Picture of Solar Thermally Pumped Hydroponic System
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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
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bydnmytym3 months ago

OK...here 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.

Yahwehselect7 months ago
Will this work with seed starts?
SixTwelve6 years ago
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?
Tool Using Animal (author)  SixTwelve6 years ago
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?
rangua2 years ago
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 rangua2 years ago
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 rangua2 years ago
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?
Justin92352 years ago
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?
Orngrimm3 years ago
"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.
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.
The concept should work equally well with metal or glass or even ceramic containers.
fozzy133 years ago
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 : )
autokymatic4 years ago
Aren't light and algae on the roots problematic? Was it suggested to make an opaque shield for the 1L top planter?
vampierwolf4 years ago
Do you think you could put this in an enclosed system... like a terrarium?
andycyca4 years ago
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...
seandogue4 years ago
very smart idea. thank you!
would this work inside a building under a grow light that's on a timer for an extended period of the day?
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.
Tool Using Animal (author)  OUTATIME12906 years ago
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 .
Sandisk1duo6 years ago
that's cool! is it better then planting straight into the ground and watering with nutrients?
Tool Using Animal (author)  Sandisk1duo6 years ago
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..
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: http://www.instructables.com/id/Solar-Thermal-Water-Heater-For-Less-Than-Five-Doll/. 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.
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.
 what is perlite?
Expanded volcanic rock used as a soil amendment, sold in garden centers.
simpkin6 years ago
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...
Dharq6 years ago
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
NaTeB16 years ago
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.
Tool Using Animal (author)  NaTeB16 years ago
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 ;-)
hootie2336 years ago
wait wait wait, what are you guys saying should be done to fix this?
Tool Using Animal (author)  hootie2336 years ago
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.
agatornz6 years ago
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?
Tool Using Animal (author)  agatornz6 years ago
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.
julesfl6 years ago
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!
kudoskun6 years ago
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?
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