My guess would be the sometimes requirement to warm up the engine. But, of course, we avoid that at all costs for our many short trips. Fortunately they also provide a kWh/100mi number which we can more easily relate to.
EPA test has city and highway cycles. The city cycle and the beginning of the highway cycle was ran in pure EV mode. In the middle of the highway cycle, the gas engine runs briefly to blend some gas. Additional information you may be wondering... For the combined 95 MPGe rating, EPA took account of electricity usage (convert it to gallon equivalent) and the actual gasoline used (which drags down the number closer to 50 MPG). The total mile driven in both test cycles, is divided by the total gallon. My actual EV efficiency for driving in the city and highway below 62 mph is 132 MPGe. My gas efficiency is 54 MPG. YMMV but I see that's about what other PiP owners are getting. EPA label has AER=6 miles, meaning all electric range of 6 consecutive miles. If the gas engine starts in the middle of the cycle, you are done and the counting stops. It is misleading but that's how they decided to test. PiP owners are getting 11-12 EV miles. PiP counts the EV mile whenever the gas engine is off and you are running on the plug electricity (charge deplete). Engine off miles in HV(charge sustain) mode is not counted as EV mile.
The only reason gas was included for PiP was because it blended some gas during the highway test cycle. Another plugin hybrid like Volt does not have gasoline included in the MPGe since it ran through the test without gas engine operation. Despite with the gas blended in at 50 MPG, PiP is still rated 95 MPGe. 2012 Volt is rated 94 MPGe (no gas) and 2013 Volt is rated 98 MPGe.
I would expect the PiP indicator to include any regeneration energy produced while in the EV mode. The PiP does such a good job of that and will extend the EV miles obtained from the original charge if the terrain is favorable. That would produce a somewhat better kWh/100mi value for a given trip. Whereas the EPA probably makes this kind of test on the flat at some average speed so as not to have the complication of the terrain.
Yes, PiP will do better on a flat terrain with no stops. I have seen some reporting 18 miles from a charge. EPA test simulates hills and stop and go traffic, all done on a dyno in order to have ability to reproduce the same result. You can see the graph right here.
If you look at the power consumption curves for various EV models (as posted in this forum), it seems that once you get above 30mph or so, air resistance is by far the dominate factor. Does the EPA test calibrate the dyno to take into account the the air resistance profile for a particular model? The Prius has one of the lowest air resistance factor of any automobile. The bogus "6 mile EV range" of the PiP is due to a simulated hill in the EPA test at 6 miles, which is "steep" enough to trigger the ICE in the PiP, but not in the Volt. If the simulated hill had been at 10 miles, the number would have been 10. It is not related to battery exhaustion.
CharlesH, how are the hills in San Jose? How does PiP do in the realworld driving there? Have you driven in San Francisco?
I suppose it's possible to get 18 miles on flat road without using the gas engine but you would have to drive very slow at a steady rate with few if any stops for 18 miles. That's not realistic outside of a test track. The reports of 18 miles of EV range that I recall involved using the gas engine to generate additional electricity back into the battery (by , for example, actively using the HV and EV buttons). Accounting for only the EV or HV portion of driving while blending both energy sources is complicated. That's part of the reason that I set up the 7-11 PiP/Volt Switcheroo earlier this year. Both cars were driven by the same drivers over the same long commute pattern for a similar number of miles over 4 consecutive days. I drove my portion of the results entirely within the EV capability of the Prius Plugin so the engine for both the Prius and the Volt only started up after all battery miles were depleted. The results are at: PiP/Volt January 7-11 Switcheroo | Page 11 | PriusChat I'm looking forward to hearing from CharlesH, but I thought the Prius Plugin was fine on my realworld commute from San Francisco to the San Jose area for my conservative driving style. Most of San Jose is generally flat except for the mountain hillsides. Many of the hills in San Francisco are likely to start the engine on the PiP in normal driving. It wasn't much of a problem for my commute since the first part was generally downhill in the morning and by the time I was going uphill on the last stretch of my commute home I had already run out of EV mode battery power. Nonetheless, I was able to average 65 mpg in HV which also included many miles driving along the rolling hills of highway 280 in addition to many flat files driving on highway 101.
That's very interesting. So the 29 kWh/100mi should be pretty realistic. It would be interesting to see these tests. "EPA has established testing criteria for electric vehicles and plug-in hybrids that are slightly different than those for conventional vehicles."
I have not driven in San Francisco, and in fact generally avoid going there if at all possible. The city has a culture which is, in my opinion, very hostile to cars. The city government is very creative about coming up with ways to separate drivers from their money... lots of arcane rules coupled with aggressive enforcement, including lots of very expensive towing for things which would be tickets elsewhere (the towing companies apparently make generous campaign contributions to the city officials, and the city gets a cut of the towing fee). In fact, at one point they were talking about setting up toll booths into San Francisco from cities to the south (it's water with toll bridges on the other sides), but the officials in the other cities blew a fuse on that one. Most of my driving is pretty flat, between the San Jose area at the south end of the bay and up the peninsula on the SF Bay side (the hills are on the Pacific Ocean side). I tend to drive reasonably conservatively, but I am not a "hypermiler". I tend to get around 58mph on trips in HV-only mode. There are some serious hills to cross over when I go the Sacramento area in the Central Valley, but I just drive and don't get paranoid about the EV/HV stuff, and it works just fine. My wife's philosophy is "just drive it", and she completely ignores the EV functionality other than plugging it in at home.
My guess that with a slow enough and flat enough drive that the PiP can do almost 25 miles on a single charge.
