Towing a Tesla at 70 MPH replenishes battery at fast charger rates

And you have to maintain water in the tower in order to keep the water distribution system pressurized.

there isn't much energy in a water tower. and that water is already doing work, pressurizing the water system.

Hydro power storage is fantastic but needs truly ridiculous amounts of water and height deltas to make sense.

In my head it still seems like it would be cheaper than digging out massive reservoirs for pumped hydro. Rail seems relatively cheap even if you do have to replace it regularly because of the wear. It also seems like you could put the rail in all sorts of geographies, big and small. Maybe it isn't worth it unless you go big though... and at that point why not hydro.

It's good questions though. No idea how the economics of it will work out vs pumped hydro.

Then collected money could eventually pay off the cost of construction, and eventually maybe even offset the maintenance cost.

If nothing else, it would certainly boast the advantage of being more fun than water storage.

Apple HQ - around 1,600ft diameter

Seneca Pumped Storage Lake: around 2,400ft diameter

Pumped storage is awesome and the most cost-efficient way to store energy. It's used as much as possible, but...

I attended a USGS [1] talk about dams (in California) a few years ago.

The key takeaway is: all places worth damming have been dammed. There are no more dammable places, hydrologically and geologically speaking.

When I drive through the central valley, I see a lot of roadside signs about "build more dams!" It's sad to see the miscommunication...

[1] https://www.usgs.gov/science-support/communications-and-publ...

(I cannot immediately find a link to the specific talk. USGS is fun: full of crusty geologists, who even in the heart of the Silicon Valley aren't particularly technologically sophisticated (a nice reminder of how niche we all are) )

Great points though!

Cruising on level terrain is a mediocre load on the traction system to offset the rolling and aerodynamic friction. Climbing a steep grade at the same speed will increase the load significantly, but that extra kinetic output energy is being stored as gravitational potential energy rather than lost like the baseline cruising load. Then, when you descend the mountain on the other side, you recover that gravitational energy to offset the rolling and aerodynamic friction. You want to be "falling" down the mountain grade at your terminal velocity where no braking and no traction force is required to maintain your cruising speed. It will not work well for winding descents where you need to brake for turns.

I've seen this work with turbocharged ICE cars with elevation gains of 4k foot or more and hundreds of miles distance. I've repeated on many trips to prove to me that it isn't simply a fluke (such as extreme headwind or tailwind). Going over a pass yields me a better trip MPG than covering the same several hundred miles on relatively flat ground.

I could see this benefit for a hybrid car too, since I believe they mostly handle highway cruise on ICE power. However, it seems unlikely for a BEV car unless there is something about battery and power electronics that I do not understand, that would give them a significant efficiency boost at high power.

Suppose you're going to make a 100 mile (160 km) trip. You have two possible routes. One is a straight shot on level ground. The other is straight, too, but it takes you up a 10% grade for the first 10 miles (gaining 1 mile in altitude), then you continue on level ground for 80 miles, and then you descend a matching 10% grade at the end.

It seems like the 80 miles of cruising on level ground at high altitude would use less battery than 80 miles of cruising at sea level (if the speeds are the same).

There will be some losses due to climbing and descending. Maybe climbing and descending is a little less efficient. Also, you're definitely traveling a very slightly longer distance. But those losses might be made up for spending the bulk of your trip in thinner air.

https://phys.org/news/2017-09-e-dumper-world-largest-electri...

I hope the prosecutor has enough leverage with the court! Justice truly is blind!

New EV users often forget that unlike 'gallons of gasoline' or 'kWh', 'estimated miles of travel' are not a true unit of energy.

Truckers will sometimes install a valve to bypass the muffler, so they can let someone know that they just cut them off, and that they should try moving out of the way.

The "squat" you see on accelerating FWD vehicles is something different called wheel climb I think and is related to the effects of braking and center of gravity that we are discussing. When you gun the throttle, the wheel torque applies an opposite force as the wheels are turning in relation to the car. This causes a lever-like interaction forcing the front up and the rear down. During the engine brake maneuver the situation is reversed, as the torque is reversed in this scenario.

Imagine you had a car with independently activated front and rear brakes: Its trivial to understand that in a front-brake it will cause the front of the vehicle to tip forwards, and the rear will respond by tipping upwards. This unloads the rear suspension causing excessive camber, reducing tire contact, and if you were applying the brakes here, braking performance.

If you apply only rear brake, it will cause the rear wheels to pull their suspension downwards tipping the car rearward somewhat. As the stopping vehicle weight then pulls on the rear axle load, it applies a weak lever-like corresponding downward force on the front axle, reducing your center of gravity over the front-brake scenario. This will improve your handling performance, like I said.

Additionally, highway vehicles are designed with proportional braking that applies more of the braking force to the front rather than the rear. This, among other reasons, is why you can fishtail when you slam on the brakes. If you want to try it out, pull your ABS fuse the next time it rains, snows or there is some other slippery conditions and tool around in an empty parking lot.

This is why power braking is more suitable for RWD vehicles. It alleviates some of the effects of proportional braking and maintains a more favorable center of balance and suspension geometry.

It isn't that it doesn't work on FWD vehicles (It works well, and I did not mean to imply that it did not) only that RWD vehicles preserve more of their handling with this maneuver because of the facts regarding how a vehicle's suspension and center of gravity respond to braking and suspension load.

And you do have to be careful not to grab too low a gear and/or don't let the clutch out too fast, or you can mechanically overrev the engine.

IMO compression braking (jake brake) would be a better analog.

Too bad VW mechatronics doesn't read the throttle position for a clue here. It all just seems so obvious.

Are we talking genuinely dumb things like forklift loaded facing forwards on a small utility trailer or the typical online pearl clutching when someone is 100lb over their tire rating?

There shouldn't be much if any shock loading because the towed vehicle will be on the brakes the whole time.

Obviously some good judgement is advised. Roads with hairpin turns or the shoulder of a major urban interstate is not the place for this.

Obviously a tow bar would be better than a rope but nobody winds up in a situation where they need to regen tow a vehicle because of an abundance of alternative good options.

I guess I was a little too generous to HN when I assumed I didn't need to include a bunch of "be reasonable about it" disclaimers in my original comment.

The following numbers roughly correspond to my 2017 Model S: At 30mph the car consumes approximately 200Wh/mi (6kW or 8hp) and at 70mph approximately 300Wh/mi (21kW / 28hp). This is the power required to maintain these velocities against all external factors, and therefore is exactly equal to the power required to tow the vehicle at these speeds.

If you have regen set to normal, the car will supply up to 50kW / 67hp through regen. TBH I don't know exactly what the minimum speed to achieve full 50kW is, but I am reasonably confident that the car will do it at 30mph since the tires have more than 10 times the required grip to do it.

Towing at 30mph = 56kW / 75hp, 89% charging efficiency, equivalent to a ~2000lb trailer Towing at 70mph = 71kW / 95hp, 70% charging efficiency, equivalent to a ~2500lb trailer

The trailer weight estimates are roughly basaed average of engine power / towing capacity figures for medium duty pickups. The tow vehicle to do this safely in my estimation should have a 250hp power plant or larger.

The biggest flaw with the linked article is that it's not necessary to go 70mph to achieve the maximum charge rate from regen, and indeed it is less efficient to do so.

So? That doesn't make it representative of typical conditions.

>If you can only tow a certain load in ideal circumstances (no hills, no sudden braking, no wind, etc) then you actually cannot safely tow that load.

So someone in Kansas or Florida should be limited by grades that aren't even with a day's drive of them? Do you seriously believe this?

This line of reasoning is even more comical in light of how the current SAE test almost always results in engine power being the bottleneck.

There's a pretty massive amount of safe behavior you can do outside the confines of the magic rating number and even more options of unsafe things you can do within the number. At the end of the day some amount of good judgement and discretion is required because there is no shortage of variables that are static in the SAE test

Your position is only a stone's through from the pitch of the slimy RV salesman who says you can tow something anytime anywhere because it's less than the magic number. I think you (and the hypothetical RV salesman) need to take your appeal to authority and desire to substitute a nuance-free number with critical though and shove them somewhere unpleasant.

> putting back electricity into the batter[y] at a rate of 65 kW

The article could be wrong, of course.

Until recently batteries with the energy density needed for trains didn't exist, so the diesel generator was a necessary part of the equation. That is changing however, and battery/electric trains are now being tested.

https://www.bnsf.com/news-media/news-releases/newsrelease.pa...

I suspect the hard part is getting every car manufacturer to agree to the same system not designing something that works.

The cost is that you'd have to re-engineer maybe ten or twenty percent of major freeways and interstates (like have two miles of charging per every ten to twenty miles of regular road), and you'd need to establish a standard for trucks and passenger vehicles and get automakers to adopt it. (Or make it simple enough that it can be added as an aftermarket kit.) You'd also need to install more electrical generation capacity. (Fortunately, charging cars while they're driving shifts most of the charging from nighttime to daytime, when solar power can be used for this purpose.)

The benefit is that you could reduce long-haul trucking fuel consumption to near zero and reduce the need for EVs to have heavy, expensive 200-mile-or-more-range batteries.