15 watt solar panel are normally 12v, so you dont need an inverter, just run the lights/appliances off 12v DC directly. I would recommend getting a charge controller though.
45w times 4hrs of effective sunlight = 180WHr of generation, but really probably only 100WHr. That could power four 10W LED lights for 2.5hrs.
Photovoltaic panels have quite some difference in their "normal use" voltage (when there is a load connected) and their open circuit voltage (nothing connected).
I do not recommend connecting anything to it before you are sure that the open circuit voltage does not fry it.
EDIT: As long as the appliance uses roughly the same power as the panel produces, some things can handle the initial voltage spike: Incandescent lamps, brushed motors and even LEDs without electronics as long as they are connected to the panel before it gets sun. But anything with electronics in it may not like it.
Allen Schneider wrote:I have 3-15 watt solar panels, a total of 45 watts, what size batteries can I use and what size inverter? I might use it to light a light bulb, just small things, Any help would be appreciated, Tganks
Allen, I assume the panels you have are one of those 3x15 watt thin film kits that are sold? Usually they come with a basic charge controller. You will want to plug them into a battery of course. Stick to 12 volt appliances and lights or usb charged devices for using the power. The losses in an inverter will eat away at your solar gain except in small doses. if you use an inverter turn it off when not in use. Those kits are a fun way to start on solar. Your true wattage will be closer to about 30 watts per hour as the manufacturers play with the numbers a bit. The panels are probably rated at 15 watts at 18 volts... so roughly .85 amps at 18 volts... You are charging at 12 volts so you will get .85 amps x12 volts off each panel or about 30 true watts per hour of sun. You will want to change the angle to the sun to get better production as the day advances as that charge controller cannot compensate for changing sun levels...
Cheers and have fun, David