Published on October 24th, 2015 | by Kyle Field71
The Hidden Benefits of EVs – Regeneration
October 24th, 2015 by Kyle Field
We spend a lot of time here on CleanTechnica discussing the many benefits of EVs but there’s one specific benefit that really surprised me – regeneration. At its core, regeneration is utilizing an onboard generator (usually the primary drive motor) to slow the car and convert that power back to electricity… but in practice, it’s much more than that and can have a large impact on the range of your EV if you know how to use it most effectively.
A 2014 study noted:
Regenerative braking is an efficient approach to extend the driving range of the EV without any additional cost; at the same time, it plays an important role in energy saving. Recently, many efforts have been focused on developing models of the regenerative braking system and improving brake performance.
Studies across the board cite regeneration as providing 10–15% of the expended energy back, which, with the range of today’s EVs, can mean the difference between making it to your destination or having to stop and recharge.
How Does Regen Work?
You have expended battery power to get the car moving (building up kinetic energy) and you need to stop, so you ease onto the brakes. Behind the scenes, as you step on the brake pedal (maybe we should rename it the “decelerator”?) the car engages the motor backwards to slow the car down and, at the same time, generates power.
A Practical Study
It seems simple and really, it is but it can have a huge impact on your range and also reveals many hidden inefficiencies of gasmobiles that were not previously as visible. One of my favorite examples of how regeneration works was on a recent hike I went on with my family in my wife’s Mercedes B-Class Electric Drive.
The start of the hike is ~39 miles from my house – not bad considering our car has a range of 87 miles, BUT the route includes 4000’ of vertical gain heading up a curvy highway back behind Ojai, California. Both gasmobiles and EVs expend more energy going uphill when compared to flatland – we just haven’t paid attention to it. The switch to range-limited EVs puts our estimated range front and center, making inefficiencies like this much more apparent. Driving up, the elevation gain took a toll on our range as if we had a leak in the battery. By the time we arrived, we were down to just 29 miles of projected range left, leaving me wondering just how this experiment was going to work out, nervously offering reassurance to my wife that it would work out.
After our hike, we returned to the car and hopped in. As the kids buckled up, I nervously glanced at the range, hoping it had miraculously recharged while we were out on the trail, but alas, it was not to be. We charged out and made our way back down the mountain. In a gasmobile, I would have been idling the whole way down hill, using friction brakes to slow down and the gas for the occasional acceleration – essentially paying to fight gravity on the way down the hill. In the EV however, we could immediately see the benefits of regeneration. We were essentially just rolling down the hill, using little to no battery power at all to propel the car. On top of that, when I put the brakes on, our momentum is converted back to electricity and stored.
In real life, as we coasted down the hill, our range stayed mostly static – even gaining a mile or two every so often. The gamble paid off, and as the miles flew by, I was confident we would make it home and in love with this regeneration thing. In a gas car, the best we could have hoped for would be to idle down the hill, using a fraction of the gas we had used on the way up but still a net negative, not to mention the wear on the brakes. The end result for us? We pulled into the driveway at home having only consuming 4 miles of our precious 29 miles of range across the 39 miles we had travelled (25 miles of range left). It sounds extreme – and it is!
This example is definitely on the extreme end but does a great job of illustrating how regeneration allows EVs to benefit from the energy expended getting the car up hills or just up to speed on flat ground. Even if you don’t live on a hill, drive up and down hills on the way to work, or even have hills in your state (I’m looking at you Kansas), regeneration will still help you make the most of the moving and braking energy in your EV. In my experience, the 10–15% increase in range is a fair estimate of what folks can expect. It’s also worth noting that you can increase or decrease this based on aggressive or conservative driving, just as you would expect to see in a gasmobile. This also helps EVs excel in low-speed, stop-and-go traffic, which makes rush hour that much more bearable.
Net – regeneration is a unique advantage of EVs that I simply had not realized would be such a significant impact that also allows users to extend the range of their EVs with little to no effort. Chalk up another advantage for team EV!