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opinion:solar:sizing.walkthrough [2022/05/27 14:38] frater_secessus [where and when we are camping] |
opinion:solar:sizing.walkthrough [2022/05/27 14:40] frater_secessus [where and when we are camping] |
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The good news is that different locations get roughly predictable average amounts of sunlight during specified months, and [[https://web.archive.org/web/20180811212703/http://www.solarinsolation.org/wp-content/uploads/2012/01/Solar_insolation.jpg|scientists have tabulated this data]]. The data is expressed in terms of hours of Full Sun Equivalent and assumes flat-mounted panels. You can think of this as "hours of laboratory-perfect conditions". The actual number of hours of sunlight in the day don't matter, nor do the average climatological conditions. 4 hours of FSE in Phoenix in summer might be 6.5 hours by the clock, while the same 4 hours of FSE in Anchorage might be 14 hours by the clock. No matter. The math works. | The good news is that different locations get roughly predictable average amounts of sunlight during specified months, and [[https://web.archive.org/web/20180811212703/http://www.solarinsolation.org/wp-content/uploads/2012/01/Solar_insolation.jpg|scientists have tabulated this data]]. The data is expressed in terms of hours of Full Sun Equivalent and assumes flat-mounted panels. You can think of this as "hours of laboratory-perfect conditions". The actual number of hours of sunlight in the day don't matter, nor do the average climatological conditions. 4 hours of FSE in Phoenix in summer might be 6.5 hours by the clock, while the same 4 hours of FSE in Anchorage might be 14 hours by the clock. No matter. The math works. |
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Example: if we need 2,317Wh and will be in an area with 4 hours of FSE in March, in theory we could get by with | |
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In practice 100% yield is not normal. After various losses MPPT-equipped systems will get more like 85%, and PWM systems around 72%.((again, if you have observed your own system and know what it does then use the actual number)). For the purposes of this article we will call this //system efficiency//. Examples: | |
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* theoretical - 1,200Wh harvest | |
* MPPT - 1,200Wh x 0.85 = 1,020Wh harvest | |
* PWM - 1,200Wh x 0.72 = 864Wh harvest | |
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==== where and when we are camping ==== | ==== where and when we are camping ==== |
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The actual hours of FSE will depend on where we are and month of the year. If we want the solar to Just Work((by itself, no help from [[electrical:12v:alt_and_solar|other charging sources]])) we have to size it for the worst average yield we will experience. Let's consider these very different scenarios: | The actual hours of FSE will depend on where we are and month of the year. If we want the solar to Just Work((by itself, no help from [[electrical:12v:alt_and_solar|other charging sources]])) **we have to size it for the worst average yield we will experience**. Let's consider these very different scenarios: |
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* vacation-camping with the family in Montana only in the summer | * vacation-camping with the family in Montana only in the summer |
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We can work backward from FSE and required Wh to get our required panel: Wh required / hours of FSE / system efficiency((I will stipulate .85 for MPPT and .70 for PWM)) = panel wattage. Assuming an MPPT-equipped system: | We can work backward from FSE and required Wh to get our required panel: Wh required / hours of FSE / system efficiency((I will stipulate .85 for MPPT and .70 for PWM)) = panel wattage required. Assuming an MPPT-equipped system: |
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* **Montana in July** - 2,316Wh((daily charging requirement)) / 6.44 FSE / 0.85 system efficiency = **423w of panel** | * **Montana in July** - 2,316Wh((daily charging requirement)) / 6.44 FSE / 0.85 system efficiency = **423w of panel** |