Answer
$$\approx 3.17\times 10^{11}W$$
Work Step by Step
Since two thirds evaporates and one third stays, then:
$$E=mgh=\dfrac {1}{3}\times p\times A\times d\times h\times g=\dfrac {1}{3}\times 1000\times 8\times 10^{6}\times 10^{6}\times 75\times 10^{-2}\times 500\times 10$$
$$=\dfrac {1}{3}\times 1000\times 8\times 10^{6}\times 10^{6}\times 75\times 10^{-2}\times 500\times 10=10^{19}J\Rightarrow W=\dfrac {10^{19}}{365\times 24\times 360}$$
$=\dfrac {10^{19}}{365\times 24\times 3600}\approx 3.17\times 10^{11}W$
