Short answer, no, a solar system is not an SDS. If there is an AC neutral from the solar that ties directly to the premises neutral then that is definitely not to be bonded again. Objectionable current and all that.
Longer answer...
Some older grid-tied systems have a transformer that isolates the solar side from the AC side. In that case you could argue that the DC side of the solar system is an SDS. But, when it comes to grounding solar systems, you follow article 690, not the stuff for SDS's in article 250. The same would be true for an off-grid system, even if there's also utility power on the site.
Most newer systems don't galvanically isolate the DC conductors from the AC conductors when operating, so are really not an SDS in any sense.
One clarification is that you can interconnect a grid-tied solar system through an SDS.
That is:
Utility <-> Transformer <-> Inverter
In this case you do treat the inverter side of the transformer as an SDS and follow the normal rules in article 250 for grounding a neutral at the transformer on the inverter side. When it comes to any grounding requirements for the inverter and solar, follow 690 again.