Why do solar trackers track sunlight?

dmillerdmiller Solar Expert Posts: 68 ✭✭✭✭
The exact position of the sun is know at any future date and time. So why do solar trackers bother with an external reference? Is it a calibration issue?

It seems to me a closed system would have fewer real world problems. It seems to me a hard reference point could be used each night to recalibrate the system. But apparently an external sensing system is better.

Comments

  • BB.BB. Super Moderators, Administrators Posts: 29,720 admin
    Re: Why do solar trackers track sunlight?

    From an engineering point of view (I have never designed a tracker--just my two cents):
    • Simple electronics (or even fluid filled balance type systems) for sun trackers. A time based tracker will require a computer/memory/algorithms for user setup and tracking. Over time and and with higher volumes, a time based tracker could probably be made pretty cheaply.
    • Need some sort of interface (buttons/leds/computer interface/display) to setup and monitor a computer based timed tracker. Much of that stuff is getting cheap these days--but just adds more complexity to the problem.
    • For standard PV Cells, you only need to track within ~10 degree accuracy--so high precision is not necessary.
    • Feedback loop--trackers monitor the suns position, so there is no other feedback circuitry (step counting, position feedback hardware) to deign/build/pay for... Position feedback via electronics can actually be a problem--power outage, error over time, electrical interference, etc.--can mean that the tracker is 30 degrees off from the sun and not even know it. A simple way to get "back on track" is to run the actuators back to a hard mechanical stop every night--then the electronics "know" where they are the start of every morning.
    • Similar issues with time--Today we have GPS time signals and even watches that can receive the low frequency time signals from Colorado... GPS time is probably not cheap (yet). National Time Broadcasts are only available for a few "large" countries--not available worldwide/universally.
    • With a non-sun tracking system, you have to "tell the electronics" where the installation is and zero it to a south/reference point.
    • You might be able to address some of the issues with a hybrid tracker... Clock to move the array, sun tracker to adjust for large errors/detect tracking failure...
    Anyway, that is my guess at the issues.

    Which is better--Probably a well designed unit of either type will work just fine.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Why do solar trackers track sunlight?

    Also time slows down the closer you get to the center of a gravity well, so a unit perfectly calibrated for sea level would be a bit off after a few centuries up on a mountain. :D
  • HuckMeatHuckMeat Registered Users Posts: 24
    Re: Why do solar trackers track sunlight?

    Not all track light. Some trackers do it from time/orbital calculations.

    (i.e. most utility grade trackers, and other residential trackers like the sunarxx)
  • dmillerdmiller Solar Expert Posts: 68 ✭✭✭✭
    Re: Why do solar trackers track sunlight?

    I find the simplest trackers the most interesting. Maybe one axis time based that is tilted manually throughout the year. Any DIY plans for one axis trackers? There have to be some great "science fair" ideas.
    Certainly the engineering challenging in the 2 axis units are costs and reliability.
  • rplarryrplarry Solar Expert Posts: 203 ✭✭✭✭✭
    Re: Why do solar trackers track sunlight?

    I built my tracker and used Redrock energies sensor. It has worked for about 5 years now with out a hitch. I can see where it could be done with a timing circuit but on cloudy days you may not be pointing at the brightest part of the sky using that method. With a light sensor you are always pointed at the brightest spot. Probably doesn't make that much difference.
    No matter, yours would be a fun project.
    Larry

    PS Check this site for tracker ideas: http://www.redrok.com/electron.htm#led3x
  • mike95490mike95490 Solar Expert Posts: 8,470 ✭✭✭✭✭
    Re: Why do solar trackers track sunlight?

    Cannot resist any longer

    > Why do solar trackers track sunlight?

    Because there is little power to be had in moonlight or starlight.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

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