my solar contractor said he would use 4 ot copper wire on the 300 ft. run from inverter to main 200 amp panel.later I found he used 1 ot alluminum.I want to know what is the difference. it is a 96.6 KW size with 42 panels

 

There is a BIG difference between 4/0 copper and 1/0 aluminum, a little over 100 Amps difference. 4/0 copper is rated for 230 amps and 1/0 aluminum is rated for 120 amps

Not sure where you are located, but here in the US we follow the National Electrical Code (NEC). The size of wire used depends on if this is for a residential use or commercial. If in a residential application you need to have at a minimum 2/0 copper or 4/0 aluminum for a 200 amp service.

 

Is that 96 kW or 9.6 kW? My 24, 230 W, panels are rated at 5.5 kW or about 20 A @ 240 V.