They are more efficient storage, but are way too pricey still for practical application in a large system. They would last much longer, but for the price of an equivelant system, you could replace the batteries every year off of the interest money one would receive by putting the difference in pricing in the bank.
A 2600 farad capacitor at 2.7 Volts stores only 9477 Joules of energy. If your string can take energy from the capacitors from full charge voltage to half of that, say from 59.4V to 29.7V for a 48V equivelant string, then you would only be able to recover exactly 75% of the energy stored or 7107.75 Joules. Most inverters and other equipment would be even more restrictive, say full voltage down to 40 volts for a 48V nominal system.
Now, one 6 volt golf cart battery with 225 amp hours of capacity at 6 volts discharged from full to 80% at the 20 hour rate would give you about 45 amp hours at 6 volts, or 972000 Joules by comparison. One would need 136.75 of the ultra capacitors (provided one could use them down to half voltage) to replace the golf cart battery to have a system of equivelant usage capacity.
The 2600 farad capacitors were about $75USD in bulk a piece last time I checked, and the golf cart batteries were about $50USD a piece. 136 of the capacitors would cost $10200.00 USD. At 5% simple interest rate from a CD, one would collect $510USD each year, and could replace the battery equivelant many times over. Even the greater inefficiency of the batteries does little to compensate for this.
They are neat toys, but way to pricey. For use as the only power storage devices in a system, the cost of the labor, need for extreme reliability, or other aspects would have to justify many times the cost of the battery.
They are neat toys, but as a sole means of energy storage, I just can not justify them at this point on cost. That said, I still want some to play with. Rich
