Thanks for the replies.
I have read up on several alternative storage systems, but all seem to have major safety issues, especially in a residential setting.
High rpms, high pressures, large weights, large footprints really don't lend itself to practical residential applications.
The "Bubba-Battery", I probrabaly should rename it to the "Hydraulic Spring" battery, would be more compact, somewhat safer except for the hydraulic lines, and be simple enough for the usual DIYer to constuct. Also, it used junkyard parts!
I am not familiar with the efficiencies of hydraulic pumps and motors which is why I posted here hoping some of you guys might have hands on experience with hydraulics.
I will have to do a little more digging to see what the relative efficiences are of springs, hydraulic pumps, and hydraulic motors.
Thanks.