Nov 3, 2024
Sarah Bishop looks anxiously out at her old cornfields. For the first time in almost 100 years, the view has had a dramatic change. Instead of bare ground and debris from the corn harvest, there is row after row of silver mirrored tubes and a faint hint of green. Sarah is one of the first large scale beta-testers of Smart Farms' brand new Winter Green Bioreactors. If everything works out as Smart Farms has advertised Sarah will be able to produce enough bio-diesel to power all of her farm and maybe even sell some fuel to neighbors. If something goes wrong Sarah will have missed her chance to lock in fuel prices for next year and could take a huge hit on the incredibly volatile oil market.
"I still can't believe Sachin (Gupta, Smart Farms' CEO) talked me into this. Lots of my neighbors think I'm crazy to try, but my kids are getting older and I want them to know that their mom took the chance to keep the farm in the family."
For so many American farmers facing the challenges of climate change, Sarah knows that business, as usual, ended 4 years ago and now she is ready to be bold. Sachin Gupta is the mastermind of this bold innovation in the algae biofuel market. "For people like Sarah winter on the farm is a lost opportunity, cold dark days mean you have 4 months where you are just anxiously hoping that the next growing season will work out. Our team wanted to create something that would help farmers become more self-sufficient while lowering emissions."
To meet the goal of promoting farmer's self-reliance Sachin's team has developed a new type of bio-reactor. Using a deceptively simple-looking collection of nested inflatable tubes the Winter Green Bioreactor helps to create a self-regulating algae growth chamber that helps convert sunlight and carbon dioxide into useful biofuel. The outer tube helps to concentrate weaker winter sunlight onto a collection of tubes nested inside where the algae can grow. By using adaptive materials and clever use of insulation the Winter Green Bioreactor will help keep the algae at just the right temperature to grow.
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| Cutaway view of the Winter Green Bioreactor |
Dotted among the silver tubes of Winter Green are non-descript boxes covered in solar panels. These boxes are another part of the secret sauce of the system. They help to move the water and air that the algae need to grow. In addition to the pumps and circulation system, the boxes will automatically filter out surplus algae.
"That was one of our biggest challenges was training the filter mechanisms. If you take out too much algae you're wasting sunlight, too little and you start running out of nutrients slowing growth"
If things go according to plan, fuel from farms like Sarah's will be producing low carbon fuel for less than $2/gallon.
Follow up
Jan 12, 2025
Sarah looks much happier now, algae growth has gone better than expected. Two weeks after the original article was published a neighboring dairy farm reached out to Sarah and the other Beta Testers. It has been a win-win for both communities, for the dairy farm they no longer need to worry about too much manure leaching into the groundwater, for Sarah, the algae on her farm have plenty of nutrients to grow as fast as the sun will let them.
"I'm pretty happy, we already have enough fuel to power all of our equipment for the next growing season and we have six more weeks to hopefully make enough for the Johnsons next door"
*welcome back to the present
This idea originally came about from my article on Agrivoltaics in farming, trying to imagine other uses for the agrivoltaic structure during the winter months when you aren't growing. Originally I was thinking that you would hang special algae growth bags, after a collection of random thoughts I cane to the concept above.
Some technical stuff
Growing algae is a balancing act of sufficient nutrients, sunlight, and temperature. The idea of having nested inflatable bags I believe could solve several of those. The outer tube would help to regulate the interior temperature as well as provide the structure necessary for the reflector elements to focus sunlight. For most algae the preferred temperature of growth is between 16 C and 30 C, there are species who can happily grow at higher or lower temperatures.
I intentionally didn't include an actual scaling value in the image because, well I'm just not qualified at the moment to have a firm value, that being said, almost every article I've read indicates that anything deeper than 3-4 inches for a thick algae growth is a waste as there isn't sufficient sunlight, so I would pretend that the center tube has only about 3 inches between the surface and the nutrient dispersal tube in the middle.
The $2/gallon value was inspired by a biofuel company's claim that their system could produce fuel at $1.27 gallon (assuming you are producing 8,000 gallons per year per hectare (1 hectare (10,000sq meters) = 2.47 acres))). I have no idea how the economics would work for a system trying to grow algae during the darkest parts of the year, but I wanted a plausible adjacent number.
The best-case scenario for these seasonal inflatable bioreactors is for people like Sarah. People who want to produce their fuel for super local consumption. If the plan is to export the biofuel hundreds of miles the environment would probably be better off having the fuel made in places where year-round production was possible. That being said I do think a part of our future will include things like algae being grown incredibly locally, it wouldn't be too crazy to imagine homes having bio-walls producing small quantities of biofuel year-round, so on those days where there hasn't been enough sun or wind to charge the batteries there is a back up energy source.
Further Reading
if you want an art project someone has a cool algae wall they made using recycled water bottles https://www.instructables.com/id/An-Algae-Bioreactor-from-Recycled-Water-Bottles/
https://www.sciencedirect.com/science/article/pii/B9780444595669000028
NASA's work with a company to develop floating algae farms https://www.nasa.gov/ames-partnerships/technology/technology-opportunity-algae-photobioreactor-using-floating-enclosures-with-semi-permeable
https://www.sciencedirect.com/science/article/pii/B9780444595669000028
NASA's work with a company to develop floating algae farms https://www.nasa.gov/ames-partnerships/technology/technology-opportunity-algae-photobioreactor-using-floating-enclosures-with-semi-permeable
As always questions and feedback are welcome
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