Two Position Mounting Ideas?

x_logox_logo Registered Users Posts: 12
I'm new to solar but old (very) to electronic-mechanical and am planning a 5KW installation by the end of the year.

Our power company has two major rates: summer: May-Oct, and winter: Nov-April with summer rates about 22% higher -- the trend, of course is ever increasing spread. This suggests two different tilt angles would optimize panel output according to cost and sun position. After doing some rough math I figure the summer angle at about 14 degrees and winter angle at about 48 degrees, more or less. (I'm in Phoenix @ 33.3 deg) At the end of April and again sometime around the beginning of September, the panels will be manually repositioned (along with roof and panel inspection). So a mounting with two positions would work.

The mounts will likely be made of welded square steel tube and light angle. We have had winds exceed 65MPH last year so these have to be somewhat stout -- I'll have a structural engineer take a look before fabrication.

Before I reinvent the wheel does anybody have any thoughts, ideas, or links on such a mounting system?

Comments

  • icarusicarus Solar Expert Posts: 5,436 ✭✭✭✭
    Re: Two Position Mounting Ideas?

    Sounds like you are on the right track. My one question is if the spacing on the panels is is that small,, are you going to have a potential to shade one string by the other at various times of the year?

    Tony
  • BB.BB. Super Moderators, Administrators Posts: 32,611 admin
    Re: Two Position Mounting Ideas?

    If you wish--take a look at the PV Watts site... Uses real data (~20 years of logged solar data, including weather) to estimate your average yearly output.

    You can input various angles and see where various settings (-15,0,+15 degrees) peak for specific months--or you can even download CSV data set with hourly output estimates.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • nielniel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Two Position Mounting Ideas?

    on the angles i am not sure how you arrived at those angles, but a dual angle system is a good idea. the average max height for the sun is your latitude of 33.3 degrees. that means that during the beginning of spring and fall the sun shall hit a max height of 33.3 degrees at solar noon, but the sun is lower to the horizon prior to and after the solar noon so the pvs should be angled further than that at that time to capture the daily average so another 5-10 degrees is warranted at that time of the year. for the summer and winter solstice max solar angle it will be roughly another 23.5 degrees for winter and -23.5 degrees for summer. the exact wobble is +/- 23° 26′ 22″ to your latitude. now if you were to choose say 40 degrees for the equinoxes then you add or subtract 23° 26′ 22″ from the 40 degrees and there's your angles optimized for summer and winter with a big gap inbetween for spring and fall so going 3 angles could be even better.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Two Position Mounting Ideas?

    Good idea. I'm a lazy bastard though, so I'd probably rig the mounting to have a couple of these incorporated into it:

    http://www.amazon.com/dp/B000BGJZMM?smid=AEQTEQOXCITS&tag=nextag-sports-mp-delta-20&linkCode=asn

    It's not going to shift position in a high wind, a little WD-40 and some grease every six months will keep it working like new forever and you can probably drive it with a cordless drill.
  • x_logox_logo Registered Users Posts: 12
    Re: Two Position Mounting Ideas?

    Thanks for the comments.

    Well, after doing some more math I am now having second thoughts. I could be doing something wrong with this - the numbers aren't as good as I imagined.

    My tilt angle and output data are based on a table from http://www.nrel.gov/rredc/

    I took the average kWh/m2/day for each month at different tilts and multiplied by the power company kWh rate for that month. This gives a dollar weighted value per m2 per month. Note that this is obviously not a realistic production number, just the potential value of energy striking the panels in terms of dollars.

    Then I separated the year into two periods where the month to month dollar difference was greatest. Turns out to be May-September and October- April, more or less. I took the low tilt vales for summer, and high tilt values for winter and added them together. Then chose (estimated) the two tilt levels which generate the maximum dollar value.

    Here are some interesting observations.

    First, for a non-adjustable tilt angle the difference between 33.4 and 18.4 degrees is only about 1.5% in terms of annual dollar value. The utility rate structure makes the tilt sort of less critical in this range. Although the optimum angle is closer to 33.4 the smaller angle might be favored due to easier and less costly mounting. Going to greater tilts, besides likely being more expensive to construct, reduces dollar output.

    An adjustable mount optimized to produce maximum dollar value for the two respective periods, and angles say of 14 deg and 48 deg, would produce about a 3.7% or so more dollars than a system with a fixed angle of 33.4%. While PV panel manufacturers would likely kill to generate an extra 3.7% output I'm not too sure it is worth it. The added cost and complexity would be a consideration. Also, the same increment in output could be achieved by simply adding an extra panel, at less tilt, with a lot less hassle.

    But there is another factor. In a larger system the winter output might exceed the power used causing a kWh billing "carry forward" into the next month. Our utility however has the month of April as an annual cutoff. No accumulated credits are applied after April. What this means is that the added dollar credits that accumulates by increasing the tilt angle in September, and thus increasing the output generated from September through April, if in excess of the total energy used over that period, would be lost (just in time for summer, by the way). This could easily exceed the 3.7% benefit of the adjustable tilt. No sense in changing angles if the added output is stolen by the power company.

    Food for thought.
  • dwhdwh Solar Expert Posts: 1,341 ✭✭✭
    Re: Two Position Mounting Ideas?

    True enough.

    (I'll play devil's advocate.)


    What may seem like giving free power to the electric company today, could easily become a very different situation with a different rate structure. Referring to the smart meter thread on this forum, it appears that a new rate structure may happen in your area sooner than later. Then you might not have to worry about giving it away free to the utility.

    Since it sounds like you are going to weld up your own mounting system, it can't be all that difficult to add a couple of pivot points and a scissors jack or two. It won't affect stability to any great degree, and the price difference would most likely be less than the cost of adding that other panel that you mentioned.

    And finally, while it looks right now like you will generating excess capacity during the winter, there are many many reminders on this forum that loads always have a way of increasing over time.


    The way I see it this - if you are welding up your own mounts anyway, it's a low cost way to add some efficiency, and that can't be bad.
  • x_logox_logo Registered Users Posts: 12
    Re: Two Position Mounting Ideas?

    Yes I have a smart meter. It has all the features for time of use and peak recording. It has a radio transceiver which communicates with the utility company radio station located somewhere in the neighborhood. My new dishwasher also has (had) a communication link to the AC line, snip snip snip....

    It would be no surprise that a rate structure can be created to simply suck up all the unused power -- period. We will see. Sounds like a little crative thinking (and rewiring) might reduce the impact of such a plan.

    I am considering the impact of TOU plans also. The weekday starting hour is 1:00 PM for the higher rates. This suggests that aligning the panels a bit toward the west would extend and increase output into the later afternoon when its needed the most. How much of a west tilt would be a good math exercise. I'll post the results here eventually. At the moment I can't use TOU but a few extra holes in the mounting brackets won't hurt.

    Sooner or later the "smart meter" or other communication device will be able to shut down major appliances and divert all the homeowner's PV output to the grid. Hang on to those old round Honeywell mechanical thermostats -- they will eventually be worth their weight in gold if the Thermostat Police don't round 'em all up first.
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