That panel is at least 20 years old, they stopped making them in 2000. I know that its not very green but these panels where never that good when they where new. With no idea of the history of the system or if it works or not, my advice would be to replace it with something newer, albeit if you do it yourself or get a professional in. Its a hard wired system and so all the cables are in place, unless they have been cut or damaged I would start by metering those if theyre okay then just update the lot, no point in having something if its going to be unreliable a annoy your neighbours