I seem to recall that 1kg/kw was current state of the art.
This is, however, far from the state of the art for flown spacecraft, which as of 2015 was 150 W/kg (6.7 kg/kW), and improving rapidly.[81] Very lightweight designs could likely achieve 1 kg/kW,[82]
The mass of the solar cell/transmitter array (including the substrate, but not the support structure) is just over 200 metric tons if Kapton is used for the substrate (terrestrial materials), and just under 800 tons if steel foil is used (lunar materials).
If support structures can be redesigned which weigh about as much as a photovoltaic array built from terrestrial materials, then overall specific power levels of about 800 to 1000 watts per kilogram may be possible for a terrestrial SPS.