Damn Dams

As an environmentalist, I thought I was pretty well informed about the causes of global warming and the sources of greenhouse gases.  Recently I watched the documentary Damnation.  The movie describes our love affair in early part of the last century of dams and then discusses the current state of dams their many weaknesses.

I think most people are aware that dams stop fish from moving upstream and have destroyed the livelihoods of many native people.  What I did not know prior to watching this documentary is that dams are a significant source of greenhouse gas emissions.

Greenhouse gases are primarily methane and carbon dioxide.  The rotting organic matter in a reservoir is generating both of these gases.  The organic matter is from both the plants that were originally flooded over when the reservoir was built but also new material when silt and plant material is washed in from the watershed above.  Brazilian researchers estimated in 2007 that methane from dams is responsible for around 4% of human-caused climate change.  Estimates range from 20% to significantly more of all man made methane is coming from the surface of reservoirs.  Methane is 30 times more potent than carbon dioxide as a heat trapping gas.

Despite a deluge of rain in December, California is in a record drought but there are a lot better solutions than building and maintaining dams.  Off stream reservoirs are better for holding water as they do not interfere with the fish life cycle.  Even more compelling is that the silt is much less likely to build up as the water that goes into a reservoir is taken off the top of the river flow.  Better yet is groundwater recharge placing the water underground in existing natural aquifers. Even better yet is simple water conservation such as washing your Tesla with one cup of water.

Stanford University has a 125 year old dam on its property, the Searsville dam.  The reservoir is so filled with silt that it only has 10% of its original capacity. The aging dam and reservoir no longer provide drinking water, flood control or public recreation access.  Stanford had stated they would determine the fate of the dam in 2014 but failed to do so.  The Beyond Searsville Dam organization is a 501(c)(3) non-profit organization and has more information about this particular dam and its impacts.  Many more dams like Searsville exist throughout the United States.

Off Stream San Luis Reservoir During the Drought - April 2014

Off Stream San Luis Reservoir During the Drought – April 2014


Driving & Charging Time

A question recently came up on the forums:

Are there any real world examples demonstrating my total time spent charging and driving when using superchargers?  If I speed up to say 85 mph, am I going to really save time or not as I will need to charge more at the next supercharger.

I had tried to real world test this at one point but then realized how next to impossible it would be to replicate the same drive at different speeds.  And I also know how difficult it is to get good charging data from the superchargers.

There are a lot of variables while driving that affect energy consumption including

  1. Temperature
  2. Wind
  3. Percipitation
  4. Traffic
  5. Replicating the exact driving behavior even with cruise control

Instead of a real world test, I could use my accurate charging data, which has previously been validated by Tesla personnel and add in EVTripplanner estimates.  The supercharger curve data is from a functional supercharger operating without problems and without sharing the supercharger pair with another car.  Although the energy given by EVTripplanner is an estimate, many owners have found these estimates quite accurate and will probably be more accurate than any real world test for a lengthy drive.

I decided to model the trip from the Harris Ranch supercharger south to the Tejon Ranch supercharger on I-5 in central California, which has a 70 miles per hour (mph) speed limit.  This leg is relatively flat 116.2 miles but has an elevation change of 656 feet.  Although I could likely find a supercharger to supercharger with no elevation change, I thought this one may be the most useful data as these superchargers are frequented on long routes.  Perhaps myself or other owners will report real world data in the future on this leg.  The trip was modeled using a 85kWh Model S with 21″ wheels and a 200 pound payload at 72 degrees Fahrenheit in the car and in the cabin.

I first graphed the data assuming the driver arrived at the second supercharger, Tejon, with only 1 mile left in the tank.  The data compares the total amount of time spent in driving plus charging in minutes versus the speed in mph.  Each charge was only to replenish the battery with the number of rated miles spent during the journey.  At 70 mph, the 116.2 mile trip from Harris to Tejon used 151 rated miles, at 75 mph 163 rated miles were used.

Total Time (Driving and Charging) vs. Speed

In looking at the data, you quickly notice that your overall time spent on the road is the fastest at 75mph.  By increasing the speed to 80 or 85, you will essentially spend the same total elapsed time!  The total time of 75, 80, and 85 mph are all within one minute.  Going  really fast at 90 actually slows down your total time because of increased time needed to recharge the battery as the energy usage increased dramatically.  So at very high speeds, the car is simply wasting energy and not saving the driver any time.  Here is the actual data in table format.


The total energy used increases as speed increases and driving time falls but the charging time increases.  The maximum effective mph is 56 mph, where time includes both driving and charging time.

The next question is what is the impact on having a battery partially full when I arrive at a supercharger.  I plotted the difference arriving at Tejon with a battery with 1, 26, 51 and 76 miles remaining.

Total Time Data Arriving at Supercharger with Varying Battery Levels

What is notable about this second graph is that the difference between arriving at a supercharger with 1 or 26 miles is not that significant.  Arriving to Tejon with 26 miles left in the tank only uses an average of 2 minutes more.  With 51 and 76 miles in the tank, that delay increased on average by 6 and 10 minutes.  I could not predict the data for the higher speeds and the higher charge levels because my supercharger data does not go to a full 100% range charge.

But even these slower total numbers are less than 10% of the total time.  I do not have the oldest A battery but I do have the 21” wheels, which are slightly less efficient.  The numbers for the A battery and a 60 kWh battery will be slower.

I generally prefer to arrive to a supercharger with around 25 miles left in the battery.  This strategy gives me peace of mind in case there is any changing weather conditions such as an unexpected headwind or rain, both of which require the car to use more energy.  I also like to take unexpected detours, so having a little reserve permits stops like an unexpected fruit stand or a detour to an interesting place.  For me road trips are more about the journey than optimizing drive time.

If one is super intent on optimizing drive time on a road trip, the best solution is to arrive with 0 rated miles left in the tank, never detour off the road and always only take breaks at superchargers.

Alternatively, a strong rumor exists that a battery swap station is being built at Harris Ranch at the site of a former car wash.   Elon announced this technology a year and half ago!  In the announcement, the demonstration took 1 minute and 33 seconds, which is faster than you can fill a tank of gas in an ICE.  But battery swaps will not be free.  Just this week a friend of mine who was traveling in an ICE talked to the construction workers there who said they were building a battery swap station, so I have pretty high confidence in this rumor.

Washing the Model S

There are a variety of ways to wash a car and they all have different environmental impacts.  Washing a car at home the old fashioned way is probably the worst.  The wash and rinse water is loaded with dirt, oil and detergent that ends up as run off into the storm drains and directly into rivers.  My storm drain waters end up in the San Francisco Bay and the Pacific Ocean.  I have not washed a car at home in years as it was not a chore I enjoyed and never balked at the prices at the automatic car washes.  I have to confess, I am not meticulous about keeping my car dirt free.

Traditional commercial car washes use less water than an average home user, and by US law they must drain their wastewater through the sewer system not the storm drains.    So the water is treated and cleaned before being diverted to the ocean.  Also many car washes recycle their own water.

When I owned the Roadster, I washed my car at two different places.  A ‘touchless’ car wash and in one of those old fashioned places where you wash it yourself but they have higher pressure water for a few quarters.  I had not washed a car myself in years, but the Roadster was so small it was a pretty easy job.  I started to go to the touchless place more regularly till at one point they said no, the car is too low.

Manual Notes on Using Touchless Car Washes

Manual Notes on Using Touchless Car Washes

When I got the Model S, I figured I’d go back to the local touchless place.  But when I got there they said they could not wash my car.  I was a little perplexed and I had no idea why.  The Model S manual warns you against the typical paint finish issues with any car.

Most automatic car washes in California work by pulling the car through the mechanisms while in neutral.  With the 4.x software, forcing the car into neutral without a driver in it was not particularly straightforward.  With the 5.x software there is a tow mode.  I am still waiting for the software update.

I was not particularly fond of this car wash, so I started to look around where other Model S owners were getting their car washed, and I discovered a better car washing method that does not use water.  I found a facility reasonably close that is much more ecologically correct.  I have now been there three times.  I mentioned earlier I am not very picky about having a clean exterior!  Also every time the Tesla was in for service, Tesla had my car washed.

I am very satisfied with this waterless method.  On a cost basis, the car wash is a little more expensive than a water based one, but I think not using water is worth the few extra dollars.

Eco Car Wash Cleaning Another Tesla

Eco Car Wash Cleaning Another Tesla

The employees and owners are informative and helpful.  A lot of Tesla owners use this particular car wash.  He said he has found a number of owners with the following three situations:

  1. Model S cars that used as family cars that are completely filthy on the inside
  2. Model S cars with a ton of scratches on the trunk, where people clearly put their groceries on top of the car and scratch up the finish.
  3. A lot of curb rash on the wheels.

I am guilty of curb rash, primarily in the front right wheel but I don’t have the other two problems.

I had noticed some grease near the moonroof, and he said that many Teslas have this problem and service can swap out the correct parts to stop the grease from appearing again on the roof.  I will have service fix this when I go in for my annual service.

Grease From Panoramic Roof Mechanism

Grease From Panoramic Roof Mechanism

At The Car Wash

Today I went to a car wash with my Tesla.  For some reason the manager on duty said there may be a problem with my car as it was too low to the ground.  I was quite surprised as I have taken it to this exact car wash at least twice before.

They tried to drive it onto the tracks but then said “no” it was too low.  The manager explained that depending upon the tire pressure that day can determine whether or not he can drive these low cars on the track.

I was quite surprised and ended up paying a lot more for them to “hand” wash it.  The job was the same quality and speed but they justified the price by saying they had to hold up the line.  For the price they charged, I will not take the Roadster back there.