Castle of Palatine Hills, Rincon, Puerto Rico

Forbes: Off-the-Grid Mansions

List Price: $4.8 million
Listed with: Exit Realty Select

This 10,000-square-foot Caribbean fortress inhabits its own private mountain on Puerto Rico's west coast. It's powered almost entirely by alternative energy methods including solar panels and a wind turbine. A private helicopter pad offers easy arrival and departure.

(Realtor.com)

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Introduction With the help of Realtor.com, Sotheby's International Realty, Coldwell Banker Previews International and Prudential Douglas Elliman, we combed the Multiple Listing Services to find available homes touting self-sustainable energy options capable of going off the grid.

(Realtor.com)

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9410 Owl Lane, B... List Price: $2 million
Listed with: Coldwell Banker Previews International

Nestled among county-protected acreage, this Rocky Mountain retreat hosts a 51-panel solar system that has a 20-year assignable contract with Xcel Energy.

(Coldwell Banker Previews International)

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Pensmore, Christ... Owner/developer: Steven Huff, chairman of TF Concrete Forming Systems
Estimated completion: 2014

In the rural Ozark Mountains, a concrete scion is erecting a gigantic 70,000-square-foot mansion that will be energy-efficient, environmentally sustainable and earthquake and tornado resistant. Constructed of concrete and Helix steel fibers, it will have solar panels, geothermal energy and rainwater collection will ensure massive manse can supply the 500-acre estate, despite natural calamity.

(Pensmore)

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The opinions expressed are solely those of the author and do not necessarily reflect the views of Comcast.
529 S. Woodsview... List Price: $12.7 million
Listed with: Coldwell Banker Previews International
Source: Realtor.com

This three-acre estate has a fully contained power system. Other amenities include a pond with stone bridge and paddle boats, a Disney-inspired treehouse and a massive interior rock wall.

(Realtor.com)

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The opinions expressed are solely those of the author and do not necessarily reflect the views of Comcast.
Melody Key Islan... List Price: $10 million
Listed with: Ocean Sotheby's International Realty
Source: Realtor.com

Accessible only by boat, this private island in the Florida Keys recently underwent a $2.5 million renovation that ensured its ability to operate independently. Technologies include a state-of-the-art solar inverter, on-demand muted generator and a water desalination system.

(Realtor.com)

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The opinions expressed are solely those of the author and do not necessarily reflect the views of Comcast.
38 Gorge View, G... List Price: $1.5 million
Listed with: New Mexico Mountain Properties
Source: Realtor.com

This 5,400-square-foot "earthship" boasts an interior waterfall in the living room and a "jungle" in which you can catch fresh fish for dinner.

(Realtor.com)

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The Cave House, ... List Price: $1.5 million
Listed with: Bisbee Realty

This man-made home carved from the side of a boulder comes with 37 acres of secluded desert land peddling natural pools and potable water that seeps from a natural spring. In total there are five buildings including a standalone library that doubles as a safe house, with a back room accessible through a roll-down metal security door hidden behind a sliding glass door. It's equipped with a Murphy bed, an air conditioner, an antique vault and a climate-controlled gun safe.

(Courtesy of Bisbee Realty)

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The opinions expressed are solely those of the author and do not necessarily reflect the views of Comcast.
915 Rosemont Ave... List Price: $799,000
Listed with: Sotheby's International Realty

On the border of Echo Park and Silver Lake, this standalone home has an energy-monitoring system, a wood-pellet stove for heating, tankless water heater and vegetable gardens.

(Sotheby's International Realty)

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The Most Outrageous Garages
Mansions you can get Married in
Homes with Notorious Histories

The opinions expressed are solely those of the author and do not necessarily reflect the views of Comcast.
Castle of Palati... List Price: $4.8 million
Listed with: Exit Realty Select

This 10,000-square-foot Caribbean fortress inhabits its own private mountain on Puerto Rico's west coast. It's powered almost entirely by alternative energy methods including solar panels and a wind turbine. A private helicopter pad offers easy arrival and departure.

(Realtor.com)

More from Forbes:
The Most Outrageous Garages
Mansions you can get Married in
Homes with Notorious Histories

The opinions expressed are solely those of the author and do not necessarily reflect the views of Comcast.
39735 Desert Sun... List Price: $1.2 million
Listed with: Coldwell Banker Previews International

This four-bedroom desert bungalow boasts a "smart electrical" system, 60 solar panels and a Life Source water filtration system.

(Coldwell Banker Previews International)

More from Forbes:
The Most Outrageous Garages
Mansions you can get Married in
Homes with Notorious Histories

The opinions expressed are solely those of the author and do not necessarily reflect the views of Comcast.
More from Forbes Click here to see even more of these amazing off-the-grid homes.

(Realtor.com)

The opinions expressed are solely those of the author and do not necessarily reflect the views of Comcast.