Introduction: Solar Thermally Pumped Hydroponic System

Picture of Solar Thermally Pumped Hydroponic System

This is a small scale test system for the idea of using temperature differentials to operate a ebb and flow hydroponic system.

The theory behind it is the idea gas law PV=mRT. That is an increase in temperature in the gas trapped in the reservoir leads to an increase in volume of the gas.

Step 1: Materials

A 2 liter bottle
a 1 liter bottle
aquarium hose and fitting
black paint

Step 2: The Coupler

Picture of The Coupler

The coupler is made by joining two bottle tops together face to face, if you heat the surface of each breifly with a lighter you can then super glue them together. Once the super glue dries drill a hole through the adjoining faces of the caps and glue in an aquarium tubing fitting, then add a length of tubing sufficient to reach the bottom of the 2 liter bottle.

Step 3: The Reservoir

Picture of The Reservoir

is made from the 2 liter bottle. Wrap the threads with tape and run a strip down one side, now spray the bottle with black paint to increase the amount of energy captured.

When dry remove the tape and fill half way with your nutrient mixture.

Step 4: The Pot

Picture of The Pot

is just a 1 liter water bottle with the bottom cut off and an overflow hole, to account for extraordinary rainfall, placed half way up the side.

Step 5: Assemble and Test

Picture of Assemble and Test

The coupler is screwed onto the reservoir bottle and the 1 liter bottle screwed on top of the coupler. Take the bottle outside and place in the sun, watch as the water is pumped up into the bottle as the reservoir is heated by the sun.

Although the original theory was based on the differential between day and night temperatures, observations showed that clouds passing in front of the sun was sufficient to cause a rapid change in the water level, providing a continual refreshing of the nutrient to the plant.

Step 6: Set It and Forget It

Picture of Set It and Forget It

Fill the "pots" with perlite and plant. In one I planted gota kola, another onion seeds and the third a basil cutting, place somewhere sunny and forget it until instructables has a bottle contest ;-).


cyodere made it! (author)2017-01-23

It is the bomb!

FrenchDavid50. (author)2016-07-07

Oh my gosh, this is GENIUS! I'm gonna do it, but using a wine bottle instead of a 2L bottle for the bottom. I hope it works...

hercyturkey made it! (author)2016-02-09

Awesome idea. I had to try it. Made some changes as well hope you can work with it and use it. I am in trial runs right now but hope to grow with this idea soon... also going to try and work on mini bottle DWC unit using "Kratzky "methods. "Think that's how it's spelled" correct me if im wrong. Now the one on the right is original idea except I added a top with holes punched in it to give it a greenhouse effect to sprout seedlings. The second is a test method to see how it works and how much water is moved. It is sealed unit (just experimenting) next will be using perlite or lava rocks in replacement of Styrofoam (on budget? It will work.) I used old seat cushion sterilized with boiling water before use

hercyturkey (author)hercyturkey2016-02-09

*left* not Right sorry my bad

bydnmytym (author)2015-05-06 is the deal -- I live in New Mexico and even now here in early May and even with the hose sitting mostly in the shade the water first coming through is hot enough to take a good hot shower. My understanding is that water and nutrients for hydroponics needs to be well under 70 degrees; leaving all that plastic in the sun will also lead to plastic properties leaching into the water and medium...and well, I gotta say it sounds a little bit Monsanto to me. I like the concept alot and it is cool from the perspective of a science project, but I just really wonder about actually growing food I want to eat...maybe flowers to keep the bad bugs away and attract the bees and butterflies -- but the heat factor is still a concern.

Yahwehselect (author)2015-01-17

Will this work with seed starts?

SixTwelve (author)2009-01-23

What a cool idea! I wonder, though, if you're having any blow-back from heating the nutrient solution? Black plastic can get pretty hot in the sun, at least in my neck of the woods. Now that you've done the proof of concept, it wouldn't take much to heat the air and shelter the fluid. Or am I being a ninny?

Nope, you're not. I responded to someone else that you could use a separate air chamber. I haven't done so, but there's no obvious reason it wouldn't work.

Would glass bottles be a good choice for the air-expansion-solar-collection-chamber? Such as 1.5 liter wine bottles?

rangua (author)2012-09-15

I've been thinking about the numbers involved. I haven't figured out how to solve the whole system at once, but just as an approximation i've worked out the following (criticism welcomed)

The gas law predicts
P*V/T = constant
at first we fill the conainter with a certain volume of water leaving V_0 volume of air at temperature T_0 and atmosferic pressure P_a.
At the peak temperature you wish your container is fully filled with a volume V_c of water, meaning that in the tank you have V_0+V_c volume of air, at temperature T, and pressure (P_a+rho*g*H) where H is the height from the water level in your container to the remaining water level in the tank.
P_a V_0/T_0 = (P_a +rho*g*H)*(V_0+V_c)/T
T/T_0 = [1+(rho*g*H/P_a)]*[1+(V_c/V_0)]
since 1 atm is about 10^5 pascals, and rho*g is about 10^4, your height is being multiplied by 0,1. say, one meter gives you a 1.1 factor already, which, for a T_0=290K=18°C is about a 30°C change! i think that's a lot, right?
Also, making your container bigger and keeping your water level low inside maximizes the efficiency for the volume part.

Please review/correct/expand my equations.

rangua (author)rangua2012-09-15

you could maximize the efficiency if you froze your tank first and then closed the caps. you could take the height waaay up :D
on the downside, youd have to freeze your nutrients everytime you refill.

DIY-Guy (author)rangua2013-02-04

Freezing water causes it to expand. It sounds counterproductive to your idea, but I have not tested it. I'm interested in learning the answer, what do you think?

Justin9235 (author)2012-12-05

Love this instructable, and considering doing my own setup on a big scale. How fast were you seeing water pump from one chamber to the next?

Orngrimm (author)2012-05-16

"place somewhere sunny and forget it until instructables has a bottle contest ;-)."
And why isnt this in the bottle contest then??? ;)

Nice idea of s imple principle. Well made and coo output.

komputernerd (author)2010-12-22

PET water bottles and 2-liters are made as one time use plastics. They will leach harmful chemicals into your nutrient solution and ultimately your plant, especially at higher temps, and in direct sunlight. Experiments with PET for hydroponics should be kept to ornamental plants only.

Nice concept however. Although, when I grow with hydroponics, my plants like my nutrients to be around 60F degrees. Any temperatures warmer and you can experience less nutrients uptake by the plants, as well as bad bacteria growth in nutrients.

macrumpton (author)komputernerd2011-12-31

The concept should work equally well with metal or glass or even ceramic containers.

fozzy13 (author)2011-12-04

This is such a cool concept, and I never thought about it before. I might make one just because of the awesome solar-pump concept. It seems like it could have other applications. Thanks for posting : )

autokymatic (author)2011-05-15

Aren't light and algae on the roots problematic? Was it suggested to make an opaque shield for the 1L top planter?

vampierwolf (author)2011-04-20

Do you think you could put this in an enclosed system... like a terrarium?

andycyca (author)2011-01-27

Brilliant idea. I've never actually tried hydroponics, so I'm going to ask a few questions that may be obvious:

1. I noticed you drilled an extra hole to prevent overflow (nice!) but I'm concerned about the seedlings getting enough water/nutrients. Did you "bury" the seeds? Did they need additional water as seedlings?

2. (I may have misread) Which hose diameter did you use? I think that is relevant to this proyect, as it affects how "easily" the solution will go up and how much will actually be feeding the "pot"

3. During the day, how much time did you have water in the "pot"? Is it constantly going up and down? Does the water level change quickly?

4. You said your reservoir didn't needed refills for months. Does anyone know whether storing the nutrient solution affects their concentracion? I mean, theoretically speaking, the compounds won't react between themselves, but they may precipitate...

seandogue (author)2010-11-01

very smart idea. thank you!

OUTATIME1290 (author)2009-02-11

would this work inside a building under a grow light that's on a timer for an extended period of the day?

downgrade (author)OUTATIME12902010-07-10

Check out some other plans, if you are willing to use electricity on the lighting you shouldn't be too worried about using an air or water pump that you would need to make this work indoors.

We come back to the problem of having a sufficient temperature change to cause the fluid to be pumped up, further down in the comments locating a remote reservoir by a heat register is suggested. But untested. The seeds were just sprinkled on top .

Sandisk1duo (author)2009-01-23

that's cool! is it better then planting straight into the ground and watering with nutrients?

It depends on where you live, if you're on a farm in Idaho, no. But if you're an apartment dweller or live in the south where we have severe problems with soil parasites, yes.

Actually it depends. On a farm you might be able to more efficiently grow a large crop load, but hydroponic grown plants usually have better nutrition as you control what goes into them. Granted someone planting in the soil could possibly control the nutrients to come up with a better plant, but it is unlikely, and nearly impossible on a large scale, but you can also mess up growing things with hydroponics... but then again this system, where as it works, isn't exactly precision based.

Haha I live in Idaho. It's rather easy to grow things here. Except our winters are cold and long as hell!

alright i'll have to try this some day..

Captainsimon12 (author)2010-01-23

Love the idea, and I'm considering making a larger-scale version at home. Can I suggest improvements?

1 - The base bottle probably softens up (however slightly) when heated. It would expand as the pressure inside builds. If a more rigid base container were used, one that (ideally) doesnt change at all, then the setup would probably be significantly more efficient.

2- If you were to somehow increase the surface area of the base container (providing a larger surface to face the sun) the effectiveness would also improve. I was thinking of soemthing along the lines of the fridge backing used in this Instructable: It is metal, and therefore absorbs the heat more effectively than a plastic bottle. Although.... it may cook the plants before they are fully grown.... Maybe if there were a resevoir between the base and the bottle with the plant in it that the water could cool in, but still maintain the pressure needed to keep the water moving....

Just a thought. This is a truly genius idea. Props.

downgrade (author)Captainsimon122010-07-10

To your first point, it makes me wonder if you could find some ducting that would wrap around the bottle nearly perfectly.. the metal would heat up pretty good and if it was tight against the bottle stop it from expanding and instead push the water up more efficiently... If you got the ducting like that which is intended for connecting to a drier or something it isn't a full cylinder so you could do something like put large zip ties around it to hold it to the bottle I would think.

woodstockbirdy (author)2010-03-17

 what is perlite?

Expanded volcanic rock used as a soil amendment, sold in garden centers.

simpkin (author)2009-04-25

Great instructable, I just happened to have some spare plastic bottles laying around and grabbed some "Soaker hose" from home depot came in about 50 feet for 8$. I did a slightly modified version using 2 Gatorade bottles one small as the growing container, a large one as a reservoir and painted them both glossy white. Then a 2 Ltr soda bottle painted flat black with an additional hose to the top of the reservoir to provide solar pressure. I was amazed at how responsive this setup was to sunlight and clouds. Going to play with it a little more and soon hope to have many setup growing veggies. depending on our soda and Gatorade intake...

Dharq (author)2009-04-21

I think if you paint the bottle white up to the water level in the lower bottle and the air filled section black, that should help keep the water cooler while still letting the air expand and contract as needed

natetetete (author)2009-04-20

No offense intended, I do like the idea of using the sun to power anything but this system has some major flaws The nutrient solution will be way to hot and stagnate, which pretty much counters any advantages of using hydroponics How will the roots get moisture at night? Also you should consider shielding the grow site from sunlight as well to help keep algae from growing.

None taken, now allow me to rebut. The temperature and oxygen content of the nutrient solution in the reservoir are, in my opinion, irrelevant, any heat is quickly lost by the fraction pumped into the growing pot, and indeed none of the plants showed any ill effects. Secondly, even if it were a concern the option of a remote air chamber is discussed further down the thread. The transpiration rate of plants at night is a small fraction of what it is during the day, there is sufficient moisture to tide the plant over in the pores of the perlite. Lastly, I didn't have any white paint ;-)

hootie233 (author)2009-04-06

wait wait wait, what are you guys saying should be done to fix this?

it doesn't need "fixing" we were discussing possible future improvements.

sorry, thats what I meant, i know that this set up would get the job done, I'm pretty excited about it either way.

agatornz (author)2009-03-28

now that is cool. i am in to passive systems or should i say those that dont rely on electricity - and i like the look of this one - so how did the test go - has it panned out?

Well actually, shortly after this was posted, a very prestigious organization contacted me and asked if I could let them use it for an exhibition the are doing, so it's in an entirely different part of the country right now. I'll post more about it when I can.

julesfl (author)2009-03-11

Do you completely cut the bottom of the bottle off? How long is the tube going into the reservoir? Waiting for mine to work. Live in Fl, so should work. Awesome concept!

kudoskun (author)2009-02-21

A half-full 2L bottle will get warm enough to push the nutrient solution into the 1L bottle? Are you expecting the rainfall to make up for the rest of the capacity of the 2L? What if you live in Az, where rainfall is rare. Perhaps then fill the 2L reservoir to capacity?

OUTATIME1290 (author)2009-02-11

AND how did you start the seeds? did you just plant them in the perlite and let it be?

Olyveoil (author)2009-01-23

This Instructable is totally cool and one that I'm definitely going to try. It combines two things that I really and gardening. Thanks for sharing.

matrix1984 (author)2009-01-23

How often does the resevoir need refilling?

I set those up 4 months ago and haven't changed it since, but generally monthly would be a good idea.

Droose (author)2009-01-22

Just a suggestion, but if you make the viewing strip even half as wide you'll increase the potential "energy capture" area by quite a bit. In this sort of system you want to try and maximize the amount of energy entering the system.

chezman1 (author)2009-01-22

looks interresting will 20/20/20 will work also instead of mircle grow

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