This should be a very simple question. What would be the proper way to calculate Dark Energy in Joules at any point in history and that is consistent with the Standard Model? I'm thinking that knowing the mass-energy of matter (after estimating the Mass of the Universe):
$$E_m = mc^2\tag{1}$$
and knowing,
$$ \rho = \frac{\rho_{m}} {\Omega_{m}}\tag{2}$$
$$\rho_{\lambda} = \rho \Omega_{\lambda}\tag{3}$$
of the universe $M$, I could get the total Energy of the Universe combining (1) and (2):
$$E_{tot} = \frac { mc^2}{ \Omega_m} $$
And then multiply by the $\Omega_{\lambda}$ factor in order to get the final dark energy.
$$DE = mc^2\cdot\frac {\Omega_{\lambda}}{ \Omega_m} $$
Of course, $\Omega_{\lambda}$ and $\Omega_m$ change overtime, so I should be able to find what they are at the given time and figure out what $DE$ is at that time. Does anyone see a problem with this calculations?