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Originally Posted by tonybelding
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The Green Car Congress press release said:
"...A new study for the US Department of Energy finds that off-peak electricity production and transmission capacity could power 84% of the country’s 220 million vehicles if they were plug-in hybrid electric vehicles..."
But the actual study by the Pacific Northwest National Laboratory, at
http://www.pnl.gov/energy/eed/etd/pd...s_combined.pdf, said:
"...If charging periods are to be constrained to a 12-hour period starting at 6 pm and ending at 6 am, the technical potential would be reduced to 43% of the LDV fleet..."
Funny how the 43% from 6 pm to 6 am stated in the study morphed into 84% off-peak in the press release. Its also worth noting that the real off-peak period is typically shorter than 12 hours.
The real study also said:
"...Providing 73% of the daily energy requirements of the U.S. LDV fleet with electricity would add approximately 910 billion kWh, an increase of about 24% of the total U.S. annual generation, in 2002 [EIA, 2006b]. Without further infrastructure investments, the current electric power system would be heavily loaded for most hours of all days.
It is questionable whether today’s electricity infrastructure and capacity mix will be able to support this level of loading on a sustained basis. Planned outages for plant maintenance would likely need to occur more frequently, making it more difficult to schedule maintenance. Furthermore, the overall system reliability could be reduced in this high-use scenario as less reserve capacity is available to the system operators for managing system emergencies..." (emphasis added)
Kind of amazing how the study's questioning whether today's electricity infrastructure can support sustained vehicle charging was transformed in the press release to the certainty that existing capacity could power 84% of vehicles.
And the real study further said:
"...While we rationalized that PHEV charging could be done without setting new system peaks and causing new transmission congestions, it represents a significant shift from a power system with peaks and valleys to one that is constantly loaded. While the bulk power system is designed to operate reliably at these levels during peak periods, sustained operation at these levels may reveal new constraints. For example,
there may be intra-regional transmission constraints that come into place when transmission lines are heavily loaded for extended periods. Specific and detailed regional studies would reveal these delivery constraints. Similarly,
the distribution system may impose some additional constraints on the delivery limits to off-peak PHEV charging..." (emphasis added)
So the real study expects transmission and distribution constraints to limit charging capability, but the press release says not so.
Indeed. Who should one believe?