X0306 4 2013-02-14 1 0001093691 PLUG POWER INC PLUG 0001044321 MARXE AUSTIN W & GREENHOUSE DAVID M C/O SPECIAL SITUATIONS FUNDS 527 MADISON AVENUE, SUITE 2600 NEW YORK NY 10022 0 0 1 0 Common Stock 2013-02-14 4 S 0 2000000 0.1234 D 6511620 I By Limited Partnerships Common Stock 2013-02-14 4 S 0 5000000 0.134 D 1511620 I By Limited Partnerships This is a joint filing by Austin W. Marxe (Marxe) and David M. Greenhouse (Greenhouse). They share voting and investment control over all securities owned by Special Situations Fund III QP, L.P. (SSFQP), Special Situations Cayman Fund, L.P. (Cayman), Special Situations Private Equity Fund, L.P. (PE), Special Situations Technology Fund, L.P. (Tech) and Special Situations Technology Fund II, L.P. (Tech2). 561,004 shares of Common Stock are held by SSFQP, 168,715 shares of Common Stock are held by Cayman, 103,251 shares of Common Stock are held by PE, 94,293 shares of Common Stock are held by Tech and 584,357 shares of Common Stock are held by Tech2. The interest of Marxe and Greenhouse in the shares of Common Stock owned by SSFQP, Cayman, PE, Tech and Tech2 is limited to the extent of his pecuniary interest. This is a weighed average price. Austin W. Marxe 2013-02-19 David M. Greenhouse 2013-02-19