A character with a High Intelligence but Low Wisdom might be incredibly book smart, but continually makes poor decisions, is absent-minded in the extreme, and tends to miss "little picture" stuff in favor of "big picture" stuff. This is the incredibly learned wizard who basically needs a handler wherever he goes due to his eccentricity. One example might be Walter Bishop from the TV show Fringe, if that makes sense.
A character with Low Intelligence but High Wisdom might be considered a dullard by society's standards, but has some matter of insight, or might be very attuned to the smaller things in life. This person might be illiterate or might be an idiot savant, but they have a way of picking up on the simple, straightforward solutions that other people miss, perhaps because they're going for the "big picture" stuff.
Those are just two popular ways to interpret the disparity in those two stats. I'm sure you could come up with other examples as well.
Remember that NPCs are people, not info dumps.
Your players are following what I'd call the video game model of NPC interaction. In a lot of RPG video games, the NPCs are infinitely patient and let you talk to them over and over, exploring all of their dialogue trees. Thus, the incentive for the player is to talk to them forever to get all of the possible information that the NPC knows.
However, in D&D, there's an actual person behind each NPC, and not just a dialogue tree. Therefore, you can respond as a person in a real conversation, instead of an infodump.
In my games, I accomplish this by giving each NPC a starting disposition toward the party and at least a skeleton of a personality. These things determine how an NPC is going to react and how much information they're willing to give. For example, a bartender might start off friendly, but if the PCs keep probing and pushing, he might become increasingly annoyed and hostile to the PCs. On the other hand, a kindly quest-giving wizard might be patient enough to tolerate any amount of questioning from the PCs.
Because you're playing a game, I find that I have the best success when these personality traits are exaggerated. For example, while a real-life bartender might only be subtly exasperated, your in-game one might become openly rude. In this way, you can give your players obvious social cues for when conversations are over.
It takes some time for your players to learn that social interaction in D&D is not the same as in video games, but they will figure it out over time. However, if you yourself are getting exasperated, you can always go for the brute-force strategy, and simply say something like "This NPC is not willing to tell you more," or "He doesn't know any more".
Best Answer
There are things a GM can prepare in advance to help exude Intelligence, other than jumping into spontaneous role-playing
I live off of high-intelligence BBEGs like wizards who are as evil as they are ingenious. For what it's worth, here's what I have done at my table, and it gets me by (but note that much of this is not specific to a Solar, rather just any high-intelligence creature or NPC):
Look up some brainy "buzzwords" ahead of time that are relevant to your scenario. These days it's easy with an online thesaurus to get a list of smarty-pants words that fit your scenario, and have them ready so that you can word-bomb as you go along. Words like: pinnacle, impetus, quintessential, jocular, pulchritudinous, disinclined, indisposed, edification, explicate, perambulate. (Make sure you actually know what they mean and can use them correctly). Because you're the GM, you can know what some of the topics of conversation will have to be, and thus can prepare a specific list of relevant brainy-words. Really it just takes a few. (Don't overdo it, or the character will sound pompous, instead of smart, as noted by LordHieros in the comments below.)
Work-up intricate traps and ploys ahead of time. Invest the time to create (or discover online) some really clever traps, cons, riddles, etc. that would require brains to create. Because you're the GM and you design the world, you can do this to enhance the seeming braininess of your character.
Describe props and preliminary scene action that support a smart-guy stereotype. Is the High-Int creature reading? Conducting experiments? Being asked its advice by nobles? All these things get across their Intelligence without you having to sound smart, but require you to be the GM who can insert these items/people in the picture.
Narrate, don't role-play. Instead of trying to sound smart, tell them that the character is sounding smart and just give it a little flavor. When I wanted to portray a genius wizard who had crafted his own modified Wand of Polymorph, I said: "He then jabbers on for ten minutes about things like 'the subject's readiness potential' and 'alternative embodiment' and 'the ontological structure of reality' until you are completely lost and have to ask him what practical difference there is when you use the wand." Again, because you're the GM, you can plan how to do this in advance, and it is more reliable than trying to "think on your feet" in spontaneous role-play.
I find that by combining at least two (or better, three) of the above I generally leave the players feeling they interacted with a genius.