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November 10, 2015
Paul Gipe

Bakersfield to Paso Robles Raises Questions on Energy Estimates


In late October we tried a new route from Bakersfield to Grover Beach where we visit a family friend. This is one of the preferred routes from Bakersfield “to the coast,” but we haven’t used it since we began driving our 2015 Nissan Leaf, a battery-powered Electric Vehicle or EV. We’d previously driven to the coast using a circuitous route. The new route pushed the boundaries of what our Leaf is capable of—and our tolerance of range anxiety.

Route

The new route required only three legs totaling a 150 miles. The old route used five legs covering 250 miles and required an overnight stay outbound. The new route is quicker and simpler, assuming you don’t run short of energy before you reach your next charge station.

Our route took us from Bakersfield to Lost Hills, then on to Paso Robles, and then to Grover Beach.

The new route was made possible by the installation of a public charge station at Paso Robles train station. While there are several Level 2 (L2) charge stations in Paso Robles they were located at either car dealers or hotels where the stations were intended primarily for customers. There were also positive reports from EV drivers who stopped at the Lost Hills RV Park near I-5. These two developments make this route possible.

The 65-mile leg from Lost Hills to Paso Robles crosses the Temblor Range.

The 65-mile leg from Lost Hills to Paso Robles crosses the Temblor Range.

Range & Capacity

The Nissan Leaf is an affordable consumer-oriented EV. As a consequence, it has limited range compared to a luxury car like the Tesla Model S. The range of the Leaf is primarily a function of its battery capacity, the temperature, speed, and whether the car is climbing or descending.

EVs consume more electricity at higher speeds than at lower speeds, and more energy climbing than descending.

The Leaf has an official EPA range of 84 miles from a 24 kWh battery pack. However, the traction battery reserves a certain portion of it its capacity for internal use. Effective capacity is 22 kWh in a new 2015 Leaf and 21 kWh otherwise. Further, no one drives a full 84 miles before charging. Thus, the effective range is 50 to 65 miles.

The leg from Lost Hills to Paso Robles is not only at the edge of the effective driving range for the Leaf, it also uses more energy than otherwise to cross the Temblors.

EVTripPlanner Estimate

We use EVTripPlanner, an online estimator, and a tabular estimator based on the work done by Tony Williams, an early PV pioneer in the Leaf. Both produce an estimate of the energy required per route segment.

EVTripPlanner performs its calculations in the background so it’s hard to tell what its assumptions are.

The tabulator is much simpler using assumptions derived from Tony Williams experimentation.

In practice, we use both. However, on this trip something was amiss and both approaches underestimated the amount of energy for the leg over the Temblors.

Leaf Spy Pro

On this trip we used Leaf Spy Pro, an app for a smart phone that reports and logs data from the Nissan Leaf’s computer. The app works on most smart phones, even Blackberry’s Z10.

Most importantly, Leaf Spy reports the amount of energy available in the traction battery. The app reports this as Gids, a unit of energy that’s applicable to the Leaf and then converts this to kWh.

The number of Gids is a function of the model year, the temperature, and the amount of degradation the battery has suffered from use. There are 292 Gids in a new 2015 Leaf or a little more than 22 kWh of usable energy.

In August, when I first began using the app, there was 287 Gids available. By late October capacity had fallen to 271 Gids, a loss of 6%. The capacity had fallen from 22 to 21 kWh. The loss of one kWh could mean the loss of from 3 to 5 miles of range.

The Trip

We noticed on the first leg to Lost Hills that we’d used more kWh that we expected. This was a sign of things to come.

The RV park is bleak, but the staff is friendly, and the place clean. The $15 cost to charge is high by EV standards, but it’s the only game in town. We now travel with a Jesla portable EVSE that can draw the maximum 6.6 kW the Leaf is capable of from the NEMA 14-50 outlets at RV Parks. We quickly made up for the charge we’d lost and nearly topped off before the long next leg.

Lost Hills is an appropriate name. It is in the middle of nowhere and the segment from Lost Hills to Paso Robles crosses a long stretch where there are no crossroads, no development, no phones, no ranch houses. There's not much of anything and very little cell-phone reception. It’s the Empty Quarter.

We reached the Paso Robles charge station with 20% State of Charge (SOC). While the SOC was less than expected, it was within my reserve requirements and the rest of the trip was uneventful.

The train station has several retail shops, including a wine bar. The D’Anbino tasting room is right next to the four ChargePoint charge stations and tt’s a popular night spot on the weekends. Across the street from the station is Vivant deli, a good place for lunch or sampling their cheese selections while charging. The business district is also within walking distance.

The return trip the leg from Paso Robles to Lost Hills put us in full range-anxiety mode. We were confident we’d make it to Lost Hills, but there was a degree of uncertainty. Our SOC was dropping much faster than we had estimated and for the last few miles I drove very conservatively. We arrived with 13% SOC, well under my reserve requirement. This proved to us that even though we’re now experienced EV drivers, planning trips with an adequate reserve still makes sense. Not only had we use more energy than planned, we used more on the return trip than outbound. This was opposite of either estimate.

We used 4 kWh more on this segment than estimated. EVTripPlanner estimated we would need 13.5 kWh when actually we consumed about 18 kWh. This is the greatest discrepancy yet that we've encountered between EVTripPlanner and our actual consumption.

Conclusion

We found a good match between kWh calculated from Gids used and from the dash display of SOC.

There was a poor match between Leaf Spy kWh and that calculated from Gids and the dash display of SOC.

There was also poor match between EVTripPlanner and calculated consumption.

While we’ll probably use this route again—we like the stop in Paso Robles--we’ll do so only with a full charge and we’ll drive conservatively.

We don’t recommend this route for newbies driving today’s consumer-oriented EVs, because they may not have experience hypermiling and may panic as the SOC starts falling away.

We also don’t recommend this route for those in older Leafs with battery degradation. If the capacity of our traction battery declines further, we may not want to attempt the route ourselves until there are more stations out there.


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