Solar Thermally Pumped Hydroponic System




Working my dream job in the Telecom industry, so chances are, i'll never have time to respond to ...

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.

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Step 1: Materials

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

Step 2: 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

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

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

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

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 ;-).

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75 Discussions


Question 10 months ago on Step 5

Hi, question, for two liter of a bottle, how much nutrition should, mean water level on this not painting spot? And how the hose should be exactly? Thanks.


3 years ago

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...


4 years ago on Introduction 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.


4 years ago

Will this work with seed starts?


10 years ago on Step 6

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?

2 replies
Tool Using AnimalSixTwelve

Reply 10 years ago on Step 6

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.


7 years ago on Introduction

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.

2 replies

Reply 7 years ago on Introduction

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.


Reply 6 years ago on Introduction

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?


6 years ago on Step 6

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?


7 years ago on Introduction

"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.


8 years ago on Introduction

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.

1 reply

7 years ago on Introduction

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 : )


8 years ago on Step 6

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


8 years ago on Step 6

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


8 years ago on Introduction

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...


10 years ago on Introduction

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