We discuss Wavelet Kronecker Tensor Product (WKT) Approximation in electronic structure calculations. Kronecker tensor products with the optimal rank provide an interesting alternative to the traditional Gaussian-type basisfunctions for orbitals and electron densities. We present low Kronecker rank approximation of electron densities for small molecules. Together with stable quadrature schemes for the Coulomb potential, low Kronecker rank approximation of electron density is used for an efficient evaluation of Hartree potential, where the individual components of Hartree potential can be efficiently represented in wavelet basis. Our results lead to a possible application in density fitting schemes.