Energy storage

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In the pursuit of green energy, storage is needed for 2 reasons:

  1. To smooth out the intermittency of solar and wind power.
  2. To store energy in electric vehicles without gasoline or diesel.


Type Metals of concern, and is there enough in the earth? Other concerns Energy footprint Labor footprint
Lithium-ion batteries Lithium: Just barely enough.
Cobalt: Not enough.
Lifespan and recyclability To be determined To be determined
Lead-acid batteries Lead: Not enough. Toxic To be determined To be determined
Iron redox flow batteries Iron: There is plenty. Not implemented commercially yet. Could be viable for grid storage but not vehicles. To be determined To be determined
Flywheels Iron: There is plenty. But other rare metals are probably needed too. To be determined. Only the highest-energy-density designs would be worthwhile, but would they work in vehicles? To be determined To be determined
Hydrogen gas To be determined - how many rare metals would be needed for the electrolysis and the fuel cells. Most likely not enough platinum. In the case of vehicles: Needs pressurized fuel tanks, which might come with safety issues and wouldn't be as energy-dense as gasoline tanks. Also, fuel cell energy losses are higher than batteries. To be determined To be determined

How much storage would be needed?


65.2 kWh
Energy capacity of the average electric vehicle battery
Useable battery capacity of full electric vehicles
1.446 billion
Without this, we'd be calculating for just personal vehicles. But we also need to factor in commercial vehicles such as buses and trucks. These vary widely in size, and data is hard to find, so for simplicity sake, we just assume that they'd add up to about the same as personal vehicles - thus doubling total energy storage needed. This assumption is based on the fact that freight trucks are a somewhat smaller share of energy demand than passenger vehicles, but the trucks probably need a longer range. * ev.battery * commercial_factor

^ This could be reduced by walkability and public transit (specifically trains).


3290.73 Mtoe/year
Global energy usage, total final consumption minus transport and industrial
Source: Key World Energy Statistics 2020 (IEA report)
We subtract transport because it was already dealt with above. We subtract industrial because - in principle, most factories/industry could just run during peak sunlight/wind, needing negligable energy storage.
24 hours
How big the "buffer" of energy storage would have to be to be resiliant against weather fluctuations
The exact number could be up for debate. Join the discussion.
other_energy.tfc * timescale

^ This could be reduced by alternative heating/cooling systems for homes/buildings.

There are more options for this type of energy storage, because it's stationary (not moving in a vehicle).

How much storage is this really?

Most people aren't familiar with terajoules. Let's express it instead in terms of "gallons of gasoline equivalent energy" per person.

7.95 billion
(other_energy_storage_needed + vehicle_energy_storage_needed) / world.population
gallons gasoline per capita

This much energy has to be stored in some other way (not gasoline).


Hydrogen gas

Energy can be used for making hydrogen gas, and later the gas can be used for energy - either by combustion or by fuel cells.


Car engines can viably be built to burn hydrogen gas instead of gasoline. However, this isn't as efficient as building an electric car powered by hydrogen fuel cells (which use chemistry to convert the hydrogen energy back to electricity, which powers electric motors that run the car).

But even hydrogen fuel cells might not be quite efficient enough:

Energy efficiency of producing hydrogen & oxygen gases from water
Hydrogen made by the electrolysis of water is now cost-competitive ... › blog › hydrogen-made-by-the-electrolysis...
Electric energy efficiency of an average hydrogen fuel cell
Hydrogen Fuel Cells Fact Sheet › uploads › files › doe_fuelcell_factsheet
electrolysis.efficiency * hydrogen_fuel_cell.efficiency

This is only half the charge-discharge efficiency of lithium-ion batteries.

Hydrogen fuel cells contain rare minerals.[quantification needed]

Hydrogen gas requires a pressurized fuel tank, which is significantly heavier than a gasoline tank[quantification needed] but probably not as heavy as a lithium-ion battery pack, for the same amount of energy. Safety concerns are similar to other pressurized fuels such as natural gas or propane.

Heating and cooking

  • Homes could be heated with hydrogen gas instead of natural gas.
  • Gas-powered stoves could easily be adapted to burn hydrogen.

Lithium-ion batteries

Lithium-ion batteries are the current standard for electric cars and most small gadgets (phones, laptops, etc).

Is there enough lithium?

3.6 volts
Voltage of a single lithium-ion cell.
It's 3.6 volts for the "cobalt type" of lithium-ion battery. Other types might have a very slightly different voltage.
0.3 grams per amp hour li_ion.cell_voltage
To store a given amount of energy in lithium-ion batteries, this is how much lithium would be needed.
The article says lithium per amp hour. We convert this to lithium per watt hour (energy), by including the cell voltage.
18425000 tonnes
Lithium metal: Total global mineral reserves
Added up all the countries: 9,200,000 + 4,700,000 + 1,900,000 + 1,500,000 + 750,000 + 220,000 + 95,000 + 60,000 = 18,425,000 metric tons
20 kg per 100 kilowatt hours
To store a given amount of energy, in lithium-ion batteries (cobalt type), this is how much cobalt would be needed.
7.1 million tonnes
Cobalt metal: Total global mineral reserves
vehicle_energy_storage_needed * li_ion.lithium_by_energy
% lithium.reserves
other_energy_storage_needed * li_ion.lithium_by_energy
% lithium.reserves

Just barely. How about cobalt?

vehicle_energy_storage_needed * li_ion.cobalt_by_energy
% cobalt.reserves
other_energy_storage_needed * li_ion.cobalt_by_energy
% cobalt.reserves

Not viable.


  • Using some other version of lithium-ion batteries, which doesn't depend so much on cobalt.
  • Marketing cheaper electric vehicles with much smaller battery capacity, for city driving only.
  • Walkability.
  • Extracting lithium from seawater (the viability of this may be questionable).

Other important stats:

When you charge a lithium-ion battery, this much of the energy is stored. The rest is lost as heat.
Range: 80 to 90 %
from wikipedia; haven't found original source yet

Iron-redox flow batteries

Iron-redox flow batteries are a type of battery made from mostly iron, an extremely abundant metal.

But this battery comes with a few challanges:

  • The iron has to be kept molten at very hot temperatures.
    • Hence it's only viable to build a battery the size of a shipping container, not smaller.
    • This battery is not suited for electric vehicles.

There would be enough iron:

85 billion tonnes
Global iron reserves - iron metal recoverable
Source: Global iron ore reserves 2010-2021 - Statista
1.95 billion tonnes/year
Source: World crude steel production 2021 - Statista

The source doesn't specify whether this is steel from newly-mined iron or steel from recycling scrap. Probably it's both combined.

85 watt hours per kg
Specific energy of an iron redox flow battery
Using half the "theoretical specific energy" of 170 watt hours per kg. This battery hasn't really been commercialized yet, so it's safe to assume that we won't be close to the theoretical maximum in the near future.


other_energy_storage_needed / irfb.energy_by_mass
% iron.reserves
other_energy_storage_needed / irfb.energy_by_mass
years iron.production

Lead-acid batteries

Besides being toxic, there wouldn't be enough lead to scale these up:

90 million tonnes
Global lead reserves 2010-2021 - Statista
38 watt hours per kg
Specific energy of a lead-acid battery
Source: Lead-acid battery - Wikipedia
How much of a lead-acid battery is lead, by mass
Source: Lead-acid battery - Wikipedia
other_energy_storage_needed * lead_acid.lead / lead_acid.energy_by_mass
% lead.reserves

The only advantage is that some people already have a few lead-acid car batteries they could use in some DIY home energy storage solution.


Flywheels store energy mechanically by spinning a heavy rotor at high speeds. This has been implemented before, both inside vehicles but not necessarily storing enough energy to power the vehicle for more than a few kilometers at best and in stationary electrical systems with a much higher specific energy.

If flywheels are made mostly of steel (which is mostly iron), we would have enough metal to build enough of them:

5 kWh per (450 kg)
Based on this product as an example:
other_energy_storage_needed / flywheels.practical.energy_by_mass
% iron.reserves
other_energy_storage_needed / flywheels.theoretical.energy_by_mass
% iron.reserves

However, it is unknown how much of other metals might be needed to make the flywheel systems - for example the rare earth magnets involved in the motor/generator components. This page needs more research.

How much energy would it take to refine all that steel?

9938 Mtoe/year
Global total final energy consumption
Source: Key World Energy Statistics 2020
sqrt(1665*4170) watt hours per kg
How much energy does it take (on average) to produce 1 kilogram of...
sqrt(5550*13900) watt hours per kg
How much energy does it take (on average) to produce 1 kilogram of... * other_energy_storage_needed / flywheels.practical.energy_by_mass
months energy.tfc

However, the energy needed to manufacture the flywheels from the steel, might be vastly more. This page needs more research.

Viability of flywheels in vehicles is unknown too. Flywheel-based vehicles have existed for over a century, but they don't store enough energy to last more than a kilometer. Perhaps vacuum-sealed electrical type of flywheel could store more energy this page needs to clarify this more in previous paragraphs, but would the bumps of the road cause energy losses too quickly? This page needs more research.