Single axis tracker idea

[madlabs]

I bet this has been thought of before, but I don't see anyone doing it, so maybe it's a dumb idea...

I want to make a single axis tracker for PV panels. My idea is this:

Set up the panles so that they move like a louvered window shade. Put a container of water on either end, say a 50 gal drum. With a small pump, move water from one to the other. As the wieght changes, the panels move to face the sun. Seems simple and not too much in the way of moving parts.

Thinking about it, I could use a conterwieght on one end, and have the two water containers at the other end. That would make only one hanging drum. Seems like it should be good in high winds too, I can just use more or less water to obtain the correct position. At the end of the day, let water siphon back to the container on the ground.

Too silly?

Jonathan

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[scottsAI]

Yes.

Pump is no less complex then few gears and motor.

Both systems need controller etc.

Freezing water. Not clear how it would tilt things for you.

Controller: http://www.redrok.com/electron.htm

You can get lost for days there.

Have fun,

Scott.

[jimovonz]

Hi Jonathan, No not too silly at all. I had great success with a very similar setup about 10 years ago. I mounted 2x60w panels on a very simple single axis pivot. At the end of the central axle I fixed a bicycle wheel rim so that rotating the wheel rotated the panels. Using a rope over the wheel in pulley fashion, I suspended a bucket and fixed the other end to a spring (from memory it was a 20l bucket and a spring from a 'baby jumper' - the type that gets suspended in a doorway). Using a simple irrigation timer I set up a hose to fill the bucket during daylight hours using a small valve to regulate the amount of water going into the bucket. From the bottom of the bucket I attached another hose with also with a valve. This bottom hose is set to flow a small amount of water constantly. The flow into the bucket is set to be greater than the outflow so that the bucket slowly fills during the day. The increased weight of the bucket causes the panels to turn against the restraining force of the spring. At the end of the day the irrigation timer switches off and the water in the bucket slowly flows out the bottom hose returning the panels to their morning position. Its a bit fiddly adjusting the inflow and outflow to the correct points but worked well once setup. Seasonal adjustments require changing the timer to adjust for the changing daylight, altering the inflow to account for the length of the daylight and changing the inclination of the pivot. I only did this a couple of times through the year. The inclination of the pulley wheel requires that you use a roller of some sort either side of the wheel to change the plane of movement to vertical. You also need multiple wraps of the rope around the pulley to securely fix the panel position relative to the bucket/spring.

I initially used a smaller bucket and spring but found that the setup was prone to 'wobbling' in the wind. More weight/spring force helps avoid this.

This is not exactly a 'precision' tracker but your not talking about a concentrating heliostat with a well defined focal point where alignment errors are magnified many times causing significant losses. I'm pretty confident that this setup would give you over 90% of the benefit of the typical tracking systems discussed here - at a fraction of the cost.

I'm sure you could quite easily adapt this method to your 'venetian blind' idea.

I cannot claim this as my own idea, but I cannot remember the original source. I vaguely remember an article in Home Power magazine?!.....

[madlabs]

Scott,

Just playing devils advocate here, but it does seem as if gears and a motor are a little more complex than a bilge pump dropped in a conatiner of water. No need to waterproof the motor and less startup surge amps. As well, my metal working skills are limited, so it seems easier that way. I don'y have too much freeze worries, the hoses might freeze occasionally but never the buckets. I'm in Northern California out on the Mendocino Coast.

[madlabs]

Jim,

Thanks for the detailed post on how you made a smilar system. I'll make a simple controller with a couple of phototransistors to set the position, I have all the stuff laying around for that. I think I'll use a weight instead of a spring. As the spring get stretched it seems like it would take more water to pull it further open.

I'm glad to hear that someone has had success with this idea. Do you still use the system, and if not, why not?

Jonathan

[jimovonz]

As long as you don't reach the elastic limit of the spring, then there is a linear relationship between the force applied to the spring and the amount of deflection.

10Kg of water in the bucket will give you 10 times the movement of 1Kg

See: http://en.wikipedia.org/wiki/Hooke's_law

[spinningmagnets]

http://www.solar-trackers.com/solar-concentrators.asp

I don't have any PV yet, but this is the single axis tracker I wish to copy. I'd configure it so it can be manually spun face-down, for an impending hail-storm.

I might try the V-mirrors, but they are easily removed if they prove to be undesireable. I have an idea for a similar water draining device (very goofy, yours is more impressive).

If you wanted a more stable spring tension throughout its tracking range, the top east edge of the panel could have a cable attached that was directed straight down to a gound-anchored pulley. Then the cable would run along the ground with a cheap and long coil spring that is held at 45% tension.

In your original layout, a short vertical spring might cycle between 20% and 80% tension, but a very long spring might cycle between 45% and 55% for the given stroke of your tracker?

Best of luck, and have fun...

[jimovonz]

The system was in use for about 18 months. It was thrown together out of scrap and didn't look too pretty. I was using the setup to power lights in a shed. Once I got the power sorted, the missus wanted it outta her sight Our water supply at the time was gravity feed from a spring. I had no problems using these volumes and returning it to the ground clean. If you are in a similar situation perhaps you could do without a pump and simply use solenoid valves? If you are not using some sort of progressive resistance then you will have to balance weights on either side which will be rather precarious... In my system movement from the wind etc was possible but there was always a reasonable force to restore the assembly back to the desired position. If I understand what your proposing, if you have 100Kg of water on one side then 10Kg on the other then it won't do a thing. 99.9Kg of water on one side and 100Kg on the other still wont do anything though its getting rather susceptible to any external forces. 100.1Kg on one one side with 100Kg on the other will cause the system to move to the full extent on the other side.

If you want to actively track the sun then I think you will need bi-directional control - were you planning two pumps?

[scottsAI]

No more metal working is necessary than the spring and buckets.

Attach a larger wheel to tracker shaft, tracker like spinningmagnets has shown below.

Motor shaft on wheel, no gears, targeting 30 to 100:1 ratio.

Controller does its thing. Simple

Could also be done with belt, gears, wood, etc. whatever is on hand or easy for you to work.

Have fun,

Scott.