Tuesday, July 17, 2012

Sunscreen SPF and Diminishing Returns

(Graph courtesy of remixyourhealth)

SPF, or Sun Protection Factor, seemed to come out of nowhere in the 1980s as people started to become aware of the need for sunscreen.  (Before that, "suntan oil" appeared to be a derivative of cooking oil that helped broil skin.)

The original explanation I heard for the meaning of SPF was that it allowed you to stay out in the sun longer by a certain factor.  My friends and I initially interpreted this as, if you were going to stay out in the sun an hour, you could stay out two hours with an SPF of 2.  Or 10 hours with an SPF of 10.  An SPF over 24?  That meant you could extend your life by adding hours to your day.

Like MPG, SPF is a hard number to build good intuitions around. The right interpretation of SPF is that, if you want sun damage of X amount, you can now stay N times as long to get the same X sun damage.  You want a an hour of sun damage?  At an SPF of 10, you can stay out10 hours and get the same amount of sun damage as one hour.

But most people don't have in mind a level of sun damage they want. Instead, they have in mind a time that they want to spend in the sun.  As with MPG, SPF is better understood once it is flipped.  Flipping it reveals that there are surprising diminishing returns.  As SPF numbers start to sound very impressive, growing from 30, to 45, to 60, to 100--and the price grows as well--the actual increase in skin protection is negligible.  More after the jump.

Saturday, July 14, 2012

CO2 Emissions, Electric Vehicles, the New EPA Label, and a Great Feature at Fueleconomy.gov

A Scientific American post in April (by Julia Pyper, originally posted on Climatewire) captured a basic challenge facing people who want to buy electric vehicles as a way of reducing greenhouse gas emissions:

An all-electric Nissan Leaf in Buffalo, N.Y., emits relatively few greenhouse gases, equal to the amount produced by a gasoline-powered car getting 86 mpg. But in Denver, the same Leaf is equivalent to only a 33-mpg vehicle, such as a subcompact Ford Fiesta.

Wednesday, July 4, 2012

Quantity versus Price

A new paper in the Journal of Marketing by Akshay Rao of the University of Minnesota shows that people have a hard time with the following sort of question:
When offered the possibility of 33% off a product or the same product with 33% more quantity, which would you choose?

Saturday, May 26, 2012

When MPG is Overstated

A UK magazine called WhatCar? has launched a website to record driver's real MPG:


WhatCar? released a report showing that the true MPG for the vast majority of cars is lower than the stated MPG. And many outlets repeated the list of the top 10 offenders:

Saturday, April 7, 2012

Why not make a whole bunch of 50-miles-per-gallon cars?

John Peterson has a grim analysis of the prospects for electric vehicles: The cost of batteries are so prohibitively high for the foreseeable future, they cannot pay for themselves even if gas were $10 per gallon.

He concludes that "even with $10 gasoline and sunshine, lollipops and roses battery cost figures, the Return on Incremental Battery Investment (ROIBI) falls off a cliff as soon you move beyond the Prius"

Peterson then shares this great quote from Bill Reinert,  Toyota's manager of advanced technology: “I used to be a big 100-miles-per-gallon guy. But I realized that we’re above the level of diminishing returns at 50 miles per gallon. So why not make a whole bunch of 50-miles-per-gallon cars and put people who are driving 20-miles-per-gallon cars into them?” (Here's a link to the original article from automobilemag.com.)

Exactly.  Then invest in energy savings in homes, truck fleets, etc.

Monday, March 26, 2012

High MPG in the News

Win $1 Billion

Republicans have created a bill that will provide a $1 billion reward to the first automaker that can sell 60,000 cars that get 100 MPG --  using regular gasoline. No MPGe here.

The (Marketing?) Value of 4 MPGe

The Ford Focus Electric was rated at 110 MPGe (see *note below), making it the "King" of electric vehicles because it beat the Nissan Leaf by 4 MPGe.  If we look at how many "gallon equivalents" are being saved per 100 miles, that works out to:
Ford Focus:  100/110 MPGe = .91 gallon equivalents
Nissan Leaf:  100/106 MPGe = .94 gallon equivalents
That's right:  The Focus saves the equivalent of .03 gallons of gas every 100 miles compared to the Leaf.  For these comparisons of efficient vehicles, "miles per anything" is a marketing gimmick.

*Note: And, as we've noted before, MPGe is a poor metric.  Besides having the wrong number on top (thereby perpetuating the bad math done with MPG), it has a highly uninformative number on the bottom:  An energy unit that is equivalent (hence, e) to a gallon of gas.  But this energy unit could come from regular gas, natural gas, electricity made from hydro, electricity made from nuclear, or electricity made from coal, all with different implications for GHG emissions.  And the electricity could cost 22 cents per kwh in Connecticut or 6 cents per kwh in North Carolina.  

Crossovers Help Drop US Oil Consumption

From  NPR: 

"The price of gasoline keeps rising for Americans, but it's not because of rising demand from consumers.Since the first Arab oil embargo of the 1970s, the U.S. has struggled to quench a growing appetite for oil and gasoline. Now, that trend is changing.

"When you look at the U.S. oil market, you see that there's actually no growth," says Daniel Yergin, chairman of IHS Cambridge Energy Research Associates. He says gasoline demand peaked in 2007 and has fallen each year since, even though the economy has begun to recover.

"The U.S. has already reached what we can call 'peak demand.' Because of increased efficiency, because of biofuels, we're not going to see growth in our oil consumption," Yergin says.

One of the reasons for the change? People are buying car-based "crossover utilities" instead of truck-based SUVs.  

Rebecca Lindland, director of research for IHS Automotive, says 27 percent of the new vehicles sold in 2011 were smaller, lighter, car-based versions of the SUV, called "crossovers." 

"Those tend to get significantly better fuel economy than our traditional truck-based SUVs that used to account for 20 percent of all the vehicles we bought," she says.

Now, those big SUVs are less than 5 percent of sales, and the average fuel efficiency of the crossovers is 20 to 30 percent higher than the old SUVs." 

This is where the national gas savings are available:  Exchanging a 16 MPG SUV for a 25 MPG Crossover.  

Friday, February 3, 2012

Honda Civic Hybrid--Suing over MPG in Small Claims Court

Heather Peters sued Honda in small claims court because her Honda Civic Hybrid did not deliver the 50 MPG promised on the window sticker.

The court awarded her $9,867 for "extra money spent on fuel, both in the past and future, the cost of the car battery, and the decrease in the car's value because of its problems."  (The court could award an amount no greater than $10,000.)

Peters reported that "'the car never got more than 41 or 42 even on its very best day.'  She said the fuel economy dropped below 30 mpg after a software update intended to prolong the life of the car's battery and improve performance."

This case reveals one of the problems caused by MPG.  EPA ratings have historically overstated actual MPG (i.e., in "real" driving conditions).  This problem was addressed in a 2008 reform.  Nevertheless, it persists.

When drivers expect 50 MPG and get only 40 MPG, the difference feels very large and disappointing.  But the difference in gas consumption is not nearly as consequential.  That different between 40 and 50 MPG is 5 gallons  of gas every 1,000 miles.  Assuming a car has a life of 150,000 miles of driving, that's 750 gallons of gas, which adds a little over $2,500 in costs at $3.50 a gallon.  The difference between 33 and 50 MPG is 10 gallons of gas every 1,000 miles, which adds a cost of $5,000 over a 150,000 miles of driving.

Saturday, August 20, 2011

EcoCAR Challenge Results

USA Today has an interesting summary of a 3-year EcoCAR competition sponsored by the Department of Energy and General Motors.  The article says:

The teams focused on design during the first year, when Ohio State University placed first. They emphasized implementing that design in the second year, when Mississippi State University in Starkville, MS.,won top honors.
In this final year, they focused on refinements to make the vehicle 98% consumer acceptable, says DeClark, adding it's nearly impossible to satisfy 100% of consumers. She says the cars won't be commercially produced but there are "many applications for these technologies."
A team from Virginia Tech won. They "started with a GM-donated Saturn Vue and swapped out the engine with one from a 2009 Chevy HHR engine. It then added a battery and electric motor and made other tweaks such as eliminating engine idle."

Tuesday, August 16, 2011

Hypermiling, Hypoconsuming.

Avoiding jack rabbit starts and coasting into stop signs can greatly improve the MPG your car gets.  These are among a long list of hypermiling techniques that, when carefully applied, have enabled attentive drivers to achieve MPG levels that greatly exceed their car's official MPG rating.

What sorts of levels can be achieved?

An Australian couple is driving across the US in an Eco Cruze with the goal of squeezing "2,000 miles from each fill-up of the car’s 12.6-gallon tank. That comes to 158.7 mpg and seems implausible, but if anyone can do it, the Taylors can."  

Or consider the performance of "Hypermiling king Wayne Gerdes and NASCAR driver Carl Edwards" who  "averaged 81.5 mpg during a three-day run that started Saturday and saw them double the 700-mile range Ford claims for the Fusion Hybrid."

Or, "Our hypermiling friends at Ecomodder.com took home three trophies at the Green Grand Prix, including top honors for an astonishing 99.7 mpg.  Darin Cosgrove, who founded the hypermiling site in November, 2007, tells us he used the “pulse and glide” technique “almost exclusively” to achieve that impressive figure during Saturday’s fifth annual event, which celebrates all things fuel-effient and alt-fueled. Four Ecomodders entered the event, held in Watkins Glen, NY."
Check out the large community of hypermilers at ecomodder.com, gassavers.org, and cleanmpg.com. (More on hypermiling at Mother Jones and Wired.  These articles also discuss the dangers of coasting, turning off engines at stoplights, etc.)
Let's look at these hypermiling numbers from a GPM perspective.  How much gas do these MPG improvements save?

Saturday, August 13, 2011

Update on Heavy Duty Trucks

Overdriveonline.com has an article summarizing fuel economy standards for heavy duty trucks.  Here are some excerpts.

A key takeaway:  New trucks are expected to cost $6,220 more because of the rule; total fuel savings over the life of the truck are expected to be $73,000.

  Access the full article here. 

New emissions rule to drive truck prices higher

The first-ever regulation for truck fuel consumption and greenhouse gas emissions, announced Aug. 9, is expected to cut diesel use by 4 gallons per 100 miles traveled by the time 2018 models are sold. New trucks are expected to cost $6,220 more because of the rule.

President Obama announced the new standard would yield a total fuel savings of $73,000 over a truck’s life. Heavy-duty trucks should expect a 20 percent reduction in fuel consumption and greenhouse gas emissions by model year 2018 under a new Heavy-Duty National Program.
The Owner-Operator Independent Drivers Association criticized the development, saying there are cheaper ways to achieve the same goals. But many organizations applauded the move.

Volvo Trucks and Mack Trucks issued generally supportive statements.
“Certainly the regulation will challenge the industry,” said Mack President and CEO Denny Slagle, “but our past success gives us confidence we’ll meet the challenge.  Our focus now is on doing so in a way that minimizes any negative consequences for our customers.”

Wednesday, July 20, 2011

Friday, June 3, 2011

Better food metrics

The US Department of Agriculture has a new way to represent nutritional guidelines.  The pyramid is gone.  The new recommendations are partitions of a plate. Simple and clear.