NY Times article
here.

...he began dreaming of a way to fly day and night without fuel,
an idea that has reached fruition in a featherweight solar airplane set for an
initial voyage across the United States starting on Friday, weather permitting.
His brainchild, the Solar Impulse, will not be the first sun-powered plane to
fly; its chief distinction is its ability to go through the night.

Another venture’s solar electric plane, which seats two and could one day find a
place in the sport aviation market, made its debut last week in Germany. The
Sunseeker Duo from Solar Flight (founded by Eric Raymond, who also worked on the
Solar Impulse project) can fly for about 12 hours at a time, said Eric
Lentz-Gauthier, a pilot and spokesman for the company. And some of the
technologies developed for Solar Impulse — which has a wingspan matching that of
a 747 but the weight of a midsize car — are already set for commercial use,
including the special batteries used to store the solar energy and the foam that
insulates them.