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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:
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:
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.
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.