Off-the-grid homes are autonomous; they do not rely on municipal water supply, sewer, natural gas, electrical power grid, or similar utility services. A true off-grid house is able to operate completely independently of all traditional public utility services.
Hydro, solar and wind power generation is often the route taken by off-the-grid people. (You will need a river if you want hydro power. An undershoot water wheel can produce a decent amount of electricity with zero environmental impact, overshoot makes more electricity but will effect the wildlife.)
Being connected to the electrical grid via a grid-tie system is more expensive due to the extra hardware costs (such as a grid-tie inverter) especially when old car batteries that can no longer supply enough current to start a car are reused.
Going off-grid can be done for altruistic reasons or to lower the environmental impact of living, as the typically limited amount of on-site renewable energy available is an incentive to reduce its use.
But if energy usage is not reduced, then it will be tricky to get the necessary electricity without having an environmental impact. Solar panels, wind mills take up space but don't produce enough power alone... but large numbers can compensate and that means more space (and thus environmental impact).
Living off the grid works best when its done in combination with lowered needs for electricity. Using a woodstove for heat. Candles and windows for lights. Minimal electrical appliances and all energy efficient appliances.
Finding and buying a green "off the grid" house is possible to do however. There is a whole market for buildings that are off the grid so that the hard part has already been done.
Websites like http://www.greenhomesforsale.com/off-the-grid-homes.php have lists of homes, descriptions, photos and prices. Other websites that specialize in off the grid homes also exist. Just Google it.
