While gas stations do indeed run out of gas, you can extend how long it lasts (in your generator/welder) by using a 1-cylinder engine linked to multiple alternators, and then only when you need to refill the storage batter(y/ies).
Solar power is free but needs direct sunlight, and really cannot keep up with most welding demands.
If you happen to be fortunate enough to get them, certain CBMs can turn you into a generator for your welder - Power storage, power generation (of any sort), and a Unified Power System CBM. On the welder side, you’d also need to get the UPS conversion mod and install it there.
Off topic:
To which I must reply: Learn to read.
Directly would be "put gas in welder, welder runs."
What could indirectly possibly mean?
Which is a vehicle part. Vehicles can run on gas. Hence, indirect gas powered welder.
I also clearly stated that you’d need to put an engine and controls on the welding cart that you can find.
I realize that the second post in the thread might stretch your comprehension skills, but do try harder next time.