Vehicle Electrification Common Sense
By Rud Istvan,
This is the first of two loosely related technology posts that ctm suggested might be interesting to WUWT. In full disclosure, the details stem from my financial interests in energy storage materials and related topics, having spent much time and money since 2007 on fundamental now globally issued energy storage materials patents for supercapacitance (the Helmholtz double layer physics that creates lightning in thunderstorms). Some of the info cited below is slightly dated because I was too lazy to make everything current. Some of this info was borrowed from my ebook The Arts of Truth and from a 2017 Climate Etc post. All conclusions nevertheless remain valid.
This post’s message (the abstract, if this were a normal clisci peer reviewed paper) is simple. Hybrid vehicles make economic and ‘climate’ sense. Plug ins may or may not depending on their architecture. Full electric vehicles (EVs) make neither economic nor climate sense.
There are various levels of vehicle electrification, so some definitions are needed. Hybrids all involve some degree of electrification of an otherwise fossil fueled vehicle. There are three generally accepted levels:
1. Simple engine off at idle, aka start/stop. This is not as technically easy as it sounds, since hydraulic fluid coupled automatic transmissions must be fully redesigned and starter batteries beefed up. Depending on drive circumstances, idle off can save about 5% fuel efficiency.
2. Regenerative braking, where the vehicle’s kinetic energy is recaptured to electrical storage and then reused in some fashion rather than dissipated as heat. Depending on vehicle size/weight and drive circumstances, regen braking can save about 7-9% fuel efficiency. Combined with idle off it is commonly known as mild hybridization, and typically cited mild hybrid values are something less than 15% net fuel efficiency gain. (There aren’t a lot of milds out there to provide real data.)
3. Full hybridization, which includes idle off, regen braking, and electric acceleration assist (plus some degree of electric only slow speed short distance motoring). Full hybrid fuel efficiency gains can be as high as 35-45%. Prius is the best known. Full details follow.
Then there are Plug in Hybrids (misleadingly aka PHEV), which can motor for some significant distance under battery alone. These come in two basic architectures. One is an ordinary full hybrid with a different or bigger battery, like the Prius Prime. The other is actually a range extended electric vehicle (not a true hybrid), like the Chevy Volt. The idea is to remove EV range anxiety, since a gasoline engine kicks in only when the battery is nearly exhausted. Details follow.
Then there are true electric vehicles like the Chevy Bolt or Tesla models. These operate on battery electric power alone, must be recharged from the grid, and commonly present ‘range anxiety’ for some subset of ordinary car use.
This post develops common sense conclusions for the following practical economic and environmental categories/cases:
-Start/Stop may make sense for both cases, but Milds do not;
-Full Hybrids almost always make sense for both cases;
-Plug Ins do or don’t make sense depending on the architecture;
-EVs never make sense for either case.
Simple start/stop makes economic and environmental sense by itself when the automatic transmission technology is changed from hydraulic fluid coupling to electronic dual clutch mechanical transmissions (DCT). Ford has announced that by 2019 all Ford transmissions (including pickups) will be DCT (which can simulate manual). Even without start/stop, the DCT alone gains 5-8% fuel efficiency by eliminating hydraulic fluid coupling losses. With a beefed up starter battery enabling start/stop, the full fuel efficiency savings are 10-13% while the incremental cost is minimal, maybe $100 for a beefier starter battery.
Mild hybridization has been tried several times, but it has almost never worked economically. There are two problems: a battery capable of accepting regen charging energy is pretty big if having acceptable vehicle life, and the extra machinery for using that electrical energy for whatever purpose. The only present commercial mild system is Valeo (a belt driven bigger combined starter/alternator for both regen and traction boost, plus a supercap plus PbA ‘hybrid’ storage system). Valeo’s system is only on a few of Peugeot’s Citroen diesels in Europe.
Full hybridization like the Toyota Prius or my 2007 Ford Hybrid Escape [i] works in several synergistic ways to improve fuel efficiency, and makes more economic sense in larger vehicles. (Note, in 2007, both hybrid technologies were identical, just scaled to different vehicles. Ford traded its European small diesel technology to Toyota in return for the Toyota Prius hybrid technology, no cash exchanged nor royalties owed.)
Full hybrid idle-off saves ~5% depending on traffic. Regenerative braking saves another ~7-9% depending on traffic. The additional power and torque of the electric motor enables two further major savings. First, the internal combustion engine (ICE) can be downsized, saving both weight and fuel. My AWD Escape hybrid uses a small 1.5L I4 engine yet is functionally comparable to the heavier AWD Escape V6. Second, the ICE can be converted from the Otto cycle to the Atkinson cycle. Atkinson ICE saves about 20% in fuel economy, but at the expense of significant torque loss. (Typical Otto ICE vehicles are ~26-30% thermally efficient, the lower number from regular gas compression ratios, the higher from premium gas compression ratios. Higher octane rating enables higher compression ratios and more efficiency.) The newest Prius I4 5th generation 2018 Atkinson ICE gets an incredible 37% thermal efficiency on regular! Atkinson ICE torque loss doesn’t matter in a full hybrid; the electric machine provides more than the lost torque. The 2018 Prius family gets combined 52MPG. It couples a 95 HP 1.8L Atkinson I4 with a 71 HP electric motor for a total of 192 HP in a mid size sedan.
There are two 2018 Prius battery choices. All models except the Prime use NiMH, same as my Escape and as Prius from its 2000 launch. The Prius Prime is their Plug In. No different than the other 2018 models in any respect EXCEPT a lithium ion battery (LIB), onboard charging, and a different battery control software scheme. To get >10 year >100,000 miles life NiMH needs to be floated between about 45% and 55% state of charge (SoC). It is only possible to motor a couple of miles at speeds under 20MPH before the engine kicks in so the alternator can recharge the NiMH traction battery. LIB allows the Plug In Prius Prime to motor 25 miles at any speed before the ICE kicks in. Prime 240V recharge time is just 2 hours. Warranty is 10 years or 100,000 miles, same as the NiMH non-plug in versions. Toyota’s only real incremental Prime costs are the incremental LIB over NiMH and associated onboard AC/DC charging electronics. Yet Toyota charges a $3,100 Prime premium (starting Prime 2018 MSRP $27,300). Makes sense for Toyota, and for enviro customers who want plug in cache. Whether it makes climate sense is a question explored below using the Volt as the example.
Prius comfortably seats 5 along with 24.6 cubic feet (cf) of cargo space (or 65cf with the rear seat folded down). Range is 633 miles from ~52 mpg. 2018 price is ≥$24,200 depending on model and trim. Toyota unsurprisingly sold ~1,170,000 Prius from 2010 (year of Volt introduction) through yearend 2015.
Now compare the alternate architecture, a range extended EV like the Chevy Volt. The 2016 Volt is powered by two electric motors providing only 149 HP, fed from a 18.4 Kwh LIB providing a marketed ~50 mile EV only range, twice that of the 2018 Prius Prime. The original all-electric range was chosen because about 2/3 of US urban trips are under 40 miles. With a 240V charger, Volt recharging takes 4.5 hours (with 120V charging, it takes 13 hours). The battery is warrantied for only 8 years or 100,000 miles. The LIB battery weights 405# (189kg) and is a 5.5 foot long T shaped monster. The range extending gasoline engine is a 1.5 liter 101HP I4 driving an onboard 54 Kw generator. With a full tank of gas and a fully charged battery, Volt range is ~408 miles. Seating is essentially only 4, and cargo capacity is only 10.6cf. For those middling vehicle values compared to Prius Prime the MSRP is ≥$33170. Unsurprisingly, Chevy has only sold about 117,000 Volts from 2010 launch through YE 2015 (the same time frame as Prius sales above, so a fair comparison). The comparable sales data say the Volt does not make much economic sense.
Do plug ins make environmental sense? Lets take the Volt, because it is more reliant on the generation grid.
EPA fuel economy ratings are required by law to be prominently placed on all new vehicles for sale in the US. This familiar sticker provides three numbers: city, highway, and combined (55/45) mpg.
Ambiguity arises from the changed plug in meaning of ‘miles per gallon’. Plug in range extended EVs like the Chevy Volt operate partly on a battery recharged from the grid, so no gallons for those miles. Volt gets a combined 37mpg in extended range mode using its gasoline engine to generate electricity. If a Volt never traveled more than about 40 miles before being recharged from the grid, its engine would never start and it would never use any gallons of gasoline. Its combined miles per gallon would be very ambiguous since division by zero is mathematically undefined.
To solve this very fundamental problem the EPA did two things. First, they calculated an energy equivalent 93 MPGe for electric ‘no gallons’ mode. We shall see that this equivalence is based on faulty assumptions. Then they explicitly assumed the Volt travels about 45% on battery alone, giving a weighted average of 60 MPGe. Except in environmental reality the Volt cannot possibly get that ‘official’ EPA mileage.
One gallon of automotive gasoline contains about 132 megajoules of heat energy. Volt’s combined ‘extended range’ (using its engine/generator) 37 MPG rating is about (132/37) 3.6 megajoules/mile. One KWh is also 3.6 megajoules; the gasoline rating is equivalent to 1 KWh/mile. This of course includes the engine/generator’s thermal losses, which are proven by the Volt’s exhaust and radiator.
The EPA sticker also says the Volt gets 36 KWh per 100 miles when the battery is powering the Volt’s electric motors! That is only 0.36 KWh/mile, 2.8 times the efficiency from the same electric motors! This discrepancy proves that the EPA MPGe rating does not include the fact that grid electricity generation is on average about 45% efficient (mixed now about half and half coal at 34% and CCGT at 61%), with up to 10% of that lost in transmission and another 10% or so in distribution. Power plants have smokestacks and cooling towers just like Volts have exhausts and radiators. Correcting for the laws of thermodynamics (which were only applied to Volt’s extended range mode), the Volt operates in battery mode about (.36/[0.45*0.8]) 1KWh/mile in comparable net energy/emissions equivalents. Of course moving the car takes the same energy in either gas or battery mode; Volt’s electric motors don’t care about their source of electricity.
EPA’s battery MPGe should be reduced to account for the thermal losses in generating and distributing grid electricity, since these were included in the 37mpg gasoline rating. The true energy equivalent battery mode is about (93*.45*.8) 33.5 MPGe. No surprise that this is even lower than 37 MPG using gasoline. Charging and discharging the Volt battery is inefficient, causing additional energy losses; the Volt battery is liquid cooled and has its own radiator partition. We can even estimate that EPA’s measured Volt battery energy efficiency is about (33.5/37) 90%. Using the EPA’s assumption about all electric driving, the final overall rating should be about (33.5*0.45+37*0.55) 35 MPGe. The 60MPGe EPA rating just nonsense, and clearly the better environmental choice by a factor of (52/35) almost 1.5x is a less expensive Prius of some sort.
A final observation. It follows without further analysis that the EV Chevy Bolt makes no sense either economically or environmentally. And by extension, neither do any other EVs. Economically the Bolt is horrible (and higher priced Teslas are worse). Range is only 238 miles. An hour of 240V recharging provides only 25 miles of range; to get 238 miles requires about 8-9 hours of charging. The Bolt essentially seats four, with only 16.9cf of cargo space. Yet the MSRP is ≥$37500. On a correctly compared environmental ‘global warming’ basis, Bolt has to be even worse than the Volt.
[i] Personal economic data from comparable vehicle functionality. My AWD 2007 Escape Hybrid (small true frame based SUV [not a crossover]) with a class 1 tow hitch is most comparable to the 2007 AWD Escape with a 3L V6 engine and class 2 tow hitch. V6 was 240 HP, my hybrid has a combined 247 HP–153 from the 1.5L I4 Atkinson ICE plus 94 from the electric motor. The 2007 MSRP hybrid premium over the V6 was ~$3400. BUT that year’s federal tax credit for this hybrid was $3500, so we were $100 better off on day one. Better, the AWD V6 EPA combined mileage was 23mpg, while my equivalent Hybrid is EPA combined 30mpg. That is 30% better mileage, saving gas for now 11 years and 85k miles. Best, the V6 used premium, my hybrid uses regular. The price difference in our area is over $1/gallon. So not only less gas, also cheaper gas. The fuel savings work out to about $6700 so far. The NiMH traction battery is still going strong and the vehicle has been basically problem free.
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