Testing the water for bioenergy crops

Aug 29, 2011
Professor Praveen Kumar, right, and graduate student Phong V.V. Le found that bioenergy crops such as miscanthus and switchgrass use more water than corn, a consideration that has been left out of the cost-benefit analysis for land conversion. Credit: L. Brian Stauffer

Many energy researchers and environmental advocates are excited about the prospect of gaining more efficient large-scale biofuel production by using large grasses like miscanthus or switchgrass rather than corn. They have investigated yields, land use, economics and more, but one key factor of agriculture has been overlooked: water.

"While we are looking for solutions for energy through bioenergy , dependence on gets ignored, and water can be a significant limiting factor," said Praveen Kumar, the Lovell Professor of civil and environmental engineering at the University of Illinois. "There are many countries around the world that are looking into biofuel energy, but if they are adopting these (large grasses) into their regular policy, then they need to take into account the considerations for the associated demand for water."

Kumar led a study, published this week in the Early Edition, detailing effects to the hydrologic cycle of large-scale land conversion, both now and as growing conditions change in the future.

and switchgrass have a very different above-ground structure from – more surface area and much denser growth. This is good for maximizing the amount of biomass that an acre of land can produce, but it also increases water use. Miscanthus and switchgrass intercept light and rain differently from corn, and lose more water through transpiration, causing them to pull more water from the soil. The result of large-scale adoption would be a reduction in soil moisture and runoff, but an increase in atmospheric humidity.

Bioenergy crops, such as switchgrass (front) and Miscanthus (rear), have very dense foliage, thus having a different effect on hydrology than traditional agricultural crops. They transpire more water, thereby reducing both soil moisture and runoff. Credit: Praveen Kumar

"All these together account for the changes in hydrology, just from land-use change," said Kumar, who also is affiliated with the department of atmospheric sciences. "Then, if you impose further – higher carbon dioxide in the atmosphere, higher temperatures and changes in rainfall patterns – they add further modulation to the water use pattern."

Kumar's group used a sophisticated model it developed to study crops' fine sensitivities to temperature and carbon dioxide changes in the atmosphere. The model incorporates the acclimation response of plants to changing climate.

Using their predictive model, the researchers found that the net water use will increase further as a result of rising temperatures and carbon dioxide. Higher levels of carbon dioxide alone make the plants more water-efficient, since their pores are open less time to absorb . However, rising temperatures counteract this effect, as the plants will transpire more while their pores are open, losing more water than they save.

This additional water loss compounds the increase in water usage from land conversion. In the U.S. Midwest, rainfall should remain sufficient to meet water demand, according to Kumar. However, areas that rely on irrigation could find they have less water to meet higher demands, which could increase the net cost of large-scale land conversion and put pressure on already stressed water resources.

"If we're going to solve energy problems through bioenergy crops, there are collateral issues that need to be considered," Kumar said. "Water is a significant issue. It's already a scarce resource across the globe, and the need for it is only going to increase. The cost of that should be factored in to the decision making."

Graduate student Phong V.V. Le and former postdoctoral researcher Darren Drewry (now at the Max Planck Institute in Germany) were co-authors of the paper.

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Scottingham
5 / 5 (1) Aug 29, 2011
Biofuels only make sense in the light of sub-standard batteries. Personally, I'm hoping that battery tech makes biofuels obsolete for the reasons outlined above (and others).
Eikka
1.8 / 5 (4) Aug 29, 2011
Biofuels only make sense in the light of sub-standard batteries. Personally, I'm hoping that battery tech makes biofuels obsolete for the reasons outlined above (and others).


One could flip that around just as easily.

Thing is, there's more potential in biofuels and synthetic fuels than in batteries, because the energy densities are an order of magnitude greater even when accounting for all the losses, and they exist outside of theoretical calculations.

Plus all the other benefits that you get from being able to take a canister of liquid fuel and actually carry 50 kWh of energy in your hand to wherever you need it.
CapitalismPrevails
2 / 5 (4) Aug 29, 2011
Plus biofuels are consumable, therefore they don't wear out. Electric cars would need a several trillion dollar upgrade in infrastructure to meet electricity demand for electric cars. I think making butanol from bacteria and organic waste is a better idea. Butanol is a lot more compatible with our existing gas tanks and gas stations.

http://www.physor...sts.html
Jeddy_Mctedder
1 / 5 (2) Aug 29, 2011
what kind of morons are on here comparing bio fuels and batteries?
batteries are energy storage, not a source of energy, as crops are. and biofuels are crop derived fuels. they are not a storage medium for energy produced from various fuel sources.
Eikka
1 / 5 (1) Aug 30, 2011
what kind of morons are on here comparing bio fuels and batteries?
batteries are energy storage, not a source of energy, as crops are. and biofuels are crop derived fuels. they are not a storage medium for energy produced from various fuel sources.


One could argue, however, that because of the energy required to agriculture, the energy required to refine the biomass into fuel, and the energy required to distribute it, biofuels at the moment are simply another way to store oil.

It's a scam, because it's cheaper for the farmer to fertilize his fields on natural gas derived nitrogen fertilizers, run his tractor on diesel, and his distillery on electricity made by coal.
Shakescene21
1 / 5 (1) Aug 30, 2011
@Jeddy

Before you start calling people on this forum "morons" you should consider what is being compared: The energy stored in a tankful of biofuel is being compared to the energy stored in an electric vehicle's battery. This is a crucial real-world comparison between electric vehicles and combustion-powered vehicles using biofuels or fossil fuels.