What exactly to buy to run TV.

Here's what I would suggest.  But these are only rough calculations:

1 - 75 Watt (or bigger) solar panel
1 - 100ah Marine Deep Cycle battery
1 - 125 Watt (continuous power) pure sinewave inverter.
1 - 10a (or bigger) charge controller

You need 75 Watts times 3 hours, or 225 Watt/Hours.

If you get 4 hours of sunlight each day, you'll get 4 times 75 = 300 Watt/Hours.

Since you don't want to discharge your battery more than 50%, you have 50ah of usable stored energy.  The inverter will draw just under 10a (DC) to power the 75 watt load.  Therefore:  50 divided by 10 equals 5 hours of TV viewing, but allowing for system inefficiencies, expect 4 hours at the most.

I have more system design information on my blog:  http://solarjohn.blogspot.com

Hope this helps, John

Awesome, thank you!  I might end up buying a 40w to start out with and to just get into the hobby, but I'll see what I can do.  Thanks again!

I like the idea of adding a meter to the charge controller, or getting a battery monitor.  I use a high-quality digital voltmeter to keep close track of my battery condition. 

The point is; it's important to have some way of monitoring your batteries, since they can easily be damaged if you don't. 

John

Vincent,

It looks like your math is correct, except that you didn’t take into consideration system inefficiencies.  To simplify my answer to your questions, consider an off-grid system with batteries to be only about 65% efficient overall.

Concerning the inverter input current that flows to provide 75-watts out, use the formula:  Power = Volts times Amps, and then consider inverter inefficiency, or:
10 (amps) times 12 (volts) times 0.65 = 78-watts.

To compensate for cloudy days, you’ll need more panels and batteries (obviously), and you can use that 65% efficiency factor to do your math.

I hope this helps.

John

No problem Vincent;

You choose an inverter that can handle all of the loads you intend to connect at the same time.  If the most you'll run is a 15-watt light, and a 75-watt tv, and a 25-watt fan, you'll need an inverter that can supply 115-watts (as an example).  Keep in mind that some motors and other devices have high starting current, so your inverter needs to be able to handle that as well.  But a 250-watt inverter would be a good choice for the example I've stated here, since it exceeds your 115-watt needs.

If you'll play around with the power formula I provided in a previous message, you'll notice something interesting:

Power (in watts) = Volts X Amps

120 Watts = 12 volts X 10 amps
120 Watts = 120 volts X 1 amp

It follows then that to power a 120-watt, 120 volt, light bulb you'll have about 1 amp (at 120-volts) at the output of the inverter, but 10-amps (at 12-volts) going into the inverter.

This is just an example, and doesn't take into consideration inverter inefficiency. 

I hope this helps to clear things up.

John

You have 80-watts of PV and expect 5 hours of sunlight each day.  80 X 5 = 400wh X 0.65 (for system losses) = 260wh.  At the load you've specified, you barely have enough power for one day.  If you doubled PV and batteries, you'll have the capacity to compensate for one full day of clouds.

Having said that, I would also add that I wouldn't want to cut it that close on batteries.  Chronic undercharging, or leaving batteries discharged for more than a day or two, will shorten their life. 

If you want to become an off-grid "expert", study batteries.  The rest is easy.   

John