Imagine a gigantic brick, packed full of tightly compressed dirt. As big as a pickup truck but — at 24 tons — about five times heavier. An elevator powered by solar panels or wind turbines hoists it over 300 feet up the side of a huge building. A trolley stows it inside, but it's not alone. An automated system lifts and stores hundreds more bricks, like giant Pez candies, as the sun shines and the wind blows. Now imagine the building's control system lowering those hundreds of bricks one by one, spinning electrical power generators in the process. They drop…