4 ms·

> Once we have better batteries for storage, what problem do we have left that requires hydrogen to solve? An obvious short-term problem is weight-efficiency -

by avmich 6y ago

> Once we have better batteries for storage, what problem do we have left that requires hydrogen to solve? An obvious short-term problem is weight-efficiency - hydrogen is still far better than best batteries, and weight is of crucial importance on aircrafts, so if you want to fly green - jets, turboprops, electric propellers - you can use hydrogen.

maerF0x0 6y ago
I dont really know the correct terminology, but I think batteries also have an issue with "burst" power loads. Think like the difference between a battery and capacitor. Some alternatives like super capacitors may bring greater power, albeit not at the same total storage? Is this correct understanding?
- sokoloff 6y ago
  That depends on the battery chemistry and construction. Li-Ion and flooded lead-acid batteries can produce fairly high surge currents. Coin-cells on the other extreme cannot.
  - gpm 6y ago
    Even with relatively high rates of discharge, my non-expert understanding is that they are still far slower than capacitors. E.g. if you're trying to build a railgun or absorb power from lightning strikes you better be using capacitors (which might be charged from a battery). That last part of sort of the point, while batteries and capacitors serve the same theoretical function (storing energy), in practice they are used differently. One as a sort of buffer, the other for actual storage.
    - magicalhippo 6y ago
      While true, even a battery pack used for small RC cars can output several hundred amps in bursts or even constant discharge. Take this[1] pack of four cells for example which is rated for 450A constant discharge and 650A bursts. And there are more extreme packs like this[2], still four cells, which is rated for over 1100A burst discharge. Sure a capacitor might do better for a brief instant, but li-io batteries can put out some serious energy quickly. [1]: https://hobbyking.com/en_us/graphene-5000mah-2s2p-hardcase-w-5mm-female-bullet-connector.html https://hobbyking.com/en_us/graphene-5000mah-2s2p-hardcase-w... [2]: https://hobbyking.com/en_us/turnigy-rapid-8000mah-2s2p-140c-hardcase-lipo-battery-pack-roar-approved.html https://hobbyking.com/en_us/turnigy-rapid-8000mah-2s2p-140c-...
- landemva 6y ago
  Yes, it is correct concerning burst energy from capacitors. The #2 heavy equipment manufacturer has a large capacitor in their regenerative excavator (which sees the most sales in Europe, not North America).
- easde 6y ago
  Power density for supercapacitors is higher than batteries, but there aren't many applications that need more power than what the best lithium polymer cells that provide. 100C cells are readily available, which can discharge their full capacity about 1/100 hour ~= 36 seconds. These are the cells that power high-speed RC planes and handheld power banks that can jumpstart your car. One caveat with high discharge rate batteries is that cycle life is not necessarily any better, and charge rates are usually much lower than discharge rates, so sometimes you will see supercapacitors used to temporarily hold a large amount of energy. Hydrogen has high power density in the sense that you can let it out of the tank very quickly and ignite it, but unless you want an explosion you are still constrained by an ICE motor or fuel cell. Those are much less power dense than batteries.
mcguire 6y ago
Ok, let's see here... Hydrogen has 142 MJ/kg and at 700 bar is 42 kg/m^3. "At this pressure, 5 kg of hydrogen can be stored in a 125-liter tank." (https://energies.airliquide.com/resources-planet-hydrogen/how-hydrogen-stored https://energies.airliquide.com/resources-planet-hydrogen/ho...). That's 710 MJ in 125-liter tank. I couldn't find the stats on a 127-liter tank, but a 49-liter, 300 ft^3 tank is 139 lbs, or 63 kg. That would hold about 2kg of hydrogen. (https://www.mathesongas.com/industrialgas/pdfs/Industrial-Cylinder-Dimensions.pdf https://www.mathesongas.com/industrialgas/pdfs/Industrial-Cy...) That's 280 MJ in 65 kg, or 4.3 MJ/kg. A lithium ion battery is 0.36–0.875 MJ/kg, but jet fuel is 43 MJ/kg. (https://en.wikipedia.org/wiki/Energy_density https://en.wikipedia.org/wiki/Energy_density)

by avmich 6y ago

maerF0x0 6y ago

I dont really know the correct terminology, but I think batteries also have an issue with "burst" power loads. Think like the difference between a battery and capacitor. Some alternatives like super capacitors may bring greater power, albeit not at the same total storage? Is this correct understanding?

sokoloff 6y ago
That depends on the battery chemistry and construction. Li-Ion and flooded lead-acid batteries can produce fairly high surge currents. Coin-cells on the other extreme cannot.
- gpm 6y ago
  Even with relatively high rates of discharge, my non-expert understanding is that they are still far slower than capacitors. E.g. if you're trying to build a railgun or absorb power from lightning strikes you better be using capacitors (which might be charged from a battery). That last part of sort of the point, while batteries and capacitors serve the same theoretical function (storing energy), in practice they are used differently. One as a sort of buffer, the other for actual storage.
  - magicalhippo 6y ago
    While true, even a battery pack used for small RC cars can output several hundred amps in bursts or even constant discharge. Take this[1] pack of four cells for example which is rated for 450A constant discharge and 650A bursts. And there are more extreme packs like this[2], still four cells, which is rated for over 1100A burst discharge. Sure a capacitor might do better for a brief instant, but li-io batteries can put out some serious energy quickly. [1]: https://hobbyking.com/en_us/graphene-5000mah-2s2p-hardcase-w-5mm-female-bullet-connector.html https://hobbyking.com/en_us/graphene-5000mah-2s2p-hardcase-w... [2]: https://hobbyking.com/en_us/turnigy-rapid-8000mah-2s2p-140c-hardcase-lipo-battery-pack-roar-approved.html https://hobbyking.com/en_us/turnigy-rapid-8000mah-2s2p-140c-...
landemva 6y ago
Yes, it is correct concerning burst energy from capacitors. The #2 heavy equipment manufacturer has a large capacitor in their regenerative excavator (which sees the most sales in Europe, not North America).
easde 6y ago
Power density for supercapacitors is higher than batteries, but there aren't many applications that need more power than what the best lithium polymer cells that provide. 100C cells are readily available, which can discharge their full capacity about 1/100 hour ~= 36 seconds. These are the cells that power high-speed RC planes and handheld power banks that can jumpstart your car. One caveat with high discharge rate batteries is that cycle life is not necessarily any better, and charge rates are usually much lower than discharge rates, so sometimes you will see supercapacitors used to temporarily hold a large amount of energy. Hydrogen has high power density in the sense that you can let it out of the tank very quickly and ignite it, but unless you want an explosion you are still constrained by an ICE motor or fuel cell. Those are much less power dense than batteries.

mcguire 6y ago

Ok, let's see here... Hydrogen has 142 MJ/kg and at 700 bar is 42 kg/m^3. "At this pressure, 5 kg of hydrogen can be stored in a 125-liter tank." (https://energies.airliquide.com/resources-planet-hydrogen/how-hydrogen-stored https://energies.airliquide.com/resources-planet-hydrogen/ho...). That's 710 MJ in 125-liter tank. I couldn't find the stats on a 127-liter tank, but a 49-liter, 300 ft^3 tank is 139 lbs, or 63 kg. That would hold about 2kg of hydrogen. (https://www.mathesongas.com/industrialgas/pdfs/Industrial-Cylinder-Dimensions.pdf https://www.mathesongas.com/industrialgas/pdfs/Industrial-Cy...) That's 280 MJ in 65 kg, or 4.3 MJ/kg. A lithium ion battery is 0.36–0.875 MJ/kg, but jet fuel is 43 MJ/kg. (https://en.wikipedia.org/wiki/Energy_density https://en.wikipedia.org/wiki/Energy_density)