For some time now I have had what i would call an emergency solar
lighting system in my house for use only at times of mains/grid
failure. This does in fact happen quite a few times during the year,
the system quite simply has one roof mounted 65w roof mounted panel
connected to two 110amp leisure batteries via a solar controller. The
batteries are in turn connected to a 600w inverter which outputs via a
mains switching feed to one 13amp conventional wall socket. The
switching feed supplies the power to the inverter as long as there is
sufficient power in the batterries. If there is insufficent power the
switch reverts to mains power and supplies the wall socket as normal
with mains/grid supply. This basic installation costs in the UK:-

Solar panel £310
Solar controller £45
Mains/grid switch £10 (available on ebay.com)
Wire and fusing etc £25

In all a cost of £390, this is of course is quite an investment fpr
what is a very occasional problem. Hopefully solar panel prices will
get cheaper when more people start buying them. More basic
instructions on how to do this project are available on the www.solaratlas.com
website.