This code is good for use on any page, inside or outside of the loop and in custom queries:

<?php $myExcerptLink = get_permalink($post->ID); ?>

This is generally how I would use it to output a link:

<?php
	$myExcerpt = get_the_excerpt();
	//$myExcerptLink = the_permalink();
	$myExcerptLink = get_permalink($post->ID);
	if ($myExcerpt != '') {
		// Some string manipulation performed
	}
	echo $myExcerpt; echo "<a href="$myExcerptLink">Read more.</a>"; // Outputs the processed value to the page
?>