The flexible PV panel doesn't generate enough electricity
to provide any meaningful power to the static battery pack.
There are prototype PV technologies that may supercede
the one being used by Toyota currently.
There are rigid PV panels that provide about 3 times the
amount of power than the type being used by the 2010
Prius but they are experimental ( NASA used them for
the Mars robotic explorer) and they are custom made
and are currently not availabe as a mass produced item.
The new Hi powered PV panels generate electricity
buy using multiple semi translucent PV panels which
are sandwiched on top of each other. Each layer is
only sensitive on a particular spectrum of light. So
while each layer is no more powerful than a regular
PV panel - since the layers are sandwiched on top
of each other the PV takes only one third the surface
area as a non-sandwiched single layer PV panel.
The last I heard, NASA was testing a 4 layers PV
solar cell technology and was getting about
33% energy efficiency.