Your answer would be that the sentence in which the underlined clause functions as an adverb clause is the following one: we can harness solar energy wherever the sun shines.
Explanation:
<em>Wherever the sun shines</em> is an adverb clause. Adverb clauses, also known as adverbial clauses, are dependent clauses that function as adverbs. Since they are dependent clauses, they must have a subordinating conjunction to connect to the rest of the sentence. Dependent clauses fail to stand alone as a sentence because they do not represent a complete thought; they depend on the main clause to complete their meaning.
In this case, the subordinating conjunction introducing the adverb clause is <em>wherever. </em>This conjunction is adding information as regards time, when the event takes place.
