<PAGE>

                                                                    Exhibit 10.1

                FIFTH AMENDMENT TO CREDIT AND SECURITY AGREEMENT

      This Amendment, dated as of March 29, 2004, is made by and between
SOUTHERN FLOW COMPANIES, INC., a Delaware corporation (the "Borrower"), and
WELLS FARGO BUSINESS CREDIT, INC., a Minnesota corporation (the "Lender").

                                    RECITALS

      The Borrower and the Lender are parties to a Credit and Security Agreement
dated as of September 24, 2001, as amended by (i) the First Amendment to Credit
and Security Agreement dated as of November 19, 2002; (ii) the Second Amendment
to Credit and Security Agreement and Waiver of Defaults dated as of March 26,
2003; (iii) the Third Amendment to Credit and Security Agreement dated as of
April 4, 2003; and (iv) the Fourth Amendment to Credit and Security Agreement
dated as of September 24, 2003 (as so amended, the "Credit Agreement").
Capitalized terms used in these recitals have the meanings given to them in the
Credit Agreement unless otherwise specified.

      The Borrower has requested that certain amendments be made to the Credit
Agreement, which the Lender is willing to make pursuant to the terms and
conditions set forth herein.

      NOW, THEREFORE, in consideration of the premises and of the mutual
covenants and agreements herein contained, it is agreed as follows:

      1.    Defined Terms. Capitalized terms used in this Amendment which are
      defined in the Credit Agreement shall have the same meanings as defined
      therein, unless otherwise defined herein.

      2.    Section 6.2(a). Section 6.2(a) of the Credit Agreement is amended
      and restated in its entirety to read as follows:

                  "(a)  MINIMUM TANGIBLE BOOK NET WORTH. The Borrower will
      maintain, during each period described below, its Tangible Book Net Worth,
      determined as at the end of each month, at an amount not less than the
      amount set forth opposite such period below. "Tangible Book Net Worth"
      means the aggregate of the common and preferred stockholders' equity in
      the Borrower less intangibles and less total intercompany indebtedness
      owing from Corporate Guarantors to Borrower, all determined in accordance
      with GAAP.

<PAGE>

<TABLE>
<CAPTION>
                Period                         Minimum Tangible Book Net Worth
<S>                                            <C>
        1/1/04 through 3/31/04                           $1,600,000
        4/1/04 through 6/30/04                           $1,600,000
        7/1/04 through 9/30/04                           $1,600,000
10/1/04 through 12/31/04 and thereafter                  $1,600,000"
</TABLE>

      3.    Section 6.2(b). Section 6.2(b) of the Credit Agreement is amended
      and restated in its entirety to read as follows:

            "(b)  MINIMUM PROFITABILITY. The Borrower will achieve, during each
      period described below, Net Income, determined at the end of the quarter,
      greater than the amount set forth opposite such period:

<TABLE>
<CAPTION>
           Period                                Minimum Net Income
<S>                                              <C>
 Three months ended 3/31/04                          $  192,000
  Six months ended 6/30/04                           $  440,000
 Nine months ended 9/30/04                           $  685,000
Twelve months ended 12/31/04                         $1,100,000"
</TABLE>

      4.    Section 6.2(c). Section 6.2(c) of the Credit Agreement is amended
      and restated in its entirety to read as follows:

            "(c)  CAPITAL EXPENDITURES. The Borrower will not incur or contract
      to incur Capital Expenditures of more than $300,000 in the aggregate
      during the fiscal year ending December 31, 2004."

      5.    Section 6.26. Section 6.26 of the Credit Agreement is amended and
      restated in its entirety to read as follows:

            "Section 6.26 Advances to Corporate Guarantors. Total intercompany
            indebtedness owing from all Corporate Guarantors to Borrower
            determined at the end of each month may not (a) exceed the
            cumulative Net Income from January 1, 2001 until such date or (b)
            reduce Tangible Book Net Worth below $1,600,000."

      6.    Exhibit B. Exhibit B of the Credit Agreement is amended and restated
      in its entirety and replaced with Exhibit B attached hereto.

      7.    No Other Changes. Except as explicitly amended by this Amendment,
      all of the terms and conditions of the Credit Agreement shall remain in
      full force and effect and shall apply to any advance or letter of credit
      thereunder.

      8.    Conditions Precedent. This Amendment shall be effective when the
      Lender shall

                                                                             -2-
<PAGE>

      have received an executed original hereof, together with each of the
      following, each in substance and form acceptable to the Lender in its sole
      discretion:

            (a)   The Acknowledgment and Agreement of Guarantors set forth at
            the end of this Amendment, duly executed by each Guarantor.

            (b)   Such other matters as the Lender may require.

      9.    Representations and Warranties. The Borrower hereby represents and
      warrants to the Lender as follows:

            (a)   The Borrower has all requisite power and authority to execute
            this Amendment and to perform all of its obligations hereunder, and
            this Amendment has been duly executed and delivered by the Borrower
            and constitutes the legal, valid and binding obligation of the
            Borrower, enforceable in accordance with its terms.

            (b)   The execution, delivery and performance by the Borrower of
            this Amendment has been duly authorized by all necessary corporate
            action and does not (i) require any authorization, consent or
            approval by any governmental department, commission, board, bureau,
            agency or instrumentality, domestic or foreign, (ii) violate any
            provision of any law, rule or regulation or of any order, writ,
            injunction or decree presently in effect, having applicability to
            the Borrower, or the articles of incorporation or by-laws of the
            Borrower, or (iii) result in a breach of or constitute a default
            under any indenture or loan or credit agreement or any other
            agreement, lease or instrument to which the Borrower is a party or
            by which it or its properties may be bound or affected.

            (c)   All of the representations and warranties contained in Article
            V of the Credit Agreement are correct on and as of the date hereof
            as though made on and as of such date, except to the extent that
            such representations and warranties relate solely to an earlier
            date.

      10.   References. All references in the Credit Agreement to "this
      Agreement" shall be deemed to refer to the Credit Agreement as amended
      hereby; and any and all references in the Security Documents to the Credit
      Agreement shall be deemed to refer to the Credit Agreement as amended
      hereby.

      11.   No Other Waiver. The execution of this Amendment and acceptance of
      any documents related hereto shall not be deemed to be a waiver of any
      Default or Event of Default under the Credit Agreement or breach, default
      or event of default under any Security Document or other document held by
      the Lender, whether or not known to the Lender and whether or not existing
      on the date of this Amendment.

      12.   Release. The Borrower and each Guarantor by signing the
      Acknowledgment and Agreement of Guarantors set forth below, each hereby
      absolutely and unconditionally

                                                                             -3-
<PAGE>

      releases and forever discharges the Lender, and any and all participants,
      parent corporations, subsidiary corporations, affiliated corporations,
      insurers, indemnitors, successors and assigns thereof, together with all
      of the present and former directors, officers, agents and employees of any
      of the foregoing, from any and all claims, demands or causes of action of
      any kind, nature or description, whether arising in law or equity or upon
      contract or tort or under any state or federal law or otherwise, which the
      Borrower or such Guarantor has had, now has or has made claim to have
      against any such person for or by reason of any act, omission, matter,
      cause or thing whatsoever arising from the beginning of time to and
      including the date of this Amendment, whether such claims, demands and
      causes of action are matured or unmatured or known or unknown.

      13.   Costs and Expenses. The Borrower hereby reaffirms its agreement
      under the Credit Agreement to pay or reimburse the Lender on demand for
      all costs and expenses incurred by the Lender in connection with the Loan
      Documents, including without limitation all reasonable fees and
      disbursements of legal counsel. Without limiting the generality of the
      foregoing, the Borrower specifically agrees to pay all fees and
      disbursements of counsel to the Lender for the services performed by such
      counsel in connection with the preparation of this Amendment and the
      documents and instruments incidental hereto. The Borrower hereby agrees
      that the Lender may, at any time or from time to time in its sole
      discretion and without further authorization by the Borrower, make a loan
      to the Borrower under the Credit Agreement, or apply the proceeds of any
      loan, for the purpose of paying any such fees, disbursements, costs and
      expenses.

      14.   Miscellaneous. This Amendment and the Acknowledgment and Agreement
      of Guarantors may be executed in any number of counterparts, each of which
      when so executed and delivered shall be deemed an original and all of
      which counterparts, taken together, shall constitute one and the same
      instrument.

            IN WITNESS WHEREOF, the parties hereto have caused this Amendment to
      be duly executed as of the date first written above.

WELLS FARGO BUSINESS CREDIT, INC.              SOUTHERN FLOW COMPANIES, INC.

By:   /s/ Patti Scudder                        By:   /s/ A. Bradley Gabbard
      -----------------                              ----------------------
Name: Patti Scudder                            Name: A. Bradley Gabbard
Its:  Commercial Banking Officer               Its:  Chief Financial Officer

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                   ACKNOWLEDGMENT AND AGREEMENT OF GUARANTORS

      The undersigned, each a guarantor of the indebtedness of Southern Flow
Companies, Inc. (the "Borrower") to Wells Fargo Business Credit, Inc. (the
"Lender") pursuant to a separate Guaranty dated as of September 24, 2001, and
for the Guaranty of Metretek Contract Manufacturing Company, Inc., as of
September 24, 2003, (the "Guaranty"), each hereby (i) acknowledges receipt of
the foregoing Amendment; (ii) consents to the terms (including without
limitation the release set forth in Paragraph 12 of the Amendment) and execution
thereof; (iii) reaffirms its obligations to the Lender pursuant to the terms of
its Guaranty; and (iv) acknowledges that the Lender may amend, restate, extend,
renew or otherwise modify the Credit Agreement and any indebtedness or agreement
of the Borrower, or enter into any agreement or extend additional or other
credit accommodations, without notifying or obtaining the consent of the
undersigned and without impairing the liability of the undersigned under its
Guaranty for all of the Borrower's present and future indebtedness to the
Lender.

METRETEK CONTRACT MANUFACTURING                METRETEK TECHNOLOGIES, INC.
COMPANY, INC.

By: /s/ A. Bradley Gabbard                     By:   /s/ A. Bradley Gabbard
    -------------------------------                  ---------------------------
Name: A. Bradley Gabbard                       Name: A. Bradley Gabbard
Its:  Chief Financial Officer                  Its:  Executive Vice President

POWERSECURE, INC.                              METRETEK, INCORPORATED

By: /s/ A. Bradley Gabbard                     By:   /s/ A. Bradley Gabbard
    -------------------------------                  ---------------------------
Name: A. Bradley Gabbard                       Name: A. Bradley Gabbard
Its:  Chief Financial Officer                  Its:  Chief Financial Officer