Try Butts of Leicester we got a 30% discount by saying we wanted the Pete Nash deal another way of getting a cheap deal was by getting a big order in that time we delt direct with Siemens. It is definatly advisable to get a regulator as you don't want to cook your batteries. Pete used his pannels on a 24volt system and they worked fine, We found them very helpful,AB Butt, Frog Island, Leicester. Tel 0116 251 3344 and on the internet its under the accessories page, Good luck, Wendy