Fort Hood is the largest U.S. military installation in the world by size, and on any given day, it is home to 25, 000 to 30, 000 people, according to an Army spokesman at the Pentagon.

CNN: Fort Hood, a home for thousands

System size: All except Portland assumed a five-kilowatt system, the average size for a residential solar installation in most of the U.S. For Portland, which has a mild climate and an incentive system that favors smaller systems, we assumed a system of three kilowatts.

WSJ: The Economics of Solar Power for Your Home

Both of these are right around the size of a deck of cards, and no software installation is required to get 'em working.

ENGADGET: Sierra Wireless intros dual-carrier HSPA+ / LTE AirCard 753S and 754S, with 319U and 320U in tow

In another large-scale art installation, Babis Panagiotidis used 18, 000 recycled computer keys to make a life-size rocking horse.

ENGADGET: Inhabitat's Week in Green: solar panel printer, gold producing bacteria and a life-size of horse made of computer keys

But building a giant battery using dry-cell technology would require thousands of individual cells - about the size of a soft drinks can - to be strung together in a massive installation.

BBC: Liquid metal promise for future batteries

Residential systems tend to be more expensive because they are smaller in size (5 kilowatts is typical), yet they still need local government and utility permits for each installation.

FORBES: U.S. Solar Market Grew 76% in 2012