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Will Electricity Challenge Ethanol?

Biomass to Fuels: Grasses like the field of Miscanthus above can create as much as 15 dry tons of biomass per acre. This can be converted into 870 kilowatt-hours of electricity to power a plug-in hybrid or electric vehicle; or into 80 gallons of ethanol to power a flex-fuel vehicle. This article compares the two choices.
Most electric vehicles were removed from the U.S. market when California withdrew the legal requirement to sell zero-emission vehicles in April 2003. It is hard to find former owners of electric vehicles who did not become attached to their cars’ noiselessness, lower fuel costs and ability to refuel at home instead of the local gas station.

Ethanol could displace most of our gasoline usage if we solve the technical challenge of making it from plant "biomass" such as agricultural waste, grasses and forest residue (known as cellulosic ethanol), rather than corn. (See Biomass Basics for background.) In our February 2006 newsletter , we described how liquid fuels derived from plant material, like ethanol, can compete with gasoline.

Alternatively, biomass can also be used to produce renewable electricity to power electric vehicles - if more powerful batteries can be developed. If cellulosic ethanol or electric vehicles - or both - become mainstream, the opportunity exists to replace significant amounts of gasoline with fuel derived from biomass.

As President Bush identified in his most recent State of the Union speech, America is addicted to oil. Alternative fuels that use less oil and produce less pollution reduce our dependency on oil, put price pressure on gasoline and diesel, and can reduce global warming pollution.

Electric Vehicle Batteries

Batteries have not been successful as automotive power sources primarily because the amount of energy in a battery is a small fraction of the amount of energy in gasoline. This problem is known as "energy density." To hold the same amount of energy as gasoline, today’s vehicular batteries would require over 100 times more space. Current nickel metal hydride (NiMH) batteries hold only about one percent of the "energy density" of gasoline.

Hybrid cars, cell phones, and a myriad of other consumer products have been driving demand for light-weight, high-capacity, rechargeable batteries. There has been a steady advance in batteries based on NiMH, such as those in the Toyota Prius, and lithium-ion in research vehicles. Lithium-ion batteries, while not yet in passenger cars, have also dramatically improved, are prevalent in cell phones and consumer electronics and have twice the energy density of NiMH batteries.

The typical lithium-ion cells used in laptops and camcorders weigh about 40-45 grams, have an output of 8.6 watt-hours, cost about $2 per cell, and have been improving in storage density at about eight percent per year. To travel 250 miles (using a projected 200 watt-hours per mile), an electric car would require a battery weighing over 500 pounds and costing about $12,000. If lithium-ion batteries continue to improve at eight percent per year, this would bring the cost down to $6,000 and the weight to 250 pounds in 10 years.

The fuel efficiency of all cars decreases as weight increases. Mile per watt-hour is the electric car’s measure of fuel efficiency, just as miles per gallon is the measure of fuel efficiency for gasoline cars. Increasing the size of the battery in the electric car decreases its fuel efficiency in proportion to the weight it adds to the car.

An electric vehicle will have much more weight in its batteries than a gasoline-powered vehicle with a full tank of gas. However, an all-electric vehicle avoids the weight of the gasoline motor (an electric motor is much lighter), the transmission and other items.

The issues of weight and efficiency have lead to three design choices:

  1. The all-electric vehicle: An all-electric vehicle is simple, reliable and produces no "tailpipe" emissions (see below for discussion of the pollution from electric generation). It is limited in range due to battery capacity, and the time to "refill the tank" (recharge the battery) is measured in hours. It is possible to augment the range of an all-electric vehicle by adding a small diesel/gasoline generator. This configuration is commonly referred to as a "serial hybrid."
  2. The hybrid vehicle: The hybrid vehicle, like the Honda Civic, Ford Escape or Toyota Prius, uses just enough battery electricity to make the gasoline engine more efficient and to absorb excess energy from braking and de-accelerating back into the battery. The hybrid’s only source of fuel is gasoline, as all electricity is generated in the vehicle. The efficiency of the hybrid’s gasoline engine is quite good compared to a standard gasoline vehicle. A gasoline engine is about 37 percent efficient only when it is on the highway. Efficiency in the city is much lower because the engine is idling at a stop or operating far from its optimum efficiency during acceleration and deceleration. The great virtue of a hybrid is that its engine does not idle. It is either off or it is operating near its optimum efficiency, so a hybrid engine actually operates at 37 percent efficiency a majority of the time.
  3. The plug-in hybrid: The plug-in hybrid provides a way to charge the battery separately and is both a complete battery-electric vehicle and a gasoline vehicle. More battery is added so the electric driving range of the vehicle is between 20 and 40 miles. (All-electric vehicles usually are designed for a 100 mile range.) For more information about current plug-in hybrids, see CalCars.
The all-electric vehicle and plug-in hybrid vehicles allow us to displace gasoline with electricity. As batteries decrease in price and increase in energy density, electricity could power more - or most - of our vehicles.

How Much Electricity vs. Gasoline is Required per Mile ?
Is There a Hybrid Premium?

We looked at 2007 Camry literature to see if we could discern a "hybrid premium" - that is, the extra cost of a hybrid vehicle compared to a gasoline engine model of comparable performance and features. The Camry is the latest hybrid offering from the highest-volume hybrid manufacturer, so it should be state-of-the-art. The following table summarizes the performance (horse power and torque) of three models of the Camry which otherwise have comparable features. The final column is the list price of these models.

Horsepower Torque
Mile per Gallon
XLE 4 cyl 158 161 24/33 $24,425
Hybrid 4 cyl 187 199 40/38 $25,900
XLE 6 cyl 268 248 22/31 $27,520

The hybrid Camry is intermediate in performance and price between the four-cylinder and six-cylinder gasoline engine models. If we scale by horsepower, we could argue that the Camry hybrid with no premium should cost $25,230, and if we scale by torque it should cost $25,787. That implies a hybrid premium of either $670 or $113. To the power-seeking consumer, the hybrid’s performance - let alone its fuel efficiency.- is justification enough for choosing it over the gas-only models.

Using the Toyota Prius as our test case, we can compare its gasoline engine performance to its electric engine performance. The author’s car actually gets 44 miles per gallon as measured over the last five years. A modified Prius developed by CalCars running only on battery power requires about 11,400 watt-hours of electricity (this is the equivalent power of 114 one-hundred-watt incandescent light bulbs turned on for one hour - or about 500 compact florescent bulbs) vs. one gallon of gas to travel the same 44 miles. CalCar’s plug-in Prius uses 260 watt-hours of electricity to go one mile. In general, recently built electric vehicles require 200-400 watt-hours per mile depending primarily on the weight of the vehicle and the battery technology.

How Far Can You Drive on a Ton of Biomass?

Both Ethanol and electricity can be produced from biomass. This is done either by using agricultural waste or specific plants such as switch grass, and either converting the energy stored in the cellulose plant cells to ethanol or combusting the dried plant material and converting it to electricity. The question becomes: Which is better?

Biomass -> ethanol -> ethanol/gasoline vehicle,


Biomass -> electricity -> electric vehicle?

According to the NRDC report Growing Energy , one can reasonably expect future conversions of biomass to ethanol to produce up to 80 gallons of fuel per dry ton of biomass.

According to the California Biomass Collaborative , one dry ton of biomass can produce about 870 kilowatt-hours of electricity.

Both ethanol and electricity have to be delivered to the vehicle and that requires some energy. In the case of ethanol, we estimate it requires about one gallon of fuel to deliver 100 gallons (assuming about 500 mile delivery). In contrast, transmission of electricity results in roughly a 10% reduction in energy. Charging the battery requires an additional 10% of the energy.

To summarize, one dry ton of biomass can deliver 79 gallons of ethanol to the vehicle or 705 kilowatt-hours into the battery of a vehicle (870 x .9 transmission efficiency x .9 charging efficiency).

A plug-in hybrid Prius goes one mile using 260 watt-hours. A "flexible fuel" Prius, one modified to run on either gasoline or ethanol, would achieve about 33% fewer miles per gallon running on 100-percent ethanol than 100-percent gasoline due to the lower energy in pure ethanol. This would drop the miles per gallon from 44 to 29. Thus, one dry ton of biomass will produce:

Prius running on electricity Prius running on ethanol
2,700 miles/ton 2,300 miles/ton

In other words, biomass-to-electricity and biomass-to-ethanol produce similar number of miles achievable per ton of biomass. However, there are major differences in feasibility today which will change over time:
  • Biomass-to-electricity and plug-in hybrid technology exists today while the potential of biomass-to-cellulosic ethanol is still unproven in volume.
  • Electricity can be transmitted to every home that an electric vehicle can be plugged in to, compared with the current limited infrastructure for delivering ethanol.
  • The auto companies have sold more than 5 million flex-fuel (ethanol-based) vehicles, but few have announced plans for electric vehicles. GM is rumored to be working on a plug-in hybrid (see GM Eyes Plug-in Hybrid . Toyota is starting to talk about their plug-in hybrid plans (see Toyota to Explore Plug-In Hybrids ).
  • According to the U.S. Department of Energy, advanced technologies for biomass-to-electricity such as gasification could double the electricity produces per ton which would provide 5,400 miles/ton.
  • Market pricing for electricity is relatively independent of oil, while ethanol directly displaces gasoline and, even though its production cost is currently significantly less than that of gasoline, tends to be priced just below gasoline.
How Much Does it Cost to Drive a Mile?

There is considerable savings in buying electricity to charge a battery vs. gasoline in today’s market. Using the night time electricity rate of 8.8 cents per kilo-watt hour, the cost to drive is about 2.3 cents/mile. At 44 miles/gallon, this is the equivalent of buying gas at $1.02 per gallon. If a driver recharges during the day, the price is likely to be 50 percent higher or more.

What are the Impacts on Greenhouse Gas Emissions?

According to Joe Romm, former head of the U.S. Office of Energy Efficiency and Renewable Energy, the "lifecycle" greenhouse gas emissions from a gallon of gasoline are about 25 pounds of carbon per gallon (20 from burning the fuel and five from making the fuel). In a Prius getting 44 miles/gallon, this equates to 0.57 pounds of carbon per mile.

The national grid averages 1.3 pounds of carbon per kilo-watt hour . Using the plug-in hybrid efficiency of 260 watt-hours/mile (plus 10 percent for battery charging), the vehicle emits 0.37 pounds of carbon per mile, or about 35 percent less than gasoline when using electricity only.

All this applies to vehicles using today’s infrastructure. We are now witnessing the deployment of E85 motor fuel (85 percent ethanol, 15 percent gasoline). (E85 is common in Brazil, but is only starting here). The decrease in the net carbon released into the atmosphere by combustion of ethanol depends on what type of ethanol is blended - 20 percent with corn-derived ethanol, 80 percent with sugar cane ethanol in Brazil, and 90 percent with cellulosic ethanol. The higher the percentage blend, the greater the greenhouse gas benefits.

There is also much discussion of carbon sequestration. Carbon dioxide generated from power plants of the future may, for example, be pumped into geological structures that formerly contained oil and/or natural gas to be sequestered from the atmosphere indefinitely.

If motor fuels go green before power generation goes green the lifecycle GHG emissions of hybrids will be lower than electric vehicles. If power generation goes green first, hybrids will compare unfavorably. In the distant future, when both power generation and motor fuels are green, it won’t make a significant difference.


As the U.S. looks to biomass as a renewable source of energy for transportation, two paths hold promise. In one case, the U.S. fleet would comprise increasing numbers of flexible fuel vehicles that can run on gasoline or ethanol. Ethanol production would transition from corn-based to cellulose-based. Alternatively, the U.S. fleet could be increasingly based on electricity, either through plug-in hybrids or all-electric vehicles.

In the first case, the major risk is the ability to produce cellulosic ethanol on a large scale. In the second case, it is the ability to develop higher-energy density batteries. Consumers are likely to find electricity significantly cheaper than ethanol. This is because electricity prices are regulated while ethanol prices are likely to be priced just below gasoline until there is a significant oversupply. E2 believes both paths should be aggressively pursued as they both offer alternatives to oil that will save consumers money and help reduce emissions of greenhouse gases.

Many thanks to E2 member Tony Bernhardt for co-authoring this article. Thanks also go to E2 members Felix Kramer and Ron Lloyd, and to Joe Romm and Brian Jenkins for providing key details.

World Clock