K. Algae canal greenhouse designs

Algae is biofuel and it also has potential for carbon capture and storage.

I don't see a future for non-algae biofuels. Apologies if you're into various biofuels, but I'm looking for top carbon sequestration, top carbon value per acre and top value per dollar.

For further reading: https://www.science.org/content/article/ammonia-renewable-fuel-made-sun-air-and-water-could-power-globe-without-carbon Ammonia can become a relatively transportable carbon-free fuel.

K1. Why algae?

Most trees can't grow back in a decade. One celled algae can double in mass given 30 minutes of sunlight. Algae will store fats or oils and then the algal cell walls are a type of cellulose. In theory it's going to be hard to beat one celled algae as a carbon dioxide-consuming and hydrocarbon-producing crop. You can buy blue-green algae in the supplements aisle of a grocery store. Algae makes a good animal feed and its oil is a nontoxic biofuel, rather safe when spilled in environmentally sensitive areas, that works in diesel engines. If you spill some, various critters will come over and eat it for you.

In practice, all sorts of animal life in a marsh or in an ocean feasts on algae, so the first problem is excluding predators. A bioreactor is a sealed growing container where all life has been pre-sterilized out of the container. Then one or more species of algae are innoculated into the container along with a supply of nutrients, oxygen at night and carbon dioxide during the daytime.

An algae canal is a long sealed growing container with a water pump at one end of the canal. Air and nutrients are introduced into the water at one end. The algae-laden water is pumped down the canal, around a 180 degree turn at the far end of the canal and back in a closed loop. The two lanes of the canal, up and back, can be placed right next to each other. So far, algae canals haven't been profitable. They deliver far too little product for all of their upkeep.

We've already discussed the creation of an incoming wall of highly concentrated all-day near-parallel sunlight. I propose that we can reflect this wall of incoming concentrated sunlight with a 45 degree mirror straight down into an algae canal.

We can run this canal almost 24 hours a day in the Alaskan summer. A sealed canal should work in seriously cold or arid areas as long as sunlight is available. A bioreactor is fully enclosed, so that we might use a dry area such as Nevada without any evaporation from the canal. Isn't it nice to hear for once that we don't need to use up valuable land in the corn belt?

K2. A type of balcony seating for algae

Many theaters and stadiums have multiple balconies that jut out in a vertical sawtooth pattern to give all patrons a view of the show. Algae canals have in the past been limited by surface algae shading out sunlight from the depths of the canal. This problem might be solved with a form of balcony seating, where the sunlight comes straight down into the tank and the balconies are all tipped 90 degees.

Picture a series of inverted vees made of solid glass, perhaps 2 inches across at the top and 36 inches deep. Concentrated sunlight focused within 10 degrees of straight down enters the tops of the vees at the surface level of the canal. Most of the light bounces off of the surface of the glass at an oblique angle farther down into the vee, where the light rays are always becoming less and less parallel as they continually bounce down the steadily narrowing vee. At all levels of the vee, some of the light penetrates through the glass and starts traveling through the nutrient-rich part of the water. In sum, the light exits the glass vees into the water at various depths.

If only the top inch of a canal could grow algae before, now the sides of the vees going 36 inches down can grow algae within perhaps an inch of the glass. If we put a strength of 36x sunlight into the tops of the vees, in a perfect system every vertical inch of the vee would get an equal amount of 1x sunlight.

Specialized glass devices are expensive. We can get the same result with two ordinary glass panes, provided that the space between the two glass panes is filled with water to equalize the pressure on both sides of the glass panes. Glass is wholesaled in 36 inch long blanks, so a canal with a 36 inch depth might be a cost-efficient option.

In practice, a ray of sunlight coming down the vee is going to hit the side of the glass at a highly oblique angle and reflect off, still traveling downward but a bit less straight downward. As the light goes downward it will bounce less and less vertically and will eventually bounce outward through the glass, to the algae. We may have more light coming horizontally into the algae at the bottom of the vee than at the top.

We have a number of possible fixes that should work on this problem to get it right. Perhaps the incoming light could be less straight downward, less coherent. A 45 degree reflective mirror over the canal with a wavy surface similar to certain shower doors might handle this job.

We might use salty water in the vees so that no fresh water algae can grow within the vee sections. Salt is already used in certain swimming pools to prevent algal growth. Pure de-ionized water might also work to inhibit algae growth in the wrong canal sections.

I would expect that just before being pulled up for maintenance or for replacement, fresh water must be substituted for salty water in each glass vee module. Then when a module is pulled up the fresh water drains out into the canal water. Going the other way, when a module is dropped into place it's flooded with algal water, but then algal water is replaced with salt water or pure water to stop algal growth within the vee.

K3. Moderating heat and coolness

Various species of algae will grow in almost any water temperature. Algae has been found in near-boiling geothermal springs. So, within limits we might be able to grow algae in the heat and in the cold. Given the extreme amount of sunlight that we're adding to the canal, I'm more worried about excess heat than cold.

We can filter infrared and UV light out of concentrated sunlight to avoid cooking the algae tank.

We may need heat-dumping radiators at each end of a canal. Thermal storage to store nighttime coolness will probably help.

Just as an overseeding mixture contains full-sun and shade-tolerant grass seeds, so an algae canal may need multiple species of algae. Today's temperature will determine which species dominates.

K4. Dimensions of a possible prototype

I'm going to assume a canal 2 meters wide, 1 meter wide in each direction, and 1 meter deep. I'll assume that the canal is 1 kilometer in length. Given vees made of standard 36 inch United States glass panes, two inches apart at the top and with two inch gaps between adjacent vees, I estimate that about half of the volume of the entire canal is prime growing territory for algae with full sun. Given perhaps 8% sunlight loss for a pane of glass at the front of the sealed bioreactor plus some screening out of ultraviolet and infrared wavelengths of sunlight, we need a wall of sunlight of about 20x normal solar strength and 2 meters tall. Every inch or centimeter of glass pane should see roughly 1x of sun on the algae side. I'm assuming that 100% of direct sun on the algae will be optimal for growth. We can decide to crank the solar input up to 150% or to 200% if that works better.

Sunlight can penetrate roughly 1 inch inward, so the panes are 2 inches apart at the top and come to a near-point at the bottom, just enough room between adjacent vees for growing space at the top, also for cleaning machinery and glass stabilization, maybe 1 inch of clearance at the bottom, and 6 inches of tank clearance on top to minimize water losses due to splashing.

Some of the sunlight will come down in the two inch gaps between the vees. We need tall, thin, vee-like mirrors in these gaps to deflect light rays approaching these two inch gaps from above, into nearby glass vees.

In moist climates I recommend seasonal water cooling fields adjacent to the canal so that the system can run hot in July. In dry climates we need lots of thermal heat storage and we need thermal heat transfer into the air during cold desert nights.

Different algae like different temperatures. Prepare tomorrow's dominant species in an innoculation tank. We can dump different species in with each other like mixing shade grass seed with full sun grass seed.

The canal is easy to build, probably with a metal or a rubber bottom and sides, maybe 36 inches high from bottom to surface because window glass blanks come in that size. The vee-shaped modular units lift out for cleaning and replacement.

We may need a regular sweeping of the glass panes if algae wants to stick to the glass. We may need a sweeping of the bottom if gunk, old algae cell husks, tends to build up down there. It's possible to have a sweeper driven by the tank's water pressure. Reversing the pump flow in the tank will cause the sweeper to traverse the length of one side of the canal, sweeping all the glass panes and the bottom of the canal also, and then running the pump in the forward direction will cause the sweeper to return to its original storage position.

K5. Adding nutrients

The canal eats carbon dioxide during sunny hours. The algae consume a bit of oxygen at night. Plants need nutrients. We need to regularly harvest algae out of the canal. If we're growing algae for animal feed, we may need to dry the algae. For biofuels, typically the algae are shaken apart with sound and then the oil rises to the top of a tank and can be skimmed off. These operations can all be handled at one end of the canal. A pump keeps nutrient-rich water circulating around the canal.

The deeper the bubbling, the greater the percentage of air gets into the water. Then again, pushing air more than 36 inches deep takes work. It's possible to juice the system with artificial carbon dioxide, in which case we need deep bubbling.

Modular glass units in the tank lock together at their ends. Individual units still lift out, assuming the lid is off. For vertically removing the glass units, it's easier to break containment between the algae-free zone and the algae zone by pulling out a plug on the glass unit's bottom. Before pulling a glass unit out, replace the chlorinated, salty or otherwise sterile water within the modular glass unit with plain old water, then lift the glass unit slowly, letting the algae-friendly water drain out the bottom as the module is pulled up. For putting a glass unit in, let the algae-friendly water drain into the module as the module is lowered into the canal, then afterwards replace the algae-friendly water in the module with chlorinated or salty water so that algae doesn't grow inside the module under heavy sun.

Light bouncing off of the greenhouse ceiling can come down in somewhat random microdirections because we have a micro-wavy mirror surface up on the ceiling. Think of the almost flat, wavy glass pattern used on one side of a shower door to distort light a bit, so that you can't quite see someone taking a shower. Craft the wavy surface and attach reflective mylar to it, or craft a wavy glass surface with reflective metal on the back side of the glass. A white surface would scatter light in many directions so that we'd lose some sunlight back out the way it came in.

I'm optimistically wishing but can't prove that downward-directed sunlight bounces back and forth on the vee surfaces and eventually penetrates the vee shapes, to the left or to the right, somewhat evenly all the way down. Getting a more even light penetration from top to bottom in the vee shapes is a second-order goal for the prototype. The vee shape polarizes the sunlight in the same polarization direction, back and forth several times, so total sunlight loss is controllable.

An algae canal needs a constant, slow water flow up one half of the canal and back down the other half. There's room at each end of the canal for bubbling air into the water, for adding nutrients as necessary and for water pumps.

We may need to squeegee the glass surfaces regularly to keep them clean and to sweep algae along in the current, rather than letting any spot of algae colonize one spot on the glass. Scrubbees with a neutral buoyancy, moving along the surfaces of the glass with the flow, might do the cleaning job. A nonstick glass surface would be valuable. Laying down some type of glass surface barrier that comes loose molecule by molecule so that the algae can't manage to stick might work.

K6. Setting a standard for sequestering carbon

We can look at two long-range scenarios. In the 100% boiling frog scenario the earth gets wildly hot. According to geologic records, the earth needs 100,000 years to sequester all of that carbon dioxide. In a far more likely scenario, humans are going to greatly inhibit the earth's temperature rise. In this scenario the planet would need about 2,000 years to naturally sequester our excess carbon dioxide.

I assume that for each carbon sequestration scheme a percentage of sequestered carbon dioxide is likely to leak back out each year. Carbon dioxide optimally needs to be artificially sequestered for a ballpark 2000 years to give nature a chance to re-sequester the atmosphere's CO2 properly. For now I'll use a 2000 year sequestration standard – A method of sequestration must be designed to hold, on average, at least 51% of the sequestered carbon for 2000 years for me to consider it a legitimate method of carbon sequestration. In other words, the carbon sink will release carbon at less than half of the world's natural sequestration rate over the next 2000 years. This sequestration standard could be subject to future adjustments.

I might question any sequestration system that releases 25% of its stored carbon in 1 year or in 100 years. Plowing carbon into the topsoil and then watching much of the carbon eventually exit the topsoil may be good for the crops, but it has a long-term carbon sequestration issue and so it doesn't earn any carbon credits from me.

Given a 2,000 year timeline, trees don't directly sequester all that much carbon per year. Their deeper roots push carbon deep into the ground where it will stay sequestered after a megafire, but the 70% of the carbon stored above ground will be gone with the wind one way or another. In particular, the dead trunks of billions of trees killed by drought or insects will soon disappear almost completely. An acre of natural prairie or an acre of bamboo will sequester more carbon than an acre of natural forest because prairie grasses have faster growing root systems.

Permanently sequestering pure carbon dioxide gas within basalt formations should pass the 2000 year test.

If the world is growing billions of barrels of biodiesel, we either can either ferment the leftover algae cellulose into ethanol or we can bury the cellulose. We might pipe the cellulose-laden cell husks to a nearby patch of desert designated as a carbon landfill, drain most of the pipe's water away for water re-use, let the carbon dry out a bit and then cap the landfill with clay. In a reasonable time the capped landfill would become bone-dry underneath, and so the dried carbon could stay undisturbed for a full 2000 years.

There's a possibility that a future civilization could mine the sequestered carbon for energy, just as our civilization has mined peat bogs for cheap fuel.

K7. Your community can grow fuel.

Our goal is a tremendous amount of algae from very little equipment. This design might be 10 times as cost-efficient as current algae canal prototypes. I have a sense that the cost of a gallon of nontoxic 100% biodiesel would be be aggressively competitive with petroleum-derived diesel fuel, and we can make all we want.

I've recently heard of a company that contemplated growing algae but in the end decided to avoid this pathway in part because of patent law. Powerful corporations can patent and monopolize new algae species. With patents he who has the gold rules. That said, we invent a better greenhouse because we want human civilization to survive, not because we want to be filthy rich. Because our planet's doom is intricately bound up with food production, humanity really needs this invention. So, who wants to live?

K8. Agricultural-scale greenhouses

A wall of concentrated sunlight can be used to illuminate a single large greenhouse, a big box store of a greenhouse with a normal building's well-insulated, opaque roof. A wall of 30x concentrated light 4 meters high could supply the equivalent of full direct sunlight all day, including fairly early in the morning and into the evening, to a 120 meter wide greenhouse. The greenhouse and the heliostat field could be as long as one kilometer if desired.

The sunlight would be squeezed in a 120 meter long vee against the ceiling, where the vee comes to a point at the far side of the greenhouse. If the bottom of the vee is panes of glass frosted on their bottom sides, the entire roof will have a sunny, even glow during sunny hours.

As with any greenhouse or sunspot, it's possible to reflect away ultraviolet light and/or infrared light from the wall of sunlight as desired.