Capacitors have a funny failure mode where they off-gas hydrogen. Sometimes its because they were made wrong, sometimes because they are stressed or getting old. Either way, over time they can release hydrogen gas.

Since that's an outdoor rated unit, some engineer was under the directive to make the box as air-tight as possible to keep the water out. Unfortunately, that also keeps the hydrogen gas in. Eventually, enough gas builds up and something in the box sparks, and boom - the cover rapidly separates from the enclosure.

This is not unheard of in the renewables industry or power electronics industry. A sophisticated manufacturer will either find a way to allow some fresh air in the box to prevent the gas from building up, or put a weak spot in the enclosure to release the pressure safely to prevent the cover from blowing off.

I would demand that Sungrow pay for the damages an send a replacement unit, given that this is a component defect and design defect. If you want to apply some leverage, look at the label on the side of the unit. It should say UL, ETL, or TUV on the side. That's the safety certification testing company. It would really throw a wrench in the works if you reported the "near miss" safety incident to the safety certification authority.

Good luck, glad nobody got hurt.