Starting on 2014, The Javalambre-PAU Astrophysical survey (JPAS) will image 10000 deg2 and measure 0.003(1+z) photo-z for 100M galaxies, becoming a very efficient alternative to spectroscopy to study the properties of Dark Energy. JPAS will use a set of 54 narrow band filters over a 1.3Gpix, 5deg2 FOV camera installed on a purpose-built 2.5m telescope at the new observatory of Javalambre, an extremely dark astronomical site with a median seeing of 0.71 arcsec near Teruel, Spain. Thanks to its innovative design, the instrumental development of JPAS involves only a small fraction of the cost and technical complexity of a high multiplexing spectrograph, yet it will produce data which enable a much wider range of Astrophysical applications; it is effectively equivalent to a 5 deg2 which will generate a 3D image of the Northern and Equatorial sky up to m~22.5.