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Watering Down the Energy Debate

Water is essential for the production of energy. Energy facilities both consume water and have impacts on the aquatic ecosystems they interact with. These interactions are complex however and it is a mistake to over-simplify – one we must avoid if we are to meet our future energy needs in the most sustainable manner possible.

Let me start off by asking a question, which of the following electricity sources has, generally speaking, the “worst” water impacts: nuclear, coal, natural gas, Hydro power, wind, solar, biomass/biofuel?

If you answered nuclear you would be wrong. If you answered gas you would be wrong.  If you answered hydro you would be wrong and if you answered wind, well you are also wrong. In fact, if you answered at all I’m afraid you have just illustrated the point I’m about to make – namely that the question of energy-water impacts has, as with so much of the energy debate, been turned into a stick with which to beat up certain energy technologies. Generalisations are at best false, and at worst they pander to our innate biases and lead us towards some potentially very bad decisions as far as the environment is concerned.

The problem is that knowing only the generating technology is not enough to come to a meaningful judgment. Missing, first and foremost, is the location. Does a coal plant on the coast have a greater or lesser water impact than a solar thermal plant in the desert? (No, I’m afraid that one doesn’t have a ready-made answer either). To understand the water system impacts we need a detailed picture of local water availability and the effects the plant has on its local aquatic environment and other potential users.

This much should be obvious to water and environment experts, and yet it didn’t stop the UNFCCC retweeting this image (figure 1) produced by the International Renewable Energy Agency.

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Figure 1: or do they?

It is honestly disappointing to see two prominent intergovernmental organisations publicly express such a tech tribal message in relation to the energy and water issue. I wish the problem were confined to these groups but evidence suggests it is not. Beyond being merely disappointing, the statement is overly simplistic, since the largest sources of renewable energy are currently biofuels and hydropower which have complex aquatic interactions that come with no assurance of low-water consumption. An additional concern, however, is that it seems to reduce the energy- water issue down to that solely of consumption. This is really not on!

An all-consuming matter

Let’s get one thing clear. There is no shortage of water on the planet. Over 70% of the Earth’s surface is covered with the stuff. Water is not destroyed upon consumption, rather it simply changes state – either transformed into steam or has materials added so that it is deemed no longer fit to be returned to the original source. Most water bodies constantly get replenished and the question of how much you should take depends fundamentally on how quickly this happens.

Concerns over water availability really relate only to those energy facilities that extract from fresh water systems. Such facilities compete with a range of other human water-intensive activities such as agriculture, mining, domestic and (non-energy) industrial activities. Agriculture alone counts for the vast majority of fresh water consumption. Energy accounts for most of the industrial consumption as shown to scale in that tiny pink bar to the right in Figure 2. It frankly makes no sense to prioritise concerns about today’s levels of energy-related water consumption over that of other human activities.

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Figure 2 estimated global fresh water use by sector. Source: UNEP:  VITAL WATER GRAPHICS An Overview of the State of the World’s Fresh and Marine Waters – 2nd Edition – 2008

I can’t speak for fossil, but most nuclear plants in the world are not sited on rivers and none draw from aquifers. They are located on the coast, or on large inland lakes with no obvious water availability issues, as Table 1 indicates. Of the nuclear plants which are sited on rivers, it is important to realise that these locations were selected based on what at the time would have been the rather ample availability of water. Even now these plants do not contribute to water shortages most of the time. In periods of severe drought or high temperatures they may contribute to water stress, but the question has to be asked – would that water stress be there minus the energy activity?

Table 1: Nuclear power plant siting and cooling sources – IAEA Efficient Water Management in Water Cooled Reactors

Nuclear plants using once-through cooling

Nuclear plants using closed cycle cooling

Sea

Lake

River

Cooling Towers

45%

15%

14%

26%

 

Figure 2 highlights one of the more interesting facts of energy related water-use. Most of what gets extracted is in fact returned to where it came from. In the case of thermal plants (which make up the majority of the world’s electricity production) the primary use of water is for cooling. Steam which has passed through the turbines needs to be cooled back to water before being fed back to the boiler. There are two main types of thermal plant cooling systems in use as illustrated in Figures 3 and 4. Both require water, but use it in different ways. Once-through cooling requires a comparatively large volume of water but returns the vast majority of this to the source albeit a few degrees warmer. Closed cycle wet cooling uses the atmosphere as a heat sink and employs cooling towers as a heat exchanger, but this still requires some make-up water input. A little-known fact is that evaporative cooling towers actually consume more water than once-through cooling does. There is also dry cooling technology used at some thermal plants. However while this process requires no water it comes at an efficiency penalty, meaning more fuel is required to produce the same amount of energy. 

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Figure 3: Once through cooling in thermal power plants. Source: BP – Water in the Energy Industry. For a typical nuclear plant withdrawal for cooling may be as high as 200m3/MWh, but consumption due to downstream evaporation will be between 1 – 2m3/MWh. The actual consumption depends on a range of factors – primarily plant thermal efficiency.

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Figure 4: Thermal plant with wet cooling tower (closed cycle). Source: BP – Water in the Energy Industry. For a typical nuclear plant make-up water withdrawal rates are only slightly higher than ‘consumption’ – which corresponds to evaporation loss of about 3 -4m3/MWh. The actual consumption depends on a range of factors – primarily plant thermal efficiency.

During periods of high temperature it is often not water availability that is strictly speaking the problem. In France, nuclear plants have occasionally had to curtail operations because of regulatory/technical limits set upon river temperatures. This bears reflecting upon, since climate change means the natural range of river temperatures may well be up for re-definition. Idling river-based nuclear plants for thermal impacts is rather counter-productive if your aim is to prevent higher water temperatures in the first place!

On the other hand thermal discharges (as the warmed water is called) can create a genuine environmental problem. Increasing water temperatures reduce oxygen levels which many organisms are sensitive to. Somewhat ironically, it can also contribute to rather spectacular blooms of jellyfish, blue-green algae and other species. Outlet water temperatures most certainly need to be effectively monitored and controlled. The process of extracting water for once-through cooling also causes impacts to aquatic eco-systems by impinging fish and other organisms on inlet screens and dragging them through the system. It is unfortunately the case that thermal power plants kill what appear to be large number of very small aquatic organisms this way – although on the local ecosystem level these numbers are not particularly significant.

As a nuclear energy supporter and someone who cares about the natural environment I tolerate these impacts, just as being a supporter of wind energy I tolerate a level of avian kills. I don’t like it in either case but accept, grimly, that all human activities have their environmental toll. The aim is to keep this low, reduce it if feasible, and certainly to avoid any biodiversity loss or large ecosystem changes.

Of course, there are a range of potential aquatic ecosystem impacts associated with non-thermal energy technologies too. The most obvious target here is large hydro, but also clearly in the firing line are wave and tidal, as well as offshore oil gas and wind facilities. Even the mining and manufacturing requirements for solar PV have on occasion led to fish kills. So why then is there not more international focus on these and how to minimise them? It is this question that underscores my sense of frustration at the current state of the energy and water debate.

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Figure 5: Three Gorges Dam. Source: Wikimedia Commons. (Author: Allen Watkin)

Against the tide

I have become sensitive to the shoddy state of the global energy-water dialogue because of my participation in the Water For Energy Framework (W4EF) initiative. This project is working towards creating a common methodology that any energy operator can employ to better understand the water risks their facility faces. On one hand, the framework considers the risk of potential impact on ecosystems and other human needs related to water consumption and discharge quality factors. On the other hand, it considers the risks to the operator related to the energy site’s water supply. The output is a set of simple indicators which illustrates these risks and informs management whether action is needed as well as allowing for better communication between energy operators and stakeholders at local and corporate level.

The W4EF methodology puts site specific water risks into a local context.  It is designed to be applied to any energy technology and doesn’t get distracted with seeking to vilify any of them in particular. Instead, it focuses on whether problems exist and what, if anything, needs to be done about them. I eagerly look forward to the next phase of the work and hope that it receives strong support from energy operators – but also the support of international associations and climate bodies that claim to act in the best interests of the environment.

Case studies from a range of energy facilities have impressed on me the fact that energy facility water interactions are not at all straight-forward. Complicating matters straight off the bat is that responsible operators seek to manage and reduce their impacts, especially where they are based in water-stressed environments. Some have created their own canal systems. Others purchase municipal waste water.  Many have invested in screens (or more advanced screens) to reduce aquatic organism kills. There are options which can be introduced to mitigate impacts for most energy technologies, not to mention innovations which may be available in the future. For nuclear plants the upgrades I would most like to see are those which will lead to improvements in plant thermal efficiency. This would reduce the need for water withdrawals and associated thermal discharges, but should also improve plant economics and performance – a win-win. It would also be rather nice to see uses explored for waste heat.

It is important that whatever steps are insisted on, they help to solve real environmental problems and not theoretical ones. Even more important is that steps don’t lead to even bigger environmental problems in the long-run – for example climate change, worsened by insisting unnecessarily upon the closure or curtailment of low-carbon generation. We can’t afford to keep getting distracted by energy ideology. The world deserves a more mature response to the water and energy challenges of the 21st century, and requires a handy tool, such as W4EF, that is up to the job.

David Hess's picture

Thank David for the Post!

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Rick Engebretson's picture
Rick Engebretson on June 29, 2015

The world needs a lot more water and people like you with an open mind. I’ll limit my comment to what I know, some basic biophysics.

Plants compete by growing bigger, faster than other plants. Plant growth rates depend on many factors, especially water and carbon dioxide. With double the CO2, plants need double the H2O to grow carbohydrates like wood. More complex but accurate chemical kinetics would likely reveal this current unprecedented atmospheric CO2 level has triggered a biological transition of unknown nature. My area of rural Minnesota, with abundant rain, is seeing freakish plant growth rates again this year.

Add in other unknowns like temperature change, population growth, pollution and desertification, and we had better sit down and take this seriously. Clearly, that is not happening.

Whatever the cause, we can’t just sit and watch California bake and burn. If off shore modular nuclear power plants using evaporative cooling can make snow in the mountains, let’s do it.

Hops Gegangen's picture
Hops Gegangen on June 29, 2015

 

I’m not sure it’s true plants need double the H2O for double the CO2. Most of the water that goes into a plant is lost to evaporation, not used to grow the plant.

http://www.sciencedaily.com/releases/2011/03/110303111624.htm

But I’m with you on the freakish growth. I also believe, and I think people are studying this, that the weeds will evolve to use the extra CO2 faster than our crops. And all the extra precipitation will wash away herbicides and insecticides. Worse yet, it will wash away fungicides just when you need them the most. Corn futures are already rising.

I took my daughter on a hike on a trail that was a road a few years ago, but is now full of weeds and tree roots, and was telling her to think about how quickly nature could take over if it were not for constant energy-intensive repaving of roads and clearing of trees.

Some people mock the CO2 issue, saying CO2 is just plant food. But they think in terms of corn given a little fertilizer, not pervasive feeding of plants everywhere. 

Plants are not all our friends. We supercharge the weeds at our peril.

 

Rick Engebretson's picture
Rick Engebretson on June 29, 2015

Thanks Hops. I didn’t want to turn this fine post into a bio sales pitch commentary. I’m just glad the energy/water/climate discussion respects some additional issues, as you point out. We are in a very new world, never before seen. We owe your daughter to think and act like adults.

Roger Arnold's picture
Roger Arnold on July 4, 2015

David,

Thanks for posting this. I don’t think I’ve seen the issues — and the problems with how they’re usually covered — so clearly stated before. I’m in full agreement with everything you wrote.

An interesting way to enhance the benefit of thermal power plants (nuclear or otherwise) that are on or near the coast is to redesign their cooling water sources to make them fresh water and mineral producers. It would entail construction of a salt water marsh / cooling pond large enough to handle the plant’s waste heat load. Make-up water for evaporative losses from the pond would be pumped in sea water, filtered through a near offshore sand well. The sand well prevents any disruption of the shoreline ecosystem. The volume of water needed is a fraction of that required for once-though cooling, so the cost of the intake system is minimal.

There would be no return brine system. Instead, salt concentration levels in the marsh / cooling pond would be maintained at about 2x ocean concentration levels by withdrawing from the pond an outflow volume one half the intake volume, and routing it to a desalination facility. The desalination facility would not be a conventional RO system, since they don’t do well with highly saline feed water. Instead, it would be a zero-discharge system of the sort being introduced to treat flowback water from fracked wells. The most likely technology is a variation on MVC (mechanical vapor compression). It would distill nearly all of the water out of the feed stream, leaving a low volume discharge stream of mostly dry solids. 

The dry solids are precipitates of salts and minerals dissolved in the feed water. When the feed water is straight sea water, the precipitates would be primarily sodium chloride, with smaller amounts of calcium and magnesium chlorides along with some carbonate. There would also be small but comercially interesting amounts of iodide and bromide salts.

The same cooling scheme can be implemented in many areas away from the coast, by using water pumped from deep saline aquifers as the feed. In that case, the precipitated solids would likely include trace amounts of various heavy metal salts. That might include commercial amounts of uranium, thorium, and rare earth metal salts. Since the salts are so concentrated and the volumes so small, it’s relatively easy to either refine them further as commercial products or reinject them in a disposal well.

The thing that I like about this type of system is that it produces fresh water both directly and indirectly. Evaporation from the warm cooling pond adds moisture to the air that will ultimately fall as precipitation somewhere. In the best case, it will fall within the local watershed, but if it doesn’t, the added moisture helps to reduce evaporative losses from local vegetation. That supplements the fresh water produced directly by the desalination unit. The only big cost is the land area for the salt marsh / cooling pond and the network of plastic pipes and tubes buried in the mud below the pond.

Rick Engebretson's picture
Rick Engebretson on July 5, 2015

Thank you Roger for brainstorming new ideas.

Along with your many simultaneous ocean by-products, may I suggest phosphorus. Perhaps calcium and potassium, also. These elements are essential for life, and mineral deposits used in fertilizer are a big question. Ocean algae has been used for centuries in places like Ireland to build soils.

Mark Heslep's picture
Mark Heslep on July 9, 2015

Water is essential for the production of energy.”

Often is, but not always, not even for fossil fuel plants.  See the working fluid for Brayton cycle machines like the gas turbine engine.  Simple air will do; steam need not apply.

https://en.wikipedia.org/wiki/Working_fluid#Applications_and_examples

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