Learn Hardcore German: Die Umwelt braucht heute mehr saubere Energie. - The environment needs more clean energy today.

Because Umwelt (environment) is a feminine noun in German, and die is the definite article for all feminine singular nouns in the nominative case. Here it serves as the subject of the sentence: Die Umwelt = “The environment.”

Why is the verb braucht placed where it is in the sentence?

In a main clause, German typically follows the V2 (verb-second) word order rule. That means the finite verb (here braucht) must be the second element. The first element is Die Umwelt, so braucht comes next, even though heute (“today”) is an adverb.

What does brauchen mean here, and does it take any special case?

brauchen means “to need.” When you say jemand braucht etwas, the person is in the nominative case and the thing needed is in the accusative. So Die Umwelt is nominative (subject) and mehr saubere Energie is accusative (direct object).

Why is it mehr saubere Energie and not mehrere saubere Energie?

mehr is used for uncountable or mass nouns to indicate “more of something” (energy here is uncountable).
mehrere is used with countable nouns to mean “several.”
Since Energie is generally uncountable in German when you mean “energy” in the abstract, you use mehr.

Why is the adjective saubere not capitalized, and how do we know its ending?

Adjectives in German are not capitalized. The ending -e on sauber- comes from strong or mixed adjective declension rules:

There is no article directly before saubere Energie (we have the quantifier mehr instead).
Energy is feminine, accusative, singular.
Thus sauber takes the ending -e: mehr saubere Energie.

Could I say sauberere Energie instead of mehr saubere Energie?

No. sauberer (comparative of sauber) would mean “cleaner energy” (i.e., energy that is more clean compared to something else).
But mehr saubere Energie means “a greater quantity of clean energy.” We’re talking about amount, not degree of cleanness.

Why is heute placed before mehr saubere Energie?

German word order allows adverbs like heute (“today”) in various positions. As long as the finite verb stays second, you can put heute after the verb or before the object for emphasis. Here heute comes between the verb and the object for a natural flow:
Die Umwelt (subject) – braucht (verb) – heute (adverb) – mehr saubere Energie (object).

Is Energie always singular, or can it be plural?

Energie in the sense of “energy” is an uncountable noun and normally used in the singular. If you talk about different types or forms of energy, you might see Energien (e.g., erneuerbare Energien = “renewable energies”), but here we mean “more clean energy” in general, so it remains singular.