We’re Betting the Planet
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The Problem with Large-Scale Wind and Solar
Mike Conley and Tim Maloney
April 17, 2015
(NOTE: This is a work in progress.
It will be a chapter in the forthcoming book
“Power to the Planet” by Mike Conley.)
Can wind and solar power the country?
It’s an enticing idea, because the raw amount of solar and wind energy is enormous. For example, the earth’s surface receives about 163 watts of solar radiation per square meter.
But even if we capture enough of it to run the country, can we distribute it through our existing infrastructure to significantly change our energy picture?
Unfortunately, no. While it sounds good in theory, feeding enormous quantities of intermittent energy into the grid wouldn’t work. In fact, it would be a disaster.
Picture this .…
A river runs deep and wide, flowing fast and smooth. Small, turbulent tributaries feed into it, but the river runs so strong that its flow isn’t disrupted and river traffic can sail with ease. In fact, the river is so big and smooth that it’s the backbone of the entire region, a commerce and transportation resource that anyone can use 24 / 7 / 365. Whole cities have sprung up along its banks.
Now imagine that same river with dozens of new canals feeding into it, bringing water from flash floods, snowmelt, bubbling springs and fitful waterfalls. Sometimes the canals flow like lazy creeks, and sometimes, with hardly any warning, they disgorge enormous bursts of turbulent water.
The river would soon become too choppy to navigate, and so rough you could hardly use it. It would no longer be the backbone of the region; it’d be a hazard. And if the disruptions were bad enough, they could break the region’s back.
Our electric grid works the same way.
From the generators in our power plants, through our entire national transmission system, and right down to your happy home, all of it—from Hoover Dam to your doorbell—has been designed to generate, transmit and use one thing, and one thing only: A smooth-as-silk alternating current running at a rock-solid 60 cycles per second. Every single piece of equipment we have is built around that idea.
Good quality ac voltage is displayed on an oscilloscope with a familiar shape you’ve seen before, called a “sine” wave. Lay a long garden hose in the driveway, and make sure it’s nice and straight. Give the end of it a big, smooth side-to-side wag, and you’ll see a sine wave travel down the length of the hose.
Quality voltage has no deviations from that shape, and no “noise” or glitches on the waveform, either. Drink too much coffee and draw a sine wave on a piece of paper. The basic waveform might be there, but you’ll see some jittery noise and glitches in the wavy line.
A quality voltage source for the American grid makes exactly 60 complete oscillations (wiggles) per second, known as 60 Hertz. A “systematically choppy” wave doesn’t count—smooth means smooth. You don’t want a waveform with noise and glitches, and you don’t want one that deviates from 60-Hz frequency, even if it wanders and comes back again in a predictable pattern.
Photovoltaic arrays (“PV solar”) are processed through a dc-to-ac inverter and wind turbine alternators are processed through an ac-to-ac converter. These devices do what they can to make waveshapes compatible with the grid. But they still produce imperfect waves, because they’re being fed with intermittent energy, and not a smooth, continuous flow from a perfectly-balanced generator.
To get an idea of just how smooth and continuous, consider this: Aside from a bit of routine maintenance every year or two, some of the hydroelectric generators that power New York City have been spinning at 3600 rpm, day in and day out, for more than a century.
Since most of the energy generated by large-scale wind and solar isn’t stored, their converters and inverters must feed it to the grid as soon as it’s generated, no matter how fleeting that energy may be. The precise instant of connection is supposed to happen when the new energy is in perfect and instantaneous time-sync with the grid’s sine wave. That would be when they’re they’re both passing through “zero-volt point,” which is the low point of the wave. Detection circuits and controllers are pretty good at making this happen, but they’re not perfect.
Once the connection is made, a strong-versus-weak interaction comes into play: The imperfections of the weak source are (hopefully) washed out by the strong source, which up to now has always been a smooth ac current generated by the grid’s “turboalternators,” the technical term for ac generators.
Turboalternators make a smooth sine-shape voltage wave because of their carefully-engineered design. The sine wave frequency is kept at 60.0 Hz (cycles per second) by precisely modulating the amount of steam (or water for hydroelectric power) that’s fed to the inlet port of the turbine. American steam-driven turbines (coal-, gas-fired, or nuclear) spin at precisely 3600 rpm, and most American hydroelectric turbines spin at precisely 180 rpm. They both generate a rock-steady 60 Hz, and for well over a century the entire national infrastructure, and every last thing we plug into it, has been designed around that standard.
When a weak new energy source connects to the grid, the strength and stability of the grid’s waveform “pulls” the weak source into nearly perfect match with the grid’s behemoth baseload generators. And so long as these disruptions are minor, the grid continues to function satisfactorily, like a booming 200-voice choir with just a couple of off-key voices, somewhere in the back.
But what if they’re all off-key?
Ever been to a birthday party where everybody’s slogging through the song, trying to find the right key? It’s pretty much like that. Imagine your toaster, your light bulbs, and your air conditioner going through that every time you use them.
Visualize a grid with a preponderance of intermittent sources. It’s a nice day, the sun is shining, and a dozen big solar farms are energizing the region. Things are fine, but now the wind kicks up and some wind farms come online. After their converters go though a brief period of adjustment, the wind farms’ power contributions achieve a good match with the magnitude (size) of the solar sine wave, as well as its 60-Hz frequency and time-sync.
The connecting switches close and the wind energy flows into the grid. But sudden electrical switching can always present the possibility of imperfect performance. Switching may be perfect 99 times in a row, but on the 100th try the switch’s timing is a tiny bit off, and a “transient” voltage surge might appear.
The problem with a grid powered by intermittent energy is that these “spurious surges” have a much greater chance to propagate down the wires (to spread through the grid) because there isn’t a steady baseload of large, rotating turbo-alternators working in perfect sync to “call the tune.” It’s like an orchestra with no conductor. A perfect example is the famous cacophony in The Beatles’ song A Day in the Life. The conductor told the London Symphony, “Every instrument plays for 16 bars. Start on this note and end on this note.” And that was it.
The presence of wave choppiness also raises the possibility of an unhappy timing coincidence, when the grid’s waveform is momentarily magnified, dampened, or otherwise perturbed by the appearance of a newcomer. There’s no conductor to make all the musicians follow the beat and the melody, because there is no beat and melody. It’s just noise. And every time the wind picks up or dies down, or the sun goes behind a cloud, another stray melodic line is played (Free Jazz comes to mind…)
Can’t we just re-design the grid?
Maybe. And maybe not. But since no one has tried it on a national scale, we don’t know if it can be made sufficiently reliable to satisfy modern expectations. Right now, the American grid consists of less than 5% intermittent sources—over 95% or our large turboalternators are powered by coal, methane, hydro, biofuels and nuclear. The German grid is about 12% wind and solar. But 9% of that 12% is river hydroelectric and biofuels, which aren’t intermittent by our definition because they spin steady-speed turboalternators, though they don’t do it as “strong” as coal-fired plants—that is, they’re not as rock-solid as a coal plant. Denmark has the highest portion of wind and solar in their electrical supply, with up to 30% in 2012.
With ingenious control engineering and sophisticated connect / disconnect equipment, it may be possible to operate a stand-alone, wide-area, high-content national grid like ours, using 50% intermittent sources. Perhaps even 80%, which is the goal of the National Renewable Energy Laboratory’s “2050 Plan.” Or maybe even 90-100%. Who knows? We don’t, and we won’t, until we try it.
But we do know one thing: What we’ve accomplished so far, by adding marginal intermittent energy on top of our national baseload, is not indicative of future success. What it does show is that small intermittent sources don’t disrupt a grid that’s firmly anchored by large baseload generators, which is how we’ve powered the nation since Niagara Falls lit up Buffalo in 1896.
The availability of wind and solar over a large region can be mathematically modeled with historic records, but the functionality of thousands of intermittent sources cannot be modeled with computer software. That kind of modeling isn’t yet possible because there are no mathematical equations that apply to any engineered system, mechanical or electrical, on such an enormous scale.
Bluntly, we don’t know if it’ll work because we haven’t done it before, or done anything vaguely like it. To find out will require a multi-trillion dollar gamble, and several precious years, or even decades, spent on a possible wild goose-chase:
It will cost something like $8 Trillion to replace 80% of our existing electrical generation with wind and solar, based on current renewables technology. Figure another $2 Trillion for the extra transmission corridors needed to bring all that energy to populated areas from the windswept, sunny wilderness.
And the price tag doesn’t even include the two things that might actually make renewables work on a national scale—a cheap and feasible means of mass-energy storage, and rebuilding and re-wiring the entire national infrastructure to accommodate a power generation system built on intermittent energy. And that means re-thinking everything from Hoover Dam to your doorbell. And then there’s the time, energy, labor and resources needed to build it all, and get it up and running with the kinks worked out. If they can be worked out.
Anything can look good on paper, and we’re all free to speculate. But when the time finally comes to decide on a course of action (and many people think that moment has already arrived), keep one thing in mind:
SEE another preview chapter Let’s Run the Numbers: Nuclear Energy vs. Wind and Solar
We’re not betting the farm, we’re betting the planet.
Copyright © 2015 by Michael Sean Conley. All rights reserved.