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The Water-Energy Dance (Why Wasting Water Really Means Wasting Energy)

RP Siegel | Friday December 21st, 2012 | 3 Comments

niagara fallsEditor: This article has been submitted for the Masdar blogging contest “Engage: The Water Energy Nexus.” The winner will be invited to Abu Dhabi January 13-17 as VIP media to cover the week’s high-profile events. Please vote!

We need water to live. That is a basic fact of life and one I doubt we will ever design or invent our way out of. Our bodies are mostly water and we need to drink it to stay alive. All of our food sources need water as much as we do, if not more. So, water, wonderful water is something we are all married to, as they say, for better or for worse.

So what do we know about this spouse of ours that (if we are lucky) pours forth so willingly from the spout? It is quite heavy, which means it takes a lot of work to carry it, or pump it, up a hill. It expands when it freezes, one of the only substances on earth to do so. (Life would not have evolved here if it didn’t). It takes a lot of energy to heat or cool it and even more energy to evaporate.

By this simple set of facts alone, it is pre-ordained that we will require quite a bit of energy just to fetch, purify, distribute, heat and evaporate the water we need to live.

But there’s more. Water is part of a closed-loop cycle. It rains, we collect it; then we use it. It evaporates and then it rains again. So when we talk about using water, or even wasting water, what do we really mean? If we stand in front of the sink, letting the water run as we brush our teeth; that is considered wasting water, right? But where does that water go? After being treated, it works its way back into the natural water system. From there, it might just get pumped to a purification facility and then back to us, where it might just come right back through our bathroom sink some days or weeks later.

The point is, when we waste water, what we are really wasting is not so much the water as the energy it took to treat, collect, purify and distribute that water.

So, we have a strong linkage between water usage and energy consumption, a dance, if you will. But it works the other way too. After all, it takes two to tango. We get our energy from a variety of sources, most of which require lots of water at one stage or another of their life cycles.

Based on USGS data from 2005, Americans used 410 billion gallons of water per day. Slightly more than half of that was used for cooling power plants. Another 30 percent went to agricultural irrigation, with the remaining 20 percent being used for everything else.

You might be surprised to learn that so much water is used in cooling our fossil and nuclear power plants. But then, it is not so much being consumed as borrowed,  passing through the cooling towers and coming back out a bit warmer, before returning to its source, though some of it, about 8 percent is lost through evaporation.

Other power sources use water too. Hydropower also borrows water and loses a fair amount to evaporation.

Fossil fuels that aren’t used for power generation, such as gasoline, use quite a bit of water per gallon, but since the energy content is so high, the amount of water per unit of energy is relatively low. The same is true for fracking, which is used to release shale gas. It takes a lot of water to create the cracks, but once they are established, a tremendous amount of gas can be extracted through them. The net result is that on a per unit energy basis, water usage is pretty low. Of course, the chemicals used in fracking can potentially contaminate large amounts of water, which would change the game entirely.

Biofuels are often considered the worst offenders, since the amount of water required to produce each gallon of ethanol from corn is high. But according to Bob Dineen of the Renewable Fuels Association, only about 10 percent of the corn grown for ethanol is currently irrigated, the rest uses natural rainfall.

You would expect solar power plants to use little or no water and mostly they do especially if we talk about photovoltaics. The same is true for wind power. For large scale solar thermal plants though, mileage may vary. Water might be required for cleaning the mirrors (Ivanpah), or directly consumed for cooling (Abengoa Solar). The difference between the two can be substantial.

Researchers at Virginia Tech recently produced a report comparing water requirements for these energy sources (which I have supplemented with additional sources).

Power sourceWater usage (gal) per MBtu – Low efficiencyWater usage (gal) per MBtu – High efficiency
Nuclear

2400

5800

Fossil fuel – thermal

1110

2200

Biofuels

732

N/A

Solar thermoelectric

230

270

Hydrogen

143

243

Geothermal

130

N/A

Gasoline

102

N/A

Hydroelectric

20

N/A

Natural gas

3

N/A

Wind power

0

N/A

Solar PV

0

N/A

Water is not distributed evenly across the planet. Trying to produce water, where it is not available through desalination, for example, is very energy intensive (since it involves evaporation) and generally not practical unless there is a confluence of resources like in places like Saudi Arabia where there is abundant sunshine, access to sea water and available land area (having a lot of money also helps). Energy systems that require lots of water might make perfectly good sense in areas with abundant water (e.g. Pacific NW, Great Lakes) but no sense at all in dry areas.

The key point is realizing that our global challenges going forward are not one dimensional, but far more complex that that. There are more boundaries or constraints to be considered than peak oil and climate change.

Right now, we are just beginning to raise awareness. Pretty soon, when people talk about cars and they ask about miles per gallon, they will need to specify if they are talking about gallons of fuel or gallons of water. In some cases, electric cars, despite using far less fuel, might actually use more water, depending on where the electricity comes from.

Low hanging fruit, such as using the waste energy currently contained in waste water streams, as in combined heat and power, will become everyday practice. Algae-based biofuel shows promise in this area.

People will need to become conversant with the fact that things like charging an iPhone overnight will require a half a liter of water. A Google search might only require one thousandth as much, but if you add up the 300 million searches collectively done every day, that’s a lot of water.

This kind of awareness could affect people’s behavior, or perhaps the choices they make when selecting their utility provider and the type of car they drive. The sooner this dance of necessities becomes part of our everyday awareness, the better off we will all be.

[Image credit: Adrian MB: Flickr creative commons]

This post is being submitted to the Masdar Engage Contest. Please go there and vote for me!

RP Siegel, PE, is an inventor, consultant and author. He co-wrote the eco-thriller Vapor Trails, the first in a series covering the human side of various sustainability issues including energy, food, and water in an exciting and entertaining format. Now available on Kindle.

Follow RP Siegel on Twitter.


▼▼▼      3 Comments     ▼▼▼

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  • roger saillant

    It might be worth noting that, if and when we begin to go to scale and use Hydrogen as an energy carrier, natural gas and water are two major sources for Hydrogen. One, electrolysis, starts with water and adds energy, and the other, reformation, adds water to the natural gas flow and uses energy in the form of heat to break methane into Hydrogen and carbon dioxide. As you note, water is essential to our energy lives.

  • jamest2

    “Biofuels are often considered the worst offenders, since the amount of water required to produce each gallon of ethanol from corn is high. But according to Bob Dineen of the Renewable Fuels Association, only about 10 percent of the corn grown for ethanol is currently irrigated, the rest uses natural rainfall.”

    This statement from the Renewable Fuels Association is highly misleading. It is true that the great bulk of the corn that is used as an ethanol feedstock is cultivated on non-irrigated acreage. What is not said, however, is that the diversion of the major portion of the corn crop from non-irrigated acreage to ethanol has caused millions of acres in more arid regions to be converted to corn production for foodstuffs and animal feed, resulting in a huge increase in water use for irrigation, and depletion and contamination of the Ogalalla aquifer.

    If you want to see some more information, try this link: http://www.evs.anl.gov/new/dsp_news.cfm?id=94 “Projected Corn-Based Ethanol Production Would Dominate Water Consumption for the Energy Sector”

    • RPSiegel

      Jamest2 Thanks. Interesting study, credible source. Of course those are projections. Right now corn ethanol production is capped at 15 billion gallons and we are already producing 14 billion. So I don’t see that growth there without those limits being raised. Still, I strenuously agree that the water dimension of this approach needs to be factored into the final analysis and direction. It’s something that needs to be moved up in the public awareness and that of decision makers. As for the increases in irrigation levels today you mention, I’d like to see that data. I’m still fairly bullish about biofuel going forward because I think as second generation (i.e. cellulosics) come online, we will have much higher resource efficiency since we’ll be using a lot more of the plant besides the starch, plus we’ll be using feedstocks that can grow on marginal lands without irrigation.