CHARGING WHILE DRIVING

Technology Improvement Pathways to Cost-effective Vehicle Electrification
Aaron Brooker, Matthew Thornton and John Rugh, April 12, 2010 (National Renewable Energy Laboratory)

THE POINT
The entire automotive world is utterly absorbed with building a better battery. The 500-mile battery has become the newest Holy Grail, the imagined solution to the inconveniences and anxieties assumed to be associated with current batteries’ limited ranges.

As the dark shadow of the Gulf oil spill has extended its ruination over a precious ecosystem, the search has intensified, symbolizing the urgency of transitioning the world away from oil dependency. The battery electric vehicle (BEV) is most certainly the answer to the ills of oil dependency but it will require drivers to learn to recharge after driving an all-electric vehicle (EV) 100 miles or switch to gasoline after driving a plug-in hybrid electric vehicle (PHEV) 40 miles. The 500-mile battery would make BEV-driving more like driving is now.

The transition to plug-in vehicles constitutes a revolution in personal transportation and - aside from ending dependence on coal for electricity, which the shift to BEVs will support - no transition today is more urgent. But according to Technology Improvement Pathways to Cost-effective Vehicle Electrification, from senior research engineers at the National Renewable Energy Laboratory, there may be an even better way to make the transition to electric personal transportation, a way that doesn’t require a miracle breakthrough in auto battery technology.

Charging on the move: An old idea born anew and wireless. (click to enlarge)

It’s called dynamic charging with inductive power transfer technology (IPT). It is as old as the concept of electric streetcars and trolley cars and as new as wirelessness.

The idea is to build highway infrastructure with the embedded capability to connect to vehicles and charge them as they pass.

The NREL study evaluated 5 ways to make EVs – like the Nissan LEAF arriving in U.S. showrooms this fall – and PHEVs – like the GM Volt arriving in showrooms this fall – cost-effective: (1) opportunity charging, (2) replacing the battery over the vehicle life, (3) improving battery life, (4) reducing battery cost, and (5) providing electric power directly to the vehicle during a portion of its travel.

The study developed a model for BEV use that considered battery cycle life, battery size and the national distribution of driving distances. Considering the best current estimates of battery life and cost, only the dynamic charging concept was a way to make extended EV driving cost-effective for the consumer. Significant improvements in battery life and battery cost will, however, eventually make PHEVs more cost-effective than the hybrid electric vehicles (HEVs) and conventional internal combustion engine vehicles (ICEVs) now on the roads.

If dynamic charging via a streetcar-like or trolley car-like connection seems impractical, it is because dynamic charging is different. It is based on a new kind of technological capability and a fact that came out of the NREL research.

The new kind of technology: Inductive power transfer technology (IPT) allows the car’s battery to be charged wirelessly via an on-board receiver as it passes by electricity generating sources embedded in the roadway.

The fact from the research: A very small part of the total road system constitutes the great portion of road use. Interstate highways are 1% of all roads but are 22% of all road use. Embedding wireless chargers in perhaps half of all roads would probably eliminate battery range as a factor in the decision to go electric.

From HaloIPT via YouTube

THE DETAILS
The U.S. imports 60% of its oil and uses 60% of all its oil for transportation.

The Gulf oil spill is an indication that U.S. oil resources are dwindling and tapping those sources remaining will be more expensive. Competition with emerging economies for other supplies will grow, making oil more expensive and dependence on it riskier.

A typical hybrid electric vehicle (HEV) reduces gas use 30% and could, with efficiency improvements, reduce it 45%. U.S. HEV sales have grown 60+% per year but, after 10 years, are still only 1% of the 237 million vehicles on U.S. roads and the 16+ million yearly new vehicle sales. Vehicles remain in use 15 years, on average.

Bottom line: Getting off oil is urgent and HEVs won’t do the job.

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Battery electric vehicles (BEVs) are the answer but today’s battery technology is inadequate to duplicate the convenience of driving a gas-guzzling vehicle with an internal combustion engine (ICEV). The state-of-the-art full-sized lithium-ion (Li-ion) battery slated for the all-electric LEAF will run it about 100 miles before the car needs a recharge. The smaller state-of-the-art lithium-ion (Li-ion) battery slated for the PHEV Volt will run it about 40 miles before the car will need to switch to gasoline.

Battery cost, battery capacity and battery life are currently considered the major concerns for BEV success.

The NREL researchers were seeking the best path to “cost-effective vehicle electrification.” Hypothetical vehicle (1) performance, (2) cost, and (3) battery life models were matched to current technologies and costs.

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Scenarios were run at various battery costs and battery life capacities and compared to ICEV and HEV costs and performances: (1) The battery was sized to last through the vehicle’s life, (2) the battery was replaced, (3) the battery was recharged at every opportunity instead of only at the end of the day, or (4) both battery replacement and opportunity charging were done.

According to auto market specialists J.D. Power and Associates, people will buy fuel saving vehicles if the fuel savings pay back the higher upfront cost and will not otherwise.

In the NREL study, insurance, maintenance, and repair costs were assumed to be the same for all the vehicles considered.

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Component costs, including the $700/kilowatt-hour battery, are higher for BEVs.

The NREL study followed others in accounting for the impact of larger batteries on cost, weight, and vehicle performance. It advances on other studies with evaluations of driving distance assumptions, battery life, battery sizing, battery use strategy, and the method for estimating fuel economy. It is reportedly the first study to consider dynamic charging.

The NREL study considered a much wider and more detailed variety of driving distances between recharges. This changed conclusions about battery life, control strategies, and fuel economy. It did this because the constant commuting distance previous studies have used is only one third of a car’s driving.

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Long trips are rare but take up a big part of total miles driven. The conclusion on this part of the study: They reduce a PHEV’s fuel economy but it is still preferable to an ICEV. Long trips are especially difficult for EVs.

The conclusion on the opportunity charging part of the study: When opportunity charging is available, it will increase the amount of electric driving, especially for PHEVs.

Trip length is affected by and affects battery life and size. Each discharge-recharge cycle shortens a battery’s life and efficiency. For purposes of the study, battery life was matched to those of the Nissan LEAF EV and the Chevy Volt PHEV. The 7,000-cycle life of A123’s Li-ion battery was targeted. Shorter trips (discharges) between recharges lengthens the number of cycles a battery is capable of and therefore its life. The conclusions on this part of the study: The battery can be smaller if it is used more for shorter trips between recharges. The smaller the battery, the lower its cost and the lower the cost of the vehicle.

The NREL paper included one of the first assessments of using a dynamic plug-in hybrid electric vehicle that, like a trolley or streetcar, "plugs in" as it drives. The conclusion on this part of the study: Because it can be powered and recharged while driving, the battery can be much smaller and the vehicle can therefore be much less expensive, probably becoming cost-competitive with ICEVs and HEVs long before the 500-mile battery or the $300 per kilowatt-hour battery becomes available.

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Roadways containing charging capability can become available at less cost and in less time than is immediately apparent because so much of all transportation takes place on so little of all roads. Interstate highways are 1% of the miles of roadway but see 22% of the vehicle miles traveled. The NREL study assumes vehicles can be connected dynamically for 50% of the distances they drive. It assumes an increase charging cost for connecting dynamically of $1,000.

The study's results:
(1) Using current battery capabilities, gasoline consumption decreases significantly but no “electrification pathways” are cost-effective compared to HEVs or ICEVs except the dynamic connection model.

(2) Increased battery power capability does not reduce fuel consumption or significantly increase fuel economy, even when electricity is cheap and gas is expensive, because it increases the cost of the battery.

(3) Battery replacement made cost-effectiveness slightly better by reducing the size of the battery required for the same life and power and by taking advantage of lower future battery costs. The advantages were largely offset by the greater wear and tear on the smaller battery from regenerative braking and more discharge-recharge cycles.

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Opportunity charging decreases the PHEV’s gas use and cost even more but increases the wear and tear on and therefore the cost of the battery. To sustain the additional wear and tear, the cost of the battery would increase the vehicle cost by $5,500 and the costs of charging by $4,400.

Opportunity charging decreases the EV cost because it doesn’t change the amount of driving done on the battery but reduces the deep discharge-recharge cycles on the EV battery and therefore extend’s its life. Other factors, howver, keep the EV cost higher than ICEVs and HEVs.

Little to no change was calculated with a combination of battery replacement and opportunity charging.

The most cost-effective option for any BEV performance was dynamic charging. Interestingly, HEVs also become more economical with dynamic charging.

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If battery cost is reduced to $300 per kilowatt-hour, the cost of a PHEV would be almost the same as an ICEV and an HEV. In such a case, battery replacement would not impact the PHEV’s competitiveness but opportunity charging, by reducing gas use, would.

Significant hypothesized improvements in battery life, by a factor of at least 10 and in conjunction with opportunity charging, would also make PHEVs and EVs cost-effective.

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QUOTES
From the NREL paper: “Electrifying transportation can reduce or eliminate dependence on foreign fuels, emission of green house gases, and emission of pollutants. One challenge is finding a pathway for vehicles that gains wide market acceptance to achieve a meaningful benefit…Using the current estimates of battery life and cost, only the dynamically plugged-in pathway was cost-effective to the consumer. Significant improvements in battery life and battery cost also made PHEVs more cost-effective than today's hybrid electric vehicles (HEVs) and conventional internal combustion engine vehicles (CVs).”

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From the NREL paper: “As domestic production of petroleum steadily declines and U.S. consumption continues to climb, imports will continue to increase. Internationally, the growing economies of China and India continue to consume petroleum at rapidly increasing rates. Many experts are now predicting that world petroleum production will peak within the next 5-10 years. The combination of these factors will place great strain on the supply and demand balance of petroleum in the near future… Each new vehicle (the vast majority of which are non-hybrids) will likely be in use for more than 15 years. With continued growth in the vehicle fleet and in average vehicle miles traveled (VMT), even aggressive introduction rates of efficient HEVs to the market will only slow the increase in petroleum demand. Reducing U.S. petroleum dependence below present levels requires vehicle innovations beyond current HEV technology.”

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- From the NREL paper: “A key benefit of plug-in electric and plug-in hybrid electric technologies is that the vehicle is no longer dependent on a single fuel source. The primary energy carrier would be electricity generated using a diverse mix of domestic resources including coal, natural gas, wind, hydro, and solar energy. In the PHEV case the secondary energy carrier would be a chemical fuel stored on the vehicle (i.e., gasoline, diesel, ethanol, or even hydrogen)…EV and PHEV technologies are not without their own technical challenges. Energy storage system cost, volume, and life are the major obstacles that must be overcome for these vehicles to succeed. Nonetheless, these technologies provide a relatively near-term possibility for achieving petroleum displacement…”