You might think that the voltage rise could be too fast for most protective technologies to save the downstream electronics, but the general case is that the temperature slowly drops and the sun slowly rises. So the voltage should slowly approach the limit.
Adding a normally-open relay and a voltmeter and a microcontroller should fix this. Relay won't close on startup unless the voltage is safe. Microcontroller will open the relay if the voltage gradually nears the limit. Should be solvable for <$5 in parts.
Dark start (when the batteries are flat w/o grid power) will be challenging. There will need to be a small battery to power the voltmeter and relay, or a high-voltage tolerant supply to power the microcontroller and relay temporarily. A 9V should likely be sufficient.
No the DC/DC converter could just turn it's transistors to short out the panels and rely on the fuse you want anyways to handle idiots paralleling more panels than allowed.
Common relays don't handle 150VDC, and I'd spec the voltage even higher even though one would think the voltage rating has more to do with arc interruption rather than creepage while off. Also a microcontroller is complete overkill, draws too much current to be easily powerable by the solar panel side, and adds complexity for something to go wrong. A simple analog comparator suffices.
The standard answer for overvoltage protection is a crowbar circuit + fuse, and I think that's what I'd aim for rather than a relay. The problem with DIYing that is knowing the input capacitance of the Delta and finding out whether it has any other problems with its input being abruptly shorted.
Adding a normally-open relay and a voltmeter and a microcontroller should fix this. Relay won't close on startup unless the voltage is safe. Microcontroller will open the relay if the voltage gradually nears the limit. Should be solvable for <$5 in parts.
Dark start (when the batteries are flat w/o grid power) will be challenging. There will need to be a small battery to power the voltmeter and relay, or a high-voltage tolerant supply to power the microcontroller and relay temporarily. A 9V should likely be sufficient.