And compare that to the battery solution:
20W light at 12V: 1.7amps continuous
4 hours x 1.7A= 7 Amp-hours
That's about the capacity of a small 12V lead-acid battery that you can carry in one hand. Weighs about 4 lbs. I use one to provide LED lighting in my chicken coop because it's too far from the house to run AC power out there.
No contest: in the absence of extenuating factors, a cheap battery is better than the "innovative" (?) water storage method for such a small amount of energy.
That's about the capacity of a small 12V lead-acid battery that you can carry in one hand. Weighs about 4 lbs. I use one to provide LED lighting in my chicken coop because it's too far from the house to run AC power out there.
No contest: in the absence of extenuating factors, a cheap battery is better than the "innovative" (?) water storage method for such a small amount of energy.