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electrical:solar:output [2023/02/11 12:53] frater_secessus [using PVWatts to find FSE and daily harvest] |
electrical:solar:output [2024/02/21 11:49] (current) frater_secessus [panel tilt] |
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Because the difference between lab and actual conditions is so large, some manufacturers also publish [[https:// | Because the difference between lab and actual conditions is so large, some manufacturers also publish [[https:// | ||
- | 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. |
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+ | ===== where and when ===== | ||
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+ | The location and season both have profound effects on solar harvest. [[opinion: | ||
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+ | You can estimate solar harvest using [[electrical: | ||
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===== lack of demand ===== | ===== lack of demand ===== | ||
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Tip: you can work backwards from cosine calculations and observed power harvests to find your system' | Tip: you can work backwards from cosine calculations and observed power harvests to find your system' | ||
+ | ==== 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: | ||
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// | // | ||
- | * hours of seasonal daylight | + | * short term |
- | * clouds | + | * angle at which rays strikes the panel (angle of incidence) |
- | * 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) |
- | | + | * 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: | + | |
* altitude (total irradiance ~+2.67%/ | * altitude (total irradiance ~+2.67%/ | ||
* humidity((https:// | * humidity((https:// | ||
+ | * 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: | Even the altitude and type of clouds can affect harvest: | ||
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==== using PVWatts to find FSE and daily harvest ==== | ==== using PVWatts to find FSE and daily harvest ==== | ||
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- | You can use [[https:// | ||
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- | === pick a location === | ||
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- | First, pick a location using the search bar: | ||
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- | {{https:// | ||
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- | === SOLAR RESOURCE DATA === | ||
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- | use the right-arrow graphic to accept the defaults. | ||
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- | === system info === | ||
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- | We need to make a couple changes here | ||
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- | * your array size in kW (200w = 0**.**200kW, | ||
- | * accept the default losses for MPPT systems. | ||
- | * if your panels are flat (most are) adjust tilt to zero | ||
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- | {{https:// | ||
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- | === results === | ||
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- | The first column is kWh/square meter/ | ||
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- | 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. | ||
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- | Example: | ||
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- | {{https:// | ||
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- | Note: the 2nd column is //rounded to whole numbers// | ||
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- | FSE x array wattage x ((100 - system losses) / 100) | ||
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- | ...which gives a more precise **605Wh/ | ||
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+ | this subsection has been [[electrical: | ||
==== insolation maps ==== | ==== insolation maps ==== | ||
Insolation maps attempt to combine the effects of the variables above to estimate hours of **full sun((1000W/ | Insolation maps attempt to combine the effects of the variables above to estimate hours of **full sun((1000W/ | ||
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Pro: | Pro: | ||
- | * +30% daily harvest | + | * optimal tilt will increase |
- | * can be used to increase harvest if roof space is maxxed (cannot add more panel) | + | * can be used to further |
Con: | Con: |