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The highest energy density listed for the electrolytes on the wikipedia page for flow batteries is 75 watt hours/kg, that is about 0.25Mj/kg. Gasoline is 42Mj/k

by jws 15y ago

The highest energy density listed for the electrolytes on the wikipedia page for flow batteries is 75 watt hours/kg, that is about 0.25Mj/kg. Gasoline is 42Mj/kg. The original MIT release claims a 10 fold improvement in energy densities over existing flow batteries, but that is still more than an order of magnitude worse than the incumbent fuel.

artmageddon 15y ago
Pardon my ignorance, but are the flow batteries you mention the same type used in existing electric vehicles? It can't be assumed that the energy density of flow batteries will ever match as gasoline, but people might be willing to accept the difference if it means more infrastructure adoption and less time spent recharging vehicles.
- jws 15y ago
  Good point. I've not seen flow batteries in existing vehicles. Electric vehicles use NiMH batteries (0.25 MJ/kg), lithium batteries (0.4 to 0.7 MJ/kg) or lead acid (0.14 MJ/kg fork trucks, but they need mass anyway). Guessing at the numbers MIT is avoiding naming in that press release, they might get to something three times better than the current lithium batteries, but you also have to add in the mass of the pumps, and the reaction part of the battery. It could "win", but it won't be a game changer. Putting aside vehicles though, flow batteries have some interesting properties for utility scale energy storage. The rate at which you can store or retrieve energy is independent from the amount of energy you can store. The first is by the size of your reactor, the second is by the volume of your storage tanks. It is possible if they are using common enough elements for their fluid that they could be a good answer for peak load shifting or production storing.
  - uvdiv 15y ago
    Here's the numbers: ...we estimate that optimized SSFC systems using established lithium intercalation compounds could have energy densities of 300–500 Wh L−1 (specific energy 130–250 Wh kg−1), which would satisfy metrics considered necessary for widespread adoption of all-electric vehicles.[4] Further improvements would be possible by ‘dropping in’ higher-energy-density or lower-cost storage compounds in the SSFC platform as they are developed. http://onlinelibrary.wiley.com/doi/10.1002/aenm.201100152/full http://onlinelibrary.wiley.com/doi/10.1002/aenm.201100152/fu... (linked from http://web.mit.edu/newsoffice/2011/flow-batteries-0606.html http://web.mit.edu/newsoffice/2011/flow-batteries-0606.html) So 0.47-0.90 MJ/kg. Based on theoretical calculations -- they haven't actually engineered this.
- deleted 15y ago
  [deleted]
colomon 15y ago
Isn't that about the level where it gets interesting? My car can go something over 400 miles on a tank of gas right now. If their new batteries can get 40 miles on a "tank", and be refueled as easily as my car can now, that seems right on the threshold of being a very viable product.
- jamesaguilar 15y ago
  Also, gas tanks could be a lot bigger without ruining cars. Things would be slightly less efficient, but if the solution is just being reused then pumping thirty gallons at once might not be the end of the world (as opposed to the ten that currently fit in my tank). If the solution weighs as much as gasoline, then that's an extra 120 lbs when the tank is full, which is a lot, but it's <5% extra.
  - sliverstorm 15y ago
    Not to mention if the tank is full of a fluid that is not particularly dangerous, you might be able to integrate it into the structure of the car, similar to motorcycles with oil-in-frame design.
- anamax 15y ago
  > If their new batteries can get 40 miles on a "tank", and be refueled as easily as my car can now, that seems right on the threshold of being a very viable product. Not really. I go 300 miles between fillups and would like to go more. 10x as many visits to the "energy station" is a huge obstacle. Not to mention that I often go on trips that are longer than 40 miles. Losing 5 minutes to fillups every 3-40 miles is unworkable. And, I often go places where the gas station density is low, so I'm going to have to fill up more often and there are places that I just can't go on a 3-40 mile tank. As a commute-only vehicle, 30-40 miles can make sense, but few of us can afford significant money for such an "extra" car.
  - ebiester 15y ago
    Single people can't, but commute-only vehicles are common for families. The minivan takes care of major trips, and the commuter car is used for the spouse with the longer commute.
deleted 15y ago
[deleted]
briggsbio 15y ago
The authors tout ranges of 300-500 Wh/L. http://www.greencarcongress.com/2011/05/ssfc-20110526.html http://www.greencarcongress.com/2011/05/ssfc-20110526.html You also have to take into account that while gasoline has a high energy density, the efficiency of the motor cuts that significantly. Definitely a lot more development on this front, but interesting.
seldo 15y ago
Does the calculation of efficiency take into account the efficiency of conversion? I know that the actual potential-to-kinetic energy conversion rate of gas-powered cars is about 20% ( http://en.wikipedia.org/wiki/Engine_efficiency#Gasoline_.28petrol.29_Engines http://en.wikipedia.org/wiki/Engine_efficiency#Gasoline_.28p... ). Wikipedia claims an electric car is 3x more efficient than that ( http://en.wikipedia.org/wiki/Electric_vehicle#Energy_efficiency http://en.wikipedia.org/wiki/Electric_vehicle#Energy_efficie... ). So theoretically, energy density of a battery tech only needs to hit one-third the efficiency of gasoline to match mileage. So the goal is 14Mj/kg, and a 10x increase would be 2.5Mj/kg -- so still lower, but getting much closer.
- invisible 15y ago
  Based on your data and a sibling comment of yours, it would mean we would simply need fuel tanks that hold 5x more fuel. That doesn't seem unreasonable as the production cost of a fully electric car can be less as the engines are MUCH simpler (esp. when ordered in mass).
  - SoftwareMaven 15y ago
    I think weight (and sloshing) would impact handling and economy in a severely negative if tanks were 5x as large. 400 pounds of liquid would be pretty bad.

by jws 15y ago

artmageddon 15y ago

Pardon my ignorance, but are the flow batteries you mention the same type used in existing electric vehicles? It can't be assumed that the energy density of flow batteries will ever match as gasoline, but people might be willing to accept the difference if it means more infrastructure adoption and less time spent recharging vehicles.

jws 15y ago
Good point. I've not seen flow batteries in existing vehicles. Electric vehicles use NiMH batteries (0.25 MJ/kg), lithium batteries (0.4 to 0.7 MJ/kg) or lead acid (0.14 MJ/kg fork trucks, but they need mass anyway). Guessing at the numbers MIT is avoiding naming in that press release, they might get to something three times better than the current lithium batteries, but you also have to add in the mass of the pumps, and the reaction part of the battery. It could "win", but it won't be a game changer. Putting aside vehicles though, flow batteries have some interesting properties for utility scale energy storage. The rate at which you can store or retrieve energy is independent from the amount of energy you can store. The first is by the size of your reactor, the second is by the volume of your storage tanks. It is possible if they are using common enough elements for their fluid that they could be a good answer for peak load shifting or production storing.
- uvdiv 15y ago
  Here's the numbers: ...we estimate that optimized SSFC systems using established lithium intercalation compounds could have energy densities of 300–500 Wh L−1 (specific energy 130–250 Wh kg−1), which would satisfy metrics considered necessary for widespread adoption of all-electric vehicles.[4] Further improvements would be possible by ‘dropping in’ higher-energy-density or lower-cost storage compounds in the SSFC platform as they are developed. http://onlinelibrary.wiley.com/doi/10.1002/aenm.201100152/full http://onlinelibrary.wiley.com/doi/10.1002/aenm.201100152/fu... (linked from http://web.mit.edu/newsoffice/2011/flow-batteries-0606.html http://web.mit.edu/newsoffice/2011/flow-batteries-0606.html) So 0.47-0.90 MJ/kg. Based on theoretical calculations -- they haven't actually engineered this.
deleted 15y ago
[deleted]

colomon 15y ago

Isn't that about the level where it gets interesting? My car can go something over 400 miles on a tank of gas right now. If their new batteries can get 40 miles on a "tank", and be refueled as easily as my car can now, that seems right on the threshold of being a very viable product.

jamesaguilar 15y ago
Also, gas tanks could be a lot bigger without ruining cars. Things would be slightly less efficient, but if the solution is just being reused then pumping thirty gallons at once might not be the end of the world (as opposed to the ten that currently fit in my tank). If the solution weighs as much as gasoline, then that's an extra 120 lbs when the tank is full, which is a lot, but it's <5% extra.
- sliverstorm 15y ago
  Not to mention if the tank is full of a fluid that is not particularly dangerous, you might be able to integrate it into the structure of the car, similar to motorcycles with oil-in-frame design.
anamax 15y ago
> If their new batteries can get 40 miles on a "tank", and be refueled as easily as my car can now, that seems right on the threshold of being a very viable product. Not really. I go 300 miles between fillups and would like to go more. 10x as many visits to the "energy station" is a huge obstacle. Not to mention that I often go on trips that are longer than 40 miles. Losing 5 minutes to fillups every 3-40 miles is unworkable. And, I often go places where the gas station density is low, so I'm going to have to fill up more often and there are places that I just can't go on a 3-40 mile tank. As a commute-only vehicle, 30-40 miles can make sense, but few of us can afford significant money for such an "extra" car.
- ebiester 15y ago
  Single people can't, but commute-only vehicles are common for families. The minivan takes care of major trips, and the commuter car is used for the spouse with the longer commute.

deleted 15y ago

[deleted]

briggsbio 15y ago

The authors tout ranges of 300-500 Wh/L. http://www.greencarcongress.com/2011/05/ssfc-20110526.html http://www.greencarcongress.com/2011/05/ssfc-20110526.html You also have to take into account that while gasoline has a high energy density, the efficiency of the motor cuts that significantly. Definitely a lot more development on this front, but interesting.

seldo 15y ago

Does the calculation of efficiency take into account the efficiency of conversion? I know that the actual potential-to-kinetic energy conversion rate of gas-powered cars is about 20% ( http://en.wikipedia.org/wiki/Engine_efficiency#Gasoline_.28petrol.29_Engines http://en.wikipedia.org/wiki/Engine_efficiency#Gasoline_.28p... ). Wikipedia claims an electric car is 3x more efficient than that ( http://en.wikipedia.org/wiki/Electric_vehicle#Energy_efficiency http://en.wikipedia.org/wiki/Electric_vehicle#Energy_efficie... ). So theoretically, energy density of a battery tech only needs to hit one-third the efficiency of gasoline to match mileage. So the goal is 14Mj/kg, and a 10x increase would be 2.5Mj/kg -- so still lower, but getting much closer.

invisible 15y ago
Based on your data and a sibling comment of yours, it would mean we would simply need fuel tanks that hold 5x more fuel. That doesn't seem unreasonable as the production cost of a fully electric car can be less as the engines are MUCH simpler (esp. when ordered in mass).
- SoftwareMaven 15y ago
  I think weight (and sloshing) would impact handling and economy in a severely negative if tanks were 5x as large. 400 pounds of liquid would be pretty bad.