BEACON POWER CORPORATION PERFORMANCE-BASED RESTRICTED STOCK UNIT AGREEMENT

EXHIBIT 10.1.24

BEACON POWER CORPORATION

PERFORMANCE-BASED RESTRICTED STOCK UNIT AGREEMENT

This Performance-Based Restricted Stock Unit Agreement (this “ Agreement ” ) , dated as of May 8, 2006 (the “ Effective Date ”), is by and between Beacon Power Corporation (the “ Company ”) and F. William Capp (“ Executive ”), an executive officer of the Company.

WHEREAS, this Agreement is intended to provide Executive deferred compensation in the form of the restricted stock units (“ RSUs ”) referenced below that convert into shares of the Company’s common stock, $.01 par value per share (the “ Common Stock ”), with Executive having the right to convert his RSUs into shares at any time after vesting;

NOW THEREFORE, it is agreed as follows:

1.1             Restricted Stock Unit Award . Subject to the terms and conditions of this Agreement and pursuant to the Company’s Third Amended and Restated 1998 Stock Incentive Plan (the “ Plan ”), the Company will be considered to have awarded an aggregate of up to 632,911 RSUs (the “ Potential Award” ) to Executive:

(a)             Conditions to be Met. The “Vesting Date” is the date on which all the vesting conditions set forth below have been met:

(i)             The Company must have achieved a positive Adjusted EBITDA (as defined below) of at least $2,000,000 for the fiscal year ending in 2009 or 2010. This must be determined in accordance with GAAP by the Company’s independent auditor. The “ Adjusted EBITDA” means the Company’s income before the effect of interest expenses, income taxes, depreciation, amortization and equity compensation expenses as set forth in the Company’s audited Consolidated Statement of Operations or the footnotes to the Company’s audited financial statements.

(ii)            The Company must have received a signed, unqualified opinion (including without limitation, any qualification as to going concern value or financial condition) from its regular auditing firm with respect to the fiscal year ending in 2009 or 2010, as the case may be depending on the fiscal year in which Section 1.1(a)(i) is achieved, and which does not characterize the Company as a development stage company (the “ Audit Opinion ”).

(iii)           The Executive must be an employee of the Company at all times from the date of this Agreement through the last day of whichever of the two fiscal years (i.e., 2009 or 2010) with respect to which the above conditions have become satisfied.

(b)             Variability of Award by Size of Adjusted EBITDA. The size of the Award will vary as shown below:

The number of RSUs actually awarded based on the Potential Award and in accordance herewith is herein referred to as the “Actual Award.”

(c)            Variability of Award by Date Conditions Are Achieved. If the conditions referenced in subclause (a), above, are met for fiscal year 2009, and yet if less than all the Potential Award is actually awarded (because the Adjusted EBITDA for fiscal 2009 is less than $4,000,000), then the as-yet unawarded balance of the Potential

Award may still be awarded with respect to fiscal year 2010 if all the conditions in subclause (a) are in fact also met with respect to 2010.

(d)             Termination if Conditions Not Met. This Agreement automatically terminates as of the date that the Executive leaves the full time employment of the Company for any reason (including without limitation by resignation or termination with or without “ Cause ”). “ Cause ” shall have the same meaning as set forth in Executive’s then-current employment agreement with the Company or, if no such agreement is in effect, “ Cause ” shall have the same meaning as set forth in Executive’s most recent employment agreement with the Company.

(e)             Transitional Rules Upon Termination. If this Agreement terminates as described above in subclause (d):

(i)             Executive may retain all RSUs (A) that have vested prior to the Termination Notice Date (as defined below) or (B) that would have vested with respect to 2009 or 2010, as the case may be, if Executive’s termination had not occurred after such year end but before receipt of the Audit Opinion for that year if Executive remained an employee of the Company long enough for the Audit Opinion to be received, so long as the Audit Opinion is actually received by the Company;

(ii)            Notwithstanding that no “ Acquisition Event ” (as defined in Section 1.3) has been consummated, in the event Executive’ employment with the Company is terminated without Cause (but not for “ Good Reason ”, as defined in Executive’s employment agreement with the Company, and not in the event of resignation by Executive), Executive shall be entitled to his “ Pro Rated Actual Award ” (as defined in Section 1.3) if and only if the “ Termination Stock Price ” (as defined below) is higher than the Target Stock Price (as defined in Section 1.3); and

(iii)           Executive shall not be entitled to receive and shall forfeit any interest in any other RSUs that are covered by this Agreement.

In the case of subsection (ii) above, “ Termination Stock Price ” shall mean the 30-day “ VWAP ” as of the date prior to the Termination Notice Date. “ VWAP ” means the daily dollar volume-weighted average price for the Company’s common stock on the Nasdaq Capital Market (“ Nasdaq ”) on any particular day on which the Company’s common stock is traded on Nasdaq during the period beginning at 9:30 a.m., New York City time (or such other time as Nasdaq publicly announces is the official open of trading), and ending at 4:00 p.m., New York City time (or such other time as Nasdaq publicly announces is the official close of trading), as reported by Bloomberg through its “Volume at Price” functions or, if the foregoing does not apply, the dollar volume-weighted average price of such security in the over-the-counter market on the electronic bulletin board for such security during the period beginning at 9:30 a.m., New York City time (or such other time as Nasdaq publicly announces is the official open of trading), and ending at 4:00 p.m., New York City time (or such other time as Nasdaq publicly announces is the official close of trading), as reported by Bloomberg, or, if no dollar volume-weighted average price is reported for such security by Bloomberg for such hours, the average of the highest closing bid price and the lowest closing ask price of any of the market makers for such security as reported in the “pink sheets” by the National Quotation Bureau, Inc.

The “ Termination Notice Date ” means the date on which Executive resigns (or if earlier, the date on which Executive notifies Company that Executive will resign), or the date on which Company terminates Executive’s employment for any or n