Fokker-Planck equations for SPDE with non-trace class noise

In this paper we develop a new technique to prove existence of solutions of Fokker-Planck equations on Hilbert spaces for Kolmogorov operators with non trace-class second order coefficients or equivalently with an associated stochastic partial differential equation (SPDE) with non trace-class noise. Applications include stochastic 2D and 3D-Navier-Stokes equations with non trace-class additive noise.