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Best solar panel angle

Discussion in 'Photovoltaics' started by Gymy Bob, Jan 21, 2005.

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  1. Gymy Bob

    Gymy Bob Guest

    What is the general best angle to point your solar panels horizontally for
    best power output daily? This is with no tracking and a fixed position.

    I figure about where the sun is at 2:00 PM but this is only in the winter.
    Does this vary from season to season.

    Are there charts or calculations posted somewhere online?

    How much difference will tracking make?

    What is a good tracking system source?

    Are there cheaper ways to set up tracking systems?

    TIA
     
  2. George  Ghio

    George Ghio Guest

    Pointing at the sun at noon.
    Yes it varies with the seasons and the angle will depend on you latitude.
    Have a look at www.susdesign.com
    Depends on the tracker. 0 to 30 or 40% when the tracker works. Trackers
    also increase the number of things that can go wrong. i.e. moving parts.

    I spend a lot of time with these problems. Because of this I am not keen
    on their use.
    Suggest you talk to Duane Johnson. One of the few here who would know.
     
  3.  
  4. The variation of angle with altitude is about 0.004 degrees from sea
    level to ten kilometers over the poles, I think he can neglect this.

    Best regards
    Miguel Gimenez
     
  5. Guest

    Wrong again. Pointing slightly below noon elevation makes more daily energy,
    with more ground reflection and a higher average incidence angle cosine.

    Nick
     
  6. wmbjk

    wmbjk Guest

     
  7. George  Ghio

    George Ghio Guest

    Wankery. Notice the absolute number "slightly". Nicks trade mark. Vagary
    and indecision.
     
  8. George  Ghio

    George Ghio Guest

     
  9. wmbjk

    wmbjk Guest

    Glad you asked. It gives me a chance to help counter the "bogus
    unrealistically pessimistic data" spread by some for decades.

    I have no reason to make the sort of measurements you requested, a
    crime which Satan is sure to thank me for when I meet him.
    Nevertheless, I do have a good idea of the increase in performance
    that tracking brings us because for a year or so one of our arrays was
    fixed, making it easy to compare to the other two. Looking out at one
    array dark and two lit during so many hours would have made me a
    believer even I hadn't been one already. I'd estimate the overall
    improvement in performance at about 30%. Less in winter, much more in
    summer of course. It might have been a little better except that
    mountains cut off about a half hour of sun in morning, somewhat less
    at evening. But there's more to tracking than just a performance
    increase. In our case, the increased length of the charging day thanks
    to tracking, combined with the input from a second source (wind), make
    for many days with almost no battery discharge at all. Contrast that
    with a fixed PV only setup, which is likely to be in discharge mode
    three quarters of the time. Longer discharge days help make for
    shorter battery life, which I'm sure you'll agree <cough> *should*
    make tracking worthy of recommending.

    Wayne
     
  10. George  Ghio

    George Ghio Guest

    Why is it no suprise that you don't have a clue. Nine years of nothing.

    Tsk,tsk,tsk.

    Just guesses and bullshit.
     
  11. tat-2

    tat-2 Guest

    I think this is a loaded question. Personally, I believe it varies from
    location to location. When I put my small system in place I wanted three
    items to maintain a constant.
    1. A relativly inexpensive mounting system.
    2.One that would fit my local without a need for permits and indiscrete. (I
    live in a city and would not want my panels stolen).
    3. Low/No maintenance, this was somthing that I was willing to trade off for
    a decent output and low cost.

    I have 180W of solar panels, flat 90 degree mounting, on angle iron mounting
    with stainless hardware. (4X45W panels about $900 delivered), mounting
    hardware about $40, wire/inter-connects $50, short-circuit protection a
    AC/DC rated breaker that doubles as a panel shut off, a miture of AGM
    batteries ranging in cost for free (trade of service, to about $20) (about
    100Ah).
    Trace c-40 with meter (honestly save yourself $50 on the meter, it is not
    worth it. I think I would have been better spending the extra $$ in new golf
    car batts.
    A few (2) cheap inverters, one is a coleman 100W with LED voltage
    meter(about $100), the original and first was a vector 400W (<$30)
    Total system cost about $1400, batteries that have lasted 2+yrs (all were
    used)
    I have about 7 day reserve power for nessecary electrical items. (CPAP,
    lights)

    Positives: "Free" energy, storage for up to 7-days (could be improved for
    less then $300 in golf cart batts.)
    No maintanence of the panels or system.
    Inital investment of a decent charge controller allows for expansion.

    Now the negatives: What I deal with each year, snow/ice coating solar panels
    losing 2-5 days without manual scraping/clearing.
    Initial start up cost high. I could have bought a great/quiet Honda
    generator for $1000 and 4 golf cart batts for another $200 and had a more
    powerful backup system.
    Also, a transfer switch for the Geny/Solar for an additional $250-$300.
    Thinking of adding better batts, and a gen backup (I own 2 other (read loud
    generators but both will charge batts).

    Ed
    this is/was an honest approach to your first system.
    Trial by fire/sun.
     
  12. ptaylor

    ptaylor Guest

    I've got a micro-PV system setup with a 10W panel a friend gave me,and a
    few assorted lead acid batts. (Just added 2 car batts to it too! about
    130AH total now!)
    It powers some small 12V PC fans,and a modem,cellphone charger,and a
    small CCFL light quite nicely.That little CCFL light has come in handy
    more than once during a power outage! Not to mention the 300W inverter I
    also have. "Free" power is great when the grid goes down. *grinz*
    One day I hope to have an off-grid(and other utils.) house.

    Anyways,I had a random thought about de-icing the panels.
    Would shorting the panels out heat them up enough to melt the ice?
    I remember reading that the cells heat up (more) when they are shorted.
    It is said to not damage panels(from what i've read),but also being
    covered with ice,they won't be at peak output anyways.(lower risk?)
    Granted,if they are covered in enough snow there will be little to no
    output at all.I would think that the ice would let some (reduced) amount
    of light through?
    Perhaps the panels wouldn't have enough output,or make enough heat
    anyways,but it was just a random thought. ;-)
     
  13. wmbjk

    wmbjk Guest

    My observations are well within accepted industry standards for the
    benefits of tracking. In contrast, your 18 years of claiming that
    tracking is good for "30% on a good day, maybe", and "perhaps 10% for
    a good year", are far outside accepted wisdom, and backed by nothing
    more than ill-informed opinion. You're now complaining that I should
    have provided more data, yet offered none when asked to back up your
    30% and 10% claims. Had you been willing to accept reasoned opinions
    on the subject, perhaps by now you'd have sold some trackers,
    providing the opportunity for long-term observation. Which in turn
    would have made it possible for *you* to be explaining the benefits,
    instead of crying "bullshit" over others' comments.

    Wayne
     
  14. ptaylor wrote:
    ....
    ....

    Perhaps you could think of it this way, PV panels absorb sunlight
    and convert some of it (10% to 15%) into electricity and the rest
    into heat. If you turn off the making electricity part by disconnecting
    them then that amount of absorbed sunlight gets converted into heat
    also.

    I've no experience with ice since I live in Sunny California (where
    it never rains or snows) but I have a few thoughts. In no particular
    order...

    You might use rain-x.
    http://www.rainx.com/frame_auto_new.htm

    If the panels are fixed mount then you might add vertically mounted
    solar air (or water) heaters plumbed to heat the underside of the
    iced over panels. Vertical panels shouldn't gather ice or snow and
    when they aren't used to de-ice the PV panels the heat could be
    directed to warm the house.

    If they are on tracking mounts then the tracker should park the panels
    in a vertical (or perhaps even slightly upside down) position when there
    isn't enough light to make power.

    Anthony
     
  15. Gunnar

    Gunnar Guest

    I believe Mr Ghio stated in a post that he used intuition as a method of
    designing.
    Are "guesses and bullshit" synonyms to intuition?

    Just curious as English is a second language for me :)

    On a more serious note though, it should be possible to calculate the
    difference in power output between tracking and fixed panels.
    If tables are supplied by the manufactures which shows the power output as a
    function og the angle of the sun above the horizon, angle of the panel and
    lattitude of the panel then a fairly accurate calculation should be
    possible?

    Gunnar.
     
  16. daestrom

    daestrom Guest

    A simple search of
    http://rredc.nrel.gov/solar/old_data/nsrdb/redbook/mon2/state.html shows the
    solar incidence for both flat plat fixed mount and tracking collectors.
    This does *not* include losses from reflection. Looking at a typical
    location in NY, the average for fixed mount seems to be 3.69kwh/m^2-day for
    mounting angle equal to the latitude and 4.84kwh/m^2-day for single axis
    tracking. So the tracking is ~131% of the fixed mount. (or if you prefer,
    the fixed mount only collects 76% of that possible from tracking)

    Now, all one has to figure out is how much is lost when the angle of
    incidence on the surface is not 90 degrees and you have your answer. This
    varies depending on the exact material used. For light entering glass at a
    90 degree angle, 4% of the light is reflected. The amount reflected doesn't
    change much for angles near 90, but it increases to near 100% when the light
    strikes the glass at very low angles.
    http://www.mellesgriot.com/products/optics/oc_2_1.htm So a tracking
    collector, that keeps the entry angle for the glass close to 90 would have
    less reflection during the 'non-noon' hours and result in further gains over
    the fixed collector.

    So if you *really* want to sharpen up the calculations, you could calculate
    the angle of incidence for a fixed collector for each hour of the day and
    the amount of light reflected from the surface. Then repeat the calculation
    with a tracking collector and compare the two results.

    daestrom
     
  17. ....

    http://rredc.nrel.gov/solar/calculators/PVWATTS/
    NREL's PVWATTS calculator has an option for 'fixed' or 'tracking'.
    From all account's it's a fairly good method of estimating performance
    that is based on real measurements at actual sites.

    This should not be news to someone like George as he has been pointed
    to the site numerous times and, it appears, he disagrees with it still.
    If George wants to argue the numbers then he can take it up with the
    government and, I suppose, try to convince us why NREL lies to everyone.

    Anthony
     
  18. Gymy Bob

    Gymy Bob Guest

    There are also many other factors e.g.: the refraction, diffraction and
    polarization of the sunlight at the change in mediums, space to air, not to
    mention the longer distances through the air to the surface.

    This is good but there are many more factors. I doubt it can be calculated
    accurately but rather best from historical measurements.

    Tracking manufacturers brag about less than 15% gains I believe. If they
    could stretch it I am sure they would.
     
  19. George  Ghio

    George Ghio Guest

    Gerat. First everyone says that "measure" is the way to go. Now it is
    "calculate". That's fine.

    Then there is reality.

    An example; Last week I get a phone call from a fellow who bought a
    property with an existing photovoltaic system. Everything had stopped.

    He pulled out the genset to charge the batteries. Didn't seem to be
    working so he called me to have a look.

    Yes mate your generator is dead.

    While I was explaining the ins and outs of solar I watched the tracker
    with six panels traverse 60 degrees in twenty minutes.

    Somewhere along the line I am sure the panels faced the sun. At least
    for a few seconds.

    Now the price of the tracker is around that of two panels. Two panels is
    33% of six.

    Want a tracking system? Fine.

    NREL. Better hope the site they used for their calculator is your back
    yard.

    One size does not fit all.
     
  20. Note to everyone else who isn't into feeding trolls.
    It's better to simply NOT reply to trolls as it does no one any good.
    Is George here a troll? I'll leave that up to the reader to decide.

    NREL's numbers are based on real measurements. The calculations are
    extensions from the measurements. For instance, how much money you
    save by installed solar PV.

    Yes, it has both Measurements and Calculations. Amazing.

    In fact, I'm going to go out on a limb here and say that both
    measurements and calculations are required to do a good job.
    NREL data is collected in the real world. They are as real as you are
    going to get short of recording numbers of your own for several decades.
    Even that would be somewhat inaccurate at predicting the future because
    the global climate is changing.
    So the tracker was malfunctioning? Was this the reason why his PV system
    was "dead"? Are you proposing that all trackers don't work because you
    found one tracker that wasn't working?

    Did you fix the tracker? Was it an expensive repair? Do you expect that
    you will need to fix this tracker often? Every month? Every year? Every
    decade? Every century?

    Yes, you've proved that a broken system doesn't work. Now the question
    is how unreliable are trackers? Is the total lifetime cost of a system
    with fewer panels and a tracker more or less than that of a system
    with more panels and fixed mounts? It seems that you are saying that
    since trackers CAN break that they are therefore too unreliable to use.
    What if you have more than six panels? The price of two panels out of
    12 is 16% and not 33%. Clearly it's only uneconomical when you are
    dealing with very small systems and very expensive trackers.

    Does a tracker have to cost the same as two panels? Wattsun trackers
    retail around $2,000 for 1200 watts of PV. PV can be purchased for
    around $4/watt today so $2000 buys 500 watts. If these are 120 watt
    panels the tracker would mount 12 of them and cost as much as 4.
    If the tracker adds 33% then this array would produce as much as 16
    panels. In this case the total cost seems nearly the same with or
    without the tracker. Of course, the numbers would favor the tracker
    if you didn't purchase it at full retail price. Discounts are common.

    Do you have to use a $2,000 Wattsun tracker? Of course not. You can
    put together your own tracking mount using a $37 Redrok tracker, a
    satellite drive and other commonly available parts. Total cost? I
    don't know but it's not likely to be $2,000 and, as I showed above,
    anything less makes tracking more affordable than buying more panels.

    Does the fact that this persons system had 6 panels on a tracker mean
    that they would have saved money to buy 2 more panels and not have the
    worry about repairing a busted tracker? Of course not. You didn't say
    how old this system was. Solar PV prices have dropped since this system
    was installed. It's quite likely that the tracker was more affordable
    at that time than more panels. Since you mentioned that the motors were
    still driving the panels then it's also likely the repair was quite
    affordable (much less than buying two more panels). For this person,
    repairing the broken tracker would then have been more affordable than
    getting rid of it and replacing it with more panels.
    Of course one size does not fit all. That's why blanket statements like
    "The price of a tracker is around that of two panels." aren't accurate.
    After all, what size panel? What size tracker? Which manufacturer?
    Clearly, not all trackers cost the same, mount the same number of panels
    and there are a wide range of sizes (and costs) for PV panels. One size
    statements like that just don't fit all.

    The same idea, that trackers don't work or that they are not worth it,
    obviously falls into that blanket statement category and is bound to
    be incorrect somewhere, sometime.

    In my (limited) experience, I've found that the choice between tracking
    and not tracking is not based on economic but rather aesthetics. Fixed
    mounts can be easier on peoples eyes, especially if the panels are put
    on the roof.

    Anthony
     
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