Many sustainable energy sources produce according to natural rhythms such as sunlight, wind, and precipitation. These cycles don't necessarily coincide with the times that humans need energy. Energy storage is therefor an essential part of most sustainable energy systems.
Electricity is among the most common sustainable energy transfer and storage mediums, however unlike combustible fuels it is very challenging to efficiently store.
Conventional lead-acid batteries tend to be the most readily available and inexpensive electricity storage option, however they have significant issues that make them unsustainable and unsuitable in many cases including:
- Toxicity Lead (and to a lesser extent the acid used in lead acid batteries) can be extremely toxic for both humans and other lifeforms.
- Short useful lifespan Most lead acid batteries have a useful lifespan of less then 15 years with a cycle durability of less then 350 cycles.
- Inefficiency The charge to discharge ratio ranges from 50–95% with a self discharge rate of up to 20% per month
- Weight Lead acid batteries have a low energy-to-weight ratio of approximately 180 W/kg
Lithium batteries are generally far more efficient and long lasting then Lead-acid batteries however they are approximately 4 times the price-per-watt of lead acid and also have significant ecological impacts.