Fireball

Pretty self-explanatory, I should think. Big fire. Shaped like tiny sun. Very hot - don't touch.
This spell is a standard fiery spell that I think is in just about all of the magic systems ever, or at least some variation of it. So yes, I had to include it. Besides, who wouldn't want to scorch their enemies alive with a gigantic fireball?
It's an easy enough spell to master for the damage output it has, and is one of the spells that solar sages are most-known for. Of course, it can be devastating to one's own safety if used without wisdom or restraint. Its teaching is saved for the solar sages that show the most restraint (which are few and far between). Though most solar sages figure it out on their own.
It's best to save this spell for wide-open areas with few flammable items.
Unless you're trying to burn down the city. 
If that's the case, then... go for it.

Effect

The caster forms a large fireball to throw in a straight line - burning up susceptible items in the way.

Side/Secondary Effects

Depending on the size of the fireball, it will leave the caster empty of an immediate magic supply for a few moments. This might not seem serious, but in the heat of battle every second counts. Many a powerful solar sage has been defeated whilst their techniques were on cooldown.

Manifestation

Big. Fireball.
Hot enough to melt flesh and sounds like a raging forest fire. Doesn't smell like anything until it burns stuff - then it smells like BURNED STUFF. So yeah, if you're queasy maybe don't incinerate your enemies.

Related School

Primal

Effect Duration

Roughly ten seconds and then the fireball dissipates

Range

Until the 10 seconds run out. The fireball forms in front of the caster - up to 20ft - and then they have to send it off.

Level

Advanced

Applied Restriction

Well, fire can't fire in water, so that's a thing. The fireball can still be cast in rain, but it'll dissipate faster and probably won't be as big to begin with.
And of course, the spell can't be used in rapid succession (with the exception of very, very few talented sages - like the Great Sage).