The Vertical Farm
Page 13
Capture sunlight and disperse it evenly among the crops.
Capture passive energy for supplying a reliable source of electricity.
Employ good barrier design for plant protection.
Maximize the amount of space devoted to growing crops.
The materials employed in the construction of the building will be dictated by the needs of the plants and secondarily by the needs of those who work inside the vertical farm. That is not to say that the environmental conditions will become intolerable for humans. Quite the contrary, plants and people go well together, so the temperature and humidity profiles maintained inside the building should allow for a very pleasant work environment as well as favoring maximum crop yields.
1. Capture Sunlight and Disperse it Evenly Among the Crops
We Are on the Same Wavelength
Designing a large, secure home for plants requires intimate knowledge of what a plant needs and how it all works together to allow for maximum growth. Those readers already familiar with the inner workings of a plant can feel free to skip this brief discourse on photosynthesis and go to the next section. For those not familiar with basic plant physiology, the following information may clear up a lot of confusion as to why the family potted plants are not doing so well. Hopefully, it will help you turn your black thumb into a green one.
Plants are fundamentally different from animals in that plants require water, a few elements including carbon dioxide, a source of organic nitrogen, and sunlight to grow. The key here is sunlight. The main plant ingredient that allows all of this, and the part that we are missing, is a microscopic organelle called the chloroplast, and there are hundreds of thousands of them in each leaf. It is a complex structure with its own genome. Chlorophyll is the familiar green-colored compound residing inside the chloroplast that captures sunlight in the form of photons. Chlorophyll then does its magic, converting photons into chemical energy that is used to link together the carbons found in carbon dioxide, forming sugar and other plant-specific products (e.g., cellulose). In the process of photosynthesis, plants discard the oxygen portion of carbon dioxide into the atmosphere, supplying all animals with one of the essential elements they require to carry out their own lives. When we eat plants, we derive the sugar (and, of course, other nutrients) from their tissues. We combine the oxygen we breathe in with the carbons of the sugar molecule, one carbon and two oxygen atoms at a time. This produces carbon dioxide and chemical energy in the form of adenosine triphosphate. We then use that chemical energy to construct our own tissues, and breathe out carbon dioxide as a waste product. Plants take up carbon dioxide and begin the cycle all over again. It’s a remarkable mutually linked association. It should be noted here that the vertical farm, in addition to producing our food, will also sequester huge amounts of carbon dioxide from the atmosphere and, most important, produce lots and lots of oxygen. So every time a worker inside the vertical farm breathes out, you will almost be able to hear the plants say, “Thank you.”
There are two major forms of chlorophyll, chlorophyll a and chlorophyll b. Both absorb light in two distinct wavelengths of the visible spectrum, blue and red (roughly 400 to 700 nanometers). Plants contain lots of other phyto-pigments, too—carotenoids, for example—but they play only a minor role in photosynthesis. The take-home lesson is that not all the energy in sunlight is needed to grow any crop to its maximum yield. We can take advantage of this fact by creating lighting exclusively for the plants. Lightemitting diodes (LEDs) have already been specifically engineered to do that, resulting in a significant savings in energy costs. In contrast, conventional lightbulbs emit 95 percent of their energy as heat (very inefficient, to say the least) and the rest as a broader spectrum of light, most of which is useless to the plant. On the near horizon are organo-lightemitting diodes (OLEDs) made of thin, flexible plastics. These contain stable organic compounds that allow for even more narrow spectra of light to be produced, saving more energy and money, while still giving plants exactly what they need. In addition, OLEDs will permit the design of lights that could be made into any configuration, placing the light source at the optimal distance from the plant, regardless of the plant’s shape. They could even be wrapped around each growing plant, offering the ultimate in custom, energy-efficient lighting for our food crops.
Here Comes the Sun
In areas of the world that already enjoy the gift of abundant sunlight—for example, the Middle East, Australia, the American Southwest, many parts of sub-Saharan Africa—using the sun as the only source of energy to grow crops would be entirely feasible and highly recommended. Photovoltaics could easily supply the energy needed to run any electrical equipment, while sunlight would supply all the energy needed to grow the crops. Orienting the footprint of the vertical farm with a north-south exposure will allow designs to capture maximum amounts of light. Narrow, long, and low—three to five stories high and perhaps as long as a half mile—might be the paradigm for designing in those sun-drenched environments, where land adjacent to urban centers is cheap and available. Buildings with deeper interiors could take advantage of newly developed, specially constructed composite plastic parabolic mirrors such as those produced by Sunlight Direct, situated outside and behind the building to first concentrate, then direct sunlight to the interior sections, while the front of the building remained exposed to the maximum amount of light. Fiber optics leading from the collecting mirrors outside to the inside of the building for each floor could further assist in the distribution of energy to the plants. Together, these two approaches should allow for any reasonable design, regardless of its ultimate shape. A crescent-shaped structure would present a uniform surface to the sun as it progressed across the horizon each day, making this design the most efficient for using passive sunlight. In that case, no further lighting would be necessary, unless twenty-four-hour grow cycles for some crops were an option.
The Visible Farm
If sunlight is the main source of energy to grow the crops, then the vertical farm should be made as transparent as possible. The designer/architect has many choices of transparent material to choose from. Glass is cheap to manufacture and durable, albeit a bit on the fragile side and heavy. Since the late 1950s, glass-and-steel combinations have led the way into the future of the skyscraper. Some of the best-known applications of glass-and-steel construction are two New York City icons of early modern architecture, the Lever House, designed by Gordon Bunshaft of Skidmore, Owings, and Merrill and built in 1952, and the Seagram Building, designed by Ludwig Mies van der Rohe, and completed in 1958. A current trend in modern building design advocates for total transparency; the Apple Store on Fifth Avenue in New York City is an excellent example of what we can expect to see more of over the next twenty years. It is now even possible to create an all-glass structure without any metal at all in the building by using special adhesives. The caveat here is that, as of this writing, the new glues used to attach sheets of glass together have only been tested for a year’s worth of wear. Insulating an all-glass building is a big problem, and employing double-glazing to provide energy-savings adds huge amounts of weight and expense to the equation.
One solution is to abandon glass altogether in favor of high-tech plastics that are much lighter in weight and more durable. Recycling transparent plastics (bottles, etc.) into clear panels used for windows and modular construction of eco-friendly structures has spawned a new industry for building materials. A leading exponent of this approach is KieranTimberlake Architects in Philadelphia. The only difficulty is that most commonly available plastics yellow over time due to excessive exposure to UVB radiation from unfiltered sunlight, excluding more and more of the wavelengths of light that plants need to grow efficiently. One newer product, referred to simply as ETFE, or ethylene tetrafluoroethylene, is a fluoropolymer plastic with many advantageous properties, including the fact that it is a “self-cleaning” material, due to its electrostatic charge. It is very lightweight, only 2 percent the weight of glass of a similar thickness; is as transpare
nt as water, allowing in all wavelengths of light; and has a high tensile strength. Most important, it does not yellow when exposed to sunlight for long periods of time, making it far superior to any other lightweight clear carbon-based polymer material on the market. ETFE has been applied to such iconic buildings as the Beijing Olympics swimming venue, the Water Cube, designed and constructed by the China State Construction Engineering Corporation jointly with Australia’s PTW Architects and Ove Arup Pty Ltd; and the Eden Project in the south of England, designed by architect Nicholas Grimshaw and the engineering firm Anthony Hunt and Associates. Both of these high-profile projects made extensive use of ETFE. These structures are now several years old and remain in good condition. Creating a double or even triple skin of ETFE for the outer glazing ensures good insulation quality and reduces the need to use large air-conditioning units or much in the way of heating. Maintaining a positive pressure inside ETFE also creates cushions of insulation. I would opt for constructing my prototype out of aluminum framing and large panels of pressurized ETFE to allow in the maximum amount of sunlight to the crops inside. A positive pressure will also allow for maximum safety and security designs, building into the vertical farm double-lock entry systems. In this configuration, invasion of the growing zones by microbial pathogens and insect pests would be greatly reduced.
2. Capture Passive Energy for Supplying a Reliable Source of Electricity
Earth, Wind, and Fire
While sunlight will be the main source of energy to grow crops in regions that have more than two hundred days of sunlight, many other regions would be left out if this were the only viable way of proceeding. Scandinavia, Iceland, most of Russia, Canada, and Alaska in the United States in the Northern Hemisphere; and Chile, Argentina, and New Zealand in the Southern Hemisphere would all need to tap into an alternative energy supply to remain independent of the municipal energy grid. Fortunately, there are many choices, and in some of the countries mentioned above, generous supplies exist. These include geothermal, tidal, and wind energies.
The Fire Down Below
Geothermal sources are abundant in the United States, Iceland, Italy, Germany, Turkey, France, the Netherlands, Lithuania, New Zealand, Mexico, El Salvador, Nicaragua, Costa Rica, Russia, the Philippines, Indonesia, the People’s Republic of China, Japan, and Saint Kitts and Nevis. It comes in several varieties: naturally occurring surface vents of steam or water, such as those found inside Yellowstone National Park, and an abundant gradient of heat from molten magma that lies at or just below the surface in places such as Italy, Iceland, and Hawaii. A third source, the geothermal heat pump, is proving to be very useful in modern construction practices and is not limited to any specific geological formation. This method can be used to either cool or heat a building. The Department of Energy describes the process thusly: “Using the Earth as a heat source/sink, a series of pipes, commonly called a ‘loop,’ is buried in the ground near the building to be conditioned. The loop can be buried either vertically or horizontally. It circulates a fluid (water, or a mixture of water and antifreeze) that absorbs heat from, or relinquishes heat to, the surrounding soil, depending on whether the ambient air is colder or warmer than the soil.” Installing current versions of these devices for individual homes has proven to be expensive because they are relatively new, but like all other things manufactured, as demand goes up, prices will go down. Once installed, they will eventually pay off themselves by the savings on fossil fuel, and will always be good for the environment. Applying geothermal heat pump technology wherever we can to the first prototype vertical farm will ensure that it will never be a negative asset to the community with respect to energy consumption.
Blowin’ in the Wind
The new “oil,” according to energy magnate T. Boone Pickens, is wind power. He has identified the entire American Midwest as the next Saudi Arabia. According to his own calculations, the United States could save some 20 percent of its total energy budget spent on fossil fuel use by converting the wind-power capabilities that that geographic region enjoys into electricity. The area’s flatness plays a major role in the abundance of wind power there. Other areas of high wind production are the world’s coastal regions; the farther north or south one goes toward either pole, the higher in strength and more reliable the wind is due to the rotation of the planet. So as long as we continue to go around and around, there will always be wind for the taking. Today, many countries have tapped into that resource and in doing so have significantly reduced their energy bills and improved the quality of the atmosphere at the same time. These countries include Canada, the United States, Germany, Spain, the Netherlands, Denmark, Sweden, India, and China.
First-generation wind turbines were based on the same principles of the old-fashioned Dutch windmill. While efficient at capturing power from the rotation of large propellers, they were not without their own unique set of unintended consequences, such as a high number of bird deaths. In addition, the blades would eventually slow down due to the friction created by the gradual accumulation of insects on their exposed surfaces. The early model generators did not yield as much electricity as theoretically possible, but they were a beginning that would eventually spawn an entire clean energy industry. The new generation of wind turbines are even larger in size than the original models and are equipped with more efficient generators. As a result, these turbines turn slower, capture more energy per turn, allow birds the luxury of seeing them so they can easily avoid collisions, and do not need as much cleaning since insects do not accumulate as rapidly as before. In fact, older-model wind turbines that have received these new generators have improved their efficiency by 10 to 25 percent. All in all, it’s been a victory for the ingenuity of wind-energy engineers, who successfully worked through each and every problem. Only one problem remains, and that has to do with aesthetics, not functionality. The old NIMBY cry can still be heard in many locations when the wind turbine issue comes up before the town council meeting.
Other wind-capturing devices have completely broken out of the old windmill mold, assuming radically different configurations. One successful design is a horizontal double-propeller-shaped wind turbine that resembles an old-fashioned hand-driven lawn mower. These new devices are attractive, efficient, and require less wind speed to operate than conventional wind turbines. Furthermore, their turning mechanisms are quiet, do not place unwanted stress on the buildings, and are easy to add on to existing structures without major reconstruction efforts. By combining wind turbines with photovoltaics, a solar/wind capture strategy can be effective in generating energy both day and night.
Burn, Baby, Burn
The vertical farm will produce food, but it will also produce a significant amount of inedible plant and animal by-products (i.e., waste). In a traditional farming operation, or even with the vast majority of low-tech greenhouses, the postharvest leftovers are typically plowed under to partially supply next year’s crops with a jump-start of nutrients, or discarded into the trash bin. Organic material, regardless of what form it takes, is a valuable resource that begs for use in any energy-recapture system. It is good to keep in mind the fact that the word “waste” does not appear anywhere in the ecosystem’s dictionary. It’s all part of the same natural loop of energy recovery aiding in the regeneration of life. If the vertical farm is to behave like an ecosystem, then the roots, stems, and leaves of crops, and the entrails of fowl and fish, all need to find their way back onto the energy grid. Incineration is the most practical way to proceed. Composting was for several years considered by many waste-to-energy experts to be a viable option for handling municipal waste streams. For small-scale situations like backyard lawn clippings and leftovers from dinner, a family living in the suburbs would still do well to compost them and employ the products of worm metabolism—so-called worm casts—as a fertilizer in gardens. Upon further analysis, though, it became apparent that the efficiency of composting was too low for anything commercial in scope: Giving 80 to 90 percent of the energy cont
ained in rotting organic waste to the microbes in exchange for a 10 percent “return on investment” in the form of methane is a no-win technology. In addition, there is residue to contend with after the anaerobic digestion process of composting comes to an end. Much higher efficiencies of energy generation can now be achieved by incinerating biomass with devices that produce minimal levels of pollutants while giving off heat for the steam generation that runs the turbines that make electricity. Most of Europe now employs some form of incineration to process its solid and liquid municipal waste streams back into valuable kilowatts of electricity. With the advent of plasma arc gasification (PAG) devices, any solid material can be reduced to its elements in a matter of seconds. PAG uses an electrical current to create a high-energy plasma, the fourth state of matter. The plasma forms when two electrical arcs unite in the center of the combustion chamber. The device requires that material first be reduced in particle size to accommodate the narrow spray nozzle that introduces it into the device. In the case of liquid municipal waste, it is only necessary to dilute it in order to achieve the proper viscosity. The intense heat of the plasma arc (approximately 4,000 to 7,000°C) exceeds that found on the surface of the sun. Pyrolysis is the process that vaporizes all compounds that pass in front of the plasma arc back into their elements. The heat released is used to make steam and generate electricity. Plasma gasification of a single ton of solid municipal waste would generate approximately 800 kilowatt-hours of electricity that could then be added to the grid or used directly by the vertical farm. The process itself uses around six times less energy than it generates. The other advantage is that at the end of the day there is no residue to deal with. Recovering energy from the inedible parts of the harvest (stems, leaves, roots, etc.) makes the vertical farm energy-efficient and opens the way for entire cities to behave similarly.