Yes we need energy storage really bad not only for solar and wind but even for hydro and nuclear energy storage - it's important! Since energy use is intermittent even nuclear can benefit because the throttling of large generators is very inefficient. So we all know energy storage is great but the trouble is the cost.
Lets look at the ZBB Zess 500 as per their news they collected $750K for that unit they sold to Ireland - that is in my book $1500.00 per KWH of storage. Currently there are no tax credits or major rebates for storage but lets for argument sake say we get a 50% credit so the cost now (after tax credits and rebates is $750 per KWH. How is anybody going to get a return on investment on that high of a price.
Let just assume the user does arbitrage meaning he buys power at night (off peak) and uses it during the day (peak) --buy at 8 cents --- uses at 16 cents = 8 cents savings, the problem is now that the system is only 70% efficient which means for every KWH stored I have to buy 30% more energy which means I have to buy 1.42 kwh to store 1 kwh.
So we purchase at night 1.42kwh at 8 cents = 11.36 cents and we are able to use 1kwh during the 16 cent period so we save 4.64 cents = per year we save 4.64 cents x 365 = $16.93 per year -- based on a cost of $750 we can calculate $750/$16.93= 44.3 years ROI so thats a no go.
Now lets assume that we are peak shaving based on the ZBB technical info (2 hour discharge time) we can peak shave 0.5kw for every 1kwh stored so lets say that the monthly cost per kw demand is $15.00 that means for every kwh stored I can save about (give or take) $7.50 per month so multiply this by 12 = $90.00 per year savings so &750/90 =8.35 years ROI -- now we are closer but the calculation is considering tax credits
Trouble is first the tax credits and rebates got to be in place because if the ROI is not 5 years or less nobody will buy it.
The argument I am making is that if the ZBB guys don't shape up and make a better and cheaper product they certainly will miss the boat
Lets compare ZBB with other companies:
Cost per KWH before Taxes
ZBB (zinc-bromine) = $1500 ---with 4500 cycles 10 year lifetime - efficiency = 70%
NAS (sodium sulfide)= $1,100 ---with 7500 cycles 20 year lifetime - efficiency = 89%
GEFC (vanadium redox) = $850 ---with 10000 cycles 25 year lifetime - efficiency =78%
Premium Power (zinc-bromine) = $400 ---with limitless life cycles - efficiency = 70%
Hitachi (lead acid) = $280 ---with 4500 cycles 10 year lifetime - efficiency = 85%

I confirmed all above prices because i got official quotes from each company (price was based on a 500KWH system including charge and discharge inverters).
In order for the investors to make money with this stock -- ZBB has to make a major change in its management and they have to hire a few competent engineers to finish their product, decrease the price and increase their lifetime cycles, to have a decent shot in this highly competitive market