Towing a Tesla at 70 MPH replenishes battery at fast charger rates • Hacker News Board

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

#191

Post by jvanderbot » Tue, Jun 22, 2021, 12:28 AM UTC

FridayoLeary wrote: post #78

ols wrote: post #56

The most spectacular example of regenerative braking are trains that are used in Scandinavia, heavily loaded with iron ore that is transported to the coast: "In Scandinavia the Kiruna to Narvik electrified railway carries iron ore on the steeply-graded route from the mines in Kiruna, in the north of Sweden, down to the port of Narvik in Norway to this day. The rail cars are full of thousands of tons of iron ore on th…

The heavy iron ore is essentially a large battery storing gravitational energy. In a way it's just another natural energy source. Maybe in the future clean power can be generated from pulling down mountains.

A thousand (1e3) metric tons (1e3 kg) of anything, up a thousand meters (1e3), has 1e9x(10)=1e10 Joules of potential energy on earth (g=~10 m/s2).

At 80% conversion (8e9 J) and assuming 1/8 of the energy is "payload" after paying for the train to go up, that's still ~1e9 or a GigaJoule.

At a -20% grade, you're looking at a 5km train ride, which reasonably might take a half hour or less (1800s). So, you're generating GJ/1800s = 555 KW by pulling down the mountain, assuming the rocks magically teleport into and out of your hoppers. (Thanks @calvinlh )

That's approximately 100-200 households per train pair, which might generate 10 K$ / month in electrical sales?

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

#192

Post by genewitch » Tue, Jun 22, 2021, 12:30 AM UTC

ErikVandeWater wrote: post #38

pcarolan wrote: post #15

We have trains in chicago that reach whiskers up to charging lines above them. Same as the trolley systems in San Francisco. What if every major city to city freeway stretch had these in a lane for electric vehicles?

Are all the cars going to reach up 13 feet in the air to the charging lines? That would be a very tough sell. Not to mention the increased danger of live power lines coming down in an accident. Also, how would lane changing work? Do they have to decouple from one set of power lines and connect to another?

Southern California has linked the carpool/ZEV lanes for several freeways, so for the best case of "north of los angeles" to "southern orange county" you wouldn't ever "change lanes" - you'd take the left fork of a gentle Y, which overhead lines can already do fine.

Speaking of Southern California, Interstate 57 had some work done around 2000, they were installing some sort of lane sensor substrate into the right two lanes of the freeway. there were some people claiming they wanted to do power delivery or collection too - like solar roadways.

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

#193

Post by jashephe » Tue, Jun 22, 2021, 12:31 AM UTC

tshaddox wrote: post #175

furiousjulius wrote: post #83

Earlier quoted context omitted.

Reminds me of this dam operation around here that pumps water up to a mountain top reservoir during the day when power is cheap and then lets it go at night when it can generate and sell the electricity for more money. I was always in awe of the lake size battery they created.

Pumped hydro is really cool. Also really bad when it fails: https://en.wikipedia.org/wiki/Taum_Sauk_Hydroelectric_Power_... > ... catastrophic failure of a triangular section of the reservoir wall and the release of 1 billion US gallons (3,800,000 m3) of water in 12 minutes. The sudden release sent a 20-foot (6.1 m) crest of water down the East Fork of the Black River. > A broad swath of dense forest was washed away…

Taum Sauk is unusual in that the dam fully surrounds the upper reservoir (i.e. the lake was made from scratch), although certainly all types of dam can fail.

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

#194

Post by cartoonworld » Tue, Jun 22, 2021, 12:32 AM UTC

extrapickles wrote: post #177

yurishimo wrote: post #170

Earlier quoted context omitted.

The only downside is it can be really loud as you shift down the gear and engine RPMs bounce around. Hence, all the signs when you approach a town that say, "No engine braking".

When correctly muffled, engine breaking is not really any noisier than the engine operating normally. 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.

Engine braking is definitely always much louder than regular braking. Don't piss off your neighbors.

The bypass valve on semi's you're referring to is not the exhaust. The huge BRAAAAAAAP that you hear coming from trucks when someone cuts them off aren't an exhaust bypass valve, its them slamming on their brakes to avoid a tragic 20-car pileup.

It is a release of the compressed air-fuel mixture momentarily before combustion called a Jake Brake or Compression Release Engine Brake[0], that Semis and large commercial vehicles are equipped with that provide for additional braking in an emergency.

What they're doing is releasing the compressed air-fuel into their exhaust, just prior to combustion. This causes the engine speed to drop instantly, slowing the truck down. It will surprise you to learn that semi trucks have pretty terrible braking performance, loaded or unloaded. They all use drum brakes.

It is strictly prohibited to bypass a muffler or emissions control device in the US. While cars get away with it all the time, a commercial truck carries additional registration, inspection, and license restrictions which makes this not only dangerous, annoying, needless and harmful, but extremely expensive.

Commercial Driver's face much steeper fines for equipment that is out of specification. Many commercial drivers are required to inspect their vehicles before they depart for even so much as a top indicator light which is burnt out, or they may face harsh penalties and fines that would make your skin crawl. $10,000 citations are levied daily.

[0] - https://en.wikipedia.org/wiki/Compression_release_engine_bra...

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

#195

Post by r00fus » Tue, Jun 22, 2021, 12:36 AM UTC

jvanderbot wrote: post #191

FridayoLeary wrote: post #78

Earlier quoted context omitted.

The heavy iron ore is essentially a large battery storing gravitational energy. In a way it's just another natural energy source. Maybe in the future clean power can be generated from pulling down mountains.

A thousand (1e3) metric tons (1e3 kg) of anything, up a thousand meters (1e3), has 1e9x(10)=1e10 Joules of potential energy on earth (g=~10 m/s2). At 80% conversion (8e9 J) and assuming 1/8 of the energy is "payload" after paying for the train to go up, that's still ~1e9 or a GigaJoule. At a -20% grade, you're looking at a 5km train ride, which reasonably might take a half hour or less (1800s). So, you're generating…

This would make for a great oatmeal comic material.

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

#196

Post by AceJohnny2 » Tue, Jun 22, 2021, 12:36 AM UTC

AdamJacobMuller wrote: post #183

codeismath wrote: post #164

Earlier quoted context omitted.

Years ago I visited the Seneca Pumped Storage Generating Station [0] reservoir in person. It's a massive man-made lake on the top of a small mountain in Pennsylvania, USA. They pump water up to it at night (when there is excess energy in the power grid), and let the water out in the day when the demand for energy is high (turning some turbines on its way down). Prior to visiting I had an intellectual understanding of…

> one BIG BATTERY > The power plant, rated at 451 MW That's a damn big battery. I love pumped storage, too bad it's not used more.

> I love pumped storage, too bad it's not used more

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) )

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

#197

Post by genewitch » Tue, Jun 22, 2021, 12:36 AM UTC

rektide wrote: post #57

pcarolan wrote: post #15

We have trains in chicago that reach whiskers up to charging lines above them. Same as the trolley systems in San Francisco. What if every major city to city freeway stretch had these in a lane for electric vehicles?

Seems like a lot of physical infrastructure spread out over a lot of area for little gain. Little gain because it doesn't feel like charging at fixed stations is so bad, and it's not something folks need to do that often. There's other challenges too. You'd also need to build some system for billing, such that people don't start to steal power. Do we trust the cars to meter themselves? Or do we try to have the line m…

Commercial drivers routinely make at least $0.50 per mile... towing hazardous materials (lithium or sulfuric acid and lead) is an endorsement that guarantees more money, as well. Add in amortized cost of the truck, charger, fuel, and batteries, you're looking at a "30 minute charge truck" costing like $25, minimum.

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

#198

Post by annoyingnoob » Tue, Jun 22, 2021, 12:37 AM UTC

codeismath wrote: post #164

FridayoLeary wrote: post #78

Earlier quoted context omitted.

The heavy iron ore is essentially a large battery storing gravitational energy. In a way it's just another natural energy source. Maybe in the future clean power can be generated from pulling down mountains.

Years ago I visited the Seneca Pumped Storage Generating Station [0] reservoir in person. It's a massive man-made lake on the top of a small mountain in Pennsylvania, USA. They pump water up to it at night (when there is excess energy in the power grid), and let the water out in the day when the demand for energy is high (turning some turbines on its way down). Prior to visiting I had an intellectual understanding of…

https://en.wikipedia.org/wiki/Castaic_Power_Plant

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

#199

Post by calvinlh » Tue, Jun 22, 2021, 12:39 AM UTC

jvanderbot wrote: post #191

FridayoLeary wrote: post #78

Earlier quoted context omitted.

The heavy iron ore is essentially a large battery storing gravitational energy. In a way it's just another natural energy source. Maybe in the future clean power can be generated from pulling down mountains.

A thousand (1e3) metric tons (1e3 kg) of anything, up a thousand meters (1e3), has 1e9x(10)=1e10 Joules of potential energy on earth (g=~10 m/s2). At 80% conversion (8e9 J) and assuming 1/8 of the energy is "payload" after paying for the train to go up, that's still ~1e9 or a GigaJoule. At a -20% grade, you're looking at a 5km train ride, which reasonably might take a half hour or less (1800s). So, you're generating…

You're off by a factor of 3600-- 1 watt is a Joule/second, not a Joule/hour. 1 GJ / 1800s ~= 555kW, not 2GW.

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

#200

Post by r00fus » Tue, Jun 22, 2021, 12:40 AM UTC

kllrnohj wrote: post #167

elihu wrote: post #120

This seems like an interesting solution to the "what to do if my battery runs out in the middle of nowhere" problem. Normally, you'd either have to have to call a tow truck or have someone with a generator come along and recharge. However, towing for awhile (probably at much less than 70 mph for safety reasons) to recharge the battery enough to get to the next town is something that could presumably be done by just a…

Only if any of those passing cars are gas-powered. If the passing cars are themselves also EVs, then there's both more obvious forms of energy transfer, but also you'll be taking that much range (and more) from the EV doing the towing.

Cost asymmetry - if I had the spare battery capacity (assuming I'm only doing local drives) I'd happily donate it to someone stranded. It's like giving a fiver to fill up emergency gas if they're broke at a gas station.