How many gallons of gasoline would it take to charge an iPhone? • Hacker News Board

Re: How many gallons of gasoline would it take to charge an iPhone?

#61

Post by drcube » Wed, Feb 08, 2012, 8:26 PM UTC

drcube wrote: post #60

herge wrote: post #42

Earlier quoted context omitted.

How many times more efficient is a gas power plant than the average use of a car?

Wikipedia says: "Even when aided with turbochargers and stock efficiency aids, most engines retain an average efficiency of about 18%-20%." http://en.wikipedia.org/wiki/IC_engine Wikipedia again: "Typical thermal efficiency for electrical generators in the industry is around 33% for coal and oil-fired plants, and up to 50% for combined-cycle gas-fired plants." http://en.wikipedia.org/wiki/Fossil_fuel_power_plant

That neglects to mention the inefficiency in distributing gasoline via gas-powered vehicles to hundreds of millions of drivers.

Re: How many gallons of gasoline would it take to charge an iPhone?

#62

Post by frankus » Wed, Feb 08, 2012, 8:44 PM UTC

bhousel wrote: post #34

frankus wrote: post #23

Petroleum is really frickin' energy-dense (leaving aside the fact that unless you're heating something only a small fraction can be turned into useful work). A mid-range home EV charger peaks out at about 20kW. By contrast, the energy flux of a gas pump is around 20MW.

A mid-range home EV charger (like the GE WattStation), is spec'ed for 30A at 240V, which is 7.2kW, not 20kW. You might be confused because a typical battery in an EV is around 20+kW h , which is why it takes a few hours for the wall charger to charge it! For comparison, a 20kW load would draw 83A at 240V. A smallish pole mounted utility transformer may supply 20kW. Of course, none of it detracts from your point that…

Good point. Most homes around here are wired with 200A, 240V power, so a 20kW charger would eat up about half of that.

So a 7.2kW charger is about 2500 times slower than a fast gas pump.

Even slow gas pump (say 10MW), used with a conventional engine (say 20% efficient), compared with a state-of-the-art fast charger (say 200kW) would still be ten times as fast in a miles-per-hour contest.

EVs make up for this somewhat by being able to charge anywhere that has a decent supply of electricity for hours at a time, but it still shows you what they're up against.

Re: How many gallons of gasoline would it take to charge an iPhone?

#63

Post by lurker17 » Wed, Feb 08, 2012, 9:31 PM UTC

martinkallstrom wrote: post #14

brk wrote: post #9

Earlier quoted context omitted.

I realize you're being slightly snarky... If the chart on the website is to be believed, gasoline is second only to diesel in terms of energy density of viable fuel sources. The power consumption of a vehicle has little to do with gasoline, though there is an important consideration for efficiency in terms of converting the fuel to linear motion (internal combustion engine and drivetrain). Vehicles powered by any met…

Upvoted because of the reasons above. Bad choice of words on my part. Should have been "Vehicles (period) are incredibly power consuming".

But now you've got a period in the middle of your sentence.

Re: How many gallons of gasoline would it take to charge an iPhone?

#64

Post by jessriedel » Wed, Feb 08, 2012, 10:45 PM UTC

tomkarlo wrote: post #26

jessriedel wrote: post #8

Earlier quoted context omitted.

All vehicles are incredibly power consuming (compared to iPods) and there are basic limits to improving this. If you want a vehicle that is large enough to hold a human and can push air out of the way at 60 mph, it's going to take a lot of energy. Driving habits, aerodynamics, and size can change this usage by a factor of order unity, but they can't do it by orders of magnitude. Thus, alternative energy sources must…

Thinking like this is what prevents real innovation. All of these statements seem to be common sense, but they're all individually false when you dig below the surface. There are huge variations in how much vehicles consume on a per-passenger basis. And there's no reason that alternative energy / electric must approach the energy density of petroleum - that assumption only holds if you're assuming that a vehicle must…

> Thinking like this is what prevents real innovation.

On the contrary, thinking like this is what spurs real innovation.

Look how many comments in this thread are about trivial changes like cutting the size of cars by half, or doubling fuel mileage, or cutting speeds in half. Likewise, think how many people assume you can make an appreciable change in global warming by recycling a bit more, driving a bit less, or buying the right brand of milk. What these all have in common is that they seem much easier to implement and, crucially, they make you feel like you're doing something.

In fact, we need major innovations. The point of my back-of-the-envelope argument isn't to assume that new solutions look like old ones. (I mean, I take it as obvious that, e.g., if we have ways to wireless beam energy to moving cars then this is an awesome solution and brilliantly defeats my argument.) The point of the argument is that you can't make minor changes; they have to be ambitious.

Re: How many gallons of gasoline would it take to charge an iPhone?

#65

Post by tomkarlo » Sat, Feb 11, 2012, 1:21 AM UTC

jessriedel wrote: post #64

tomkarlo wrote: post #26

Earlier quoted context omitted.

Thinking like this is what prevents real innovation. All of these statements seem to be common sense, but they're all individually false when you dig below the surface. There are huge variations in how much vehicles consume on a per-passenger basis. And there's no reason that alternative energy / electric must approach the energy density of petroleum - that assumption only holds if you're assuming that a vehicle must…

> Thinking like this is what prevents real innovation. On the contrary, thinking like this is what spurs real innovation. Look how many comments in this thread are about trivial changes like cutting the size of cars by half, or doubling fuel mileage, or cutting speeds in half. Likewise, think how many people assume you can make an appreciable change in global warming by recycling a bit more, driving a bit less, or bu…

What I mainly took issue with was the conclusion: "Thus, alternative energy sources must approach the energy density of petroleum if they are to be competitive."

That seems utterly faulty to me, as I pointed out - there are multiple ways to solve the problem, none of which would necessarily require increasing the energy density of alternative power sources. All you have to do is reduce the amount of energy that needs to be stored in the vehicle, either by reducing use or required range between charges.

For what it's worth, there are already ways to beam energy to moving cars. http://www.extremetech.com/extreme/101581-inductive-car-char...

Re: How many gallons of gasoline would it take to charge an iPhone?

#66

Post by jules » Tue, Feb 14, 2012, 12:43 PM UTC

Adaptive wrote: post #56

soren_dahl wrote: post #13

Earlier quoted context omitted.

"We don't mine batteries from the ground" Er...

Maybe rephrase your question to be clearer, but I'm assuming you mean mining the chemical components of batteries. Not what I was referring to. I'm talking about the fundamental difference between a battery of any variety (chemical, flywheel, etc.) and petrochemical energy sources . The article compares energy density of gasoline and other energy sources with "electric". It's a poor comparison. These are different ca…

Actually, lithium is a very depletable resource just like oil and coal are. Not in the sense that we use it up for energy, but in the sense that if you want to run all cars on lithium batteries there simply isn't enough easily mine-able lithium in the world. In this sense it is valid to say that we mine batteries. The same story goes for most solar panels.

Comparing the energy density of gasoline with the energy density of a charged battery is obviously also valid.