Water consumption of energy alternatives

I noticed a new Greenpeace report “Great Water Grab” on how coal use is deepening a water crisis. I glanced at the report and used it as an opportunity to learn new things about a topic I don’t follow closely. What struck me first was the authors clear unwillingness to put the water footprint of coal into a broader context. Report reads as if coal is THE reason for water stress. Even I know that almost all the water humanity uses is used in agriculture, but this you will not learn from this report. Even though it is by far the largest driver of water consumption, the word “agriculture” (and variants of it) only appears 12 times and then in the context that coal water use conflicts with agricultural use. Incidentally “coal” appears 448 times. So I googled to learn how much do we actually use or withdraw water. The first figure shows the result…

We seem to extract around 4000 cubic kilometers of fresh water a year and this is massively dominated by agricultural use. We can dig a bit deeper and learn from FAO that, for example, despite rapid economic growth  and modest population growth Chinese water withdrawals have only increased moderately, by about 10% since 1990. India has seen more substantial increase in withdrawals, but essentially all of this increase has been in agriculture and their growth in water consumption corresponds closely to the population growth. Greenpeace report tells that the coal use is  responsible for about 7% of all withdrawals, but if we look at the water consumption this relatively small number is reduced even further. I am sure there are places so close to the edge that even small extra withdrawals are relevant, but are there any places where water use for energy is the main cause of water stress?

Coals water consumption (includes mining) was 22.7 km³ according to Greenpeace. (Never mind  the last decimal point.)

What about household use? We (finns) use on average 155 litres per day for household use. Our household of four consumes about 10kWh of electricity a day, which might consume around 5 litres of water per person. Following figure illustrates the relative importance of different ways we use water. “Great Water Grab” on the left.

  
 I don’t like coal, but just attaching any apocalyptic concern on it is bad form. The real issues are serious enough and we should aim to give a fair overall picture. I don’t think the report does this, but maybe “Relatively Minor Water Grab” would have been too boring title and we all have our preferences.

And then there is the usual promotion of chosen alternatives without actually demonstrating improvements in a meaningful way. “Switching from coal to renewable energy is one of the most effective and actionable ways to save water, and ensure clean water supply for people, agriculture and environment.” Sigh… Report gives an estimate of water consumption of various power sources. The source for the graph seems solid and probably the data is reliable (although Meldrum et al. report very large ranges for consumption figures, so large uncertainties exist) Notice how concentrated solar power tends to have the highest water consumption of all. According to the latest incarnation of Greenpeace E[R] advanced scenario world is supposed to get roughly twice as much electricity from CSP at 2050 than we get from coal today. Now what am I missing? If we produce twice as much power from something which has higher water footprint, won’t this mean dramatic increase in water consumption? Would not these CSP plants be predominantly located in areas with high water stress like deserts?

Water use of different sources of electricity according to Greenpeace based on Meldrum et al 2013. (Notice, however, that several nuclear power plants actually use seawater for cooling and for example Diablo Canyon power plant in California desalinates seawater for its use. Plant has excess capacity for desalination and this could be used to reduce water stress elsewhere. If desalination requires about 3kWh/m³, desalination would require about 10kWh of electricity for each MWh produced. Doesn’t seem like a deal breaker.)

What about bioenergy? Greenpeace+GWEC+SolarPower Europe E[R] scenario actually relies less on bioenergy than some other scenarios loaded with renewables. Nevertheless, in power production bioenergy goes from 379 TWh (2012) to almost 3200 TWh (2050). Biofuels for transport about triples to about 8000 PJ/a and in heat supply there is an increase of about 12000 PJ/a from bioenergy. Energy crops can consume 70-400 times as much water than coal so the bioenergy increases Greenpeace promotes will likely require massively more water than coal use requires today. The energy requirements for desalination are so high that for energy crops it is unlikely to make any sense.

Why do I get a feeling that the left hand doesn’t know what the right hand is doing? Maybe my mistake is to actually read these reports assuming that they are intended to reflect a coherent plan as opposed to myopic lobbying effort. Both coal and water use are serious challenges, but in this report water problems are used as a tool to attack coal and (incoherently) lobby for E[R]. In doing so attention is drawn away from the real causes of water stress which does disservice to an important issue that needs to be addressed. World is a complicated place and to make wise decision we need to acknowledge the complexities and trade-offs and try to navigate among alternatives as well as we can. 

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