Walking into the wind takes a little extra effort than
walking in still air. Walking into a
strong wind takes a lot of extra effort.
Bicycling into a strong headwind really slows you down, and that’s only
at a speed of about 15 to 20 miles-per-hour.
So, you can imagine my surprise at how quickly the power depletes from
my car’s battery while driving down the freeway into a strong headwind. At first I thought that maybe the tires were
a little low and in need of a good pumping up.
Then I looked at the tree tops.
(The palms are a dead giveaway.)
The top branches were swaying in the wind, suggesting a strong wind was
working against me.
How big is the difference in energy consumption driving into
the wind? Normally, my drive from home
to the exit I would usually take for work (and to visit mom, and to drive up to
the winery) uses about three ticks of energy on the gauge. Driving into a strong wind, I noticed that
the energy used at any moment to maintain speed was slightly higher, but
shortly after taking my exit, I noticed the forth tick drop off. I cover a distance of about 13 miles,
suggesting that the extra wind load uses about 20% more energy. Considering that the battery performs a
little worse in colder weather (such as typically happens with a strong wind),
I would attribute about 10% to 15% of the extra 20% power drain to the wind itself.
The impact of this extra power drain is more significant
than it seems, especially for freeway trips.
Under better conditions, my now four-year-old battery can travel about
58 to 62 miles on a charge, mostly on the freeway. If I am driving into a strong headwind, that
range drops to 49 to 56 miles. Even when
I was working in Palo Alto, the 49 miles was enough to get me to work and back,
and a quick trip for tacos nearby for dinner.
But, if I had planned to visit the wine store (an “errand”) in Redwood
City during lunch, then that would add another 12 miles to my trip, meaning
that I would be at risk of not making it home from work on a windy day. When the battery was newer, the range was
closer to 70 miles, and even a 15% drop in efficiency would still get me to the
wine shop and home.