It is a known fact among EV owners that their cars use regenerative breaking systems to help charge the car’s battery and extend its range. Regenerative breaking is defined as:
“In a battery-powered electric vehicle, regenerative braking (also called regen) is the conversion of the vehicle’s kinetic energy into chemical energy stored in the battery, where it can be used later to drive the vehicle. It is braking because it also serves to slow the vehicle. It is regenerative because the energy is recaptured in the battery where it can be used again.” Source Tesla Motors. Read more of Greg’s great article on regen here.
“Vehicles driven by electric motors use the motor as a generator when using regenerative braking: it is operated as a generator during braking and its output is supplied to an electrical load; the transfer of energy to the load provides the braking effect. Regenerative braking is used on hybrid gas/electric automobiles to recoup some of the energy lost during stopping. This energy is saved in a storage battery and used later to power the motor whenever the car is in electric mode.” Source Wikipedia
Regenerative Breaking mechanisms have been used for over a century, have a very fascinating history, have many very interesting applications including early experimentation with the Amitron and Voltswagon concept cars by AMC. Regenerative systems developed by are now used on the worlds best selling electric vehicle, the Nissan Leaf and all other EV’s and hybrids on the roads today.
An interesting video on how the Nissan Leaf’s power/regen system works:
I have owned my 2012 Nissan Leaf now for 13 months and have been keeping detailed daily notes on SOC, distance driven, temperature and other data points of interest. Recently I started taking notes on the regeneration that my car produces during my daily commute. Specifically a the 3.4 mile section of my commute that is almost all downhill (see a graphic representation of the route below).
Map from www.mapmyride.com
Recently I began to wonder just how far per day this 3.4 mile descent with 845 feet of elevation loss would take me on braking and gravity produced free fuel. In the hopes of answering that question with some degree of accuracy I developed an experiment with the procedure listed below.
Every day I used in the experiment I drove as I do on a normal day; in ECO mode and with all possible environmental variables such as road conditions, traffic conditions, different routes*, elevation loss or gain, temperature, humidity, wind resistance, tire resistance, speed, accessories used, and others variables in order to keep it as real world as possible. *I do not drive the same route every day due to errands I often to run after work.
UPDATE 1/25/15; Speaking of environmental variables effecting regeneration, on one recent occasion I had to drive the 3.4 miles section of route immediately after a motor-grader had scraped the road. The road surface was the consistency of something like thick beach sand mixed with damp oatmeal. The car bogged down a bit but powered through it but the regenerative breaking system was practically useless since I had to keep gently accelerating in order to keep moving forward. At the bottom of the 3.4 mile route I had regenerated only 1 mile of range. I am sure this will lower my overall average just a bit once I recalculate the numbers at some point this spring but science can be a harsh mistress.
The data (so far)
Regenerated potential range at the end of the route for seven days during November 2014
16.0, 14.0, 11.0,13.0, 7.0,14.0,15.0
= 90/7 = 12.85 average miles of potential range regenerated per day.
However, as we EV drivers know, this potential driving range is not an accurate representation of real world driving range due to the variables mentioned previously. In the attempt to deduce just how far in reality the car would go on the regenerated power from the 3.4 mile daily descent, I needed to calculate the distance the car would travel before reaching the pre-route SOC on the GOM (my Leaf is a 2012 so it does not show battery state of charge as a percent–it is a calculated guess by the on-board computer of mileage remaining based on vehicle system health, environmental conditions and driving style.)
I first recorded the SOC from the GOM at the top of the route, drove the 3.4 mile route, stopped at the bottom and recorded the number of regenerated miles, reset the trip odometer to 0 and drove until I had reached the first recorded SOC from the top of the route.
The resulting number is the real world miles driven on Leaf regenerated free fuel. The 7 day adjusted test results are listed below:
16.5, 9.0, 13.1, 7.5, 8.0, 8.7, 9.3
= 72.1/7 = 10.3* average miles of potential range regenerated per day!
*I continue to keep a daily record of regeneration on this route, so this number will change as I average in those numbers. In the spring of 2015, I will post an update to this story with the updated findings.
Based on the data for the short time period in question, the results seem to indicate that during this 3.4 mile descent my car generates an average of 10.5 miles of potential real world range per work day when driving this route. This data also suggests that the Leaf often powers itself home for free since the route is only 9.3 miles in length from the bottom of the descent to my home. I have documented this fact many times when upon reaching home the SOC is at or above the starting SOC when I left work.
This ads up to a substantial amount of Leaf produced free fuel, but how much in a year is possible?
10.3 miles per day!
10.3 x 5=51.5 miles per week.
51.5 x 4 = 206 miles per month.
206 x 12 = 2472 miles of Leaf generated free electric fuel per year.
If these numbers are accurate, then my car, simply by rolling downhill on the same 3.4 mile route described above, for 5 days each week, regenerates enough power in a year to power itself for the equivalent of two months worth of driving*, all freely powered by the Nissan Leaf! *I drive an average of 300 miles per week (300 x 8 = 2400)
I use a Kill A Watt meter to keep track of my Leaf’s power consumption.
How much has this potentially saved me in power costs for the Leaf?
Driving my leaf costs an average of .03 per mile so .03 x 2472 = 74.16
$74.16 potentially saved each year just driving home from work every day!
And this is only for this one route. I drive several other routes where I pull a good amount of regeneration from long descents so I wonder how much am I saving in power costs from those routes?
In a rough comparison, if I had to drive my 1999 Toyota 4Runner the same distance that my Leaf has driven on freely produced regenerative power, it would have taken me around 8 tanks of gas and cost me around $360.00 in gas at current fuel prices of $2.84/gal! (2472 miles at 2.84 (per gallon) x 16 gallons = $45.44 x 8 (tanks) = $363.52)
Let’s just think about this fact – is there a consumer available, stock built, gasoline or diesel powered vehicle anywhere that will produce it’s own fuel. No. The facts are in: petroleum powered vehicles only take hard earned money from the owner, give nothing back but a ride, require lots of expensive fuel and maintenance, are often noisy, contribute to a polluted environment, enable the continued destruction of the Earth’s ecosystems through oil drilling/strip mining and pipeline construction in fragile environments, are not energy secure, and even fund terrorism. EV’s give so much back, have very low maintenance costs, are quiet and fun to drive, can be fueled on domestically generated energy and renewable energy generated at home or work and are therefore energy secure, do not fund terrorism, and produce a portion of their own fuel…for free! It is no wonder that some automakers, fossil fuel corporations and their supporters, and certain oil soaked politicians, are afraid of EV’s and will stop at nothing to ruin their image with negative ad campaigns and tactics.
The simple reality is this; while the currently available electric vehicles do have some range limitations, they are far better in so many ways than petroleum powered vehicles. Given time, advancements in battery technology, expanded charging infrastructure, and the support from the people and our purchasing power, the EV will one day dominate the roads. Once a person drives an EV and experiences the joy of driving electric, freedom from the gas pump and from years of costly maintenance, more money in their pocket, the resulting cleaner air and environment that comes from driving EV, and with the ever growing option of powering their EV from home generated renewable energy such as solar, wind and micro-hydro–they will see that driving electric is the better choice and will hopefully trade in or recycle their old gas guzzler in favor of the future of transportation, the EV.