The amount of solar panel energy generated on a daily basis can be computed using solar irradiance; this will give you an estimation of the solar panel capacity you will require.

An estimated figure is all one can calculate, since the actual capacity requires the following to be taken into consideration:

• Site deviations
• Solar panel position and angle
• Obstacles to sunlight at various periods of the year

All of these points will need to be taken into consideration when computing the total amount of power output you will require as you design and install your solar electric system.

An easy calculation is to divide the daily watt-hours figure by the month with the lowest solar irradiance figure for your location (the figures you can expect your system to function with). You can get Solar Irridiance Data for the US here. 

A vacation home that is usually used between March and October would require the solar system to power up sufficient electricity for a long winter weekend. That is, the batteries must be sufficiently large to store enough electricity for some days, regardless of insufficient power for constant usage during the winter.  Moreover, more than enough electricity is generated by the solar electric system during the summer. This is acceptable for powering the occasional electric appliance that has been left on standby, or for a light that has been left burning.