The idea of vampires burning in the sun, turning into ashes, or maybe even exploding, is so common that many people take it for granted. However, if you look into folklore, or into Bram Stoker’s novel Dracula, you will see something else. Not exactly vampires enjoying the sun, but not exploding as soon as the sunlight touches their skin, either.
In the Serbian folklore (which is where the word vampire comes from), vampires are usually nocturnal, but the sunlight doesn’t harm them. In some stories, vampires spend the days in their graves, rise at night, strangle people and suck their blood. Or visit their wives (who are officially widows) and make some babies, especially if the wife is still young and pretty. There’s a theory stating that the idea of vampires visiting their wives was invented to explain how a woman whose husband died in a war got pregnant. Whatever they choose to do at night, it’s not because the sun would kill them. They’re chthonic creatures by nature and prefer nighttime because that’s when they’re strongest, but they won’t die in the sun.
In other stories, vampires might leave the area where they lived while they were alive, become butchers or blacksmiths (or choose another occupation traditionally associated with chthonic and otherworldly) somewhere, and start new families. It is perfectly logical to ask, since butchers or blacksmiths would normally work during daytime (unless we’re talking about the village of the butchers), how does it fit with their nighttime preference. The answer is: folklore isn’t consistent. According to the folklore, vampires are supposed to fear sharp objects and tools because they could pierce their skin so that the liquids their bodies mostly consist of leak out — and yet, they works as butchers and blacksmiths, constantly in contact with the very tools they should fear more than anything else. There are many such examples. Some aspects may be consistent, like the idea that vampires won’t die just because the sun is shining upon them, but others will be contradictory.
When it comes to the Bram Stoker’s Dracula, if you’ve read the book, you’ll remember that it wasn’t the sun that killed him, it was a chest wound (which coincided with the sunrise). Dracula didn’t have his superhuman strength during daytime, but he could freely walk around in the sun, and nothing happened to him because of it.
So, where does the sun-kills-a-vampire idea come from? The Hollywood movies, or, more specifically, Murnau’s Nosferatu (do watch the movie if you get a chance and if you like truly creepy movies), a silent classic from 1922. And it became a canon so much that people might laugh at you if you write about vampires who freely walk in the sun, and tell you that’s not what the “real vampires” are like. Of course, you’re then free to laugh at them, both for their ignorance and the “real imaginary creatures” part. Or you could try to educate them, if they’re willing to learn.
What does all of this mean to a writer? The usual: create your world well, give good explanations, and you can do whatever you like. It’s your world, after all. You’re the one who knows best what works there, what doesn’t, how and why.