<PAGE>
                                                                    Exhibit 24-A

                                POWER OF ATTORNEY

                                   ----------

            I, KEVIN MOUG, do hereby constitute and appoint JOHN D. ERICKSON my
Attorney-in-Fact for the purpose of signing, in my name and on my behalf as
Chief Financial Officer and Treasurer of Otter Tail Corporation, the Annual
Report of Otter Tail Corporation on Form 10-K for its fiscal year ended December
31, 2002, and any and all amendments to said Annual Report, and to deliver on my
behalf said Annual Report and any and all amendments thereto, as each thereof is
so signed, for filing with the Securities and Exchange Commission pursuant to
the Securities Exchange Act of 1934, as amended.

Date: February 4, 2003.


                                                    /s/  Kevin Moug
                                              ----------------------------------
                                                         Kevin Moug

In Presence of:


      Pat Murray
---------------------------------


      George Koeck
---------------------------------

<PAGE>

                                POWER OF ATTORNEY

                                   ----------

            I, JOHN C. MAC FARLANE, do hereby constitute and appoint JOHN D.
ERICKSON and GEORGE A. KOECK, or any one of them, my Attorney-in-Fact for the
purpose of signing, in my name and on my behalf as Chief Executive Officer and
Director of Otter Tail Corporation, the Annual Report of Otter Tail Corporation
on Form 10-K for its fiscal year ended December 31, 2002, and any and all
amendments to said Annual Report, and to deliver on my behalf said Annual Report
and any and all amendments thereto, as each thereof is so signed, for filing
with the Securities and Exchange Commission pursuant to the Securities Exchange
Act of 1934, as amended.

Date: January 27, 2003.


                                                /s/  John C. MacFarlane
                                            --------------------------------
                                                     John C. MacFarlane

In Presence of:


     Dee Fletcher
----------------------------


     Penny Mosher
----------------------------

<PAGE>

                                POWER OF ATTORNEY

                                   ----------

            I, THOMAS M. BROWN, do hereby constitute and appoint JOHN D.
ERICKSON and GEORGE A. KOECK, or any one of them, my Attorney-in-Fact for the
purpose of signing, in my name and on my behalf as Director of Otter Tail
Corporation, the Annual Report of Otter Tail Corporation on Form 10-K for its
fiscal year ended December 31, 2002, and any and all amendments to said Annual
Report, and to deliver on my behalf said Annual Report and any and all
amendments thereto, as each thereof is so signed, for filing with the Securities
and Exchange Commission pursuant to the Securities Exchange Act of 1934, as
amended.

Date:  January 27, 2003.


                                                 /s/ Thomas M. Brown
                                           -------------------------------------
                                                     Thomas M. Brown

In Presence of:


      Donna M. Hull
---------------------------------


      Vivian J. Brown
---------------------------------

<PAGE>

                                POWER OF ATTORNEY

                                   ----------

            I, DENNIS R. EMMEN, do hereby constitute and appoint JOHN D.
ERICKSON and GEORGE A. KOECK, or any one of them, my Attorney-in-Fact for the
purpose of signing, in my name and on my behalf as Director of Otter Tail
Corporation, the Annual Report of Otter Tail Corporation on Form 10-K for its
fiscal year ended December 31, 2002, and any and all amendments to said Annual
Report, and to deliver on my behalf said Annual Report and any and all
amendments thereto, as each thereof is so signed, for filing with the Securities
and Exchange Commission pursuant to the Securities Exchange Act of 1934, as
amended.

Date: February 2, 2003.


                                                    /s/ Dennis R. Emmen
                                            ------------------------------------
                                                        Dennis R. Emmen

In Presence of:


      Gary L. Tygesson
------------------------------

      Lauris N. Molbert
------------------------------

<PAGE>

                                POWER OF ATTORNEY

                                   ----------

            I, MAYNARD D. HELGAAS, do hereby constitute and appoint JOHN D.
ERICKSON and GEORGE A. KOECK, or any one of them, my Attorney-in-Fact for the
purpose of signing, in my name and on my behalf as Director of Otter Tail
Corporation, the Annual Report of Otter Tail Corporation on Form 10-K for its
fiscal year ended December 31, 2002, and any and all amendments to said Annual
Report, and to deliver on my behalf said Annual Report and any and all
amendments thereto, as each thereof is so signed, for filing with the Securities
and Exchange Commission pursuant to the Securities Exchange Act of 1934, as
amended.

Date: February 2, 2003.


                                                 /s/ Maynard D. Helgaas
                                            ------------------------------------
                                                     Maynard D. Helgaas

In Presence of:


    Nathan Partain
---------------------------------


    John MacFarlane
---------------------------------

<PAGE>

                                POWER OF ATTORNEY

                                   ----------

            I, ARVID LIEBE, do hereby constitute and appoint JOHN D. ERICKSON
and GEORGE A. KOECK, or any one of them, my Attorney-in-Fact for the purpose of
signing, in my name and on my behalf as Director of Otter Tail Corporation, the
Annual Report of Otter Tail Corporation on Form 10-K for its fiscal year ended
December 31, 2002, and any and all amendments to said Annual Report, and to
deliver on my behalf said Annual Report and any and all amendments thereto, as
each thereof is so signed, for filing with the Securities and Exchange
Commission pursuant to the Securities Exchange Act of 1934, as amended.

Date: January 27, 2003.


                                                        /s/  Arvid Liebe
                                                   -----------------------------
                                                             Arvid Liebe

In Presence of:

      Melody Kunde
---------------------------


      Kathleen Schweer
---------------------------


<PAGE>

                                POWER OF ATTORNEY

                                   ----------

            I, KENNETH L. NELSON, do hereby constitute and appoint JOHN D.
ERICKSON and GEORGE A. KOECK, or any one of them, my Attorney-in-Fact for the
purpose of signing, in my name and on my behalf as Director of Otter Tail
Corporation, the Annual Report of Otter Tail Corporation on Form 10-K for its
fiscal year ended December 31, 2002, and any and all amendments to said Annual
Report, and to deliver on my behalf said Annual Report and any and all
amendments thereto, as each thereof is so signed, for filing with the Securities
and Exchange Commission pursuant to the Securities Exchange Act of 1934, as
amended.

Date: February 2, 2003.


                                                   /s/  Kenneth L. Nelson
                                                --------------------------------
                                                        Kenneth L. Nelson

In Presence of:


     Maynard D. Helgaas
-----------------------------


     Nathan Partain
-----------------------------

<PAGE>

                                POWER OF ATTORNEY

            I, NATHAN PARTAIN, do hereby constitute and appoint JOHN D. ERICKSON
and GEORGE A. KOECK, or any one of them, my Attorney-in-Fact for the purpose of
signing, in my name and on my behalf as Director of Otter Tail Corporation, the
Annual Report of Otter Tail Corporation on Form 10-K for its fiscal year ended
December 31, 2002, and any and all amendments to said Annual Report, and to
deliver on my behalf said Annual Report and any and all amendments thereto, as
each thereof is so signed, for filing with the Securities and Exchange
Commission pursuant to the Securities Exchange Act of 1934, as amended.

Date:  February 2, 2003.


                                                    /s/  Nathan Partain
                                                ----------------------------
                                                         Nathan Partain

In Presence of:


     Maynard D. Helgaas
--------------------------------


     Gary Spies
--------------------------------

<PAGE>

                                POWER OF ATTORNEY

                                   ----------

            I, GARY SPIES, do hereby constitute and appoint JOHN D. ERICKSON and
GEORGE KOECK, or any one of them, my Attorney-in-Fact for the purpose of
signing, in my name and on my behalf as Director of Otter Tail Corporation, the
Annual Report of Otter Tail Corporation on Form 10-K for its fiscal year ended
December 31, 2002, and any and all amendments to said Annual Report, and to
deliver on my behalf said Annual Report and any and all amendments thereto, as
each thereof is so signed, for filing with the Securities and Exchange
Commission pursuant to the Securities Exchange Act of 1934, as amended.

Date: February 2, 2003.


                                                        /s/  Gary Spies
                                                ----------------------------
                                                             Gary Spies

In Presence of:


     Gary L. Tygesson
--------------------------------------


     Lauris N. Molbert
--------------------------------------
<PAGE>

                                POWER OF ATTORNEY

                                   ----------

            I, ROBERT N. SPOLUM, do hereby constitute and appoint JOHN D.
ERICKSON and GEORGE A. KOECK, or any one of them, my Attorney-in-Fact for the
purpose of signing, in my name and on my behalf as Director of Otter Tail
Corporation, the Annual Report of Otter Tail Corporation on Form 10-K for its
fiscal year ended December 31, 2002, and any and all amendments to said Annual
Report, and to deliver on my behalf said Annual Report and any and all
amendments thereto, as each thereof is so signed, for filing with the Securities
and Exchange Commission pursuant to the Securities Exchange Act of 1934, as
amended.

Date: January 28, 2003.


                                                      /s/ Robert N. Spolum
                                                 -------------------------------
                                                          Robert N. Spolum

In Presence of:


       Daniel N. Kraatz
-------------------------------


       Joy Marshall
-------------------------------