How often tracker should act

Hello everyone.

I have one question about the tracker action frequency. In other word, how often the tracker should be moved to next position? Some tracker manufacture said their product precision can reach 1°, so for azimuth angle, the tracker act one time every 4 minutes. What I wonder is whether it is necessary for flat plate PV, you know, too frequent action will do much damage to mechanical device. Who can tell me the relation between azimuth angle difference and PV power output?

Thank you!

Comments

  • mike95490mike95490 Solar Expert Posts: 8,569 ✭✭✭✭✭
    Re: How often tracker should act
    rgs315 wrote: »
    Who can tell me the relation between azimuth angle difference and PV power output?

    Not me ! By looking at my PV''s power curve, a tracker update every 20 minutes, should be pretty efficient. That's about what 95% - 100% of peak takes to wax and wane. More often does not gain much, less often will see losses.

    That's my opinion.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • BB.BB. Super Moderators, Administrators Posts: 29,980 admin
    Re: How often tracker should act

    If your tracker is off by 10 degrees:

    cos 10 deg = 0.9848 (about 2.5% loss due to 10 degree error).

    360 degrees / 24 hours = 15 degrees per hour earth's rotation...

    60 min / 1 hour * 10deg err / 15 degree per hour = 40 minutes of non-tracking would give ~2.5% loss of power...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,965 ✭✭✭✭✭
    Re: How often tracker should act

    What time of year are you talking about? It makes a huge difference at the solstices? At my latitude near Yosemite it is 242 degrees in June and 117 in December. It needs to respond fast enough so that if there is a clearing of clouds for 15 minutes you can capture the energy. It needs not to get fooled! About 3 minutes in winter is what I see on a clearing where the sun intensifies.

    If you are offgrid tracking the sun is the key to getting charged in bad weather. If you are offgrid in the Southwest US or places in the world like Southwest it is the key to not having to run a generator. That is my humble opinion!

    You can of course try this with a solar panel into an ammeter and "be the tracker"
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • westbranchwestbranch Solar Expert Posts: 5,180 ✭✭✭✭
    Re: How often tracker should act

    Dave, If I read you correctly, the tracker RGS mentioned (no name) is almost as good as one can get for winter conditions 3 min vs 4 min... between movements.

    What is your gut feel for summer where one gets lots more sun, like up here in the north...???

    thanks
    Eric
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,965 ✭✭✭✭✭
    Re: How often tracker should act

    Eric,
    Look at http://www.wattsun.com/

    There are spread sheets and charts.

    My gut says too far North!
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: How often tracker should act

    At 10 degrees sun angle, you only lose about 1.5%, so not worth getting too excited about it. Even at 25 degrees, you only lose 10-12%.
  • rgs315rgs315 Registered Users Posts: 9
    Re: How often tracker should act

    Dave, I cannot understand why there is huge difference between different seasons. Whatever it is summer or winter, the earth rotate at 15 deg per hour, and you should also decide how often the tracker should update its position, 3 min, 4 min or 10 min, 20 min……?

    Bill, is it linear relation between PV efficient and azimuth angle cosine?

    Mike90045, would you please describe your PV system more detailedly? Because I cannot understand why the tracker manufacture make their product precision to 1 deg if there is no big difference for 5°error (20 min)?

    Thank you!
  • rgs315rgs315 Registered Users Posts: 9
    Re: How often tracker should act
    Windsun wrote: »
    At 10 degrees sun angle, you only lose about 1.5%, so not worth getting too excited about it. Even at 25 degrees, you only lose 10-12%.



    If so, 1 degree tracker precision will make no sense for flat plate PV. Then, why the manufature do this? you know, the cost is different.
  • BB.BB. Super Moderators, Administrators Posts: 29,980 admin
    Re: How often tracker should act

    The Sine/Cosine functions are not linear... You can look at a graph and see that the "peaks" of the function are fairly rounded and as the you move from +/- 10 degrees--the function "goes to zero" more quickly.

    For a flat plate collector (such as solar panels), the accuracy does not need to be that high. For those with lenses and parabolic mirrors, typically the accuracy needs to be greater.

    Once you have a certain number of steps (and tracker geometry)--it is not that difficult to track with better than a couple of degree of accuracy.

    I think that Dave was warning that if you had a sun tracker, and the sun was behind clouds for a period of time, that a "slow tracker" would take significant time to slew back to correct sun position and be "on track"...

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: How often tracker should act

    There are other factors involved once you move past the 25-45 degree mark (depends somewhat on panel design and weather). Most modern panels are designed to minimize losses due to off angle as much as possible, through such things as cell surface texturing and anti-reflective methods, but you can only carry that so far. In theory at 45 degrees you should still get 70.7% power, but in a couple of panels that we tested a while back, it was more like 68% - not drastic, but the relationship to cosine is not perfect after a certain point.
  • mike95490mike95490 Solar Expert Posts: 8,569 ✭✭✭✭✭
    Re: How often tracker should act
    rgs315 wrote: »

    Mike90045, would you please describe your PV system more detailedly? Because I cannot understand why the tracker manufacture make their product precision to 1 deg if there is no big difference for 5°error (20 min)?

    Thank you!

    Fixed roof mounted array, faces west. Hits peak power AFTER noon, because panels face west. They are fixed, and with the chart here:
    http://www.mike-burgess.org/images/MB_May-3-2007.htm
    you can see the peak at about 2:30 pm Ignore the clouds that ruin collection! You can see around the peak time, there is little drop off from the best angle, 20 or 30 minutes either side, not much difference, but an hour off, and you see a sharper drop.
    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

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • Dave AngeliniDave Angelini Solar Expert Posts: 4,965 ✭✭✭✭✭
    Re: How often tracker should act

    How about "they do it because they can"

    That may not work here so let me say it is an analog system with theoretical infinite resolution. The motor is as old as time 24vdc. When the photo sensor peaks compared to it's neighbor on each side DC is supplied to the motor. There is a circuit to slow the response.

    My comment on 'what slight losses make little difference" They all add up and on the grid there is little consequence. Offgrid it is the difference between being able to make power decisions like our grid friends or going into generators or wait until tomorrow mode. The first 12 years I was a non believer in tracking also. I also live in a place that it make sense.

    Got to prove it with yesterdays weather, AGAIN !
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • WillWinstonWillWinston Solar Expert Posts: 45
    Re: How often tracker should act

    Well this is 'timely'

    I was just ordering the Hugo Muller 'astro timer' that calculates the sunrise and sun set based on the lat and longitude and day of the year and fires a relay (or 2)

    http://www.alliedelec.com/Search/ProductDetail.aspx?SKU=090SPEC&MPN=SC+28.23+PRO&R=090SPEC&SEARCH=090SPEC&DESC=SC+28.23+PRO

    My idea is to just run the tracker motor at a constant slow rate starting at sun rise and ending at sun set

    I plan to adjust the speed to account for the length of the daylight

    about 9 hours in Dec to about 15 in June

    a side benefit would be that the panels will always be pointed at the sun whether the sun is obscured by clouds or not

    it sounds like a 5 degree inaccuracy is not significant -- this is a big help in design
  • WindsunWindsun Solar Expert Posts: 1,164 ✭✭
    Re: How often tracker should act
    My comment on 'what slight losses make little difference" They all add up and on the grid there is little consequence. Offgrid it is the difference between being able to make power decisions like our grid friends or going into generators or wait until tomorrow mode. The first 12 years I was a non believer in tracking also. I also live in a place that it make sense.

    While that is true up to a point, there is also a point where it simply becomes a lot cheaper to just buy more panel than to spend a lot of money on precision tracking etc.
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,965 ✭✭✭✭✭
    Re: How often tracker should act
    Windsun wrote: »
    While that is true up to a point, there is also a point where it simply becomes a lot cheaper to just buy more panel than to spend a lot of money on precision tracking etc.

    I think we can agree to disagree! What do you mean by precision boss? I am just making the case for tracking. All this math you guy's are into here is a moot point. Is the array pointing at the sun as a storm goes by during those four 15 minute periods when the sun breaks through? Does the array point at the sun in a "warm" place like Arizona at 7pm in the summer? Do you need it to?

    There are plenty of people who have gone thru this argument over the decades! I really think if you were offgrid in a place like Arizona you might feel differently.
    The brute force method you describe wastes materials (silicon) and is not very elegant. In my opinion!

    Sorry to be so opinionated of a Friday! The storm went by us yesterday and it is wall to wall blue in the Sierra's. No need to track the sun today ! CAVU
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • rgs315rgs315 Registered Users Posts: 9
    Re: How often tracker should act

    Thank you all for the information.

    Whether to use tracker is not my point, and that depends on economic analysis. I agree with someone that when the panel price go down to some point (such as 3 $ per watt), it is no need to use tracker.

    My question about tracker accuracy is also based on the economic factor. What is the point that profit getting from frequently updating its position is more than its wasting (power and mechanical maintenance)? It sounds 5 degree inaccuracy is suitable, and then the tracker should update its azimuth angle every 20 min.

    Besides theoretic analysis, can anyone provide more practical experience about the degree inaccuracy?
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,965 ✭✭✭✭✭
    Re: How often tracker should act

    RGS315,
    Hope this helps, the Wattsun trackers consume 20 watthours in summer to track. They use less in winter. No matter how you feel about maintenance which involves a grease gun 4 times a year, I would think 20 watt hours per day would be negligeable. In the noise as they say in electronic measurement.

    If you do get a rare failure of a tracked array it becomes a fixed array!;)
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: How often tracker should act
    RGS315,
    Hope this helps, the Wattsun trackers consume 20 watthours in summer to track. They use less in winter. No matter how you feel about maintenance which involves a grease gun 4 times a year, I would think 20 watt hours per day would be negligeable. In the noise as they say in electronic measurement.

    If you do get a rare failure of a tracked array it becomes a fixed array!;)

    to me it doesn't make sense cost-wise to track. that 20wh may be in the noise as you say, but when it is solar noise it is more precious as it is more expensive. people go to great lengths to get quality low tar inverters and mppt controllers to save a few watts where it is possible. the gain represented by tracking will not yield great quantities of wh over the same system fixed recognizing that there is a gain, but at what cost? you say it is a rare thing for trackers to breakdown, but from what i've heard those rare occurrences are about every 3 years or so and are not minor breakdowns cost-wise. when it does breakdown you don't know if it will be pointed in that holy direction of south either. the costs of the cheapest trackers can get you quite a bit of pv that will far outdo what these trackers will do and even if you can match the initial costs by finagling, the maintenance costs of the tracker throw it all out of the window as a fixed array has none of that maintenance other than a good washing being common to both.
    to me trackers are just a spin on the old magic. just my opinion.
  • Solar GuppySolar Guppy Solar Expert Posts: 1,962 ✭✭✭
    Re: How often tracker should act

    With UL panels now under 2.50 watt for Gridtie and for off grid, the non UL Evergreens $2/watt trackers make no financial sense. The only reason on would use a tracker these days is for limited space. For example, a tracker that can hold 1kw of panels cost MORE than 1kw of panels based on pricing I looked at .. so for the same $$ double the panels or get a sometimes 20-30% boost with the tracker.

    When panels where 10 bucks a watt, trackers were a great idea, the times are a changing
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: How often tracker should act
    Windsun wrote: »
    While that is true up to a point, there is also a point where it simply becomes a lot cheaper to just buy more panel than to spend a lot of money on precision tracking etc.

    Just my opinion but this is nearly always true. The one advantage to trackers of any type is if you don't have the area for more panels, in which case the expense of a tracker is the only way to maximize power for the available space. Otherwise, you could buy more panels with the money and realize a greater gain in Watts without the additional potential problems of the tracker.

    But then again I've got the H1N1 virus so I could be talking gibberish. :p
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,965 ✭✭✭✭✭
    Re: How often tracker should act

    It is like the movie "ground hog day" This just keeps going.

    For Offgrid a tracker will find the energy you need in bad weather (reasonable locations)
    You could also have fixed arrays at south east, south, and southwest.
    You could also run a generator.

    It has been my experience that my clients do their system once and do not play arround with adding panels all over their yard. They are off the battery earlier in the morning and on the battery later in the day. They certainly do not want to go up on a roof! They do not have to deal with snow when it snows! They make life easier! As the saying goes

    "In theory there is no difference between practice and theory.
    In practice, there is!"

    Our experience of close to 18 years is pretty solid and as it says below....
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭
    Re: How often tracker should act

    Don't get me wrong; I really like the idea of trackers.

    Recently I looked into Zomeworks units. What I found is that the price of the tracker for my four existing 175W panels would buy me two more panels, and that tracker price did not include the post and ground setting. But would the tracker give me a 50% daily increase over my existing panel install? Maybe, maybe not. Location was a bit problematical as well. Fortunately I have lots of roof space available so adding two more fixed panels is the obvious solution.

    But trackers certainly have advantages in certain applications.:D
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,965 ✭✭✭✭✭
    Re: How often tracker should act
    Don't get me wrong; I really like the idea of trackers.



    But trackers certainly have advantages in certain applications.:D


    Ahhhh thank-you Marc

    Living offgrid is almost entirely about strategy for making electricity, water, and temperature non issues. There are many ways to skin a cat while money can be a big one, it is results that count! I'll change the avatar in your honor to customer 31.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • System2System2 Posts: 6,290 admin
    Re: How often tracker should act

    Well my single axis tracker moves about every 30 min.
    & it only cost me around $200.00 I'll be building 2 more soon.
  • Dave AngeliniDave Angelini Solar Expert Posts: 4,965 ✭✭✭✭✭
    Re: How often tracker should act

    More info Dave! A pix? If you post it I will post my development unit a 3 axis tracker!

    This whole thread really is about the need to have the array point reasonably close to the sun if you want to complete charge in poor solar weather. There are many ways to to do this from using a generator to flashlights. The people I work with want it to be easy for the most part and not have to make many decisions.
    "we go where power lines don't" Sierra Mountains near Mariposa/Yosemite CA
     http://members.sti.net/offgridsolar/
    E-mail [email protected]

  • westbranchwestbranch Solar Expert Posts: 5,180 ✭✭✭✭
    Re: How often tracker should act

    How much power is yor homegrown unit using? 8)

    Eric
     
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
Sign In or Register to comment.