... Normally, yes, but the following link shows what I was talking about.
http://www.wstestsystems.com/eis3.htm...
Yes electrodes at both ends, often sticking thru a glass or ceramic insulation disk are quite common for small capacitors, but not for high voltage energy storage capacitors. You do understand that 20nF and 42 nF are very small values, nano, not micro farads. As MacGyver points out you would need 100 million of them to store, fully charged, 500MJ.
They are not used to store energy, but mainly in the near discharged state hung across a pair of wires that might get a very brief, but high voltage spike across them to protect down steam device from the high voltage spike. Judging from the stated weights, 20 &42Kg, I would guess their volumes at least 25 & 50 liters (100 million of them then 2.5 & 5 billion liters. It might be more informative for you in cubic feet. (1 liters = 0.0353146667 cubic feet). E.g. 50 liters is 1.765,733,335 cubic feet. So 50 billion of these is 1,765,733,335 cubic feet. Now a cubic mile is (5280)^3 cubic feet or 278784x5280 < 279x528E4 = 1,473,120,000 so your are speaking of more than a cubic mile large storage system for storing 500MJ when only working at 140Kv.
Recall from my prior post that to store the SAME energy at a voltage a thousand times greater, you need 1000 times more volume. Thus even if you were speaking of only storing at 140Million volts you would need significantly more than 1000 cubic miles for your storage system.* Your planned 100 billion volt system would occupy about a billion cubic miles if made with these nano Farad capacitors.
When I said your storage system might fit inside a dielectric oil tank whose base area was the size of Manhattan Island and whose side walls were "miles high," I was assuming you would use many individual capacitors in the tens of micro Farad range, not in the nano Farad range. The energy storage to volume ratio of these capacitors of your link is much less than those bigger units several posters have shown photos of.
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*Let me explain the physics of this to you: Just as the energy in a compressed steel spring is stored by slightly compressing the equilibrium inter atomic spaces between atoms, the energy stored in a capacitor is by compressing the space between dielectric atoms. In both cases there is a structural break down limit. Thus, if you want to store twice as much energy at just below this limit you will need twice the amount of storing material (dielectric or steel).
If you also want to store the energy at twice the voltage, then the plates of a simple capacitor must be twice a far apart (to keep the electric field below the breakdown field). This will reduce the capacitance by a factor of two. However the stored energy is 0.5C V^2 so the V^2 factor is 4 times greater and the C factor is half as large. Thus the energy stored is in fact doubled with twice the volume stressed to near the dielectric limit.