The best for who? For you, for the Industry, for mankind?

I think the best system is an intelligent crowd storing system. You do not store your produced energy, but all people who are involved do it together, for example in their electric cars.

- you do not need additional batteries

- it is resistant against dropouts

- peaks in consumption and production can be balanced much better than in individual facilities.

- decentral facilities are much more resistant against sabotage.

Well, may as well give it a crack, since I've been looking at this a lot recently. The DOE has a number of resources; although their database of installations is rather incomplete, it gives an approximate picture of the technology landscape and global markets for large-scale energy storage.

To toss the non-batteries in there first - without question, the cheapest and most plentiful energy storage is pumped water storage (effectively running a hydroelectric dam in reverse) - installed capacity around 20 GWh globally, but ultimately limited in many respects. I'm on the fence about compressed air and flywheel storage - simple techs and in principle super cheap but again only good in fairly specific use-cases. There are more than a few lead-acid storage systems, including to a large scale, but it's a mature tech with well-established lifetimes and costs, and I don't see it winning long-term.

As far as real batteries go, for all use-cases, Li-ion is the most popular and well-developed, and without a doubt the best for energy density. They're the incumbent for a reason, but I don't see them as the best long-term at a larger scale than home use, even if they're the largest capacity non-hydro tech for grid level energy storage, although switching to polymer membranes could preserve their lead for awhile depending on how fast new tech is adopted.

Redox flow batteries are the runners up and superior long-term in my view. Also there's no danger of spontaneous discharge - bonus, but especially important at the >MWh scales. Vanadium Redox Flow Batteries are second most developed battery storage tech and have a lifetime cost advantage over Li-ion today in all but home and ultra fast discharge systems (less than 10 mins charge/discharge), and I see them as liable to overcome those relatively soon given better separators. UET has demonstrated 270,000 deep cycles in a system with >2% capacity fade (overkill, but quite the demo). They're building a 200 MW/800 MWh battery (~6x larger than the big Australian Li-ion one that's getting all the attention), plus in general you can fully separate capacity (electrolyte tank size) and peak charge/discharge power (MEA area) to hit desired system requirements perfectly.

There's a few other flow battery techs that are alternate contenders - Zn-Br is the second most popular flow battery chemistry - rather corrosive, so this may cause some materials limitations, but I don't know much about it. Mixed metal systems have greater capacity fade issues, that ESS has solved with a mixed iron Fe2+/3+ couple RFB that looks very promising. These or zinc-air batteries could be the least expensive long-term. The ultra-cheap component play died with Aquilion - 'sodium battery' concentrator cells. Wildcard goes to water electrolysis / fuel cell pair, of which there are more than a few large installations globally. Round trip efficiency isn't the best at rated power, but comparable to flow batteries at lower power, plus unlike all the other techs can operate in the current market where simultanous storage+generation is necessary. Best part is that electrolysis is effectively a 'limitless capacity' battery, and there's a tonne of uses for high-quality hydrogen.

Hello Prof. Ritt,

I'm very delighted for your excellent comment.

Yes, sometimes, the electric cars may be the power supply to our Smart Home System.

Big Thanks!!!

Hello Britton,

I've great pleasure for your comprehensive comments

Great Thanks!!!

I too am looking into this issue and believe in DG/DS (distributed generation and supply) but i can't wrap my head around how to best store the energy in a sustainable fashion, my key desires are:

good energy density to favour some mobility

-safety in regards to toxicity 

- robustness 

- good DOD and charge rate

- maturity

-cost effectiveness 

i find myself falling still on lead acid batteries and can't figure out which to choose in an African context(Nigeria)

Hello Karim,

Thanks a lot for your good answer.

However, maintenance free  battery are more appropriate.

Have a Nice Day!

Sincerely,