Tuesday, December 22, 2015

Range Anxiety never goes away completely

The longer you drive your electric car the more you grow accustomed to how much energy it will consume along the routes you regularly drive.  The occasional new route is usually no sweat because you already know your safe driving radius from your home.  I know I can generally count on driving 4 miles per tick (out of 16) on the charge-level gauge, with each tick representing about 1KWh of charge.  So, I can safely drive about 60 miles without much worry and still have a margin of about 4 miles remaining.  My drive to work regularly uses up nine ticks, leaving me with six or so to run errands near home after work.  Most places I’ll visit are within 5 miles of home, so this works out well.  The problem comes when I start traveling unknown routes that extend to the range of my safe-driving radius, especially when a significant elevation change is involved.

The case-in-point happened last Mother’s Day (actually, the day before – to avoid the crowds).  My siblings decided to treat mom to a picnic at one of the nearby wineries in the Saratoga foothills.  Ordinarily, the trip from my house to the winery is about 16 miles, with the final 3 miles involving a significant climb in elevation.  32 miles round-trip is easy to do.  But, it was my turn to bring along mom, so I had to drive first to her place (14 freeway miles) and then to the winery (10 miles), for a total distance of 48 miles round-trip.  But, that morning I had to run an errand and used up 9 miles of charge already, making the total trip for one charge about 57 miles.  Factoring in the uphill climb was starting to make me nervous about completing the trip.  Fortunately, I had surface streets as backup options for the return trip home.

The trip went better than I had expected, thanks in part to two factors.  First, my morning errand was done entirely on city streets, which uses about 20% less charge to drive the same distance.  The second factor was more significant.  I keep thinking like I did in my gasoline powered car …  If I started my trip with 14 ticks on the gauge,  I would need 7 remaining by the time I reach my destination or I might not make it home.  As I was about a mile from the winery, the seventh tick cleared and I knew I would only narrowly make it home if I didn’t plan my driving carefully.  But, I wouldn’t have to worry about that until after the picnic at the winery.  Then, on the way home, the second factor kicked in.  Driving three miles downhill give me back one tick on the charge gauge, meaning that I had an extra four miles I could drive, and I used nothing for those three miles – for a total of seven miles.  (I’m telling you, it’s a mind game driving the hills in an electric car.)  The end result is that I had two ticks remaining on the charge gauge when I pulled into my driveway, and I was even able to run to the local store and back for dinner supplies.

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