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opinion:solar:sizing.walkthrough [2022/04/20 14:24] frater_secessus [charge controllers] |
opinion:solar:sizing.walkthrough [2022/05/27 14:59] frater_secessus [Solar sizing walkthrough] |
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* how much power we will require - every single watt | * how much power we will require - every single watt | ||
* where we will camp, and what time of year we will be there | * where we will camp, and what time of year we will be there | ||
- | * avoiding shade and so the panels can actually work | + | * avoiding shade so the panels can actually work |
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4,168Wh / 12.0v nominal voltage = **347Ah** of lead-chemistry required. | 4,168Wh / 12.0v nominal voltage = **347Ah** of lead-chemistry required. | ||
+ | Also see the [[opinion: | ||
==== lithium ==== | ==== lithium ==== | ||
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Solar harvest directly affects how much panel we will need, but [[electrical: | Solar harvest directly affects how much panel we will need, but [[electrical: | ||
- | 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. | + | The good news is that different locations get roughly predictable average amounts of sunlight during specified months, and [[https:// |
- | + | ||
- | Example: | + | |
- | + | ||
- | In practice 100% yield is not normal. | + | |
- | + | ||
- | * theoretical - 1,200Wh harvest | + | |
- | * MPPT - 1,200Wh x 0.85 = 1,020Wh harvest | + | |
- | * PWM - 1,200Wh x 0.72 = 864Wh harvest | + | |
==== where and when we are camping ==== | ==== where and when we are camping ==== | ||
- | 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: | + | 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: |
* 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: | + | We can work backward from FSE and required Wh to get our required panel: |
* **Montana in July** - 2, | * **Montana in July** - 2, | ||
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MPPT controllers are more expensive so they often sized to the average solar harvest wattage rather than rated panel wattage. | MPPT controllers are more expensive so they often sized to the average solar harvest wattage rather than rated panel wattage. | ||
- | Example: | + | Example: |
==== minimum charging current ==== | ==== minimum charging current ==== | ||
+ | |||
+ | Note: if your offgrid system will use lead-chemistry batteries and needs to last for years then read this section. | ||
Lead-chemistry batteries have minimum and maximum charging current specifications. | Lead-chemistry batteries have minimum and maximum charging current specifications. | ||
- | Lead acid typically require a minimum of [[electrical: | + | Lead acid battteries |
- | * increase our panel and controller to cover it. 34.7A x 12v nominal / 0.85 system efficiency = 490w and a 40A controller. or, | + | * increase our panel and controller to cover it. 34.7A x 12v nominal / 0.85 system efficiency = 490w and a 40A controller.((this is //only// about charging current, not the panel required to charge the batteries fully over time)) A pleasant side effect is the system would make more power (+16%) than we strictly need for charging, so we might be a little looser with power use. Or might do a little better under adverse solar conditions. and/or, |
- | * add alternator charging or other high-current source (see below) and let that system | + | * add alternator charging or other high-current source (see below) and let that system |
Lithium batteries do not have a minimum charging current spec in the normal sense. | Lithium batteries do not have a minimum charging current spec in the normal sense. |