You can't use any regular cable for your solar power system. Specialized cables custom-made for residential solar power plants are used to ensure minimal loss of electricity being generated. They are UV-protected and strong and long-lasting enough to withstand the rigours of nature - be it peek of summers, incessant rains, or thunderstorms. The use of any ordinary cable is a big health hazard as well with high chances of electrocution for the people in the vicinity of the system. The bad quality wire will not only make your solar power system ineffective but will result in being more expensive as you will end up changing the wires of the entire system in the exposed parts get deteriorated resulting in the risk of electrocution.