Re: 2 Panels Instead Of 3?
Quote:
Originally Posted by
mohawk
I've looked through the post here and on web sites and I'm not sure on how many solar panels we will need. We have a 30' rnd pool-not 27' like I thought earlier, it was a long winter. I want to run 2-4x20 panels side-by-side down the length of the deck. Do you think 2 would keep the water in the upper 80s ? Can you run the panels side-by-side(length to length) with ease or am I going to have alot of plumbing on the ground? Does this make sense to you-I'm not sure if I'm explaining it right.:confused:
Let me see: 30' round is 707 square feet. I think you need at least one more panel.
However, the good thing is you can put in 2 panels, see if they are enough, and, if not, add another. My parents had the same ratio of pool area to panels, only got 6 direct hours of sun a day and the water stayed in the low 80s. You'll need to keep the panels on the ground, because they will heat the ground, and then the ground will, after the sun passes, warm the water some more. Remember: As long as the water from the panels is even 1 degree warmer than the pool it's adding BTUs--heat energy. You'll also need to be good about using your solar cover when you aren't swimming.
If you mean can you hook the panels in parallel rather than in series, the answer is not only "Yes" but that it's better that way. If all the water must first go through one panel, then the next, it sets up back pressure and makes your pump work harder. Your flow of water through the panels will be less, so it won't heat your pool as effectively. But in parallel, resistance will drop and more water will flow.
A few years ago I split my system from strictly series (one panel after another) into 2 parallel systems. My water warmed up far faster because I got double the flow. It worked even better than I hoped!
Remember: the more water you flow through your system, the warmer your pool will be. Basically, if your panels are cool to the touch on a blazing hot day, or at least don't burn you, they are doing their job efficiently.
There are lots of technical reasons why TOO fast a flow loses efficiency, but for most people they really do best by moving as much water through their panels as they can. "Letting the water heat up" with a slower flow SEEMS to make sense, but, in fact, is wrong.
Remember: the more BTUs you can add every hour, the more your pool will warm. It's not temperature--you just want the panel water warmer than the pool. A match burns at around 750-800 degrees but a 5 gallon bucket of 90 degree water will add FAR more heat energy to your pool than the match.
Re: 2 Panels Instead Of 3?
If I have them at a 45 angle, wouldn't that heat the water better than on the ground? The panels will face south west and will get direct sun most of the day. I was hoping for less panels cuz I still need to buy the solar reel which will run over $300.
Re: 2 Panels Instead Of 3?
Quote:
Originally Posted by
mohawk
If I have them at a 45 angle, wouldn't that heat the water better than on the ground? The panels will face south west and will get direct sun most of the day. I was hoping for less panels cuz I still need to buy the solar reel which will run over $300.
That depends on how they are exposed. If they are FULLY exposed to the sun, it doesn't matter if they are flat or angled. You only need to angle them if they don't get full sun otherwise. But the ground is your friend: It asks as a giant heat sink and storage device that allows you to continue to use your panels after the sun passes. Besides, a rack costs money as well. You can always add that if you need to.
Re: 2 Panels Instead Of 3?
If you are at a very northern latitude where the sun is not very directly overhead in the summer, then angling the panel will help. However, the effect is rather small until the sun is quite a ways away from being directly overhead (at noontime). The loss in heating goes as the cosine of the angle difference between the incidence of the sun and the perpendicular of the panel.
For example, if the sun is 20 degrees away from directly overhead, then you get about 94% of what you would get if your panel were angled 20 degrees to "point at" the sun. If the sun is 40 degrees away from directly overhead, then you get about 77%. I'm ignoring any positive effect from ground heating that Carl mentioned and that may more than make up for the loss during the day.
Richard
Re: 2 Panels Instead Of 3?
If you are the computer inclined, here is an application that can help you determine what your average temp is with and without solar. You can specify not only what direction the panels are but also, what type of material they are over (i.e. roof, ground etc.). It takes a bit of time to set up but it is better than a swag.
http://www.canren.gc.ca/tech_appl/in...aId=5&PgID=484
Re: 2 Panels Instead Of 3?
Thanks for the info. We live in a suburb of Minneapolis and I have no idea what degree the sun would be at noon. I'll ask the husband but he'll probably give me that funny look-like why do you want to know that? Denise
Re: 2 Panels Instead Of 3?
Quote:
Originally Posted by
mohawk
Thanks for the info. We live in a suburb of Minneapolis and I have no idea what degree the sun would be at noon. I'll ask the husband but he'll probably give me that funny look-like why do you want to know that? Denise
Um, there is no hard and fast answer. It changes every day of the year. Of course, it will be highest at the Summer Solstice, when the sun reaches its maximum latitude of 23 degrees and some minutes (The latitude of the Tropic of Cancer--there, when the sun is at its highest, it is directly overhead--90 degrees). So you have to know your latitude (probably 42 or 43 degrees), so the sun at its highest will probably be about 70 or 71 degrees.
If you really want to be exact, get your lat/long off your GPS if you have one. Then you'll need a Nautical Almanac (though you can find them on-line) to find out at exactly what time, at GMT, the Sun is at its highest "Declination" (latitude). You have to adjust for the time difference and then subtract the Declination from your latitude. Then subtract THAT number from 90 and you'll have the sun's angle at exactly that time.
But if your latitude is 43 degrees, the sun will be about 70 degrees....
Re: 2 Panels Instead Of 3?
And 70 degrees is 20 degrees away from vertical 90 degrees so the lower efficiency by having a flat panel vs. angled is 94% so isn't that much (i.e. just a 6% loss in efficiency). Like I said, I think this "angling" difference will only be an issue for you if you live way, way north in Canada, but at least now you have the tools to know for sure.
As Carl says, the angle of the sun at noontime depends on the time of year. The main reason to have the panels angled isn't so much for the summer solstice time as it is for the beginning and end of the swim season when you more desperately need and want solar heating of the pool. At such times of the year (spring and fall) the sun is lower in the sky (at noontime). Those that live at the equator don't worry so much about these problems, but I suppose they've got other things to worry about!
Richard
Re: 2 Panels Instead Of 3?
I think flat on the ground sounds good--now if only my brain would stop spinning.:D Denise
Re: 2 Panels Instead Of 3?
Mohawk,
Unfortunately you inadvertently turned on one place where I like all the calculations--the old celestial navigation via sextant became a hobby of mine several years ago...usually I like to avoid the math and buzz words, but with that stuff I get like Chem_Geek!:p
(first time I plotted my house's lat/long I cheerfully informed my wife the 1200' hill we lived on was 200 miles out to see!:eek: )
But in more practical terms, my panels are perfectly flat--because they are also my pool deck. My strongest sun is still mid-day, but I get a lot of morning and late afternoon sun--they are aligned well for that. I don't get the ground effect but the water keeps my deck cool!
Normally, the pool stores and solar companies say you need about half the surface area of your pool as panels--but I think that's only for very early spring and late fall. Otherwise in mid summer your water will hit 100! You are at the low end, just over 20% but I guarantee you can make a solid difference with that--been there, done it. I have about 35% of my surface area in panels, and that's more than enough--but I use a solar cover if it's going to cool off at all...and yes, I do have a reel for it.
