Challenge: Low Consumption Electric Rotation?

[MaximeMalou]

Dear Engineers,

I am designing a sun tracking system for pv panels. The idea is simple: you want the panels to be at 90 degrees to the sun's rays. Meaning you must track the sun from east to west as the day progresses.

The tracking system must perform 2 mechanical tasks:
-rotate from east to west everyday.
-tilt very slightly every couple of weeks to adjust for the seasons.


Here's the challenge:
What kind of off the shelf components would best be suited to perform these tasks given that you want to consume as little energy as possible (very important).
The tracking of the sun is not important here, but rather, what kinds of mechanisms could be used to perform the described movement.

First thoughts: The mechanism used in a rotating fan comes to mind.
For the tilting, i thought linear drive actuators could be fitting.


Looking forward to hearing what you can come up with!

 

[TheTick]

Stepper motors.

 

[MikeHalloran]

Even a small stepper, or clockwork, can work nicely, if you put the assembly on an "equatorial mount". Look it up.


Mike Halloran
Pembroke Pines, FL, USA

 

[tr1ntx]

You're reinventing the wheel. These systems exist. Sounds like schoolwork.

 

[MiketheEngineer]

They make some pretty cheap ones for telescope use -- Some hook to your PC - type in your Long & Lat and tell it what star to track and it locks and stays on track. Look at Edmunds Scientific.

 

[MaximeMalou]

I appreciate your inputs everyone!

The idea of stepper motors is intriguing. Will certainly do research on their applications.

Mike, the similarities between solar tracking systems and telescopes have come to mind before. I will look into their design for further inspiration.

tr1ntx, you are right to say that systems like these alreasy exist. However, they are not cost effective enough for residential owners to install. Knowing that tracking systems improve the efficiency of your solar panels by at least 30%, a simple low cost system could certainly be of interest.

Thank you all once again for your responses!

 

[asimpson]

If you really want to go cheap ditch automatic elevation adjustment. Manual setting every week or so shouldn't make much difference.

You need a structure strong enough to withstand wind. Perversely heaver might be better. mounted on a cheap lazy susan bearing to slew around and track sun.

http://www.google.ie/images?hl=en&s...san&gbv=2&aq=2&aqi=g10&aql=&oq=lazy+&gs_rfai=

Drive DC gear motor through a small friction wheel running on base. Assuming smooth surface available. Could be integrated in lazy susan arrangement.

 

[MiketheEngineer]

As I am a structural type (dumb about these things but always interested)- I have a question about the solar panel designs. Why not make them "rounded" in both directions so that while never at the optimum angle - they would "cover" most angles - most of the time - thereby providing a very consistent output with no fuss??

Hey - if they can fry people with concave hotel walls in Las Vegas - see news highlights this day - then we should be able to solve this.

 

[gadkinsj]

I've been intrigued by well designed bimetalic beams that can bend to the changes in weather and account for temperature changes between summer and winter. this is not exact and will vary form day to day but will get it pretty close.

Also take a look at acme jacks for cheap movement.

 

[MikeHalloran]

The problem with _not_ tracking is that if you are using a parabolic or similar concentrator, you are trying to focus the sun on a small target, and off-axis orientation causes the concentrated beam to miss the target entirely.

There are, however, cylindrical concentrators, which are curved in cross section only, and focus the sun on a long horizontal pipe instead of a point target. Because the focus is not perfect at non-normal orientation, they have to be less efficient than parabolic concentrators, but they have to be much cheaper to make, partly because of the simpler geometry and partly because they don't desperately need a tracking drive in either azimuth or elevation.



Mike Halloran
Pembroke Pines, FL, USA

 

[Compositepro]

Focused collectors must be pointed accurately to work at all. Flat plate collectors rarely use tracking because the increase in efficiency is not worth the added cost and complexity. Most residential application have limited real estate (i.e., roof area) You get the most energy by filling the roof with flat plates. Tracking collectors must stay out of each others shadows. Spacing between collectors will lose collection area during the time of maximum sun power.

 

[dgallup]

I have seen totally passive solar tracking systems for residential PV arrays. There are black tanks on either side of the system and some kind of liquid which pumps itself from the hot side to the cool side. Works remarkably well. I've seen the array move from the West stop where it was parked overnight to the East stop within 15 min of sunrise. The one I saw was a 4 panel system. It did not compensate for seasonal change in inclination. That is such a slow change the home owner could do a manual adjustment once a month, if it's even worth it. I don't know how much it would be affected by wind, probably would want to shelter it from the prevailing wind.

 

[sreid]

Since the title of the post was "Low Cosumption" [I assume that means minimal power], Permanent Magnet Stepper Motors have some magnetic detent with no current driving them at all. And they can be designed to have high detent holding torque. This means zero power consumption when not moving and for solar tracking the duty cycle for burst moves would be very small.