Science Buddies: "Ask an Expert"

Hello.
This is, in a respect, a continuation of the question 'Ideas for google science fair'.
My project for google science fair involves a farm growing over the sea. This is like a final confirmatory presentation before I start the prototype. I wish to inquire about:
1. The feasibility of this idea (are there any pitfalls?)
2. How much does it rain (approximately) over the sea?
2. Is the plan of my prototype the correct type of experiment? If not, what is?
The (cylindrical) farm floats close to the shore, over the deeper end of the continental slope, to avoid breaking waves and mainland pests, yet stay accessible to manpower.
This explanation is based on the attached diagram.
1. plants grow in soil on top of floating structure of an impermeable material like high density plastic. The structure keeps the farm about five meters above the sea level so as to avoid waves, the average height of which about are 2m.
The plants receive water from:
-rain
-drip irrigation from storage tank

2. The top of this structure is sloped to the centre , which has a hole, to act like a drain. Excess water is drained from here and goes to the storage tank. Due to solar energy, evaporation occurs from the sea surface. Water condenses on the underside of the surface currently being discussed. Due to gravity, It gets pulled down to the pipe and reaches the tank.

3.The sea surface is heated by direct sunlight and sunlight reflected from reflectors. It regularly feeds the tank.

4.The reflectors can be adjusted (with the help f motors?) to reflect maximum sunlight to the required area and follow the movement of the sun.
They also serve as a catchment area for rainwater. When it rains, they are partially erected. The collected water, through pipes, joins the storage tank.
They also shield crops from high winds.

5.The storage tank apart from storing water contributes in flotation. There will be additional floats for the farm, but fresh water, less dense than salty water, should contribute, however minutely, in flotation.

6.The water from the tank is pumped up to irrigate the plants. Drip irrigation can be used at is a very water - efficient technique.

Prototype:
1.A large plastic bottle is cut from the top. It is filled partially with water (to keep it from capsizing). (basic structure)
2. A plastic wrap is put across its mouth and has a depression in the centre has a hole (this is the top surface)
3. A smaller bottle is placed in it (storage tank)
4. This setup is placed in a big, shallow pan/vessel filled with salty water.
5. Cotton is kept on the top. Sprouts are grown here.
6. Sprouts are watered. Amount of water given is measured and compared with the amount of water got when a container of the same area filled with water is heated with a solar cooker. The lid is covered in cotton which is weighed before and after to see how much of the water requirements can be satisfied by this method

Experiments of similar nature I've already done indicated that 30% of water is covered by this process.

I have around 15 days left in which to do the experiments, and post the results.
Thanks for the previous answers as well as in advance for the answers to come.

I think you have a very interesting and creative idea. Naturally you are a long way from a detailed feasibility study; your project is in the exploratory phase. In my view the most important thing for you to do right now is get your actual experiment going, since growing plants takes time, and you may need more than one try to get your model project going well enough to make a good presentation.

You had three specific questions:

1. The feasibility of this idea (are there any pitfalls?)

There are a huge number of pitfalls. That is to be expected at this very early phase of development of your idea. A partial list of these pitfalls would include:

--The height of the farm platform needs to be roughly twice the width of the cylinder in order to make room for the mirrors and the incoming/outgoing rays of sunlight — just as you have drawn your system. In order to make efficient farming possible it may be necessary for this width to be fairly large, in excess of 50 meters. Supporting the great weight of the growing platform > 100 m above the sea might be very difficult.
--The farming platforms might be quite vulnerable to the large waves, high winds, and sea level “surge” that will occur when a typhoon strikes.
--The cost per hectare of the growing platform may be uneconomical compared to the cost of doubling the productivity of the same area of ordinary land-based farms.
--The platforms might have serious adverse effects on natural marine life below the platforms if the platforms extend over a large area of sea.
--Wind speeds under typical conditions might be much higher than for conventional farms because wind velocity increases with height above the surface and with the extent of the unrestricted path for the winds, both of which will be much greater than for conventional farms. Continuous high winds in turn may be bad for plant pollination and, for taller crops, normal plant growth. (OTOH you could exploit the winds by generating power using wind mills or wind turbines,)

This is a daunting list. But bear in mind the words of the great inventor Thomas Edison:

“I would construct a theory and work on its lines until I found it was untenable. Then it would be discarded at once and another theory evolved. This was the only possible way for me to work out the problem. ... I speak without exaggeration when I say that I have constructed 3,000 different theories in connection with the electric light, each one of them reasonable and apparently likely to be true. Yet only in two cases did my experiments prove the truth of my theory.”

2. How much does it rain (approximately) over the sea?

As close to the shores as you propose I would guess about the same, but I am not an atmospheric physicist nor a meteorologist.

2. Is the plan of my prototype the correct type of experiment? If not, what is?

I think it is reasonable, and, besides, you absolutely need to get going ASAP. If even better models occur to you, then you can add them to a list in a “future research” section of your report.

Thanks a lot. That list makes the project seem much more serious and real.
I just really didn't understand the point about the height - width ratio.
Here is my (partial) solution.
Will it work?
There is a ring of highly saline tolerant mangroves around the farm grown by a similar method (on a floating platform), except their roots suck water directly from the sea.
They act as wind breakers, and transpire water to make the atmosphere even more humid, reducing transpiration of the farm. They also act as the first line of defence from nature's elements (the second is the reflectors).
Windmills source electricity for the pumps and reflector - controlling motors.

I can't think much for the economic factor or marine life, practically,
The only advantage the floating farm has economically is that pesticides may not be as required and no irrigation expenditure, Which is far outweighed by the installation prices of the farm.
But then again, this is the first time such a concept has been introduced. Someone better qualified than me would probably refine the model before it is actually made practical.
I started the experiment. Evaporation is much lesser than I had anticipated.