X0202 3 2005-05-24 0 0001103345 BEACON POWER CORP BCON 0001288003 PERSEUS 2000 EXPANSION LLC 2099 PENNSYLVANIA AVENUE NW SUITE 900 WASHINGTON DC 20006 0 0 1 0 Common Stock 1666667 D Warrant to purchase Common Stock 1.008 2005-05-24 2010-05-24 Common Stock 800000 D (1) The reporting person is a member of a Section 13(d) group that owns more than 10% of the issuer's outstanding common stock. Perseus 2000 Expansion Fund, L.L.C. By: Rodd Macklin, Chief Financial Officer and Treasurer 2005-05-26