Since April 2010, photovoltaic panels on the Museum roof have been generating electricity and feeding it back to the electrical grid.
The Theater of Electricity draws energy from the grid, and averaged over time, the energy produced by our solar panels makes up for the energy consumed by our Lightning and Electricity shows.
Why doesn't the theater draw directly from the power collected by the panels? Consider that the Sun is not always shining (especially in Massachusetts), or the giant Van De Graaff generator is in use only some of the time. Our moment-to-moment energy supply and demand varies, so the electrical grid acts like a buffer that compensates for these ups and downs.