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opinion:solar:sizing [2022/05/24 15:11] frater_secessus [solar sizing - the Big Picture] |
opinion:solar:sizing [2023/10/22 11:08] frater_secessus [solar panels] |
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In general, bigger systems (higher wattage panels, bigger controllers, | In general, bigger systems (higher wattage panels, bigger controllers, | ||
- | Broadly speaking, lithium chemistries are most cost-effective when the camping experience is expected to last for many years and the batteries stored inside.((Note that it is false economy to pay for 10 years of battery cycling (as with lithium) if one is going to wreck it in 2 years)). | + | |
==== days of reserve ==== | ==== days of reserve ==== | ||
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Your **reserve requirements** will profoundly affect the size, complexity, and cost of the system. | Your **reserve requirements** will profoundly affect the size, complexity, and cost of the system. | ||
Sizing for an overnight camping trip is easy; sizing for a three day trip a challenge; | Sizing for an overnight camping trip is easy; sizing for a three day trip a challenge; | ||
+ | |||
+ | ===== battery bank ===== | ||
+ | |||
+ | Once you know your daily power and reserve requirements you can spec out a battery | ||
+ | |||
+ | Broadly speaking, lithium chemistries are most cost-effective when the camping experience is expected to last for many years and the batteries stored inside.((Note that it is false economy to pay for 10 years of battery cycling (as with lithium) if one is going to wreck it in 2 years)). | ||
+ | |||
+ | Having an **undersized bank** means //running out of power// at night. | ||
+ | |||
+ | Having an **oversized lead bank** for your charging ability results in [[electrical: | ||
+ | |||
+ | IMO, with lead chemistries((flooded, | ||
+ | |||
+ | |||
+ | After figuring your rough capacity requirements, | ||
+ | |||
+ | You will **need somewhat more Ah capacity** | ||
+ | |||
+ | * if you have undersized solar | ||
+ | * you have lead-chemistry battery bank | ||
+ | |||
+ | You will need **somewhat less Ah capacity** | ||
+ | |||
+ | * if you run loads in the daytime instead of at night | ||
+ | * if you have [[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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- | The bare-bones | + | The absolute |
Most people will do best with much more panel-to-battery depending on battery chemistry, [[opinion: | Most people will do best with much more panel-to-battery depending on battery chemistry, [[opinion: | ||
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- | |||
You will **need somewhat more solar** | You will **need somewhat more solar** | ||
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* 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. | ||
* 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: | ||
- | * to charge lead-chemistries | + | * to charge lead-chemistry |
You will **need somewhat less solar** | You will **need somewhat less solar** | ||
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* if you live in an area with a great deal of sun, like the American Southwest. | * if you live in an area with a great deal of sun, like the American Southwest. | ||
* if you camp recreationally mainly in the summer when solar harvest is easier | * if you camp recreationally mainly in the summer when solar harvest is easier | ||
- | * if you [[electrical: | + | * if you [[electrical: |
* if you live in the vehicle part time (PT) and can charge consistently from [[electrical: | * if you live in the vehicle part time (PT) and can charge consistently from [[electrical: | ||
* if you voluntarily reduce your power consumption | * if you voluntarily reduce your power consumption | ||
* if you time-shift loads to periods like the afternoon when [[electrical: | * if you time-shift loads to periods like the afternoon when [[electrical: | ||
+ | * 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: | ||
+ | * 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) | ||
+ | |||
+ | You may find it easier in the long-term to model this kind of thing in a spreadsheet. | ||
+ | |||
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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:// | ||
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* you have a lithium battery bank but camp in long stretches with minimal solar. | * you have a lithium battery bank but camp in long stretches with minimal solar. | ||
* you have enough solar to [[electrical: | * you have enough solar to [[electrical: | ||
- | |||
- | ===== battery bank ===== | ||
- | Having an **undersized bank** means //running out of power// at night. | ||
- | |||
- | Having an **oversized lead bank** for your charging ability results in [[electrical: | ||
- | |||
- | IMO, with lead chemistries((flooded, | ||
- | |||
- | You will **need somewhat more Ah capacity** | ||
- | |||
- | * if you have undersized solar | ||
- | * you have lead-chemistry battery bank | ||
- | |||
- | You will need **somewhat less Ah capacity** | ||
- | |||
- | * if you run loads in the daytime instead of at night | ||
- | * if you have [[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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* disadvantages - in-place camping makes DC-DC charging less cost-effective. | * disadvantages - in-place camping makes DC-DC charging less cost-effective. | ||
- | This isn't a game or vacation anymore; | + | FT boondocking |
Battery banks tend to be either lithium or flooded 6v golf cart((CG2)) batteries in series, both of which have lifetime $/kAh costs under $2. | Battery banks tend to be either lithium or flooded 6v golf cart((CG2)) batteries in series, both of which have lifetime $/kAh costs under $2. |