver a couple volts at that current. The rest of the power would be used for heating the wire.

Anyone doing the math for a DC data center has to deal with this real math to power the load. DC distribution is not done at 12 volt. It still is delivered at a much higher voltage and is still dropped at the load with a switched mode power supply. The DC to DC supplies are more efficient than AC to DC supplies in all the computers and much more efficient than distributing 12 volts to the floor.

Here is an article on using 48 volts and the problems of going more than 35-50 feet.
http://powerquality.com/mag/power_data_center_power/
http://www.leonardo-energy.org/drupal/node/2239

Often Data Centers use 72 volts to 350 volts.
http://datacenterjournal.com/index.php?option=com_content&task=view&id=955&Itemid=99999999

575 volts is proposed here;
http://www.edn.com/blog/1470000147/post/1670020967.html

Hmmmm. Ok, so 125MW is bigger then 1Gw by your reckoning.

This is just a marketing stunt.

Quote: "Burning hydrogen is inefficient

Secondly, if hydrogen is the energy carrier of choice, then why not use fuel cells instead of an internal combustion motor? A fuel cell car needs about 14 litres of hydrogen for a 100 kilometre trip, while the BMW Hydrogen 7 needs 50 litres for the same distance. Moreover, for use as a liquid in an internal combustion engine, hydrogen has to be cooled down to -253 C. This requires an additional level of unnecessary energy expenditure. When you add all this up, the consumption rate of the BMW Hydrogen 7 corresponds to more than 20 litres fossil fuel for a 100 kilometre trip, or about the same amount as a heavy truck with diesel engine."

CC.