Just standard 14 or 16 gauge extension cords will do, but it depends on how long the cords are and what size charger or amps of charging current. If you let me know that I can run some numbers. You want to keep the voltage loss low, like a volt or less, for best results, or charge time will be longer.

I have used "Newpowa" solar panels with chargers from eBay, they are simple and cheap but seem to do the job.

Dave