Photovoltaic Modules are small solar panels that convert sunlight into electricity. They usually produce less than 100W. Their purpose is to charge small devices like mobile phones, cameras, ligters, etc. Photovoltaic panels that produce more than 100W are called Solar Panels. Their output voltage is standardized at 12V, wich means that you can connect it to a deep cycle battery to store the power produced. If more modules are linked in series, the output voltage will be multiplied.
The costs of Photovoltaic modules depend on the amount of electricity produced.