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Because of what it pumps back into the system, a zero-energy home ends up consuming no energy at all. See more green science pictures.

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When it comes to energy use, not all homes are created equal.

First, there's the traditional electric house. A typical, all-electrically powered home in the United States uses about 10 kilowatt-hours (kWh) per square foot per month, or about 120 kWh per square foot in a year [source: ToolBase].

A higher-efficiency home, such as one with a solar water heater, a small photovoltaic system and high-efficiency appliances, brings the energy use down to about 84 kWh per square foot in a year [source: ToolBase].

And then there's the zero-energy home, or ZEH. At the end of that same year, a ZEH ends up consuming no energy at all.

Well, actually, it's a bit more complicated than that, but it does work out to a net-zero energy consumption. A zero-energy home is about as efficient as a house can get without giving up electricity altogether. It has all the comforts of a regular house -- it heats, cools, entertains, washes and dries. It just does it all more efficiently. And then, when it's done, it generates enough solar electricity to cover its own low-energy needs.

It seems pretty futuristic, but zero-energy homes aren't just a concept anymore. In the United States, they're starting to pop up for sale in the sunniest states, like Arizona, Texas and California, where solar fuel is most abundant. There are even some home-construction companies that focus almost exclusively on the ZEH or near-ZEH market.

In this article, we'll find out what these homes are all about -- how they use 60 percent less energy than a typical home, how they end up with a net-zero energy consumption, and whether they end up saving a homeowner money in the long run, or if the benefit is purely environmental.