[Greenbuilding] Solar Water Heater Tilt
Gennaro Brooks-Church
info at ecobrooklyn.com
Mon Feb 9 09:55:05 CST 2009
RE: The standard answer for tilting your solar water ehater collector
is latitude plus 15 degrees.
Does this general rule of thumb apply to solar PV too?
Gennaro Brooks-Church
Cell: 1 347 244 3016 USA
www.EcoBrooklyn.com
On Mon, Feb 9, 2009 at 10:24 AM, Gary <gary at builditsolar.com> wrote:
>
>> From: Lawrence Lile <LLile at projsolco.com>
>> Subject: [Greenbuilding] Solar Water Heater Tilt
>> To: GB REPP <GREENBUILDING at listserv.repp.org>
>> Message-ID:
>>
>> <AC254829C2A6324CB4DF94CED1DB37FB46818F16E7 at exchange.ProjSolCo.local>
>> Content-Type: text/plain; charset="us-ascii"
>>
>>
>>
>> The standard answer for tilting your solar water ehater collector is
>> latitude plus 15 degrees. For my latitude that is about 54 degrees.
>>
>> This article
>> http://www.macslab.com/optsolar.html
>>
>> seems to indicate that you can do a little better overall if you tilt a
>> little more toward the winter sun. For my latitude (38.9 deg.) the author
>> recommends about 64 degrees.
>>
>>
>> However, others have argued that you don't really get much sun int he
>> winter, more cloudy days, colder ambient, and you don't really gain so much
>> from optimum tilt. it is "good enough" just to surface mount the collectors
>> on a south facing roof and be done with it. It is a lot simpler to mount a
>> collector flat against the roof than tilt it, and they say it makes little
>> difference.
>>
>> Overall I expect this system to produce all of my hot water in the summer
>> and about half of it in the winter. I have enough metering history on my
>> hot water heater that I'll be able to tell, very closely, if this is the
>> case.
>>
>> My South roof is 4:12, or about 18 degrees. So the question is, how much
>> difference will it make if I mount solar collectors flat against the 4:12
>> roof, versus at one of those two angles? I'd like to be able to say "yes,
>> that will make such and such quantifiable production of hot water".
>>
>> If you need to know, I have two AEC 4X7 ft. collectors and 85 gallons of
>> water storage.
>>
>> Would RETscreen be able to answer such a question? That alone would be a
>> good reason to get it running, I haven't really tried it out.
>>
>>
>> -Lawrence
>>
>>
>
> Hi,
> You can get a pretty good idea just by running Radiation On Collector for
> the two tilt angles and do the "calculate for months". Free download here:
> http://www.builditsolar.com/Tools/RadOnCol/radoncol.htm
>
> Runs for 18 degs and 55 degs are pasted in below.
> The last column is the one you want to compare.
> You may have to change to a fixed width font to make the output readable.
>
> On total radiation, 18 degrees wins by a bit year round, but 55 degrees
> provides much more even year round radiation, and may provide more hot water
> if you can't actually use all the hot water that 18 degrees produces in the
> summer -- so maybe this does not really answer the question after all :)
> Bear in mind that the outputs are for a fully sunny day.
>
> As yet another approach, I use a large collector area and a very steep tilt
> angle (70+ degs) -- this seems to be working well in the fall/winter (90%
> fraction so far), and I think will also do fine in the summer without
> overheating so much:
> http://www.builditsolar.com/Experimental/PEXColDHW/Overview.htm
>
> Radiation On Collector Runs:
> 18 degrees tilt:
> Month by Month Summary of Sun on Collector
> (100% sunny weather)
>
> Collector Area: 1.0 (sqft)
> Collector Azimuth: 0.0 (deg) measured from South
> Collector Tilt: 18.0 (deg) measured from horiz
> Latitude: 38.9 (deg)
> Altitude above SL: 0.0 (ft) Above Sea Level
>
> Date ---- Sun ---------------- Collector -----------------------
> Month Day Direct Di- Total Direct Difuse Total
> Normal fuse
> 1 21 2238 130 2368 1353 127 1480
> 2 21 2639 158 2797 1713 154 1867
> 3 21 2932 208 3140 2015 203 2218
> 4 21 3095 302 3396 2148 294 2442
> 5 21 3155 383 3538 2187 373 2561
> 6 21 3162 423 3585 2173 413 2586
> 7 21 3054 415 3469 2124 405 2529
> 8 21 2914 354 3268 2041 345 2386
> 9 21 2729 254 2982 1893 247 2140
> 10 21 2467 179 2646 1613 174 1788
> 11 21 2168 136 2304 1310 133 1443
> 12 21 2038 117 2155 1179 114 1294
> Sum 32591 3059 35649 21749 2984 24733
>
> Radiation in BTU/day
>
> 55 degree tilt:
> Month by Month Summary of Sun on Collector
> (100% sunny weather)
>
> Collector Area: 1.0 (sqft)
> Collector Azimuth: 0.0 (deg) measured from South
> Collector Tilt: 55.0 (deg) measured from horiz
> Latitude: 38.9 (deg)
> Altitude above SL: 0.0 (ft) Above Sea Level
>
> Date ---- Sun ---------------- Collector -----------------------
> Month Day Direct Di- Total Direct Difuse Total
> Normal fuse
> 1 21 2238 130 2368 1879 102 1981
> 2 21 2639 158 2797 2078 124 2203
> 3 21 2932 208 3140 2072 164 2236
> 4 21 3095 302 3396 1811 237 2049
> 5 21 3155 383 3538 1575 301 1877
> 6 21 3162 423 3585 1465 333 1798
> 7 21 3054 415 3469 1520 327 1847
> 8 21 2914 354 3268 1713 279 1992
> 9 21 2729 254 2982 1934 199 2134
> 10 21 2467 179 2646 1965 141 2105
> 11 21 2168 136 2304 1824 107 1931
> 12 21 2038 117 2155 1735 92 1827
> Sum 32591 3059 35649 21573 2406 23979
>
> Radiation in BTU/day
>
> Gary
>
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