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Old 2013-08-21, 01:11   #23
kladner
 
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Quote:
Originally Posted by chappy View Post
And what I can tell you from personal experience is that DC hurts when it bites you. But don't those Thyristor stacks (DC voltage Valves!) look awesome?
Not only does the plate voltage of a tube hurt if you bump into it, but leaving skin on metal edges as you involuntarily yank your hand out of the chassis is no picnic, either.

However, there are ways that AC can be worse. My late brother did sound and lighting installations which involved running wires through various areas such as above suspended ceilings. This was often done with a long, telescoping "fishing rod" to which you attached the end of the wire, or a cord for pulling wire.

One time, he was up on a metal ladder, shoving through above a ceiling, and his pole ran into 240 VAC which some idiot had left exposed. A characteristic of AC in this range of voltage is that you may clamp on through muscle spasm and not be able to turn loose. This happened to him. I saw him later and he was moving very painfully. This was not directly because of the shock. Rather, he was unable to let go. He said that it took real concentration and self-control to rock the ladder enough to make it fall over. This caused him to fall on his side on the stairs leading to the night club dance floor, from perhaps twelve feet up.

Some of you are probably familiar with "The Bricklayer's Tale/Lament/Accident Report." It involves a related sort of mishap.
http://www.whiteblaze.net/forum/arch...p/t-10209.html
I am pretty sure that a recording I have heard of an older British gentleman recounting this sad story, ended with "I respectfully request sick leave."

Well wouldn't you know.....
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Old 2013-08-21, 01:16   #24
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I think this is a pro-HVDC way to phrase it "in the area of twice as efficient" .....
That was actually my hedging statement of something imperfectly remembered, which I did not at the time feel like tracking back to. But I suppose that I am somewhat partial to the concept of HVDC. For one thing it has a nice ironic reversal component, given the battle between Edison and Westinghouse over DC versus AC respectively, which Westinghouse won.
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Old 2013-08-21, 01:56   #25
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I'm pro-DC as well, despite working at a magnet-spinning factory.
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Old 2013-08-21, 02:37   #26
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...and yes, large, high voltage structures of many sorts are amazing sculptures, and quite awe inspiring.
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Old 2013-08-21, 14:22   #27
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As a data note, here is the current state of battery storage:
Japan Solar Energy Soars, But Grid Needs to Catch Up
Quote:
World's Largest Battery

To address the issue of integrating solar energy onto the grid in Hokkaido, METI said it has set aside 29.6 billion yen (US$294 million) to install a large storage battery at Hokkaido Electric's Minami Hayakita substation by March 2015 to stabilize the flow of solar power onto the grid. By installing the new battery, expected to be the world's largest with a storage capacity of 60 megawatts, the regional utility will be able to receive an additional 10 percent more electricity. (It would be nearly double the size of the largest battery currently operating in the world, at 36 megawatts, installed in 2012 in China to help integrate renewable energy onto the grid in Zhangbei, Hebei Province.) (See related quiz, "What You Don't Know About Batteries.")

But the installation alone provides no fundamental solution, and the ministry said it "will continue to ask business enterprises to seek locations other than Hokkaido for large-scale solar power plants."
An earlier paragraph describes the rapid growth of solar installation in Japan
Quote:
Domestic photovoltaic module shipments were up 271.3 percent compared to last year, according to the Japan Photovoltaic Energy Association. U.S. research firm IHS predicted the Japanese photovoltaic market would surpass Germany as the largest solar revenue market with 120 percent growth this year, installing more than 5 gigawatts of new capacity, with projects more than 2 megawatts in size being the major driving force behind the triple-digit growth rate. Bloomberg New Energy Finance predicted that such commercial and utility-scale projects would boost solar installations to a range of 6.1 gigawatts to 9.4 gigawatts in 2013, making Japan the largest solar market in the world after China.
The rest of the article is about problems, politics, infrastructure, background of Japan's nuclear situation, etc.
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Old 2013-08-21, 15:48   #28
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That is, of course, a 60 megawatt-hour battery (a 'redox flow' battery, whatever those may be).
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Old 2013-08-21, 16:26   #29
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Quote:
Originally Posted by fivemack View Post
That is, of course, a 60 megawatt-hour battery (a 'redox flow' battery, whatever those may be).
A corresponding Bloomburg article, Japanese Battery Trial Seeks to Transform How Grids Work: Energy, has this on a photocaption:
Quote:
A member of the media walks past a redox flow battery at Sumitomo Electric Industries Ltd.'s plant in Yokohama, Japan. The Hokkaido project gives Japan and Sumitomo a chance to showcase the vanadium redox flow technology to utilities around the globe that need to integrate renewables into the grid.
http://en.wikipedia.org/wiki/Vanadium_redox_battery
Quote:
The vanadium redox (and redox flow) battery is a type of rechargeable flow battery that employs vanadium ions in different oxidation states to store chemical potential energy. The present form (with sulfuric acid electrolytes) was patented by the University of New South Wales in Australia in 1986. [2]
[...]
There are currently a number of suppliers and developers of these battery systems including Ashlawn Energy in the United States, Renewable Energy Dynamics (RED-T) in Ireland, Cellstrom GmbH in Austria, Cellennium in Thailand, Prudent Energy in China[6][7][8], Sumitomo in Japan and H2, Inc. in South Korea[9]. The vanadium redox battery (VRB) is the product of over 25 years of research, development, testing and evaluation in Australia, Europe, North America and elsewhere.

The vanadium redox battery exploits the ability of vanadium to exist in solution in four different oxidation states, and uses this property to make a battery that has just one electroactive element instead of two.

The main advantages of the vanadium redox battery are that it can offer almost unlimited capacity simply by using larger and larger storage tanks, it can be left completely discharged for long periods with no ill effects, it can be recharged simply by replacing the electrolyte if no power source is available to charge it, and if the electrolytes are accidentally mixed the battery suffers no permanent damage.

The main disadvantages with vanadium redox technology are a relatively poor energy-to-volume ratio, and the system complexity in comparison with standard storage batteries.
[...]
Applications

The extremely large capacities possible from vanadium redox batteries make them well suited to use in large power storage applications such as helping to average out the production of highly variable generation sources such as wind or solar power, or to help generators cope with large surges in demand.

The limited self-discharge characteristics of vanadium redox batteries make them useful in applications where the batteries must be stored for long periods of time with little maintenance while maintaining a ready state. This has led to their adoption in some military electronics, such as the sensor components of the GATOR mine system.

Their extremely rapid response times also make them superbly well suited to UPS type applications, where they can be used to replace lead–acid batteries and even diesel generators.

Last fiddled with by only_human on 2013-08-21 at 16:33 Reason: added link to Bloomberg article
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Old 2013-08-21, 17:48   #30
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Quote:
Originally Posted by kladner View Post
...and yes, large, high voltage structures of many sorts are amazing sculptures, and quite awe inspiring.
I thought the 150 kV mercury arc valve was pretty damned impressive, too. (Larger image file at link.) It's almost like a pipe organ.
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Old 2013-08-21, 19:59   #31
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This topic really has my interest at the moment. Here is an informative segment of the linked article which discusses advances in DC>AC conversion.
Quote:
Widely used in motor drives since the 1980s, Voltage-source converters started to appear in HVDC in 1997 with the experimental Hellsjön–Grängesberg project in Sweden. By the end of 2011, this technology had captured a significant proportion of the HVDC market.
The development of higher rated insulated gate bipolar transistors (IGBT), gate turn-off thyristors (GTO) and integrated gate-commutated thyristors (IGCTs), has made smaller HVDC systems economical. The manufacturer ABB calls this concept HVDC Light, while Siemens calls a similar concept HVDC PLUS (Power Link Universal System) and Alstom call their product based upon this technology HVDC MaxSine. They have extended the use of HVDC down to blocks as small as a few tens of megawatts and lines as short as a few score kilometres of overhead line. There are several different variants of VSC technology: most HVDC Light installations built until 2012 use pulse width modulation in a circuit that is effectively an ultra-high-voltage motor drive. Current installations, including HVDC PLUS and HVDC MaxSine, are based on variants of a converter called a Modular Multi-Level Converter (MMC).
Multilevel converters have the advantage that they allow harmonic filtering equipment to be reduced or eliminated altogether. By way of comparison, AC harmonic filters of typical line-commutated converter stations cover nearly half of the converter station area.
With time, voltage-source converter systems will probably replace all installed simple thyristor-based systems, including the highest DC power transmission applications.[5]
http://en.wikipedia.org/wiki/High-vo...ters_.28VSC.29

This, and the following section discuss the economics of DC versus AC for transmission. The methods explained above, as noted, extend the applications of DC to smaller domains. The comparison to motor drives is of particular interest to me.

Last fiddled with by kladner on 2013-08-21 at 20:00
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Old 2013-08-23, 01:36   #32
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Quote:
Originally Posted by chris2be8 View Post
Storing several hundred GigaWatt-hours of electricity would be expensive. Work out how much 100 GigaWatt-hours of battery capacity would cost.
I used the phrase "storage capacity" precisely because batteries are not the only means of energy storage.

Quote:
Also how many countries in north Africa would you think stable enough to rely on to provide your electricity supply?
When you're raising straw men, you could list quite a few of them, couldn't you?

Quote:
I used to work in the electricity industry so I know quite a lot about the subject.
Then let your posts demonstrate that you know enough about "Economic prospects for solar photovoltaic power" (topic) to be able to argue without employing straw men and without ignoring non-battery energy storage.

Last fiddled with by cheesehead on 2013-08-23 at 01:47
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Old 2013-08-23, 16:30   #33
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Quote:
Originally Posted by chris2be8 View Post
Storing several hundred GigaWatt-hours of electricity would be expensive.
Not unspeakably expensive, just a bit cumbersome; 300 gigawatt-hours is a billion tons of water - a lake a hundred metres deep and ten square kilometres surface area - a hundred metres up a mountain. Bloody great dam at the western end of Loch Morar, similar on the north and south sides; since it's basically a fjord and some dozen kilometres from the far side of the middle of nowhere, that's probably reasonably practical.
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