Tuesday, December 9, 2014

First trip up the mountain

After driving the i-MiEV for several months, I wanted to test its capability and range under more unusual driving conditions.  I knew that the car used more electricity driving uphill than on a level surface, and it had been a while since my last visit to the mountaintop winery near me, so I decided to head up the mountain.  The first thing I checked was the distance to the winery from my home.  The routing suggested by Google Maps was the obvious and most direct route.  This route starts off with 11.2 miles of freeway (each way) which would draw down the battery by about 7kwh round-trip, or a little less than half the charge.  That left more than half the charge to get up the mountain and back down.  It was another 3.5 miles to the start of the mountain climb, and 4.3 miles up the mountain (about 1,500 feet of elevation change).  I figured that if I could make it up the mountain on 6kwh, I would get home safely.  (That amounts to 0.72 miles per kwh, which is terrible.)  So I decided to go forward with the trip.

Google Maps' proposed route up to Ridge's Monte Bello tasting room
As I started driving, I created turn-back thresholds for the battery consumption in my mind, beyond which I would have to turn the car around and head home before reaching my destination.  This is the sad impact that range anxiety has on us poor fools who overthink or over-worry about their electric cars.  Of course, it’s better to be prepared for failure than to deal with the consequences of going too far up a mountain road.  As I reached the base of the road up the mountain, the charge meter showed that I had used four ticks (which amounts to 4kwh), as expected.  So, I continued up the hill.  You can imagine my shock after driving the first mile and watching another tick (1kwh) disappear from the gauge.  Still, at this rate, I would make it to the winery with energy to spare, so I trudged on.  The second and third ticks disappeared with less of a shock as I noticed the rate continued at about 1kwh per mile.  Finally I arrived at the winery with about a half a charge remaining.  The drive home would use less energy, so I knew I would make it home safely.

After enjoying a modest wine tasting and giving my body a little time to process the tasty stuff, I left the winery for my drive home.  Much of the drive down the mountain required very little energy, and often times I was regenerating while the road sloped downward.  Nearly as shocking as watching the first tick disappear while driving up was watching the first tick reappear on the way back down.  This time, the shock put a smile on my face.  By the time I had reached the bottom of the hill, I had regenerated about one and a half ticks (1.5kwh).  Now I was faced with driving the remaining 12 miles on the highway with the 9kwh charge remaining in the battery (about 30 miles of range), which I could do easily.  So, in all my worry about getting up the mountain, I forgot to factor in the regenerative effect of driving back down the mountain, which changes the amount of charge needed to complete the trip. 

So, here is the mind game about driving an electric car with regenerative braking up and down a mountain.  I used about 3kwh of electricity to drive about 9 miles up and back down the mountain.  This rate of energy consumption is a little worse than it is when driving on the freeway.  But, the trick is that without at least 4kwh of charge in the battery, I never would have made it to the top of the mountain.  I needed more than I used on the whole trip just to get half-way.  It is conundrums like this that have me thinking I’ll stick to being a flat-lander.

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