I'm thinking about using a very large home made capacitor as an energy storage device for a light duty off grid application, running some led lights and some 500w loads for a few hours each evening. I've done some calculations and I'm surprised by the results, it's been a while since I've done anything like this and I want to make sure I haven't made a silly mistake. So I'm planning on a flat multi plate capacitor made with tin foil and cling film. I have the permittivity of the dielectric at 3 and it is about 10 microns thick. The plates are 2x.3m and there's 21 of them giving 20 actual capacitors. So the calaculation I made is
e0xe1 x number of plates-1 x plate area / dielectric thickness
8.84x10^-12 x 3 x 20 x 0.6 / 1x10^-11 = 31.824F
Is my math correct?