Dumping excess solar energy

I'm starting to think I'm going to have to bite the bullet and go fully lithium, but hopefully I can make my AGMs last a couple of years yet and prices will fall in the meantime.
 
It was back in March/April when we had those weeks of really decent sunny weather when I started thinking about all this. Every day for a couple of weeks the batteries were fully charged before noon and the rest of the day the panels were registering less than half nominal power. The last week or so I’ve seen 75W out of a nominal 80W on some days when the battery was relatively low at the start of the day. Today for example, when the battery is almost full I’m seeing about 35W in cloudless sky in the early afternoon. I would seriously expect my controller to be making the most of the available power.
 
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