Welcome!
Sorry to hear about your potatoes Stuart
Solar set ups are a bit more involved than plug-in electric systems. I'm no expert, but I do use a lot of electric fencing here at my place.
Is the solar panel connected to the energizer as a single unit? Or are they separate.... Do you have a controller? Or is everything in that cube?
You don't mention what is the output of your energizer/cube is..... How much fence line are you covering with this equipment?
A 12 volt, deep cycle battery would be much better. And the zap you get from the battery means little when troubleshooting a fence set up.
Assuming your equipment is working correctly - AND - is potent enough.
#1 fence issue is improper grounding. The most important issue here is enough metal in the ground with proper moisture in the soil for an effective ground. So what have you set up for grounding?
And can you provide us some pictures? The brand names of the equipment you bought?
I'll try and help if I can ~