Tapping the Wind and Sun to Save Water
This post is by Dr. Bill Chameides, Dean of the Nicholas School of the Environment and lead author of the forthcoming blog The Green Grok.
Everyone knows we need green energy to fight global warming. But there’s another big reason to tap renewable power sources –- not enough water.
Large swaths of the Southwest and Southeast are in the throes of debilitating droughts. North Texas and Oklahoma’s recent dry spell dragged on from 2003 to the spring of 2007 (more on U.S. droughts). Droughts have even wiped out entire civilizations like the Anasazi (see Jared Diamond’s Collapse and Eugene Linden‘s Winds of Change).
But today’s water problems are far more profound than those of the Anasazi. The huge quantities we use — unprecedented in human history — make us more vulnerable to drought. Our water woes stem from an ever-increasing demand for water to slake the thirsts of a growing population on the one hand and to irrigate crops to feed that same population on the other.
Few people appreciate that yet another sector is clamoring for more water — the power industry. Fortunately we have the technology to wean this one from our dwindling supplies.
Another water hog: Conventional power plants
Have you noticed that power plants tend to be located near rivers, lakes or oceans? Do you know why? Easy, they need lots and lots of water.
Conventional and nuclear power plants, like the coal-fired plant pictured here on Lake Erie, are usually located by a lake or river because they need lots of water to operate. NREL/David Parsons
Coal-burning, natural gas-fired and nuclear power plants (which together produce about 90% of the country’s power) all generate electricity through a thermal process. They burn fossil fuels or split atoms to generate heat to boil water. The resulting pressurized steam turns a turbine that drives a generator that produces electricity.
It’s a process that produces lots of waste heat, which must be dissipated to keep the plant from overheating. So in addition to the source of water needed to make the steam (usually the nearby river or lake), even more water, generally much more than that required to make the steam, is needed to cool things down.
Because water is so integral to conventional and nuclear power production, strained water supplies put energy production at risk. A case in point is the Corette Power Plant in Billings, Montana, which siphons water daily from the Yellowstone River to produce electricity. The plant needs the river flow to be above 1,500 cubic feet per second to stay online. A recent dip below this level prompted a shutdown.
Unfortunately, this is not anomalous. Reduced water supplies are wreaking havoc across the country, fueling debate and water wars. A list of troubles includes:
- Florida’s Polk County trying to generate electricity without drying up wells,
- the decade-long fight between Alabama, Florida, and Georgia over who gets to draw how much water when (see this recent AP report and CNN video) and
- the receding waters of the once majestic Rio Grande, which failed to reach the Gulf of Mexico during much of 2001 and 2002.
Prognosis: Global warming means less water
Predicting the precise impacts of global warming is difficult, but by almost all indications things are not going to be pleasant. More specifically, there is a strong scientific consensus that water will be a big casualty of climate change. Higher temperatures will cause soils to dry out faster, making us more prone to long stretches of drought.
If this comes to pass, it could devastate our water system as increasing demands compete for a shrinking supply. Even without droughts, a warmer world will stress conventional power plant operations. The water used for cooling plants, which must be returned to its source after cooling, cannot be so hot that it undermines the river’s or lake’s ecosystem.
Severe heat waves can render cooling systems inoperable and cause shutdowns of power plants at the very time when demand for electricity is often the highest. During the 2007 heat wave, for instance, the Tennessee Valley Authority had to shut down a nuclear reactor because of high temperatures in the Tennessee River. Similar episodes have occurred in Europe.
We’re all too familiar with power outages and brownouts during hot spells, when the power grid is stressed to capacity. Global warming could make these events commonplace.
Among existing solutions, green power is the most potent
But it does not have to be that way. Weaning our power system off water would make it less prone to disruptions from shortages and rising temperatures while leaving more water available for municipal and agricultural needs.
Photovoltaic power plants, like this SunEdison plant in Colorado, draw very little water to generate electricity. As the world continues to wrangle over dwindling water supplies, green power could be a powerful solution. NREL/Steve Wilcox
A small number of tweaks to our current system is helping staunch the slowly evolving water crisis, but more needs to be done. Newer plants are being designed to use less water. Unfortunately, such efficiency doesn’t help the hundreds of old plants supplying much of our power. Alternative cooling methods are also being pursued, with several plants using dry or air cooling. But while such technology exists, a scant 600 plants worldwide use it.
Renewable energy offers a wide window of hope. Green power sources like wind and solar photovoltaics require tiny amounts of water. While such green solutions comprise only about three percent of our electricity, this could change and almost certainly must if we are to meet rising demands for drinking water and irrigation in a warming world.
Some say that green energy won’t be able to provide a significant portion of our electricity needs. But solving big problems usually requires thinking out of the box. Now I am just a dean, albeit at a great university, so what do I know about business, you might ask? I certainly wouldn’t suggest taking investment advice from me, but my guess is that the time is ripe for investing in green power. And high time it is.
Read more about Dr. Bill Chameides, Dean of the Nicholas School of the Environment.
There are several logical flaw in this article.
First, nuclear and coal power plants do not ‘take’ allot of water.
They take in allot of cool water, and expel exactly as much slightly warmer water.
Silicon solar cells take tons of water to make, and the waste water afterwards is polluted (unlike a nuclear power plant’s discharge).
On the other hand, corn ethanol takes tons of water to produce. The water is used for irrigation and is not reclaimed.
Power production in general has nothing to do with water supplies. This article advocates the correct behavior, alternative energy, for the wrong reasons.
Good post and important topic. Here’s my post on water and power. More comments:
1) Most water withdrawn for cooling is “useless” in some way: too hot, polluted or evaporated.
2) A LOT of cooling water is seawater. Lots of it BUT discharge can still be bad for animals.
3) Many energy plants get away with using so much water because they claim little consumptive use (as RK points out), but they are surely disrupting the system in the same way as a dam “interrupts” a river’s flow.
4) Charging plants for water intake would help them find ways to reduce use. Factories cut their water discharge (and thus intake) by 90% when discharge fees rose. They just built recirculation systems.
Thank you, rk! I wonder sometimes why people who obviously know very little about power generation present themselves as experts on the subject. I am no expert myself, but I have been employed by one small power plant and three large facilities with power houses on site.
Quality boiler water is a precious commodity, and it takes quite of bit of money and effort to produce. It must be filtered down to a few microns to remove all of the solids. It must be demineralized to prevent scaling on the boiler tube walls. It even has to be treated to keep trace chemicals that exist naturally from corroding the boiler tubes. As such, it exists essentially in a closed loop although some make-up water is necessary. Superheated steam gets condensed back into liquid water after passing through the turbine in order to be reheated and used again and again and again. Most steam plants are an elaborate counter-flow heat exchanger. Boiler flue gas flows on the outside of the tubes one direction, and boiler feed water flows inside the tubes in the other direction. As such, the water that cools the intense heat of combustion is the same water that gets transformed into steam to drive the turbine.
Similar - although not quite as intensive - treatment is require of the cooling water used in the condenser and/or cooling towers. The condenser has cooling water tube side and turbine exhaust shell side. Its purpose is to transform the steam leaving the turbine back into liquid. Cooling towers are necessary in some applications to cool the cooling water after it is heated up in the condenser. Except for the water needed to make up for the vapors leaving the cooling towers, a cooling water system also operates in a closed loop.
It may be a good time to invest in green energy, but please refrain from misrepresenting the existing methods of producing electricity. The examples cited are not representative of the entire industry.
David - Thanks for making the point about how much water is required to produce ethonal. Now the question is how to undo the e-debacle.
Undo? Simple — remove government subsidies for corn, mandates for ethanol and barriers to imported ethanol. Tax carbon emissions. Let the market work instead of special interests.
[Ok — not so simple…]
Bill Chameides responds. Thanks for the responses. It’s always nice to know that someone out there is paying attention. Here’s what comes to mind after reading the comments.
The bottom line: You can talk about how power plants operate, and how they process water, and how they recycle water all you want. It does not change the fact that conventional power plants can not operate without having large quantities of water on hand. Some use more than others, but all require water. (See USGS stats.) When water is in short supply (for example because of a drought) or when temperatures get too high (for example because of a heat wave), the operation of the vast majority of conventional power plants becomes problematic. That is just a fact.
And yes, conventional power plants most definitely do take or withdraw water from rivers and lakes. It is true that much of the water they take is not consumed and is returned to the lake or river from which it came, but it most certainly is used. And the water that is returned is not the same as the water that was taken — it is hotter and that exacts an environmental toll.
It is incorrect to refer to recirculating water-cooled power plants as “closed loop.” They use what is called “makeup” water to replace evaporative losses and maintain water chemistry and thus are not closed loop. In fact, while recirculating water-cooled power plants withdraw less water, they often consume more water than non-recirculating plants. For example, coal plants with recirculating tower cooling systems require about 6,000 to 10,000 gallons per minute of makeup water; that’s a factor of 2-4 times more water than non-recirculating coal plants use.
There are alternate designs for conventional power plants that lead to much lower water consumption rates — namely, air cooled power plants. These were one of the water-saving alternatives featured in my original post.
Now let’s talk about water and solar photovoltaic (pv): @rk points out that “silicon solar cells take tons of water to make, and the waste water afterwards is polluted.” The issue raised here relates to what we call “life cycle analysis” — assessing the environmental impact of a technology through its entire life cycle. It’s an excellent point. Most of the water consumed by solar pv is actually consumed in its production rather than its operation. But let’s be careful and be sure to use a level playing field. If we consider how much water is consumed producing solar cells, then let’s also consider how much water is used and how much is polluted to mine coal and uranium, as well as how much is used and how much is polluted to produce the steel and cement to make power plants. The picture changes, don’t you think?
Finally this thing about corn ethanol. I absolutely agree that corn ethanol is an environmental loser — in part because of all the water it requires. I don’t even consider corn ethanol to be “green energy.” But I also don’t recall mentioning corn ethanol in my post. The post was about generation of electricity and how solar and wind power might help. What does this have to do with corn ethanol? I would love to be invited back to give a post on the pitfalls of the rush to corn ethanol. It’s just not relevant to this discussion.
Great reply Dr. Chameides. It’s nice to see someone make a post and be prepared to defend it. Here are a few responses by paragraph.
P1 => Yes, all steam based power plants require a considerable amount of water. And yes, they perform better when cool atmospheric and water temperatures prevail, because the improved condensing of exhaust steam from the turbine draws more vacuum on the turbine thereby yielding greater efficiency. Nonetheless, your original post gave the impression of a “once through and out” cycle.Those based upon gas turbines require much less, but since there are markets for steam they often produce it for sale.
P3 => Government regulations exist for all industrial water discharge points. They regulate such things as chemical content and temperature. Breaking these regulations result in fines.
P4 => That’s news to me and seems counter-intuitive.
P5 => Air cooling requires much more surface than water cooling, because water’s potential for heat absorption is considerably more than air’s for a given volume. Why not use a refrigeration (Freon) based cooling system?
P6 & P7 => I did not discuss either of these topics.
[…] water shortages are causing power outages. […]
Dr. Bill Chameides responds.
For the record, we did not say water shortages are causing power outages.