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--- electrical:solar:output [2023/02/11 12:51]
frater_secessus [using PVWatts to find FSE and daily harvest]
+++ electrical:solar:output [2024/11/22 11:44] (current)
frater_secessus [where and when]
@@ Line 14: / Line 14: @@
 Because the difference between lab and actual conditions is so large, some manufacturers also publish [[https://www.infiniteenergy.com.au/difference-between-max-power-stc-noct/|NOCT]]((Nominal Operating Cell Temperature)) specs, a //derated// (lowered) set of specs which might or might not be more indicative of what you will see in your use case.  NOCT is another tool in the toolbox, not gospel truth.
-In practical terms, it's common to see a maximum of 75% of STC under good conditions, more under great conditions, and much less under poor solar conditions.
+In practical terms, it's common to see a maximum of 75% of STC under good conditions, more under great conditions, and much less under poor solar conditions. And about half of that in winter.
+===== where and when =====
+The location and season both have profound effects on solar harvest. [[opinion:frater_secessus:panelsizesforinsolation#representative_areas|For example]], Phoenix AZ has **over 8.5x the amount of solar power** available in summer as Seattle WA in the winter.  For any given location, winter harvest can tiny compared to summer harvest.
+For more specific numbers you can estimate solar harvest using [[electrical:solar:pvwatts|models like PVwatts]].
 ===== lack of demand =====
@@ Line 79: / Line 89: @@
 Tip:  you can work backwards from cosine calculations and observed power harvests to find your system's overall efficiency in different conditions.
+==== paradox of big solar ====
+All other things being equal, peak harvest will happen at local solar noon((rarely clock-noon)) when the sun is highest in the sky.
+This leads to a paradox:  some systems with [[electrical:solar:overpaneling#vs_battery_bank|relatively large arrays]] will have completed Bulk charging before solar noon and so do not have the chance to demonstrate full output.  In this scenario a smaller array could theoretically show higher //peak// output power but could not produce more overall Wh over the course of the day than the larger array.
@@ Line 86: / Line 101: @@
 //Insolation//((**In**coming **Sol**ar Radi**ation**)) is the the amount of solar power reaching the panels.  This can be affected by:
-    * hours of seasonal daylight
+    * short term
-    * clouds
+      * angle at which rays strikes the panel (angle of incidence) due to time of day.  At low angles effectively less panel area is exposed to sunlight.
-    * rain, fog
+      * amount of atmosphere the rays have to penetrate (less at solar noon, more at other times or anytime sun is relatively lower on the horizon)
-    * angle at which rays strikes the panel (angle of incidence).  At low angles effectively less panel area is exposed to sunlight.
+      * clouds
-    * amount of atmosphere the rays have to penetrate (less at solar noon, more at other times or anytime sun is relatively lower on the horizon)
+      * rain, fog
-    * air quality:  \\ smoke((http://www.cheaprvliving.com/forums/showthread.php?tid=26592&pid=333826#pid333826)),((http://www.cheaprvliving.com/forums/showthread.php?pid=331627#pid331627))
+      * air quality:  \\ smoke((http://www.cheaprvliving.com/forums/showthread.php?tid=26592&pid=333826#pid333826)),((http://www.cheaprvliving.com/forums/showthread.php?pid=331627#pid331627))
     * altitude (total irradiance ~+2.67%/1000')((https://www.sciencedirect.com/science/article/abs/pii/S1011134496000188))
     * humidity((https://www.researchgate.net/publication/338412686_Performance_study_of_Monocrystalline_and_Polycrystalline_solar_PV_modules_in_tropical_environments))
+    * long term - roughly speaking, you can expect ~half the harvest in winter compared to summer
+      * solar angle due to **time of year**.
+      *  hours of seasonal daylight
 Even the altitude and type of clouds can affect harvest:
@@ Line 124: / Line 143: @@
 ==== using PVWatts to find FSE and daily harvest ====
-You can use [[https://pvwatts.nrel.gov/index.php|PVWatts]] to find solar info for a particular place and month.
-=== pick a location ===
-First, pick a location using the search bar:
-{{https://img.mousetrap.net/misc/pvwatts0.jpg}}
-=== SOLAR RESOURCE DATA ===
-use the right-arrow graphic to accept these defaults.
-=== system info ===
-We need to make a couple changes here
-  * your array size in kW (200w = 0**.**200kW, mind the decimal!)
-  * accept the default losses for MPPT systems.  PWM systems should use something like 30%
-  * if your panels are flat (most are) adjust tilt to zero
-{{https://img.mousetrap.net/misc/pvwatts-annotated.jpg}}
-=== results ===
-The first column is kWh/square meter/**day**, AKA Hours of Full Sun Equivalent.
-The second column is kWh harvested per **month**. To find average maximal harvest per day divide this figure by the number of days in that month.
-Example:  In January in this location the system could make 17kWh.  17 divided by 31 days = 0.548kWh/day,  (**548Wh/day**).
-{{https://img.mousetrap.net/misc/pvwatts2-annotated.jpg}}
-Note:  the 2nd column is //rounded to whole numbers//.  This makes little difference with large residential installs but can distort the result with our small systems.  You can use the FSE number to do the math for your setup directly:
-  FSE x array wattage x ((100 - system losses) / 100)
-...which gives a more precise **605Wh/day**.  You may want to plug that formula into a spreadsheet for easy re-use.
+this subsection has been [[electrical:solar:pvwatts|moved here]]
 ==== insolation maps ====
 Insolation maps attempt to combine the effects of the variables above to estimate hours of **full sun((1000W/square meter)) equivalent** (FSE) per day for large areas.  This can be helpful when planning [[camping:snowbirding|moves around the country]].
@@ Line 234: / Line 203: @@
 Pro:
-  * +30% daily harvest is possible, depending on the sun's position((peak harvest may be much higher at some times but daily harvest is more applicable for offgrid vanlife))
+  * optimal tilt will increase harvest when the sun is low and skies are clear.((peak harvest numbers are more impressive but of less import.))
-  * can be used to increase harvest if roof space is maxxed (cannot add more panel)
+  * can be used to further increase harvest if roof space is maxxed (cannot add more panel)
 Con:
@@ Line 264: / Line 233: @@
 [[https://www.sciencedirect.com/science/article/pii/S1876610214011874|According to lab testing]], dusty panels cause a derating of 5%-6%.
+===== sensitivity to light spectrum =====
+Note:  these differences exist but are of little practical effect.
+==== differences in light ====
+  * direct sunlight is broad-spectrum (a mix of light wavelengths)
+  * when the sun is near the horizon the available light is more red (longer wavelengths)
+  * when skies are overcast or otherwise diffused the available light is more blue (shorter wavelengths)
+Since the latter point is counterintuitive:
+>> at visible wavelengths, overcasts are far from spectrally neutral transmitters of the daylight incident on their tops. Colorimetric analyses show that overcasts make daylight bluer and that the amount of bluing increases with cloud optical depth. Simulations using the radiative-transfer model MODTRAN4 help explain the observed bluing: multiple scattering within optically thick clouds greatly enhances spectrally selective absorption by water droplets.((at visible wavelengths, overcasts are far from spectrally neutral transmitters of the daylight incident on their tops. Colorimetric analyses show that overcasts make daylight bluer and that the amount of bluing increases with cloud optical depth. Simulations using the radiative-transfer model MODTRAN4 help explain the observed bluing: multiple scattering within optically thick clouds greatly enhances spectrally selective absorption by water droplets. ))
+==== differences in panel sensitivity ====
+{{ https://img.mousetrap.net/misc/Spectral_Response_PV-annotated2.jpg?125}}
+Note:   visible light is roughly 400-750nm.((https://en.wikipedia.org/wiki/Light)).  Below that is UV and above that is infrared.
+  * [redder end]
+  * CIGS (copper indium gallium selenide) thin-film panels have peak sensitivity around 950nm.
+  * monocrystalline silicon panels (mono, c-Si) tend to have maximal spectral response around 900nm
+  * polycrstalline silicon panels (poly, mc-Si,pc-Si)((mc-Si and pc-Si are both made from multiple crystals.  Grain size differes.  See https://www.pveducation.org/pvcdrom/manufacturing-si-cells/types-of-silicon)) slightly lower than mono.  We will stipulate 850nm.
+  * GaAs (gallium arsenide) thin-film panels have peak response around 825nm.
+  * CdTe (Cadmium Telluride) flex panels, the most popular thin-film type, have peak response around 750nm.
+  * amorphous silicon panels (a-Si, the original noncrystalline panel) - have peak response around 550nm.
+  * [ bluer end ]

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