GnuAE - open source solar/wind design software
GnuAE is a GNOME/GTK compliant GUI for designing photovoltaic and wind powered houses with compliance to the National Electrical Code. As GnuAE has a database of components and current average prices, it can help you judge the total cost of a system by experimenting with different options like using a propane or DV fridge, or more or less reserve days or hours of sun.
The link address is: http://savannah.gnu.org/projects/gnuae/