I use an 80 watt kyocera and one deep cycle to power a 13 inch flat screen tv, laptop, and 12 volt dvd player for several hours a day.
putting the panel behind a window will reduce efficiency as the window will deflect some rays. better to put it outside and angle to 45 degrees in winter if possible.
Kyocere 80 watt panels are about $400 on ebay. deep cycles about$70, and a small power controller $50. 400 watt inverter $50
You can see my website for ideas: