Energy cannot be created or destroyed; it can only be changed from one form to another.
This much quoted line from one of the greatest minds the world has known (Albert Einstein) remains true, which is why the storage of energy, in a useful form, still remains the key.
Photograph by Orren Jack Turner, Princeton, N.J.
Modified with Photoshop by PM_Poon and later by Dantadd., Public domain, via
Wikimedia Commons
For well
over 150 years hydrocarbons have been the main energy carrier that the world
has exploited, but now due to carbon emission concerns, we are looking to other
energy vectors.
Energy storage comes in different forms with no single
solution fitting all applications in terms of power density, discharge rate,
life-time and efficiency. Rechargeable
batteries (specifically Lithium Ion) are the front runner for a number of
applications at present due to their ability to provide a good fit-for-purpose solution
for many uses. Batteries are very good at variable discharge rates and
efficiency and with the price of lithium-ion batteries declining sharply in
recent years (having been developed and scaled for widespread use in phones,
laptops, cars etc..), they certainly have a role to play in the world’s energy
management solution.
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However, Lithium
Ion (Li-Ion) batteries are not best placed for long-term or large quantity
energy storage. HydroGenesis’ stationary storage solution requires the ability
to power a house, factory or power-hungry data centre for many hours per day,
for consecutive days, weeks or months. High cost and short life-cycle restricts
the use of batteries in power storage systems; this is where the hydrogen and fuel cell
double-act step in.
The
operation principle of batteries is comparable to that of hydrogen and fuel
cells, both technologies transform chemically stored energy into electrical
energy. In a battery the chemical energy is stored internally, whereas
in a fuel cell the chemical energy (hydrogen) is supplied externally and can be
continuously replenished (in our solutions via an onsite electrolyser). A
future article will delve deeper into how fuel cells work.
Return of energy
On average,
80% to 90% of the electricity used to charge the battery can be retrieved
during the discharging process. For the combination of electrolyser and fuel
cell, approximately 40 to 50% of the electricity used by the electrolyser for
hydrogen production can be retrieved by the fuel cell as electricity (for comparison
hydrocarbons are only 20-35% efficient when used in an engine). Batteries are
clearly favourable from this perspective but as long as the hydrogen is
generated from excess renewable energy then there is still a net energy benefit
especially for long term, large quantity energy storage. From a purely
financial perspective, as long as the hydrogen is created via an onsite
electrolyser from excess solar or wind production then the round-trip
efficiency is not an issue.
Other than
electricity, fuel cells produce heat, which accounts for the majority of the electrical
efficiency losses. If this heat is captured, stored and used, then the overall
system efficiency increases and can reach levels equivalent to (or even better
than) battery round trip efficiencies.
Green?
There are environmental
concerns to consider for both battery and hydrogen technologies. Production of Li-Ion
batteries is energy intensive with a high carbon footprint, and their disposal
is an environmental concern. Lithium at scale is often associated with resource
depletion, ecological toxicity, and human health impacts, similarly with another
Li-ion battery component, cobalt. A grid-scale hydrogen fuel cell solution has
a far smaller environmental footprint than a battery storage facility of
comparable scale and hydrogen fuel cells require no toxic chemicals, often associated
with the manufacture of Li-Ion batteries. However, the storage of gaseous hydrogen
requires thick steel walled cylinders (if Type I) and the steel industry is the
third biggest industrial producer of carbon dioxide, globally.
The steel
used to fabricate a Type I compressed hydrogen storage cylinder is less
energetically costly, per unit of stored energy, than the materials that store
electric charge in a battery (electrode paste, electrolyte, and separator). With
more research and manufacturing of Type IV cylinders (made from composite material
such as carbon fibre with a polymer liner), which are used in fuel cell cars
and mobile storage, the material cost and energy cost of this storage type will
decrease in the future, improving the green credentials of the hydrogen fuel
cell storage solution.
Time
Most large
scale battery-based solutions store energy from one to four hours.
Longer-lasting solutions (12+ hours) are typically not cost-effective. Batteries
last for a finite number of recharge cycles, have long charging durations, self-discharge
over time, have a limited lifespan and are difficult/impossible to economically
recycle. When correctly
stored, hydrogen will retain its energy indefinitely, not “leak” like batteries
and can be used to store larger amounts of energy economically.
Batteries offer fast responsiveness and high charge/discharge capacities so are capable of providing and absorbing large power gradients. While batteries respond in milliseconds, fuel cells require multiple seconds up to minutes to react; this is why the decision can never (at present technological stage) be either hydrogen or battery, it has to be both.
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