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electrical:solar:output [2022/08/01 12:05]
frater_secessus [panel temperature] |
electrical:solar:output [2024/05/28 19:01] (current)
frater_secessus [cleanliness] |
| 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. | 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. |
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| 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. |
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| | ===== where and when ===== |
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| | 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 will be about half of summer harvest. |
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| | You can estimate solar harvest using [[electrical:solar:pvwatts|models like PVwatts]]. |
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| | ===== lack of demand ===== |
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| | Solar panels do not //push// power; they respond to the [[electrical:solar:charge_controller|solar charge controller]]'s demand as it tries to meet your present needs. When those needs are minimal (battery already charged, small loads) the controller and panels will be loafing. |
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| | Related: [[electrical:solar:status|is my solar working?]] |
| ===== charge controller type ===== | ===== charge controller type ===== |
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| [[electrical:solar:charge_controller#mppt|MPPT]] controllers can run the panel at max output when needed, but are much more expensive. | [[electrical:solar:charge_controller#mppt|MPPT]] controllers can run the panel at max output when needed, but are much more expensive. |
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| | ===== overpaneling ===== |
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| | Perhaps counterintuitively, setups with [[electrical:solar:overpaneling#vs_charge_controller|ample panel]] may see lower peak outputs than smaller setups. This occurs because the overpaneled systems can get the bank charged before local solar noon when maximal harvest can be observed. This is a feature, not a bug. Overpaneled systems are built to meet needs under less-than-optimal conditions. If you want to see Big Numbers, start a huge load at local solar noon under good solar conditions. |
| ===== wiring losses ===== | ===== wiring losses ===== |
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| ===== zenith angle ===== | ===== zenith angle ===== |
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| The sun will climb in the sky until it reaches its highest point for the day (local solar noon), then will start dropping again. For a given latitude and time of day [[https://www.esrl.noaa.gov/gmd/grad/solcalc/azel.html|the sun's location in the sky is calculable]] and can give you the //cosine of solar zenith angle// ("cosine" hereafter).((the complement of elevation angle)). You can use the cosine to understand how much power your system might put out. | The sun will climb in the sky until it reaches its highest point for the day (local solar noon), then will start dropping again. This affects how much power you can harvest: |
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| | {{ https://www.solarreviews.com/content/images/blog/post/212-PSH.jpg?500 }} |
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| | For a given latitude and time of day [[https://www.esrl.noaa.gov/gmd/grad/solcalc/azel.html|the sun's location in the sky is calculable]] and can give you the //cosine of solar zenith angle// ("cosine" hereafter).((the complement of elevation angle)). You can use the cosine to understand how much power your system might put out. |
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| Examples: if you have 200w of panels, your mppt controller typically yields 83% after derating, and the calculated cosine is .70 then you might expect ~116w in clear conditions at that time in that location. (200 x .83 x .7 = 116.2). | Examples: if you have 200w of panels, your mppt controller typically yields 83% after derating, and the calculated cosine is .70 then you might expect ~116w in clear conditions at that time in that location. (200 x .83 x .7 = 116.2). |
| Another way of thinking about this is that panel ratings are given for 1,000w/meter<sup>2</sup>. At that time and place only 700w/meter<sup>2</sup> land on the panel. (1000 x .70 = 700) | Another way of thinking about this is that panel ratings are given for 1,000w/meter<sup>2</sup>. At that time and place only 700w/meter<sup>2</sup> land on the panel. (1000 x .70 = 700) |
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| | Tip: you can work backwards from cosine calculations and observed power harvests to find your system's overall efficiency in different conditions. |
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| | ==== paradox of big solar ==== |
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| | All other things being equal, peak harvest will happen at local solar noon((rarely clock-noon)) when the sun is highest in the sky. |
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| | 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. |
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| //Insolation//((**In**coming **Sol**ar Radi**ation**)) is the the amount of solar power reaching the panels. This can be affected by: | //Insolation//((**In**coming **Sol**ar Radi**ation**)) is the the amount of solar power reaching the panels. This can be affected by: |
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| * 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)) | * 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)) | * 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 |
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| Even the altitude and type of clouds can affect harvest: | Even the altitude and type of clouds can affect harvest: |
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| | ==== using PVWatts to find FSE and daily harvest ==== |
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| | this subsection has been [[electrical:solar:pvwatts|moved here]] |
| ==== insolation maps ==== | ==== 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. | 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]]. |
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| [[https://web.archive.org/web/20180811212703/http://www.solarinsolation.org/wp-content/uploads/2012/01/Solar_insolation.jpg|cities FSE by month]] | [[https://web.archive.org/web/20180811212703/http://www.solarinsolation.org/wp-content/uploads/2012/01/Solar_insolation.jpg|cities FSE by month]] |
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| | [[https://solarpanelpower.ca/wp-content/uploads/2018/06/Full-Size-Solar-Power-Map-Canada.png|Canadian FSE]] |
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| ==== Derated output X FSE ==== | ==== Derated output X FSE ==== |
| Pro: | Pro: |
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| * +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) |
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| Con: | Con: |
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| [[https://www.sciencedirect.com/science/article/pii/S1876610214011874|According to lab testing]], dusty panels cause a derating of 5%-6%. | [[https://www.sciencedirect.com/science/article/pii/S1876610214011874|According to lab testing]], dusty panels cause a derating of 5%-6%. |
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| | ===== sensitivity to light spectrum ===== |
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| | Note: these differences exist but are of little practical effect. |
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| | ==== differences in light ==== |
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| | * 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) |
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| | Since the latter point is counterintuitive: |
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| | >> 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. )) |
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| | ==== differences in panel sensitivity ==== |
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| | {{ 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. |
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| | * [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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