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Can you hear it? The buzz on smart grids is getting louder. News reports on green jobs are peppered with talk of a "smart grid." Google returns 929,000 pages for the term. Even Congress is in the swim, greening the stimulus package with $11 billion for a smart grid. So is Congress wise to fund it? Or are we buying an electrical bridge to nowhere? In this and a post to follow, we'll look at why smart grids are a smart move.
Google "electric grid," and you'll likely find a statement describing it as the "largest single machine in the world." According to Robert Galvin and Kurt Yeager in Perfect Power, America's grid:
- is connected to some 16,000 power plants;
- uses more than 300,000 miles of high-voltage transmission lines to power hundreds of millions of homes, offices, and factories; and
- is valued in the neighborhood of $360 billion
Impressive. So what's the problem? Let's start with some basics.
Electrical Circuits 101
Electricity is characterized by three parameters:
1. Current (I)- the rate at which electrons flow through a wire;
2. Voltage (V) - the energy difference between the circuit's two ends, which causes the electrons to flow;
3. Resistance (R) - a sort of friction that slows the flow of electrons.
The amount of power in a circuit is equal to its current multiplied by its voltage (I*V). So, to send a lot of power down a transmission line you can use:
- a very high voltage V,
- a very high current I, or
- reliability – today's grid is too vulnerable to brownouts and blackouts that can compromise modern electronics;
- flexibility– today's grid cannot integrate large amounts of renewable energy from intermittent and distributed sources;
- efficiency – today's grid is unable to fully utilize generation capacity and rapidly adjust production to meet varying demand.
But not all the power flowing through a wire can be delivered to the other end. The resistance dissipates some of the power as heat at a rate of I(squared)*R. So while the power carried in the circuit is proportional to its current, the loss of power is proportional to the square of its current. This means that increasing current results in less efficiency. For this reason sending a lot of power down a transmission line is best done using a high voltage V.
Distributed vs. Centralized Power Generation
The evolution of our electric grid pivots on a disagreement between two famous Americans: inventor Thomas Edison and entrepreneur George Westinghouse.
Edison envisioned a distributed infrastructure with a plethora of small power-generation plants supplying electricity to a few homes or a neighborhood – a system well-suited to direct current, where the current flows in one direction. The power needed to flow through individual transmission lines is modest, meaning the resistance losses aren't large and the small amount of voltage entering homes isn't overly dangerous.
But as the demand for electricity grew, the viability of Edison's distributed system diminished. Electricity was needed not just in individual homes but also for streetlights, cable cars, factories. George Westinghouse saw that great economies of scale could be realized with a centralized system – with large power plants generating electricity for whole cities.
But a centralized system posed a problem: large amounts of power surging through transmission lines. Remember that 1) transmitting a lot of power requires lots of current, lots of voltage, or both, and 2) large currents in transmission lines aren't good because of unacceptable I(squared)*R losses. High voltages are not so good either - they're not safe going directly into homes. If you have high voltage transmission lines you have to "step down" (or transform) the current to a lower voltage before it enters the home. And there's the rub -- there's no easy way to step down the voltage of a direct current. And so Edison remained confident that his distributed system design would be the clear victor.
Central Power Finds a Fix
Enter Nikola Tesla, a Serbian immigrant. Tesla invented a new type of power generator capable of making alternating current – where the flow of electrons switches back and forth from one direction to another. And this made Westinghouse's vision of a centralized system possible. Why? Because in contrast to direct current, the voltage in an alternating current is easily transformed to a lower voltage (see photo). This makes it ideal for a centralized system. Now high power could be transmitted from centralized power plants at high voltage and low current (to minimize resistance losses) and then stepped down (to lower voltages) before entering individual homes. Problem solved.
And so Tesla and Westinghouse helped design the architecture for today's electric grid. Not surprisingly their 19th century design does not meet all our 21st century needs for:
In the next post we'll see how a smart grid can remove these deficiencies and in so doing resurrect Edison's vision of a distributed power generation system.
"3. Resistance (R) - a sort of friction that slows the flow of electrons."
Which is not to say that the SPEED of those electrons are reduced, just the number of electrons delivered per unit time is reduced. I once had a tour of a hydroelectric dam and the young lady doing the tour said that the voltage was stepped up so as to make the electrons go over the wires FASTER! No... it's so that you don't need to use transmission lines a foot thick.
"Because in contrast to direct current, the voltage in an alternating current is easily transformed to a lower voltage (see photo)."
Until now! Thanks to the wonders of modern semiconductors it is now possible to step up and down the voltage of DC at will. This will allow the use of high tension DC transmission lines which are more efficient than AC at a given voltage.
alancj05 - All true and good points: (i) I used the terms "friction" and "speed" somewhat loosely to make the post more accessible for those not familiar with circuitry, my mistake; (ii) at the time the debate over distributed and centralized power systems was being played out (the subject of the post) there was no practical, efficient way to step down the voltage in a direct current. How things stand today will be covered in my next post.
One great way to make a green grid more efficient is simply to make darn sure that the power lines are as short as they possibly can be, because electrical resistance in a long powerline is like a tax that never goes away.
About 35 years ago I got quite a lesson in how powerline routers think when I received a certified letter from the Bonneville Power Administration notifying me that, due to the necessity of constructing a huge new high voltage powerline from Colstrip, Montana, to Seattle, it was going to be necessary to put a 90-foot tall transmission tower in my back yard, about 12 feet from the glass slider door to my patio.
In the next few months I found myself elected vice chairman of a vigorous citizen protest movement. The BPA used every type of manipulation technique you can imagine on us, including setting up phoney focus groups and giving us lots of free legal advice on how hopeless our resistance would be and how absolutely set in concrete the proposed route of the powerline had to be for the greater good of apple pie, motherhood, and everyone in the USA.
Somehow we managed to hold our property owner resistance movement together until finally the BPA had to cough up something they had kept remarkably secret for the first four months they dealt with us, that being a detailed map of exactly where the powerline would run. We could kind of guess from the locations on the original certified letters in a general way where the main line ran, but we had no idea what it was doing before it got to us or after it left our little valley on its westward march.
At the time I was a 26-year-old undergraduate engineering student at the Montana College of Mineral Science and Technology at Butte. I was a bit old for an undergraduate, but my education had been delayed by a splendid, lengthy, paid vacation in scenic Vietnam.
I knew as soon as I laid the BPA map out on my kitchen table that something looked wrong. With a compass and protractor I started measuring out line segments, added them up, then I drew some new line segments about ten miles to the east and added them up. For some reason the BPA powerline appeared to be almost two full miles too long at a cost (in 1977 dollars) of over a million dollars a mile.
In more due time a big show-down was scheduled between about seven or eight BPA bigwigs and just me, by my lonesome. I knew I would be up against at least three electrical engineers and even more seasoned construction experts. I spread out my map with a new transmission line route pencilled in and made my spiel for it, expecting as soon as I finished that the assembled technocrats would blow my idea out of the water and then laugh at me.
Instead, they all rubbed their chins, whispered between each other guiltily, then the senior one of them told me, "Well, actually we routed the line across the valley at this point because otherwise we would have had to cross U.S. Forest Service land and they would have made us do a complete environmental impact statement. . ."
The BPA didn't want to get in a pissing contest with another federal agency that had the firepower to out piss them, that was the whole of the matter.
The reason this long anecdote is relevant today is that alternative energy sources are frequently sited in remote locations and getting the electricity they produce to the grid will require many miles of new transmission lines. For instance, huge lines will have to be built across Texas from the high-wind West Texas regions to the power consuming populations of East Texas. Already in California green power projects are being held up because power line routes are being gerrymandered around endangered swamps and vistas where powerful people do not want their views ruined, like the Kennedys of Hyanasport and the offshore wind farm they vetoed.
The penalty for making serpentine power line routes is that the nasty old resistance tax still has to be paid for every foot of powerline cable. Once you build it too long you pay that penalty forever, which sabotages the already dubious economic justification of many green power ideas in the first place. For instance, the month of March is coming up and it is the windiest month of the year, which means it will be the only truly profitable month for some wind farms.
Mike - Thanks for the post and what a great story. The issue of transporting renewable power over long distances is
addressed in my next post in the series. Check it out tomorrow.
Dean, Duke University
Nicholas School of the Environment
www.nicholas.duke.edu | www.TheGreenGrok.com
Thank you for you !
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