They do compete against each other. They also compete with other forms of energy generation. Did you think there was only a single company in USA that made solar panels?
Not sure how you came to that conclusion that I believe one company manufactures panels in the U.S. but, for the sake of argument, if 30% more than foreign solar panels is the best price we can come up with than 1) that's not working and 2) a tariff will not solve pricing it only removes competition. Again, if they do not have to worry about lower-price competition, what incentive would U.S. manufacturers have to lower prices aside from a lack of demand? You seem to only be concerned about manufacturers in your statement and not the general public using these panels.