Last summer, an engineering nonprofit group called New York Sun Works opened a new urban farm—and set it afloat on the Hudson River. The Science Barge, which reopens in May, is totally off the electrical grid, and grows tomatoes, peppers, and squash with zero carbon emissions and no runoff. The marine location offers some relatively inexpensive real estate and, more important, makes visible the project’s true self-sufficiency—look, no wires! Last year, some 9,000 people came aboard to learn about sustainable food and energy consumption. The barge takes these concepts out of the abstract for visitors, who learn about solar energy while standing in front of solar panels and about energy-efficient produce in front of tomatoes on the vine.