Super-critical QED-effects via VP-energy

The properties of the QED-vacuum energy \hbox{\cal E }_{VP} under Coulomb super-criticality condition $Z>Z_{cr,1}$ are explored in essentially non-perturbative approach. It is shown that in the supercritical region \hbox{\cal E }_{VP} is the decreasing function of the Coulomb source parameters, resulting in decay into the negative range as $\sim -Z^4\mathrm{/}R$. The conditions, under which the emission of vacuum positrons can be unambiguously detected on the nuclear conversion pairs background, are also discussed. In particular, for a super-critical dummy nucleus with charge $Z$ and $R(Z) \simeq 1.2 \ (2.5, Z)^{1/3}$fmthelowest$1s$-level dives into the lower continuum at $Z_{cr,1}\simeq 170$ (the model of uniformly charged ball) or $Z_{cr,1} \simeq 173$ (the spherical shell model), whereupon there appears the vacuum shell with the induced charge (-$2\mathrm{\mid }e\mathrm{\mid }$) and the QED-vacuum becomes charged, but in both cases the actual threshold for reliable spontaneous positrons detection is not less than $Z^{\ast }\simeq 210$.