Friday, July 18, 2008

The 80-20 Rule



Often when I talk about Plug-Ins, I say that PHEV's are a perfect embodiment of the 80-20 rule. There are a lot of versions of the rule and it has been written about a lot. But in the case of the PHEV, the logic goes something like this:

Roughly 80% of our daily trips are under 35 miles. And the remaining 20% are longer trips. So why carry around five times more battery storage and weight for that 20 %? Take care of that 20% with a small, efficient gasoline engine that runs at its optimum speed.

This so called Pareto principle is everywhere. As a business, 80% of your income comes from 20% of your products. 20% of your time gets 80% of the work done. 20% of the population has 80% of the wealth. However, 70% of vehicles can apparently be fueled with no increase of electrical capacity.

There are a lot of facts and misstatements about Plug-Ins that circulate these days about water consumption, pollution, the need for new power plants, and the like.

This post from Climate Progress deals very nicely with a lot of them. Here's a piece of it:

Why do PHEVs reduce greenhouse pollution?

A study by EPRI, the California Air Resources Board, the National Renewable Energy Laboratory, Argonne National Laboratory, and others (5.3MB PDF) concluded that plug-in hybrids produced substantially lower greenhouse gas emissions than either conventional gasoline cars or unplugged hybrids. The reduction in emissions results from electric operation being much more efficient than gasoline operation.

Don’t PHEVs and BEVs just shift pollution from the tailpipe to power plants?

No. The proper comparison between vehicle types is the “wells-to-wheels” basis, where the pollution from extracting the raw materials, shipping, transformation (e.g. refining), and use are added. BEVs and PHEVs running on electricity have zero tailpipe emissions, but there are still mining and power plant emissions. Those emissions are however much lower than the corresponding crude oil extraction, refining, and tailpipe emissions. Pollution here includes greenhouse gases such as carbon-dioxide. The grid is getting cleaner each year, and will continue to do so as we replace fossil power plants with renewables, while a gasoline car gets dirtier as it ages.

Fueling a car on gasoline made from coal (Coal-To-Liquids or CTL) emits twice as much greenhouse gas as gasoline from crude oil.

Why is fueling a PHEV from coal electricity better than gasoline?

Two reasons: (1) Electric motors are extremely efficient compared to internal combustion engines, and this efficiency more than compensates for the dirtiness of coal. (2) The U.S. grid is only 49% coal (natural gas is 20%, nuclear is 20%, hydro is 7%, and other renewables are 2.4%). Thus power to charge PHEVs is not all from coal, and some is from zero emission sources.

Are the batteries ready?

Yes. According to EPRI, “battery durability testing sponsored jointly by EPRI and Southern California Edison demonstrate that current lithium-ion batteries are likely to retain sufficient capacity for more than 3000 dynamic deep-discharge cycles–about 10-12 years of typical driving.” The excuse “the batteries aren’t ready” has been used frequently because it is convenient, and few people bother to check. Any manufacturer sells what it has, and automakers are no different. When there are failures of planning in the board room, it is convenient for a manufacturer not to admit their mistake, but to blame the lack of a product on something beyond their control. That is PR.

The current absence of plug-in vehicles from America’s showrooms has been conveniently blamed on the batteries. In reality, existing, proven NiMH batteries, such as found in hybrids and BEVs could easily power PHEVs. However, automakers would like to switch from NiMH to Li-Ion batteries for PHEVs because they are lighter, smaller, and potentially cheaper. Common Li-Ion batteries (Lithium-Cobalt), such as found in cell phones and laptops have lifetime and safety issues, which allowed the automakers to claim lack of readiness.

However, other Li-Ion chemistries have existed for some time, so this claim was not accurate. For example, Lithium-Iron-Phosphate batteries are inherently safe and will last the lifetime of a vehicle. Also, the issues with Lithium-Cobalt batteries can be solved with the addition of other elements such as nickel and manganese. For example, Sanyo uses a mixture of Ni, Mn, and Co for the positive electrode, thereby producing a safer battery that exhibits power retention ratio of 80% or higher after 10,000 cycles (10-15 years in a hybrid vehicle). (more)

The good news is this.


And it won't be long before you can drive one.

And 80% of your transportation fuel can be 100% green.











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