Loading JDBC driver in custom SearchComponent

I'd like to access a postgres database from my custom SearchComponent but unfortunately, I get the following error:

java.sql.SQLException: No suitable driver found for postgres
        at java.sql.DriverManager.getConnection(DriverManager.java:689)
	at java.sql.DriverManager.getConnection(DriverManager.java:247)
	at ch.guidelines.util.SimpleDataSource.getConnection(SimpleDataSource.java:50)
...

... when I try to connect to the database using:

private String dbUrl = "jdbc:postgresql://db/mydb";

public Connection getConnection(String dbUser, String dbPasswd) throws SQLException {
    this.dbUser = dbUser;
    this.dbPasswd = dbPasswd;
    this.conn = DriverManager.getConnection(dbUrl, dbUser, dbPasswd); // line 50
    return conn;
}

I already use the DataImportHandler using the Postgres JDBC driver successfully. I tried putting the driver's jar in different locations:

• /opt/solr/dist (with added <lib ... /> entry in solrconfig.xml)
• /opt/solr/lib
• /opt/solr/server/lib
• /opt/solr/server/lib/ext
• /opt/solr/server/solr/lib (lib-folder in the solr.solr.home directory)

But nothing worked so far... How can I get the driver loaded in my custom SearchComponent?

I'd really appreciate your help.