Energy storage

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.

How much would be needed?

Vehicles

ev.battery

65.2 kWh

Energy capacity of the average electric vehicle battery

Useable battery capacity of full electric vehicles
https://ev-database.org/cheatsheet/useable-battery-capacity-electric-car

world.cars

1.446 billion

How Many Cars Are There In The World in 2022?
https://hedgescompany.com/blog/2021/06/how-many-cars-are-there-in-the-world/

commercial_factor

2

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.

world.cars * ev.battery * commercial_factor terajoules vehicle_energy_storage_needed (calculation loading) ^ This could be reduced by walkability and public transit (specifically trains).

Other

other_energy.tfc

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.

timescale

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 terajoules other_energy_storage_needed (calculation loading) ^ 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.

world.population

7.95 billion

(other_energy_storage_needed + vehicle_energy_storage_needed) / world.population gallons gasoline per capita (calculation loading)

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

Types

Hydrogen gas

Hydrogen gas does not occur in nature, but can be generated using green energy (by electrolysis).

Vehicles

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:

electrolysis.efficiency

80%

Energy efficiency of producing hydrogen & oxygen gases from water

Hydrogen made by the electrolysis of water is now cost-competitive ...
www.carboncommentary.com › blog › hydrogen-made-by-the-electrolysis...

hydrogen_fuel_cell.efficiency

50%

Electric energy efficiency of an average hydrogen fuel cell

Hydrogen Fuel Cells Fact Sheet
www.californiahydrogen.org › uploads › files › doe_fuelcell_factsheet

electrolysis.efficiency * hydrogen_fuel_cell.efficiency % (calculation loading) 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?

li_ion.cell_voltage

3.6 volts

Voltage of a single lithium-ion cell.

https://www.cei.washington.edu/education/science-of-solar/battery-technology/
https://www.fluxpower.com/blog/what-is-the-energy-density-of-a-lithium-ion-battery
It's 3.6 volts for the "cobalt type" of lithium-ion battery. Other types might have a very slightly different voltage.

li_ion.lithium_by_energy

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.

https://batteryguy.com/kb/knowledge-base/how-to-calculate-the-lithium-content-in-a-battery/
The article says lithium per amp hour. We convert this to lithium per watt hour (energy), by including the cell voltage.

lithium.reserves

18425000 tonnes

Lithium metal: Total global mineral reserves

https://www.statista.com/statistics/268790/countries-with-the-largest-lithium-reserves-worldwide/
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

li_ion.cobalt_by_energy

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.

https://www.energy.gov/eere/vehicles/articles/reducing-reliance-cobalt-lithium-ion-batteries

cobalt.reserves

7.1 million tonnes

Cobalt metal: Total global mineral reserves

https://www.statista.com/statistics/264930/global-cobalt-reserves/

vehicle_energy_storage_needed * li_ion.lithium_by_energy % lithium.reserves (calculation loading) other_energy_storage_needed * li_ion.lithium_by_energy % lithium.reserves (calculation loading)

Just barely. How about cobalt? vehicle_energy_storage_needed * li_ion.cobalt_by_energy % cobalt.reserves (calculation loading) other_energy_storage_needed * li_ion.cobalt_by_energy % cobalt.reserves (calculation loading)

Not viable.

Solutions:

• 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:

li_ion.charge_discharge_efficiency

85%

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

li_ion.charge_discharge_efficiency % (calculation loading)

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.

Flywheels

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, an extremely abundant metal), we would have enough metal to build enough of them:

flywheels.practical.energy_by_mass

5 kWh per (450 kg)

Based on this product as an example: http://www.rosseta.de/texte/pdat-t4.pdf

flywheels.theoretical.energy_by_mass

500 kJ/kg

https://web.archive.org/web/20100710052927/http://www.pddnet.com/article-next-gen-of-flywheel-energy-storage/

iron.reserves

85 billion tonnes

Global iron reserves - iron metal recoverable

Source: Global iron ore reserves 2010-2021 - Statista

other_energy_storage_needed / flywheels.practical.energy_by_mass % iron.reserves (calculation loading) other_energy_storage_needed / flywheels.theoretical.energy_by_mass % iron.reserves (calculation loading)

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?

energy.tfc

9938 Mtoe/year

Global total final energy consumption

Source: Key World Energy Statistics 2020

steel.recycled.production.energy_by_mass

sqrt(1665*4170) watt hours per kg

How much energy does it take (on average) to produce 1 kilogram of...https://www.lowtechmagazine.com/what-is-the-embodied-energy-of-materials.html

steel.new.production.energy_by_mass

sqrt(5550*13900) watt hours per kg

How much energy does it take (on average) to produce 1 kilogram of...https://www.lowtechmagazine.com/what-is-the-embodied-energy-of-materials.html

steel.new.production.energy_by_mass * other_energy_storage_needed / flywheels.practical.energy_by_mass months energy.tfc (calculation loading) 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.