Wall Street Journal: Every now and then, Dorothy and Dan Oberhausen take a little detour to check in on their solar panels. The two panels aren’t much to look at. They are just standard-issue photovoltaic cells, facing due south and angled skyward, set in a scruffy, weed-choked field. Not only are they participating in the nation’s first co-operative solar farm–a pioneering venture set up by the electric-utility co-op serving their area–they are playing a small role in an emerging and potentially …