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opinion:solar:sizing [2022/11/08 19:29] frater_secessus [solar panels] |
opinion:solar:sizing [2023/12/26 11:57] frater_secessus [battery bank] |
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You will **need somewhat more Ah capacity** | You will **need somewhat more Ah capacity** | ||
- | * if you have undersized solar | + | * if you have undersized solar (lithium banks only) |
- | * you have lead-chemistry battery bank | + | * you have lead-chemistry battery bank (50% usable capacity rather than 80% usable) |
+ | * if charging is time-limited and you want maximal harvest from the alternator, shore, or other high-current charging source. | ||
You will need **somewhat less Ah capacity** | You will need **somewhat less Ah capacity** | ||
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* if you run loads in the daytime instead of at night | * if you run loads in the daytime instead of at night | ||
* if you have [[electrical: | * if you have [[electrical: | ||
+ | * if you drive often and have [[electrical: | ||
* you have lithium-chemistry battery bank((can be ~0.62% the size of the lead bank, due to deeper [[electrical: | * you have lithium-chemistry battery bank((can be ~0.62% the size of the lead bank, due to deeper [[electrical: | ||
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You will **need somewhat more solar** | You will **need somewhat more solar** | ||
- | * if you live in an area with relatively little sun, like the American Northwest. | + | * if you live in an area with relatively little sun, like the American Northwest, Northern Europe, etc. |
* if you want to run more [[electrical: | * if you want to run more [[electrical: | ||
- | * if you live offgrid full time (FT) | + | * if you live offgrid full time (FT) or spend long periods [[camping: |
* to run things off [[electrical: | * to run things off [[electrical: | ||
* to charge a bigger [[electrical: | * to charge a bigger [[electrical: | ||
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* to charge lithium banks | * to charge lithium banks | ||
+ | === calculating real numbers === | ||
+ | |||
+ | |||
+ | **Accurate calculations** would involve: | ||
+ | |||
+ | * the Ah/Wh to be replaced | ||
+ | * the charging efficiency of the battery chemistry (We might ballpark, 99% for Lithium, 80% for FLA, and 90% for AGM. | ||
+ | * overall efficiency of the solar setup (we can ballpark 85% for MPPT setups, 70% for PWM) | ||
+ | * [[electrical: | ||
+ | * the contribution of any other charging sources | ||
+ | * minimum charging current requirements, | ||
+ | |||
+ | Let's assume a 200Ah AGM bank depleted to 50% SoC, wintering in [[camping: | ||
+ | |||
+ | - 200Ah x 50% = **100Ah to be replaced** | ||
+ | - converting to Wh, 100Ah x nominal 12v = **1200Wh to be replaced** | ||
+ | - battery charging efficiency of 90% means we need **1333.33Wh of actual charging power** to replace the 1200Wh (1200Wh / 0.90) | ||
+ | - the solar install operates at a 85% efficiency, so we need **1568.63Wh of harvestable sun** power landing on the panels (1333.33Wh / 0.85) | ||
+ | - [[electrical: | ||
+ | - So we need **590W of panel** (1568.63Wh / 3.08 hours) | ||
+ | |||
+ | In practice you probably won't be drawing your bank to the lowest allowed level each day; substitute your [[electrical: | ||
+ | |||
+ | |||
+ | **Note**: | ||
==== solar charge controller ==== | ==== solar charge controller ==== | ||
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[[electrical: | [[electrical: | ||
- | A common **rule of thumb for sizing PWM controllers** is to divide [[electrical: | + | A common **rule of thumb for sizing PWM controllers** is to divide [[electrical: |
MPPT sizing is less straightforward. These tend to cost 2-3x as much for a given rating as PWM, so oversizing can get $$$. MPPT have the ability to [[electrical: | MPPT sizing is less straightforward. These tend to cost 2-3x as much for a given rating as PWM, so oversizing can get $$$. MPPT have the ability to [[electrical: | ||
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* 300w of panel might make 249w under good conditions. | * 300w of panel might make 249w under good conditions. | ||
* MPPT smaller than 10A are rare, so 100w-150w of panel are usually put on 10A mppt. | * MPPT smaller than 10A are rare, so 100w-150w of panel are usually put on 10A mppt. | ||
+ | * [[https:// | ||