By Dr Michael Wrinch
Energy storage technologies such as electro-chemical batteries are some of the most watched innovations in the world. For this reason I put together the following table to compare some battery performance metrics. This list is not exhaustive but it covers the most prominent types of market ready batteries available.
As a point of reference, the top 3 considerations for battery selection are:
- Energy density (Joules per kg and Joules per Litre)
- Cost per kWh (kilowatt hour)
- Lifespan (charge cycles)
That said, there are a number of other factors included in the table which help paint a more complete picture. Much of this information is readily available onlinet but I also sourced some harder to access datasheets and an IEEE Power and Energy issue on storage technology.
The types of batteries displayed here are as follows:
- Lead Acid
- NiCd - Nickel Cadmium
- NiMH - Nickel Metal Hydride
- Li-Ion - Lithium Ion
- NaS - Sodium Sulfur
- VRB - Vanadium Redox Flow
I have not gone into too much detail with Lithium batteries but there are multiple types of Lithium technologies with varying performances. The most commonly used Lithium battery to date is Lithium ion manganese-oxide battery (LiMn2O2), x`which is used for these charts.
These charts are a snapshot of 2017 technology and I expect these values to change over the next few years as R&D is progressing quickly.
|In use since||1800’s||1950||1990||1991||1970||1986|
|Energy Density (Wh/kg)||25-50||25-90||60-120||75-200||150-240||10-30|
|Power Density (W/kg)||75-300||150||250-1,000||500-2,000||150-230||80-150|
|Energy Volume (Wh/L)||25-75||75-175||100-300||250-375||350||15-25|
|Capital Cost (USD/kWh)||100-300||800-1,500||900-3,500||300-2,500||300-500||150-1,000|
|Round Trip Efficiency||75%-85%||70%-90%||65%||85%-97%||75%-90%||75%-90%|
|Self Discharge (%/month)||5%||20%||30%||5%||Negligible||Negligible|
It's important to note batteries are not the only way to store energy, and other methods can be more appropriate depending on the situation. For example, if you want GWh levels of storage capacity coupling a system to a hydro-electric dam may be the optimal choice. However, if you have a low voltage, microscale application supercapacitors (10 kWh / kg) may be the way to go.
All this said, batteries remain the most promising and versatile solutions for mobile applications, but as technology develops we'll just have to wait and see which technologies win in the end.
On that note, let me leave you with a few links to some interesting developments that may lead us into the future.
Dr. Michael Wrinch is a Canadian Functional Safety Professional Engineer and President of Hedgehog Technologies whose expertise is in the design of complex electrical and controls system.