Argonne National Labs has released a report showing that the reduction of Greenhouse Gases (GHG) is smaller than you might expect from transitioning from gasoline vehicles to plug-in hybrids – only a reduction of between about 20-50% reduction, with a petroleum reduction between 40-60%. So whats going on here?
The report (via Green Car Congress) lays out a number of profiles for PHEV usage – both geographical (CA, IL, NY states) as well as the type of fuel and secondary generator – ICE with gasoline, E85 or diesel, or hydrogen fuel cells with various H2 sources. The report is through, determining regional power generation mix, marginal fuels used to supply power for the plug-in vehicles and factoring that into the GHG pollution.
After reading the report, the few things that struck me as odd. First was their calculation of miles traveled on electricity vs. fuel. Even for the 40-mile all-electric range (AER) PHEV (PHEV40), their utility factor (how much driving was done on plug-in power) was only 63%. This means that the average person is only driving 63% on electricity from the utility, and the other 37% of the time they are running on whatever electricity-generation system they have built into the car (Section 4 p.21, Table 7 & Figure 8).
This number seems odd to me because it is rather low for my personal expectations (85-95% UF), and the average miles traveled per registered vehicle in the US is 12,000 miles. Even averaging all of that driving over a 5 day (weekdays) window and no weekend driving, that’s 46 miles per vehicle per day, the 7-day average is about 33 miles per day. The report indicates that with a PHEV40, at 63% UF, the driver would drive 63.5 miles before recharging (assuming a full recharge) or more likely, using less energy from the wall and more energy from combustible fuels or a fuel cell.
The issue, which is even acknowledged by this report and the research it relied on for the PHEV vehicle mileage figures, is that there isn’t a lot known about driving and how PHEVs would fit into that scheme, as well as the lack of clarity of the size of the window for the PHEV investment to pay for itself. A detailed analysis of VMT figures – not just averages and totals, but rather average miles traveled on a workday (assuming a 5 day work week), miles traveled on non-work days, miles traveled on trips outside of the standard weekday/weekend patterns (a three hour drive to grandma’s house for example) is really needed to see what the UF of PHEVs will be when they start to arrive in stores next year. Beyond that, is there a psychological factor that would cause people to change their driving habits in such a way as to try and say on electric only, and how would that psychology be affected by gas prices – $2/gal gas people may not care much, but $5/gal gas would make people stay electric only as much as possible (plugging in at work, while they shop, etc).
Next is the use of “marginal” fuels to provide the power on the grid. The study used peak power oriented sources (sources that can be spun up and down as the grid demands change) to account for additional night time demand. However I think this is questionable – as PHEV usage increases this demand is (hopefully, from a grid operators perspective) spread out through he night. Rather than having a secondary night time peak, the peak would be distributed in such a way that demand is flat throughout the night – a valley filling approach rather than a second peak. Because this approach will be valley-filling, this would increase the amount of baseload power needed. This would support building nuclear, geothermal, and other baseload generating facilities.
Finally, I question the use of a blended-charge depletion mode. In order to reduce the size of the battery (specifically, the peak power output needed from the cells), the operating strategy is changed to allow for the use of the engine during charge depletion mode (in vehicles like the Volt, this is not expected to be the configuration). This would increase petroleum usage and vehicle tailpipe GHGs. This did however have the effect of boosting charge depletion mode to above 45-miles range (vs. the standard 40 miles in a pure charge depletion mode). This is questionable however as the targeted 2020 battery price and performance parameters would provide enough power to not require the use of an engine to supplement peak power. They do use a model 2015 year car, however it would seem odd to characterize this as the future of PHEVs.
The Japanese 2020-battery spec would allow for a pack half of the size and weight of the Volt pack (90kg vs. 180kg) but carrying the same usable of energy (8kWh, 14kWh total) and generating more power (160-200kW vs 120kW) of the current Volt pack at a price 25% of what the Volt pack is estimated to cost. Whether or not the battery comes to fruitioin is another question as it would require about a 10%/yr increase in battery performance characteristics, or double the historical average. With such a larger market, additional investment could drive additional technology gains.
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