  We consider the determination of the solar neutrino oscillation parameters
$\Delta m^2_{21}$ and $\theta_{12}$ by studying oscillations of reactor
anti-neutrinos emitted by nuclear power plants (located mainly in France) with
a detector installed in the Frejus underground laboratory. The performances of
a water Cerenkov detector of 147 kt fiducial mass doped with 0.1% of Gadolinium
(MEMPHYS-Gd) and of a 50 kt scale liquid scintillator detector (LENA) are
compared. In both cases 3$\sigma$ uncertainties below 3% on $\Delta m^2_{21}$
and of about 20% on $\sin^2\theta_{12}$ can be obtained after one year of data
taking. The Gadolinium doped Super-Kamiokande detector (SK-Gd) in Japan can
reach a similar precision if the SK/MEMPHYS fiducial mass ratio of 1 to 7 is
compensated by a longer SK-Gd data taking time. Several years of reactor
neutrino data collected by MEMPHYS-Gd or LENA would allow a determination of
$\Delta m^2_{21}$ and $\sin^2\theta_{12}$ with uncertainties of approximately
1% and 10% at 3$\sigma$, respectively. These accuracies are comparable to those
that can be reached in the measurement of the atmospheric neutrino oscillation
parameters $\Delta m^2_{31}$ and $\sin^2\theta_{23}$ in long-baseline superbeam
experiments.
