I am pretty sure i am not understanding this correctly. For a DC String system(SolarEdge SE10000 for example). when the system is disconnected from the grid do the DC strings stay energized? If they do disconnect i think the only thing that can do that is the optimizers. Would a system without optimizers just stay at series DC voltage? Seems like a huge negative over a microinverter setup. Thanks in advance!
The optimizers stop the module voltage at the optimizers, and the optimizers only output a shutdown standby voltage of 1 Volt, when the circuit is off. This allows for diagnostics and polarity confirmation, but it also keeps the string voltages within the rapid shutdown limit.
The uncontrolled open circuit voltage of the module is still present on the input leads to the optimizer, but the optimizers use an internal switch (or solid-state transistor), to prevent the full voltage from accumulating with the next optimizer.
Uncontrolled PV would produce the full string open-circuit voltage when disconnected, so this will happen for a ground-mount or a pre-2017 array, prior to module-level rapid shutdown was a requirement on buildings. Optimizers and micro-inverters are not the only option for rapid shutdown, but module-level power electronics (MLPE) in general will be required in some form or another, if this rule applies. Module-level rapid shutdown isn't written in the NEC in those exact words, but it is a logical consequence of the voltage constraints from 690.12.
The simplest version of MLPE that can do this, are devices that use a power line carrier signal to maintain the device's ON-state. When the signal ceases to be produced, the device shuts off the module's input circuit to the device, and prevents its voltage from accumulating with the rest of the string. The transmitter can be integrated in the inverter, or it can be a separately-installed transmitter. This kind of MLPE only turns the circuit on or off, and doesn't have any other functionality like monitoring or power processing for optimization (which optimizers and microinverters provide).