About 71 percent of the earth is covered in water. The open ocean isn’t currently an environment humans can survive in forever. Energy, food, and water supplies eventually run out and require a trip to land. What would it take to build a sustainable city on the water?

It took until 1804 to reach the first billion humans on earth. It only took us 207 years to add six billion more people. We are running out of space on land to support humans. Better utilizing the oceans could help us with our growing pains, whether or not we decide to live on floating cities full time. 

The backbone of a community at sea is energy production. An answer to the problem could be shockingly low tech. Ocean thermal energy conversion (OTEC) is partially solar, partially thermal stratification. Lifescience.com stated, “OTEC relies on the fact that water near the surface is heated by sunlight while seawater deep in the dark is much colder. OTEC plants use warm surface water to heat ammonia or some other fluid that boils at a low temperature. The resulting gas is used to drive turbines that produce electricity. The gas is then cooled by cold water pumped up from the ocean depths and the resulting fluid is recycled to help generate power.”

According to Energy.gov, “OTEC technology is not new. In 1881, Jacques Arsene d'Arsonval, a French physicist, proposed tapping the thermal energy of the ocean. But it was d'Arsonval's student, Georges Claude, who in 1930 built the first OTEC plant in Cuba. The system produced 22 kilowatts of electricity with a low-pressure turbine. In 1935, Claude constructed another plant aboard a 10,000-ton cargo vessel moored off the coast of Brazil. However, weather and waves destroyed both plants before they became net power generators.”

The major limitation of the large-scale OTEC model is that you have to have your system in the warm water very close to the equator with a few thousand feet below for cold enough water to run the refrigeration cycle. With more efficient, low temperature refrigeration cycle possibilities, we could expand beyond the warm equatorial waters. HVAC contractors and manufacturers could develop the key energy system required to live at sea. 

Weather is obviously another hindrance of OTEC plants. The open ocean is a tough environment for any equipment, much less a power plant. The combination of sun, salt corrosion, and storms are a much less stable environment than a piece of land in the Midwest for a power plant. Oil platforms are designed for tough weather and could be repurposed as OTEC plants in the right locations. 

The advantage to OTEC is the 24-hour consistent supply of energy. Wind and solar are limited by the flow of energy they receive. OTEC wouldn’t necessary need a battery to supply consistent electricity. 

Lockheed Martin is building a new 10 Megawatt OTEC plant off the coast of China. This site will be an interesting modern test of the ocean technology. Smaller plants are easier to fund and build, but have a longer return on investment. Large-scale plants have the best opportunity to turn a quick profit, but would require billions to be built. The Lockheed site in China could help get a vote of confidence from other larger funders if it works well. 

Let’s say we had a functional OTEC power plant. How could we eat and drink on the platform sustainability? Desalinization of ocean water is possible. Unfortunately, it takes an enormous amount of energy to get the salt out of enough water to support a large number of humans. Beyond just drinking water, we would need fresh water to irrigate produce. 

Reverse osmosis (RO) has been the technology of choice for filtering out seawater salt. The issue with RO water is that it is an energy intensive process. In the commercial scale RO process, you need a high-pressure pump to get pure water molecules through the semi-permeable membrane. 

National Geographic discussed some alternatives to RO filtering. Carbon nanotubes are one proposed technology. Salt ions have a positive charge. If we had a filter membrane that had a slightly positive charge at the end of pores barely big enough for water to pass through, you would repel the salt ions and just let H20 pass through. For water purification to work best with OTEC, we would need major plumbing advancements in filtration, with the least energy intensive processes being the best. 

Once you have enough fresh water and power, could you actually farm enough food to live on these platforms? You would need a lot of surface area to grow enough produce to feed residents. You could fish, but another option is to submerge big porous tanks into the water near your barge. Like at a trout farm in a pool on land, you could farm captive fish for food instead of searching for it on the open water. 

Blue Revolution is a group based in Hawaii that is trying to put all the pieces together and develop a system that could sustain life at sea. The prospect of moving to the sea is called seasteading. The plan Blue Revolution has is to build a 3,000-foot diameter platform with a 25 Megawatt OTEC plant. They would also have a 100-acre lagoon for growing algae for food and fuel. 

OTEC isn’t cheap and isn’t as convenient as other sources of energy. In my lifetime, we will probably run out of cheap and convenient energy. The reason we are even aware of the Alberta tar sands and natural gas fracking is that the low hanging fruit energy options are becoming scarce. There is an abundance of clean energy in the ocean; we just don’t know how to harness it yet. 

The idea of living full time at sea doesn’t really sound like something I want to do. Within this seasteading movement, there are the people who may want to leave land for good and people who live adjacent to the sea, which could use this technology to supplement their fuel, water, and food needs. If you live in places like San Diego, Calif., OTEC energy could be very helpful. About 40 percent of the world’s population lives less than an hour from the ocean, yet we haven’t utilized the power available with OTEC plants. In our search for easy energy, we have been overlooking the most abundant resource we have on earth. 

Max Rohr is a graduate of the University of Utah. He is currently an outside salesperson at Shamrock Sales in Denver. He has worked in the hydronics and solar industry for 10 years in the installation, sales and marketing sectors. Rohr is a LEED Green Associate and BPI Building Analyst, and is RPA’s Education Committee Chairman. He can be reached at max.rohr@mac.com.