At only 120ft You have no problem. I run 175 ft by using a roll of under ground type 10-2 with ground in the air. Used it for years with no problem. Then I decided I needed more power and run 200ft of number 1 tri-plex from a box under my meter at my home---underground---to that building which only cost between $200 to $300. I use a 220/240 volt saw and electric welder and other 120 volt equipment. Its been hooked up now for about 20 years----no extra meter----just one electric bill. I personally did not want to go to the expense of a "service", inspection, etc, etc just to power it.
I just invested in a kit...cant wait to set if up...heres the set up I'll do> solar panels hooked to controller hooked to marine battery hooked to converter w/outlets. There r tons of quickie how to on utube. If u add a nice big marine battery..the solar panels will charge the battery..this way u will have available power supply after the sun goes down. Theres a kit sold by harbor freight that is popular for beginners. Solar kits are also sold by Amazon, eBay, etc. You will still need to buy a marine battery and converter.
They are not hard to hook up but small set-ups will work for a light on every now and then, but not for heat---all night long. I bought a 45 watt Harbor freight kit----built a timer so the lights(that come with the kit) came on about 3ish in the mornings and the automatic door opens a few minutes later----worked good. But not Heat/not even a 60 watt incandescent bulb would run off this set-up all night with 2 big batteries. Now I have about 2200 watt of solar panels on a array with 8 golf-cart batteries and I would not count on it keeping a good size heat lamp going(because of the cloudy days) with my chicks life.
