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opinion:solar:sizing.walkthrough [2022/04/20 14:51] frater_secessus [minimum charging current] |
opinion:solar:sizing.walkthrough [2022/05/27 14:40] frater_secessus [where and when we are camping] |
Solar harvest directly affects how much panel we will need, but [[electrical:solar:output|harvest will vary wildly]] depending on conditions, type of [[electrical:solar:charge_controller|solar charge controller]], time of year, location, even ambient temperatures and altitude. | Solar harvest directly affects how much panel we will need, but [[electrical:solar:output|harvest will vary wildly]] depending on conditions, type of [[electrical:solar:charge_controller|solar charge controller]], time of year, location, even ambient temperatures and altitude. |
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The good news is that different locations get roughly predictable average amounts of sunlight during specified months, and 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 have 300w of panel in an area with 4 hours of FSE in March, we could //theoretically// harvest 1,200Wh per day. 300w rated panel x 4 hours FSE = **1,200Wh**. | |
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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 = 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** |