Solar-powered Algae Bioreactor

Creating a solar-powered, no running cost, algae bioreactor.

Step 1: Finished Bioreactor

I apologize for not getting any pictures during construction of my solar-powered algae bioreactor, but I only decided to make an instructable out of it after the fact. There are many diy's about making biodiesel out of oil, and algae has been discussed far and wide as a great source of vegetable oil for conversion. However, I've only seen a few homebrew solutions for actually GROWING the algae. There's a great one here on instructables, but it uses CO2 bottles to provide the algae with the carbon dioxide which they need to grow. As a proof of concept that's fine, but I don't think it makes any sense in the long run -- bottled CO2 is probably more expensive both cash-wise and environmentally than the algae grown from it. There's CO2 available in the air, but only a flat, shallow pool of water has adequate surface area to absorb enough CO2 for algae growth. Here's my solution: a solar-powered small aquarium air pump, which aerates the water inside a five-gallon water bottle. Notice that the water is cloudy after only a couple of days; that's the algae starting to grow. If you look closely you can clearly see the air bubbles which prove that the air pump is still running; the sun has set on the system in this early-evening shot, but the rechargeable batteries are keeping the pump running.

Step 2:

I bought the battery-powered aquarium air pump (complete with tube and air stone) on eBay; IIRC it cost around $8 with free shipping. I constructed the solar panel from five 3" x 3" solar cells (handcut from 3" x 6" cells as you can probably see in the main picture). This gives an open-cell voltage of 2.75V, and a short-circuit current of 1.75A, according to the solar cell specs, and verified by measurement after construction. I didn't get fancy with the construction; I just cut two pieces of plexiglass about 12" x 9" from some scraps I had from another project, glued the cells down with hot glue, then glued the pieces of plastic together with more hot glue. I glued the pump to the back of the panel with some five-minute epoxy I had lying around, and drilled holes for a wire to hang the panel from the neck of the bottle. Cost for materials:

$8 air pump
~$7 solar cells (from a pack of 50 I bought on eBay)
$16 NiMH D-cell batteries (2 @ $8 each)

Stuff I had lying around that other people might have to pay for:

hot glue gun & hot glue
5-minute epoxy
2 pieces 1/8" plexiglass 9" x 12"
electrical wire to attach solar panel to pump
picture-hanging wire
Schottky diode (see next step)
5-gallon water bottle

Step 3:

Inside the body of the air pump, you can see the two NiMH D-cell batteries which charge off of the solar panel and keep the pump operating after the sun goes down. The pump draws 0.55A (measured), so the ~1.75A supplied by the solar panel in direct sun can charge the batteries fast enough to run for twice a many dark hours as sun hours (for example, 8 hours of sun will keep the pump running on batteries for 16 hours). The batteries are rated at 9.5 Amp-hours each, so between the two of them they'll keep the pump running for almost forty hours without recharging. Longer dark periods (like a stretch of bad weather) will cause the pump to stop, but a lack of sun also means the algae aren't growing much if at all anyhow. I drilled a small hole in the side of the pump to bring in the wires from the solar panel (which reminds me I need to get the hole caulked up now that it's wired), and you can also see the Schottky diode I added to keep the solar cells from discharging the batteries when there's no sun. And that's all there is to it!

Step 4: Project Update

Unfortunately, before I was ever able to see any significant algae growth, my cheap battery-powered air pump failed. I guess these things are primarily intended to be used for a few hours when you're moving your aquarium, not to run continuously for weeks/months on end. Either that, or my solar charging circuit (consisting of one Schottky diode) wasn't up to the task. I was hoping that the NiMH batteries would limit the overvoltage experienced by the pump motor, but it may not have worked. When the sun is shining fully on the solar panel, it puts out close to two amps, and the batteries and the motor may not be sufficient load to keep the voltage under control, especially after the batteries are fully charged. I was hoping an extremely minimal charging circuit would be enough -- no regulators or anything -- but I guess all I can say at this point is 'lesson learned'. I'm an EE so a fully-designed system is well within my reach; I was just hoping that I wouldn't have to spend that much money, time and effort on a rigorously complete solution.

In any event, the air pump quit just a few days after I put the unit out in the back yard. There wasn't enough time to find the optimum amount of sun exposure (for the algae, not the solar cells -- the solar cells want as much exposure as they can get!), nutrients, or anything else.

Someday I hope to get back to this project, but my time these days is totally occupied by other, hopefully paying, projects. Maybe they'll show up on instructables once I get them working!



    • Remix Contest

      Remix Contest
    • Faux-Real Contest

      Faux-Real Contest
    • Build a Tool Contest

      Build a Tool Contest

    43 Discussions


    2 years ago

    Just a thought, though it may not be very economical, couldn't you provide a carbon source for photosynthesis by adding NaHCO3? (The chemical equation seems to balance out correctly...)


    2 years ago

    For your algae to receive the proper light you could 3d print a honeycomb type of plate then add a strand of fiber-optic cable to each one.

    I think he's referring to having a separate container w/ some sugar and yeast in it, with a tube running from that container into the algae bottle. The evolved CO2 would pressurize that container and maybe not even need a pump to bubble through the algae bottle. It's an interesting thought, but I would have to keep the fermentation chamber supplied w/ sugar and get rid of the alky somehow. Though the biodiesel conversion does require alcohol.....maybe I could build a solar still and buy sugar to make my own alcohol instead of buying the alcohol? Refined sugar is very cheap.

    I see. So if one brewed beer that could provide a supplemental source of CO2, as could the fermentation output from the tanks of a registered small fuel producer.


    Reply 3 years ago

    yes and if you brew in your green house your plants will also thank you

    actually again depending on the algea. there are type(s) that thrive in the the production vats. just ask coors an budwieser abut it.


    6 years ago on Introduction

    ok just read the entire thread ....some good ideas...some bad.... firstly why bother with solar ???? a regular sized aquirium pump consumes 25 watts ... it will have to run for 40 hours to cost you a single unit of electricity (1kw) ...not worth the polava ... secondly for lighting use LEDS .... white,red and blue ... also next to no cost on your bill !!! .... as for CO2 .... have two ponds adjacent to each other ..... 1 for algae that emitt o2 ... the other fish .. (algae eaters) ..that emitt co2 ... feed the fish algae biomass waste ... have an air pump running in each .... closed eco system of sorts ... was thinking of setting up with talipia ...good fish to eat! using a windmill to stir up water on windy days...just a thought


    7 years ago on Introduction

    Does anybody know where I can supply algae starter culture to make biodiesel in England or in Europe? As I understood the best strain is either diesilna or scenedesmus, and dieselina is difficult to grow. Is that right? Thanks


    Reply 8 years ago on Step 4

    I didn't get any, sorry to say. I may try again someday but I doubt it....I've been working with silicon solar cells lately and having a lot of fun. I think algae may have more promise long-term -- it consumes carbon dioxide as it creates fuel -- but the solar cells are much more direct in creating usable power. It's a lot easier to work with on a smaller scale; there's no need to process it, convert to a usable fuel and THEN use it to make power.


    9 years ago on Step 1

    You're correct in thinking that bottled CO2 is a waste, but it works for many companies because the algae grown can be worth $$$$/kg. In Germany, Factories with operations that produce CO2 use bioreactors to mitigate their pollution and sell off the algae as product. Just cool the CO2 exhaust before pumping it into the algae-they are sensitive to temperature. That said, your pH needs to be monitored closely as you inject CO2. The CO2 dissolved in the water will create a carbonic acid, lowering your pH and killing your algae. Another thing to note is that algae needs photosynthesis to grow. Optimum depth of solution should be 6-10cm. You can grow in a water bottle, but not to high density. Before a inoculating a large water bottle, the algae needs to be grown to optimum density in smaller containers. Gradually algae bioreactors move up in size, as the amount of inoculum needs to be 1/4 the volume of your container, to allow for further growth. If you simply throw algae in with nutrients in a large container, many more things can grow with the algae, and very possibly overtake it. Healthy algal growth is seen as a pleasant green, no foaming or floating debris. Get a simple microscope, and you can see the ratio of algae to predators. Chlorine in small doses can leave an environment clean of predators, and free for algae to grow well. It can hurt algae, but in higher doses. Nitrates and phosphates are your nutrients needed for algae, they're cheap and easy, and every algae likes slightly different ratios; don't use any animal droppings, please. Hope this helps, and I like your solar powered pump :)

    7 replies

    "don't use any animal droppings, please."

    Why do you say this? Algae grow perfectly in lakes, ponds, streams and other sources where the primary nutrients come from aquatic life waste and soil.

    I already explained why. Any number of contaminating factors may be present in animal droppings. Instead of helping the algae grow, you can just begin a cesspool. If nothing else, because it's gross. Your point about aquatic life waste is correct, of course, as long as the mitigation of waste by corresponding aquatic plants and fish are monitored. Perhaps I could rephrase that for "land animal droppings," lol. The irony of the algae farm is that, though algae appears to grow easily without any assistance or problems naturally, there's actually much more than meets the eyes. What you see in a lake could be several different species of algae trying to outgrow eachother. While the waters may be densely green, not one of the species would be of adequate density to be of any use to anyone. Creating a healthy algae "bloom" for any farm application, requires a deal of work including monitoring the introduction of specific levels of sterile nutrients and measuring the amount of sunlight received by each algae cell, or PAR should be kept to 400-700nm (PAR, PhAR: photosynthetical active radiation), pH Values and temperatures must be monitored constantly and kept to specs for the culture grown.
    Here's what I mean: See the two pictures? The large algae production is a aerial shot of an algae farm in Taiwan. It has 43 biologists and an entire crew underneath them to monitor the health of the 10 cm depth, 76 acre open system. They bleed in chlorine and CO2 at different points, trying to keep the numbers of predators at bay. They closely monitor the amounts of everything added to the system, and at no point would they allow the addition of any more uncontrolled anomalies. The size must be immense order to produce enough algae to be worth the cost of the farm operation. The other photo is a 10 liter high density algae bioreactor in our lab. It receives the ideal light 24/7 and grows the same amount of algae as a 1 acre open pond. The algae is free of contaminates, and the pH, Temperature, density, and nutrient levels are monitored by a small computer.
    As for obtaining a particular strain, and its specific nutrients and growth conditions, I recommend anyone to visit these two sites:

    Controlled High Density Bioreactor.jpgTaiwan BioPlant.jpg

    How is the light provided to your bioreactor? If it's generated electrically, how does that effect the power balance? i.e. what fraction of the power represented in the oil harvested get offset by the need to create the illumination? Of course it would be a moot point if there was a solar collection system to power it....a couple of solar panels could power the unit for harvest after harvest. Even just some reflectors and a variable shutter would be able to use sunlight when it's available.

    Of course I have no chance of getting very close to ideal growth conditions in my silly homebaked experiment. Then again, maybe I don't need to. A commercial operation needs to be highly optimized but my backyard tank doesn't necessarily need to be. It's possible I could grow some algae, make a little bit of biodiesel, fire up a generator once in a while and generate some free power to help offset my electrical bill.

    I think the long pole in your tent isn't going to be growing the algae, its going to be converting it to biodiesel. The algal conversion isn't the same as that used for vegetable fats and involves much more complexity.

    If you're ultimate goal is simply to produce biodiesel you might be better to to plant a small plot of rapeseed, corn or other high content oil bearing plants which can be readily converted.

    Also consider waste oil from local eateries. In most locations they have to pay to have their grease hauled away. If you're prepared to pick it up weekly and give them $50 a month for the privilege you can probably have a virtually unlimited supply of feedstock.

    I've already done the conversion, several times. it's a pretty simple reaction and not difficult to learn. Even the titration process is reasonably straightforward.

    From what I've read, I don't believe there is any difference in oil from algae or any plant source as far as the conversion process is concerned. Extraction is a bit more difficult with algae but from what I've read there are relatively simple and cheap solvent processes (such as hexane extraction) that can be used.

    As far as restaurant waste oil is concerned, been there done that. It's yucky, smelly, nasty stuff, the storage cans are very heavy and invariably filthy, it requires a ton of filtering and processing to get ready for the conversion, and it's not worth the time and energy. Worst of all it's boring.

    Rape does grow pretty well in my area (San Diego) but it's nowhere near as space efficient as algae. I could devote a pretty large flower bed to it and not harvest enough oil to be worth talking about. But my real objection is again that it's boring. I know how to grow weeds. I just want to know if it's possible to easily grow algae in my back yard, and I have no intention of actually using it -- I don't own a diesel generator and have no intention of buying one. People like GodOfGreen are busy making commercial grade hardware, I just want to know if there's a cheap, easy, fairly effective version for home use. If my solar powered rig ever works, I could say it's CONCEIVABLE that someday I could grow my own fuel oil in my backyard. I'll never do it, but I could.

    I'm very interested in what progress you make in this area. I think the process for algae is different but would be fascinated to hear about practical application. Don't you folks have an aquarium down there? I suspect if you were to contact the aquarium they have algae in abundance which they are trying desperately to get rid of....

    I just wanted to show the two extremes. I didn't get into the full process, because that would take up tens of pages, even abridged. This small bioreactor is the ultra high end, and isn't commercially viable unless it's an 8000 Liter model using the CO2 emissions from a production plant. It does make perfect sen$e when the algae grown is used for coloring, EFAs, DHA, cosmetic products, and food additive. BioDiesel has not been cost effective, save for one project in AZ. That one broke the bottleneck on biodiesel manufacturing at a natural gas power plant! It was funded entirely as a Dept of Energy , NETL program. But, the DOE called it quits last March, after the local utility went bankrupt and fired all it's chief staff. There's another mysterious crate in the Indiana Jones locker...
    Anyway, you can grow algae for a variety of home uses, very cost effectively.
    Maybe I should write an instructable? In a nutshell, research the species you want to use. Know its ideal pH, temperature, and nutrient needs. Depending on its purpose, you can grow the algae under different conditions. Using a basic kiddie pool and some pool supplies (like a pH and Temperature reader, and maybe an aquarium or fountain pump for agitation-this is why your solar pump is neat), you can get by easily. To harvest, you can scoop out the algae with a net, as long as you are not growing microalgae. If you are going to grow microalgae, or prefer a complete harvest, stop the pump for an hour, and let the algae settle to the bottom. Then, scoop the algae to the drain plug and spread the "soup" onto cookie sheets. let them dry in the sun. It's fully dry when you see the algae as flakes. Scrape it off and grind it up into a powder. Next, you may add it to a chemistry set to get its extract or take it to the biodeisel refinement (a note on this, if going to biodiesel, it will initially be a crude black green oil-under analysis only a portion of the carbon chains will be usable biodiesel, and they'll need to be separated. The rest can be used for lubricant or cooking oils). You can just use the powder or soup for any number of applications- fertilizer, skin moisturizer, food coloring, healthy food, (it all depends on the method and species grown). To minimize predators and bacteria, you may add Cl at 10PPM (every so often), and even throw a greenhouse liner over the top(open it every now and then to prevent O2 poisoning). Carbon can come from CO2 injection or the nutrients (an ingredient like baking soda). BTW, Carbon from waste requires larger farms, and applications that never mind a little poop in the sauce.
    The main thing is the research on the strain you want to grow- there are 30,000 known species, and 10,000 of them have been studied for applications :)
    There are also any number of ways to grow and harvest Algae. But this way I just described is the easiest and most sterile backyard project off the top of my head.