Cost, Land, Air and Water

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Posted January 22, 2008 with 94 reads

Keywords: alternative energy, biofuel, biomass, climate, energy, vinod khosla, Environmental Policy, Biofuels

With the appropriateness of biofuels for the transportation sector in question and the increasing call for “a more granular assessment of the benefits and impacts of different biofuels”, Vinod Khosla¹ proposes to the Gristmill audience one approach to assessing sustainability.

We think a good fuel has to meet the CLAW requirements:

C — COST below gasoline
L — low to no additional LAND use; benefits for using degraded land to restore biodiversity and organic material
A — AIR quality improvements, i.e. low carbon emissions
W — limited WATER use.

Cellulosic ethanol (and cellulosic biofuels at large) can meet these requirements.

Sustaining our environment for future generations may mean biomass-based power generation rather than biofuel production.

With investments in Range Fuels, Coskata, and others, Khosla certainly wants an image of viability to prevail for ethanol as an alternative transportation fuel. Gristmill commentator justlou finds his arguments fantastically optimistic!

Khosla provided a set of assumptions with a scenario for biomass to liquid fuel.

1. Cellulosic production is assumed initially to represent ethanol demand not met by corn — by 2030, it is equal to the numbers of gallons of ethanol equivalent needed to replace all light-vehicle gasoline usage. I assume the mileage discount for ethanol vs. gasoline declines from 25% in 2020 to 15% in 2030.
2. Biomass from waste production is not explicitly modeled here — I believe this has the potential to meet 10-20% of biomass need.
3. Current CAFE laws are assumed to reduce gasoline demand. Additional ICE engine efficiency / higher CAFE could substitute for higher efficiency on ethanol assumed above.
4. Yield projections (tons per acre) are based on fertile land. The usage of degraded land will result in lower yields. Yields projections (gallons / ton) go from 90 tons per gallons today to 110 tons per gallon in 2030.
5. I assume that the primary source of dedicated land for energy crops will be cropland, but commercial reduction in today’s forest resource usage (i.e., more paper mill closures) could be offset by using it for biofuels, while also reducing the amount of cropland needed.
6. If winter over crops do not provide any biomass, I project energy crop usage of 57M acres in 2030 — furthermore, if yields are 18 tons/ac instead of 24, I project total land use at 76M acres.
7. I believe that replacing diesel may require an additional 18m acres in cropland, but it is not included here.

Yield Density
Source: David Bransby & Ceres (PDF)

Khosla writes, “In my opinion, cellulosic ethanol plants need to reach production levels of 100m gallons per year per plant to achieve economies of scale. (Expensive fuels don’t sell! A local conversion plant near the field and distributed supply would be ideal, and I continue to investigate technologies that might make this possible).”

He perceives that per year each plant would need a supply of around 1,000,000 tons of feedstock. The processing of such quantity is a significant undertaking, and a reason that Khosla would prefer cellulosic ethanol produced from readily available, already prepared feedstock. Yet a recently released study, i.e., the Zah study, which used two criteria: 1) greenhouse-gas emissions relative to gasoline, and 2) overall environmental impact—an aggregated measure of natural resource depletion and damage to human health and ecosystems, showed ethanol from grass as nearly equal to gasoline in overall environmental impact.

Such finding stress the importance of a more extensive analysis of biofuel sustainability. For instance, if one simply examines GHG emissions in the most optimistic scenario, cellulosic ethanol is a winner. “Regular” gasoline has a value of 85-92 g CO2 eq / MJ, while cellulosic ethanol, when derived from municipal solid waste, has a value of about 5 g CO2 eq / MJ.

Not only is the emissions profile relatively favorable, the feedstock is readily available. Khosla writes:

Promising waste feedstocks include municipal sewage, even municipal solid waste — the paper, wood, construction waste, even lawn clippings that are brought to a landfill. Something that has been a problem (especially with disposal) may soon become an opportunity!

There is sufficient municipal waste to produce tens of billions of gallons of ethanol. The waste is available in large enough quantities (in most major cities) to justify waste-specific plants and actually has a negative cost (usually a tipping fee).

How promising depends upon who and what you ask. Some of Khosla’s optimism may be predicated on which part of the elephant grasped. We consider EROEI “a less important variable than carbon emissions per mile driven,” he states. But, if you diminish the thermodynamics, then your prospects probably will be overly optimistic.
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