Announcement

Collapse
No announcement yet.

Pool Solar Tilt and Azimuth

Collapse
X
  • Filter
  • Time
  • Show
Clear All
new posts

  • Pool Solar Tilt and Azimuth

    I am installing ground mounted solar hot water heater panels for my pool. The location is south facing and sloped. I have used the California Solar Initiative (CSI) calculator to determine the optimum tilt and azimuth to maximize the solar heat into the pool during the months of March/April and October/November. I am assuming my panels will have excess capacity to heat my pool in the months of May through September. The CSI calculator is set up for electric solar panels, but I'm assuming the heat generation will be proportional. I have determined 190 Deg azimuth and 42 Deg tilt will generate about 5% more in the shoulder months and 2% more overall than the 180 Deg azimuth and 17 Deg tilt normally recommended. I realize this is pretty small but I don't see any downside and wondering if anyone has some thoughts about this. Comments are appreciated.

  • #2
    Since you're asking:

    You're on the right railroad but you may want a spur line for shoulder season pool heating and not the main line as an analogy to using a PV model for pool heating. Still, at your latitude,of ~ 34 deg., sounds like you're headed mostly in the right direction.

    As a general concept, heat generation of a solar thermal collector will follow the same general pattern as the PV electrical generation, with the solar thermal having more noticeable seasonal variation because the thermal losses will lower in warmer weather, particularly with a pool heater.

    As a general concept, for full season pool heating, assuming no heat is required in the off season from, say, mid fall to late spring or so, one suggestion is to tilt an array at local latitude minus 15 deg. or so.That will tend to maximize summer production.

    However, for lower latitudes - that being something less than ~ 38 - 40 deg. latitude or so, and for other reasons as well, that lower tilt will tend to generate more heat for the high season which may result in overheating or heat dumping in summer, and also perhaps some shoulder season shortfall because the array is at too low an angle for max. heat production for those spring/fall times.

    One way to look at array tilt is to match the production to the task. If more heat is neede in the shoulder seasons - your application - and probably less heat in high summer when it's warmer and perhaps sunnier, you might want to consider a tilt that is closer to you latitude, maybe a few degrees more, which more closely coincides with the tilt that minimizes the integrated minimum solar incidence angle on a solar device at the equinoxes.

    At 42 deg. tilt (latitude + 8 deg. or so for you), I might consider a bit less tilt by a few degrees or so, but I'd not get sticky knickers over it. Most of solar energy is not rocket science.

    I'm at ~ 32 deg. latitude and while not a pool heating application, I modeled my solar domestic H2O heater using some stuff I wrote and TMY3 data for Miramar, and determined the optimum orientation to maximize year round production, AND minimize spring/summer/fall overheating as a secondary goal. The result is an array tilt of ~ 50 deg. (lat. + 18 deg.) and an azimuth of ~ 175 deg. for my domestic water heater, with the primary goal of maximizing Dec./Jan. production, and a secondary goal but still some consideration for summer overheating. Sounds like you don't need concern for winter heating.

    FWIW, optimum PV orientation for max. yr. round electricity production for me is ~ 29 deg. tilt and 188 deg. az.

    So, while domestic H2O heating and pool heating are not exactly the same, they do share a trick that allows users to shift some perhaps unwanted heat production to the colder parts of the year by a slightly higher tilt angle than is optimal for other applications such as PV.
    Last edited by J.P.M.; 01-25-2017, 12:29 AM. Reason: Corrected and shortened 2d paragraph.

    Comment


    • #3
      Thank you for the great comments. I think I heard that the CSI calculator is a reasonable tool to use for approximating best tilt/azimuth, but due to seasonable temperature impacts it isn't perfect. I'm thinking where the lower off-season temps helps panel power generation, it hurts hot water generation. I wonder if I would be better off to calculate the angle of the sun to my location in March/April and Oct/Nov at noon and use that tilt/azimuth. Wouldn't max heat absorption occur at a 90 Deg angle to the sun?

      Comment


      • #4
        Originally posted by Ward L View Post
        Thank you for the great comments. I think I heard that the CSI calculator is a reasonable tool to use for approximating best tilt/azimuth, but due to seasonable temperature impacts it isn't perfect. I'm thinking where the lower off-season temps helps panel power generation, it hurts hot water generation. I wonder if I would be better off to calculate the angle of the sun to my location in March/April and Oct/Nov at noon and use that tilt/azimuth. Wouldn't max heat absorption occur at a 90 Deg angle to the sun?
        You're welcome. I'll let others determine the value of my comments. Opinions vary.

        Long story short/abstract of what follows: At your location, for best guess at most heat production during shoulder seasons, tilt the collector at ~ 35 - 40 deg., maybe a bit less, and an azimuth of ~ 185 - 195 deg. or so. Your initial estimates may well be as good.

        IMO, you are like a diamond in the rough - you're thinking seems sound. More information to think about and you'll make more refined choices - maybe not better, but more information doesn't hurt.

        I'd be careful about using a PV model for solar thermal, mostly for reasons similar to those you state, and I wrote of.

        For any solar device, PV, solar thermal flat plate/batch/concentrator/etc, passive solar or anything else, the analysis begins with what's called an "energy balance" - no more than energy accounting really. The basic premise is: Energy that goes into, say, a flat plate collector equals what leaves the collector via useful heat, or leaves as losses - both thermal and from reflection of sunlight from any glazings to the environment via several ways, plus/minus energy that stays in the collector (with that stored energy manifested as a temp. change of the solar collector assembly). For most analyses, the energy storage is small and ignored, so --->>> what goes in == what goes out.

        Since solar pool heater losses are rather weak function of collector orientation, maximizing the input for any period, time of year or season(s) will tend toward maximizing the useful output. To maximize the potential for what goes into the solar collector - stick with me for a second here - (and as you basically wrote), it's usually best to minimize the time integrated angle of incidence that the beam portion of the solar radiation makes with the collector.

        For stationary collectors and a constantly moving sun, as a practical matter, there will never be more than a few times/year when there is perpendicularity. So, what's done is to use the time integrated value of the (solar intensity * cosine angle of the incidence product) for the max. value for the conditions/times of use under consideration and as the goals warrant.

        Here's the bottom line: (thanks for hanging on) - long story short - to max. the useful gain means fishing around for the collector orientation that gives the highest value of the incident radiation over some period with perhaps (and likely) tradeoffs for the many conditions and considerations, some of which will probably be at odds with others.

        Some of the results of a 40 yr. fishing expedition is what the opinions expressed in the second paragraph of this post are all about. Take them for what you think they may be worth.

        Question everything, including my stuff and continue to think critically. You'll be fine.

        Good luck.

        Comment


        • #5
          Very good professor! I understand pretty much what you are saying. Two other questions.

          Would it be worth the effort, in possible energy gain, to install something like a plastic corrugated shield under the ground mounted panels? I wouldn't think so, but thought I would get your opinion. The mounting system will be a couple of feet off the ground.

          As I age it seems the simplest things become difficult. I got out my handy phone with a compass to find due south and it seems to vary a little each time I use it. It may be just me thinking it is slightly different each time. Do you have any experience with the accuracy of a phone compass compared to an actual compass? Maybe I should get my real compass out and see if the compass magnetic south is consistent with the phone.

          Comment


          • #6
            Originally posted by Ward L View Post
            Very good professor! I understand pretty much what you are saying. Two other questions.

            Would it be worth the effort, in possible energy gain, to install something like a plastic corrugated shield under the ground mounted panels? I wouldn't think so, but thought I would get your opinion. The mounting system will be a couple of feet off the ground.

            As I age it seems the simplest things become difficult. I got out my handy phone with a compass to find due south and it seems to vary a little each time I use it. It may be just me thinking it is slightly different each time. Do you have any experience with the accuracy of a phone compass compared to an actual compass? Maybe I should get my real compass out and see if the compass magnetic south is consistent with the phone.
            Question everything until you understand (or think) it's not B.S.

            Yes/no on the sheet under the panels. Yes from the standpoint of providing some rigidity to the panels and perhaps adding some dead air space that may add some insulating value. No, or probably not, for the possibility of trapping debris/bugs, etc.that will rot/smell/perhaps corrode panels. Some folks use wire mesh. I've used 2"X 4" welded wire. The trick may be to figure out a way to hold the panels down for wind considerations while still being able to have some assurance of reasonably quick/easy access/moving the panels to clean out the gunk that will, in spite of everyone's best efforts and design, get under an array.

            Also, a lot of the time - by no means all the time - but perhaps more in the fall around So. CA, air temps. around an array during at least some solar collection times of day may well be higher than the water in the array, making insulation around the panels somewhat counterproductive, at least at some times.

            I'm mostly a Luddite with respect to things sold as various means to simplify my life and therefore can't live without. As a consequence of that choice, I have no experience with the devices you mention - another consequence being I'm also and probably the only person on earth w/out a cell phone. Anyway - I have a working compass and know how to use it. Seems to me using a phone as a compass is like using a radio as an alarm clock when I already have one (an alarm clock).

            A real compass with correction for mag. declination seems to work for me and is probably close enough. There are more accurate, but slightly more involved methods that involve putting a (straight) stick in the ground, making sure it's vertical w/a level and then noting the shadow it casts on a sunny day at solar noon, which shadow will be pretty much N-S aligned. I've used that method several times. For determining the actual time of solar noon, an approx. measure of solar noon, ~ +/- 1 minute or ~ 0.25 deg. or so can be found either from the net or by taking the mean of sunrise and sunset for any particular day as available from various sources. I use that method and a 6 ft. piece of pipe when I need more accuracy. Other methods are also possible.
            Last edited by J.P.M.; 01-26-2017, 11:25 AM. Reason: Spelling. + added a sentence or two.

            Comment


            • #7
              Solar Pathfinder used to have a free trial version available for down load for ST and PV.
              Try to download it and play with the tilt and orientation of your panels until you find the most desirable for your application.
              In my experience 10 degrees either way doesn't make that much of a difference in total BTU production.
              The software allows you one location per trial
              Last edited by LucMan; 01-26-2017, 02:36 PM.

              Comment

              Working...
              X