Before we say how much energy it has, we have to make some assumptions:
A single ZPM is capable of powering the star drive and shield simultaniously, allowing the city ship to escape (at least) an Earth-size planet, meaning it is capable of achieving at least 11m/s delta V, under sublight engines.
The maximum capacity for powering the shield, under constant load, is 3333.3 recurring years.
The ship's engines are capable of 100% electrical/kinetic energy efficiency.
Let us also assume that 100km (100000 metres) straight up is enough to reach a stable orbit.
Conservatively, assuming the city-ship comprises a mass of around 22 trillion kilograms (60x Empire state buildings), and has no mass nullification tech, would require 242 trillion newtons of force, to reach escape velocity instantly.
So, the ship would have to fly for at least 9000 seconds, with both shields and engines + essential system active.
E = (1/2 M V^2), so E = 1331 GJ per second for 9000 seconds, which is roughly 12 Million Giga Joules. This translates to approx 3.2 Billion KW, or 3.2 TeraWatts
This is only for engine operation, for two and a half hours.
For shield operation, which is likely to be quite exhaustive, this would take up the bulk of power consumption, so lets assume, 4 times that, under high load conditions: 12.8 TW. Add that to our engine consumption and you have around 16Terawatts.
This also means that under low power/drain conditions, that the shield will consume 4.8Gigawatts per year, when submerged.
This is a bare minimum figure, with conservative estimates. I would imagine an electromagnetic shield capable of deflecting high speed space debris, energy weapons, and millions of tons of water for thousands of years, would consume considerably more.
On a side note, if a city-ship of that mass every crash landed like it is depicted doing twice in the series, it would likely cause an extinction event, if it's descent was uncontrolled.