Sunday, February 22, 2009

On the Decrease in Texas' CO2 emissions from 2000 to 2005


On January 29, the Environmental Defense Fund, together with the UK Consulate, hosted a climate conference at the capitol: “Texas’ Changing Economic Climate.” At the beginning of the conference, we heard a personal message from Prince Charles of Wales to the State of Texas imploring Texans to lead the US, and hence the world in climate mitigation. At the end of the conference, one of our elected officials suggested Texas may in fact already be a leader in carbon emissions mitigation while at the same time increasing the gross state product. And if Texas has been taking this leadership role by promoting things like a business-friendly environment and a deregulated electricity market, then perhaps other states, and countries, should look to Texas for how to mitigate carbon emissions.

Are those claims true? Is Texas a leader in reducing carbon emissions while increasing economic productivity?

On the surface, it seems plausible. From 2000 to 2005, total CO2 emissions in the state decreased 4.4 percent while economic output increased 16.5 percent. But dig deeper, and claims of real leadership on climate mitigation evaporate. It turns out that global energy prices were the main drivers of those changes, not the state’s regulatory environment or business initiatives. Much of the CO2 reduction came from decreased natural gas use by the chemical industry as a result of the rising cost of natural gas. Electricity deregulation in Texas fostered the increased use of natural gas combined cycle technology for electricity generation – helping to maintain relatively steady electric sector CO2 emissions since 2000. Much of the rise in the state’s economic output is attributable to the oil and gas industry, buoyed by the same rise in global energy prices.

It is a mistake to think that significant steady and long term CO2 emissions reductions, together with increased gross state product, can be achieved by simply continuing actions of the past five to ten years.

This report examines the data behind claims that Texas has been a leader in reducing carbon emissions while increasing economic productivity. The data shows that the external economic factor of higher energy prices was the main driver in decreasing emissions in Texas from 2000 to 2005, not our pro-business or deregulatory policies. Furthermore, Texas must prepare for the future. Federal climate legislation is on the horizon. This legislation is likely to impose constraints on the Texas economy that will demand even greater reductions in emissions. Texas and the rest of the US states should work to understand how specific industries and consumers will be affected by a federal CO2 constraint. By promoting those businesses that are well-positioned and facilitating restructuring for those ill-positioned, Texas can successfully transition to and maintain leadership within the new carbon-constrained energy economy.

Texas CO2 emissions data

In looking at aggregated data from the Energy Information Administration of the Department of Energy, from 2000 to 2005, the CO2 emissions of Texas went from 654 million metric tons (MtCO2) to 625 MtCO2 – a decrease of 4.4%F F. By looking at the data in Figure 1, one can see that the peak year for Texas CO2 emissions was 2002 at 672 MtCO2. Emissions in both 1999 and 2001 were less than in 2000 with the decrease from 1999 to 2005 being only 0.2%, as Texas’ CO2 emissions in 1999 are listed at 626 MtCO2. Thus, in thinking about a specific baseline year for CO2 emissions, the choice can have a large impact. This fact provides reasoning for using a running average that can level out short-term fluctuations in the economy and energy prices.

The evidence for the emissions decrease is revealed by looking one level deep into the data – emissions from the industrial sector (see Figure 2). In 2005, the Texas industrial sector was responsible for 179 MtCO2 compared to 218 in 2000 – a 17.6% decrease. As a comparison, the drop in the overall US industrial sector emissions was only 6.4%. No other major sector, transportation or electric power, decreased in emissions in Texas during the 2000-2005 span. Furthermore, the Texas industrial sector is dominated by the consumption of natural gas as they are correlated very closely: Texas total consumption of natural gas dropped 21% from 2000 to 2005.

Figure 1. Texas’ CO2 emissions by fuel.

Figure 2. Texas’ CO2 emissions by sector.

Table 1. Comparison of US and Texas CO2 emissions from 2000 to 2005. Emissions in Texas and the US (MtCO2)

Table 1 presents a comparison of Texas and total US CO2 emissions. From the 2000 to 2005 time span, US emissions increased 2.4% and Texas emissions decreased 4.4% such that in 2005, Texas accounted for 10.3% of US CO2 emissions. With an estimated population of just over 24 million, Texas residents are approximately 8% of total US population. As is often noted by Texans, their disproportionately high emissions per capita has much to do with a large industrial base that exports products and fuels to the rest of the US and the world.

Interpreting Texas CO2 emissions data

There is an important question to ask in terms of interpreting the data showing a drop in industrial natural gas usage and subsequent emissions: Did the industries in Texas quit making as many goods or find a way to make the same amount, or even more, goods while consuming less natural gas?

From 2000 to 2005, the Texas Comptroller of Public AccountsF F shows that the gross state product increased from $850 billion to $989 billion in constant 2005 dollars. This is a 16.5% increase in economic output. During that same 2000-2005 span, Texas’ total industrial output dropped a few percent before coming back to 2000 levels (see Figure 3). The only industries with substantial economic growth were oil and gas extraction, refining, and primary metals (not shown). The real price of oil and natural gas rose 40% from 2000 to 2005 – and roughly doubled from 1999 to 2005, providing substantial income and revenue to the Texas oil and gas sector, as well as the state budget. However, the chemical sector, which uses substantial quantities of natural gas as a feedstock was down 11%, perhaps tied to the increase in cost of natural gas. Additionally, a 13% drop in employment in the chemical industry from 2000 to 2005 provides some evidence to a drop in the number of chemical goods produced.

Figure 3. Industrial productions indices for Texas.

One can still ask what industrial energy efficiency improvements occurred early this decade in Texas. At the beginning of 2000, approximately 10.3 MW of cogeneration was installed in Texas. By the end of 2005, this was 17.5 MW – a 71% increase in capacity in six yearsF F. This is important because cogeneration, also commonly known as combined heat and power facilities, get more useful energy out of the same amount of fuel. Generating electricity and heat from more efficient systems decreases fuel consumption and emissions when it displaces less efficient systems.
However, electricity generation within the industrial sector was relatively constant from 2000 to 2005. Electricity generation from combined heat and power (CHP) facilities increased from 70 to 97 million MWh from 2000 to 2002, and then decreased to 85 million MWh by 2005. Overall, CHP generation increased 21% from 2000 to 2005, practically all outside of the industrial sector. Thus, many CHP facilities were installed, but the demand for their services did not seem to hold up.

The signing of SB 7 in 1999 began the deregulated electricity market in Texas. This change in policy ended up launching a tremendous increase in the installation and use of natural gas combined cycle units (NGCC) for electricity generation (see Figure 4). However, the move to NGCC generation technology had already begun in the early 1980’s. The NGCC units use the excess heat from a combustion turbine to generate steam for a steam turbine. This combination makes NGCC power generation much more efficient than generating electricity from either the steam or combustion turbine alone. Amazingly, Figure 4 shows the clear impact that deregulation policy had on the strategy in the electric power sector. From 2000 to 2005 the installations of NGCC units increased by 400%.

Figure 4. The cumulative installed capacity of natural gas plants in Texas shows that installation of combined cycle plants increased significantly starting in 2000F F. ST = steam turbine operating stand-alone, CT = combustion turbine of an NGCC plant, CA = steam turbine of a NGCC plant, GT = gas combustion turbine operating stand-alone, and CS = an NGCC plant where the combustion turbine and steam turbine are connected mechanically.

The employment situation in the industrial manufacturing sector shows a marked contraction (see Figure 5). Employment in the chemical and plastics industry was representative of the overall Texas manufacturing employment trend from 2000 to 2005. Employment in the oil and gas extraction industry was slightly up from 2000 to 2005, and followed the continually climbing energy prices through 2007. Interestingly, even in some industries that saw economic growth during the time span of interest due to an increase in prices for the manufactured good, employment went down (e.g. primary metals). Also, industries that experienced decreasing employment are many of those that are energy and natural gas intensive.

Figure 5. Employment indices for the overall Texas manufacturing sector as well as selected industries.


What this analysis shows are a few major points regarding Texas gross state product and CO2 emissions from 2000 to 2005: (1) the major growth of the Texas gross state product increased during the first half of this decade due to a rise in global energy prices and increased value of chemical products, (2) the boom in natural gas cogeneration installations does not nearly account for the 32% drop in natural gas consumption in the industrial sector as the generation from these facilities only slightly increased from 2000 to 2005, and (3) a drop in cogeneration systems from 2002-2005 together with a drop in output from the chemical industry accounts for a large portion of the decrease in natural gas consumption, and subsequently Texas’ CO2 emissions. Texas’ emissions may have even slightly decreased since 2005 with continued increases in natural gas and oil prices.
It is a mistake to think that significant steady and long term CO2 emissions reductions, together with increased gross state product, can be achieved by simply continuing actions of the past five to ten years. High energy prices benefit some Texas industries while hurting others, and there is evidence to suggest that higher energy prices have been influential in decreasing emissions from 2000 to 2005. Impending federal climate legislation will impose constraints on the economy that go beyond the reductions in emissions that have occurred in Texas as a consequence of external factors rather than by directed policy. Texas and the rest of the US states should work to understand how specific industries and consumers will be affected by a CO2 constraint. By promoting those businesses that are well-positioned and facilitating restructuring for those ill-positioned, Texas can successfully transition to and maintain leadership within the new carbon-constrained energy economy.

Wednesday, January 14, 2009

Texas Renewable Energy Assessment is out

The new State Energy Conservation Office report regarding the Renewable Energy Potential of Texas is now available online at:

This report is an update from the original 1995 report. As another major reference

Myself and Dr. Michael Webber are co-authors on the chapter regarding energy from water resources in Texas. This water chapter is not that exciting for Texas, but we do describe some of the latest concepts in the chapter. You can also see how much (really how little) electric generation comes from hydropower while you recall the large impact that the Colorado River hydropower facilities on the quality of life for those in the Hill Country. Thank LBJ for lobbying ... or whatever he did to "get things done" ... for those back in his early days.

For further general reference, also see the State Comptroller's Texas Energy Report on overall energy resources and usage in Texas.

Monday, January 12, 2009

Oil Import Interactive Map and Energy Consumption over Long Time Scales

The Rocky Mountain Institute has created an interesting way to view how oil imports into the U.S. have changed over time. You are able to see the magnitude of oil flowing from each exporting country for each month since 1973. Notice how imports from Iran go away after the second oil crisis.

Personally, I like to view view fossil fuel usage from a more historical perspective. The image below is a different "hockey stick" graph than the one most commonly referred to that shows CO2 or temperature increases in the last 30-40 years.

Figure 1. The world primary energy consumption and GDP over the last 300 years.

The image of Figure 1 shows the primary energy consumption and Gross Domestic Product (GDP). The basic point here is that the large increase in energy consumption has only been enabled by fossil fuels. Notice the first steam engine was built in 1712 by Newcomen. What does this graph look like when we look over the time scale of human civilization? I would not call it a hockey stick shape any more, but perhaps a wall of energy consumption (see Figure 2). Think about energy independence and sustainability when you contemplate Figure 2.

Figure 2. The world primary energy consumption and GDP over the last 6000 years.

Tuesday, December 9, 2008

Water and Transportation Fuels

View my white paper on Sigma Xi regarding the water consumption required for various types of alternative fuels. See: (also see below for full text of article if link).

In this white paper I refer to an article I wrote in Environmental Science and Technology on this same subject of the Water Intensity of Transportation. In this paper I calculate the "gallons of water per mile" that are embodied via consumption (meaning mostly evaporated) and withdrawal (taken from a water source and returned to the source) during farming, mining, processing, and refining of feedstocks into fuels.

Feedstocks studied are petroleum, coal, natural gas, sun, wind, biomass (corn and soy).
Fuels studied are ethanol, gasoline, diesel, biodiesel, electricity, hydrogen, and natural gas.

On the Water Consumption for Transportation Fuels
Carey W. King, Ph.D.
University of Texas at Austin
Center for International Energy and Environmental Policy

Driving light duty vehicles (LDV) on most alternative fuels and energy sources will
consume more water per mile driven than by driving on gasoline and diesel1. The
exceptions are using compressed natural gas with natural gas powered pumps, electricity
derived from non-thermal renewable electricity (e.g. solar PV and wind), and hydrogen
derived from either electrolysis of water using non-thermal renewable electricity or steam
methane reforming. To effectively plan for the environmental consequences of moving
from high energy density petroleum to lower quality fossil fuels and biomass, we must
not unduly distribute fuels with low energy return on investment. Water consumption is
just one environmental attribute for focus, but an important one from a quantity and
quality perspective.

In 2003 the average fuel efficiency of the U.S. LDV fleet was 20.5 mpg of gasoline.
These gasoline vehicles consume, via embodied water in mining and refining, 0.1-0.2
gallons of water per mile (gal H2O/mile). Using tar sands, coal, and oil shale converted to
liquids consumes 0.3-0.5 gal H2O/mile. If using electricity from the average U.S.
generation mix, driving a car using an electric motor from a battery consumes 0.2-0.3 gal
H2O/mile. If the grid electricity is used for electrolysis of water to create hydrogen, using
that hydrogen in a fuel cell vehicle results in consumption of 0.4-0.5 gal H2O/mile. Using
non-thermal renewable electricity for electric and fuel cell vehicles consumes less than
0.05 gal H2O/mile, and obtaining the hydrogen from steam methane reforming of natural
gas consumes just under 0.1 gal H2O/mile.

The other major category of potential LDV fuels is biofuels. If the biomass feedstock is
irrigated, using so-called “blue water” from aquifers and reservoirs, the water
consumption for corn-based ethanol (E85) and soy-based biodiesel is orders of magnitude
higher than other fuels with U.S. averages of 28 and 8 gal H2O/mile, respectively. Note
that only 10% of soy and 15-20% of corn bushels are irrigated in the U.S. However, some
highly irritating regions of the U.S. could embody over 100 gal H2O/mile by growing
irrigated corn converted to E85. Cellulosic-based irrigated grasses could result in 1-9 gal
H2O/mile of consumption. Without irrigation, fueling today’s fleet of LDVs using E85
ethanol and soy biodiesel would consume 0.1-0.4 gal H2O/mile, comparable to
unconventional fossil conversions.

For almost any product or application, but certainly for agriculture, the embodied water is
essentially transferred to drier regions. For instance, in providing food aid to developing
nations, the U.S. essentially becomes a net exporter of water – that is water embodied in
the exported food. If a given region does not have the climate, or irrigation water source,
1 King, C. W. and Webber M. E. Water Intensity of Transportation. Env. Sci. & Tech. Online
9/24/08 at:
for growing a certain crop, importing that crop may be a good option. However, should
the irrigation water be drawn from a fossil aquifer, the same crop grown under a different
circumstance will not be sustainable in the long term and should be considered a fossil
fuel itself simply based upon its supply chain, or life cycle. The irrigation of biomass
represents the growing of that biomass in areas with insufficient rainfall. This
relationship itself does not necessarily imply a lack of sustainability. For instance,
diverting nearby river water into a reservoir can create a stable supply source that can
withstand the normal climactic variations in rainfall.

The embodied water concept for agriculture can also be applied to biofuels but with
additional focus upon thermodynamics and energy return on investment (EROI). Many
regions may import some sugar cane-based ethanol from Brazil, yet don’t have the
climate to grow the sugar cane. Because of the relatively high EROI of cane ethanol over
corn ethanol, international shipping can make sense. Thus, the history, or supply chain, of
the biofuel is important, not just its final properties. The supply chain of fossil fuels will
also become more important over time as lesser quality resources are extracted. There
was no need to pay attention to EROI from the early coal beds and oil wells because they
so clearly allowed increased lifestyle and leisure relative to the world before the
industrial revolution.

In the concept of moving to non-petroleum fuel sources, the Renewables Fuels Standard
(RFS) of the Energy Independence and Security Act (EISA) of 2007 has been both good
and bad from a policy perspective:

Bad in the sense that the RFS initially pushes a feedstock-fuel combination, corn
ethanol, that has detrimental environmental consequence in terms of nutrient runoff
and low EROI. But, the consequences of runoff can be minimized by not overfertilizing,
more widespread use of better tilling practices, and buffer strips next to
major rivers.

Good in the sense that the RFS has pushed forward the scrutiny of how we use energy
resources, biomass included, and focused much attention on how we can create better
biomass to fuel conversions. It has also raised worldwide awareness on the ethics of
how agricultural land should be used: food, fuel, or both?

Today, the struggle for new fuel supplies is clouded because it is not obvious what
options best provide for increased or even continued levels of lifestyle and leisure. What
is more obvious is that there are geographic regions that can sustainably grow certain
kinds of biomass that other regions simply cannot. Unconventional fossil resources such
as tar sands and oil shale have lower EROI and higher water consumption needs than
conventional petroleum. The need for more water in industrial fuel systems is an
indicator of moving to lower energy efficient sources.

Lawmakers creating future policy regarding agriculture and energy need to be cognizant
that the tie between energy and water will only increase into the future. Generally, energy
sources with lower energy density tend to require more water for mining, farming,
refining, and processing. Certainly an increase in vehicle fuel efficiency decreases the
“gallons of water per mile” traveled, but in then end, fresh water sustainability is
measured on only one “per” basis: “gallons of water per Earth”.

Saturday, August 16, 2008

Pop Culture now involved in Energy is Good!

Many people have seen the Paris Hilton advertisement regarding "her" energy plan that is a compromise between the mainstream competing plans by the presidential candidates McCain and Obama. She was responding to the John McCain advertisement that compares Obama to celebrities such as Hilton and Britney Spears.

In reality, both candidates have fairly comprehensive energy plans because it doesn't make any sense not to. Drilling offshore is already done in the western Gulf of Mexico and everyone knows we need to bring on alternatives and some conservation through concepts such the as CAFE standards that are already going to increase.

So we can thank John McCain for luring in the popular culture of the US into the political and energy discussion. Now more people are involved. Great job Senator! He reached out of the aisle this time.

Thursday, July 24, 2008

Ethics: Allocation factors for renewable energy systems

I recently wrote for Worldchanging about how allocation factors can possibly be representative of our ethics. Allocation factors are the fraction of the energy input into a renewable system, usually for analyzing biofuels, that is associated (or allocated) to each of the products.

For example, the main product from corn ethanol is the ethanol, and coproducts are distillers grains for cattle feed. Because these allocation factors can be based upon the energy, mass, or economic content of the coproducts, different analyses of the same process results in different outcomes in terms of the sustainability or renewability of the process. One of the major issues is that what is economically most attractive is often not the most energetically efficient. A possible policy goal could be to guide these two concepts together.

Click allocations factors and ethics to go to Worldchanging website for the article, or read text below:


Moving toward a sustainable, or renewable energy-based economy, stresses the views of how people value their time and exertion. Our system of economics puts value on products and services that allow people to spend less time and/or exertion while performing a task. This value system is exactly why fossil fuels have been the driving factor for increases in accumulation of material goods and leisure time over the course of the industrial revolution.

Historically, fossil fuels have had such high energy density (and energy return on that invested to mine them) that we haven't worried too much about how to allocate the energy invested. When a barrel of oil is refined or a cubic foot of natural gas is burned, it has been obvious that we can produce more products and spend more time in leisure or progressive work. It is because of the concerns of fossil resource scarcity together with environmental effects (air pollution, greenhouse gases and climate change, etc.) that alternatives to fossil resources are sought.

By contrast, when it comes to renewable energy products, particularly biofuels, we've applied intense scrutiny to figuring out the energy return on total energy (or fossil energy) invested because the returns are not as easily determined as being sufficiently greater than one. Part of this scrutiny is because of the inherently lower energy density of carbohydrates (i.e. biomass) versus hydrocarbons (i.e. fossil fuels). Another part of the scrutiny derives from the knowledge that fossil fuels currently permeate the vast majority of the manufacturing and agricultural practices of the industrialized world, and understanding the optimal manner in which to deal with their reduced presence, and possible absence, is not obvious.

Allocation factors are an example of the struggle of society to understand the value of output of renewable energy systems and processes. The allocation factor is a term used to describe how much of the total energy input to a renewable energy system should be “allocated” to, or associated with, both the primary product output (e.g. ethanol, biodiesel, biocrude, etc.) as well as any process coproducts. These allocation factors are also used to assign greenhouse gas quantities to compare competing energy systems. Renewable energy systems that output electricity, such as photovoltaic solar panels and wind turbines, are fairly straightforward in giving an allocation factor of one. That is to say, all of the energy and material inputs that go into manufacturing, operation, and maintenance of the system are used to produce the only output: energy in the form of electricity. There is no product other than the electricity.

Assigning an allocation factor for biofuel production is more difficult. Biofuels originate from some form of biomass (e.g. corn, soybeans, cellulose, etc.) that can be used for multiple purposes (e.g. food and fuel) and the extracting them creates output products besides the fuel itself, termed coproducts. For example, in the typical processing of biodiesel from soybeans, the major outputs are the primary product of biodiesel plus the coproducts of soy meal and glycerin [1]. Fossil fuels have similar product/coproduct distinctions (e.g. natural gas for fertilizers and petroleum for plastics), but because we know there is no long term sustainable use of them, there has been no need to scrutinize how we derive their various products.

So a question arises: for every unit of energy input from field to fuel, how much of that input should be responsible for each product? To answer this question, there are multiple proposed allocation concepts. The different allocation methods for coproducts are three non-energy methods and three energy-based methods [2] that are designated by whether the energy consumption of the processes is allocated according to:

Non-Energy Methods
• the 100% principle such that all energy consumed is allocated to the primary product (e.g. biofuel).
• the mass fraction of each of the products,
• the economic market value of each of the products,

Energy-based Methods
• the energy content (calorific value) of each of the products,
• the energy displaced by each of the products with respect to an existing or customary way of producing the product, or

100% Principle
Allocating 100% of energy inputs to renewable energy systems is the most simplistic and uninformative. There are no decisions to be made, and it removes the capacity for society to learn how to use all available resources and technologies while reusing and recycling as much as possible. On the other hand, its simplicity easily allows policymakers and consumers to understand the impacts and benefits of renewable systems. Essentially, the 100% principle is the extreme case that assumes no useful coproducts are possible, or that coproducts are free in terms of monetary or energy input.

Mass Fraction
Allocating by mass fraction is very straightforward and easy to understand. Techniques that minimize coproducts should be viewed as positive since otherwise, they would not be coproducts but instead the primary product. We can likely assume the primary product is the most market viable, at least at the time the renewable energy project is begun.

Market Value
Using market value to allocate coproducts is the method most akin to the free market principles. Brazil’s past and continued focus upon sugar cane as a cash crop theoretically enables their companies to decide how much sugar versus ethanol to produce from the same crop. If one price is up, they can focus on that product versus the other. Currently, the ethanol price is up as a group of Brazilian companies has arranged the first “practical application of verified sustainable ethanol” trade with Sweden [3]. Thus, a market value of coproducts potentially allows a producer to tune his process according to the rather short time scales of commodity fluctuations. The main drawback of this method is that market prices change, and what could be a good energy balance one day could be a poor one a week later [1].

Energy Content (calorific value) of Products
Focusing upon the energy content of the products seems like a fundamental method because the purpose of renewable energy systems is to produce a product with high energy content. The primary product should in fact contain more energy than the coproducts, otherwise the system may have to be reanalyzed in terms of thermodynamic efficiency. This suboptimal energy content ratio could possibly occur if there is pressure to tailor a biofuel to existing infrastructure (which would be a pressure from the market). The difficulty with this method is that it does not indicate the effort required to achieve the energy intensive fuel or product. For instance, lasers contain high power concentrated in a tight beam, but much power is required to get the energy in that form.

Process Energy Input
Allocation due to the energy input into the renewable system seems like a logical choice because we are, after all, trying to figure out how to allocate the energy consumed in the renewable energy process. However, this allocation method can be somewhat confusing when the primary product and one or more coproducts results from the same subprocess. For example, if there is an unavoidable coproduct that results from the feedstock processing steps, how much input energy went into that unavoidable byproduct? What if the coproduct has no use, meaning it is actually a waste? Nonetheless, this method can often be more straightforward as in the case with wet-milling corn ethanol since during pre-treatment the starch (used for ethanol) is separated from the grain (used for coproducts), and thus subsequent energy used for processing the grain can easily allocated to the coproducts.

Energy Displaced (energy for replacement coproduct)
Allocation due to the energy displaced is an inherently comparative methodology. It requires diligent astute knowledge of the field of the product in order to know the energy input into replacement products. Also, an equivalent replacement product must exist. Here, the energy required for producing the primary product is reduced by the amount of energy required for the replacement product. For instance, Shapouri assumes that animal feed products (e.g. DDG) produced from corn ethanol processing can directly replace soybean meal. A difficulty arises if soy meal, itself a possible coproduct from biodiesel production, might use corn-based animal feeds as a replacement product as well. They can’t both replace each other. So there can be multiple choices of replacement products that can provide a range of answers for the primary product.

Can these allocation factors reveal something about culture, society, and how we value our energy and time? Is there a correct or more ethical method?

Pradhan et al. suggest that the correct method depends upon the question being asked. If renewability is the question, they say the mass fraction should be used, but if economic sustainability is to be determined, then the market value allocation approach should be used [1]. For philosophers who like to find the ultimate truth, this solution is rather non-satisfactory, and it avoids the question of whether the market should recognize that energy return on energy invested (EROI) is the major driver for economic growth or if economic growth potential is the driver for the choice of energy resources. The tail can’t wag the dog, but hopefully with enough flow of accurate information the EROI and economic return will continuously feedback to each other and arrive at the same solution.

[1] Pradhan, A.; Shrestha, D. S.; Van Gerpen, J.; and Duffield, J. 2008. The Energy Balance of Soybean Oil Biodiesel Production: A Review of Past Studies. Transactions of the American Society of Agricultural and Biological Engineers. 51 (1): 185-194.

[2] Larson, E. A review of life-cycle analysis studies on liquid biofuel systems for the transport sector. Energy for Sustainable Development. June 2006, Vol. X, No. 2: 109-126

[3] Guardian, UK. June 25, 2008. Brazil signs deal to export sustainable ethanol.

Tuesday, May 27, 2008

Water and Energy Nexus: Nature Geoscience May edition

I have recently written a commentary for Nature Geoscience in which I and my co-authors discuss the tie between energy and water usage. For those who have a subscription to Nature, you can link to the article here. Alternatively, you can sign up for free and read the article OR just read my pasted text below:


Water and solar energy enable trees and plants to grow today, just as hundreds of millions of years ago. Creation of the deposits of biomass that became fossil fuels depended on these two resources. The technological advances that have changed human life profoundly over the past decades and centuries have altered, but not resolved, this close coupling between water and energy. Current technologies for power generation, with some exceptions such as wind turbines and photovoltaic solar cells, rely heavily on the availability of large amounts of water. Primarily this water is needed for cooling thermoelectric plants and supplying fluid pressure and flow for hydroelectric power generation. But in a changing climate, it is not clear whether sufficient volumes of water will continue to be available where needed. And if, in an attempt to combat climate change, petrol is replaced by biofuels at a significant scale, more water will be needed for irrigation. Furthermore, clean fresh water is a basic necessity for human health and development. Large quantities of water can be provided — as long as sufficient energy supplies are available to reach deep aquifers, treat dirty water or desalinate the oceans. But a scarcity of energy implies a scarcity of water, just as constraints on water availability threaten the supply of energy, at least with the current infrastructure. Because of this interconnection (Fig. 1), water and energy cannot be treated in a disaggregated fashion, as is common today with both

markets and policy makers.


Large power plants present a strain on water resources. In the US in 2007, thermoelectric power generation, primarily comprising coal, natural gas and nuclear fuels, generated 91% (3,500 million MW h) of total electricity. These thermoelectric power plants require cooling by water, air or a combination of the two (Table 1), amounting to 40% of US freshwater withdrawals. Open-loop (or once-through) cooling withdraws large volumes of surface water, fresh and saline, for one-time use and returns nearly all the water to the source with little of the overall water being consumed by evaporation. While open-loop cooling is energy efficient and low in infrastructure and operational costs, the discharged water is warmer than ambient water, causing thermal pollution, which can kill fish and harm aquatic ecosystems. Thus, environmental agencies regulate discharge temperatures, taking into account a water body’s heat dissipation capacity. Closed-loop cooling requires less water withdrawal because the water is recirculated through use of cooling towers or evaporation ponds. However, because the cooling is essentially achieved through evaporation, closed-loop cooling results in higher water consumption (Table 1). The alternative, air-cooling, does not require water, but instead cools by using fans to blow air over a radiator similar to that in automobiles. The power efficiency of this is lower, up-front capital costs are higher and real-estate requirements are larger, making it a less attractive option economically.

Water is obviously central to power generation in hydroelectric dams. In the US in 2006, hydroelectric power plants generated approximately 7% (268 million MW h) of total electricity. Fifty-eight percent of US hydroelectricity is generated in California, Oregon and Washington alone, making the power supply vulnerable to regional changes in water availability. Though hydroelectric power is attractive for many reasons, it is least reliable during droughts when the need for water may take precedence over hydroelectricity.


The relationship goes the other way too, in that energy is necessary for producing and delivering fresh and potable water, just as water is necessary for generating energy. For example, energy is needed to convey, heat and treat fresh water and waste water. Heating water in homes and businesses for cooking, cleaning and other municipal and commercial uses consumes 3.6 quads, or 3.6%, of total US energy consumption. Thus, the need for hot water represents an important enduse for energy. Combined heat and power systems are efficient because they use otherwise wasted heat to do useful tasks.

Supply and conveyance of water is one of the most energy-intensive water processes, estimated to consume over 3% of total US electricity1,6. However, the energy use for supply and conveyance of water varies widely depending on the local infrastructure. Many gravity-fed systems require little energy, whereas long-haul systems, such as that in California, require vast energy investments to move water across the state and over mountain ranges. The average surface water treatment plant consumes over 370 kW h Ml–1. Tapping into groundwater sources also requires energy for pumping, which is dependent on aquifer depth: at a depth of 120 m, 530 kW h Ml–1 is required1,6.

Recent news articles illustrate these competition between water resources and power generation: the debate of whether to use water from a reservoir to serve municipal needs for drinking water versus generating hydroelectric power arose with Uruguay’s Salto Grande dam and the US Colorado River lakes; a natural gas power plant and private landowners argued over groundwater rights in Texas; and hydroelectric dams were taken offline in response to drought in Georgia, among others2–5.

As freshwater supplies become strained, many have turned to water sources once considered unusable, including brackish ground water and sea water. Although use of these water sources mitigates constraints on drinking-water supplies, treatment of brackish ground water and sea water requires as much as 10–12 times the energy use of standard drinking-water treatment. However, usually, untreated saline water can be used to cool the thermoelectric power plant that may be required for desalination.

Partly because of the high energy requirements, proposed desalination water treatment plants in Carlsbad, California, and Chennai, Tamil Nadu India have been opposed7,8.

Wastewater treatment also requires large amounts of energy, which will increase as discharge regulations in the US become stricter, requiring increasingly energy-intensive treatment technologies.

Estimates range from 250 kW h Ml–1 for trickling filter treatment, which uses a biologically active substrate for aerobic treatment, to 350 kW h Ml–1 for diff used aeration as part of activated sludge processing, and 400–500 kW h Ml–1 for advanced wastewater treatment that uses filtration and the option of nitrification6. Sludge treatment and processing alone can consume energy in the range of 30–80% of the total energy used in a wastewater plant; other physical and chemical treatment processes use much of the remaining percentage.


Two of the earliest fuels were wood and dung. They are still the major primary energy fuels for many regions of the world, providing 8.5% of the primary energy globally10. Trees require water for growth, as do the animals that supply dung. But modern liquid fuels such as gasoline, ethanol and diesel also require water for their extraction, farming, processing and refining. This ‘embodied water’ is not directly used in a vehicle, but rather indirectly required to make the fuel.

Water use for transportation can be considered in a similar fashion as for power generation in the form of withdrawal — that is, the amount of water that is necessary, but may eventually be returned to the system — and consumption, for example, through evaporation. However, in the context of transportation, consumption can additionally be associated with irrigated farming and as a feedstock. Generally, while driving light duty vehicles using current petroleum-based gasoline (assuming an average fuel economy of 20.5 miles per gallon (mpg) = 8.7 km l–1) and diesel (28.2 mpg = 12.0 km l–1), embodied water is withdrawn and consumed from nature at rates of up to 1.5 l km–1 and 0.3 l km–1, respectively.

Using liquids converted from other fossil fuels (coal, oil shale and tar sands) means that the rates of water consumption and withdrawal are 2–4 times and 1–2 times higher, respectively, and they are much more concentrated in regions where the fossil fuel resources exist.

Propelling vehicles using hydrogen and electricity also has substantial water impacts when drawing from the average US electric grid (owing to water used for power plant cooling as discussed earlier). Under these assumptions, driving ‘electric’ miles using a fuel-cell vehicle with hydrogen via electrolysis and a plug-in hybrid electric vehicle (PHEV) or electric vehicle (EV) consumes water at 0.9 and 0.5 l km–1 while withdrawing 27 and 17 l km–1, respectively11,12. Using wind and photovoltaic solar power to supply required electricity for transportation makes water intensity negligible. However, even if every US light duty vehicle mile were driven via US electric power with current technologies, US water demand would only increase by 0.9% (3.4 billion litres per day). Most of the fuels under consideration to replace petroleum are more water intensive, with biofuels residing at the top of the list. Only for fuel crops that are not irrigated is the water intensity comparable to petroleum fuels. But many fuel crops are irrigated, and accounting for irrigation can cause water consumption rates to be 2–3 orders of magnitude higher than without irrigation. Although only 15–20% of US corn and 5–10% of US soybean bushels are irrigated to any degree, there was still a substantial water contribution to biofuel crop farming at nearly 5,700 gigalitres (3.5% of US water consumption) in 2005 for the production of ethanol alone. Given that agricultural irrigation is the most water-consumptive sector of the US economy, high water usage is not surprising. But by switching to biofuels, this water consumption is likely to grow.

Additionally, competing water demands oft en make the siting of ethanol plants difficult because they require large amounts of water. Ethanol processing plants consume water for cooling processes, including the exothermic fermentation reaction, requiring 1–3 million litres per day to produce 250,000–750,000 litres per day of ethanol13,14.


We see trends towards more water- intensive liquid fuels, more energy-intensive water sources and a growing population that will require more of both. These challenges will be exacerbated by climate change, which may cause geographic and temporal changes in the amount, annual distribution and form of precipitation (for example, as rain or snow). Because cities and their infrastructure are built on the basis of past precipitation patterns, such climatic changes may require substantial adjustments. In regions where water becomes scarcer, people must weigh the pros and cons between moving the people to the water and moving the water to the people (the latter of which requires continuous additional energy).

Regional climate projections will be needed to inform planning and policy. When siting new power plants, governments and power generators need to consider water availability over the plants’ lifetimes, normally on the order of several decades. Policy for energy and water resources should be integrated to consider less-water-intensive options in agriculture, such as forestry, and in electricity generation, such as wind, photovoltaic solar and air-cooling technologies. In the fuel sector, water consumption and withdrawal need to be included in environmental impact analyses such as those dictated by the Energy Independence and Security Act of 2007, which requires life-cycle analysis for understanding the greenhouse-gas impacts of renewable fuels. Like diversified long-term financial investment strategies, future water and energy infrastructure should also be diverse and multiscaled in order to create resilience in an uncertain climate and energy future. For example, Ghana has had highly fluctuating reliability of electricity supply owing to heavy dependence upon hydropower or other single energy sources, without extensive electric grids to help transport electricity in tough times.

Distributed energy systems provide smaller-scale systems and add resilience to electric grids dominated by large centralized power plants, but they are usually considered more expensive owing to conventional financial and appraisal systems that account for capital but not operating expenses. For new power plants at greenfield sites in the US, open-loop cooling has been outlawed for all practical purposes by the environmental constraints on water intake velocity. The trend since the 1980s has been towards closed-loop cooling. However, closed-loop cooling makes the use of sea water more difficult, because evaporating water with high proportions of dissolved solids can create foul-up problems. Nevertheless using sea water, waste water and other low quality water for cooling should be encouraged where possible.

We also need policy that allows the operating costs and energy consumption of buildings and homes to be integrated into the construction, sales and finance phases of development. More energy efficient buildings within larger cities require less bulk city services. We must ask ourselves why we require no energy return on investment for crown moulding yet claim photovoltaics do not pay back fast enough. Fortunately sustainable concepts such as LEED (Leadership in Energy and Environmental Design) and projects such as the China EcoBlock18 guide and demonstrate integrated water and energy infrastructure via whole system design.

Water and energy cannot be separated. With an unlimited supply of available energy, we would be able to supply as much clean water as the world needs. In the real world of resource constraints, we need to simultaneously conserve water and energy. Thankfully, water conservation and energy conservation are synonymous with each other, so we have the opportunity for swift progress.