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opinion:solar:sizing [2022/05/24 15:15]
frater_secessus [battery bank] |
opinion:solar:sizing [2023/06/13 21:13]
frater_secessus [solar charge controller] examples |
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| The bare-bones minimum for solar, assuming everything goes exactly right,((shallow discharge, excellent solar conditions, well-designed system)) is [[electrical:solar:panel-bank_ratio|1:1]] panel-to-Ah. e.g. 150w for a 150Ah battery bank. In reality, solar that small is often insufficient unless one has unusually small power needs or adds in another form of charging (see below). [[opinion:frater_secessus:beginner_mistakes|Newbies typically think their power needs are small]] until they sit down to read those power labels on the stuff that want to run. D'oh! | The absolute minimum for solar, assuming everything goes exactly right,((shallow discharge, excellent solar conditions, well-designed system)) is often said to be [[electrical:solar:panel-bank_ratio|1:1]] panel-to-Ah. e.g. 150w for a 150Ah battery bank. In reality, solar that small is often insufficient unless one has unusually small power needs or adds in another form of charging (see below). [[opinion:frater_secessus:beginner_mistakes|Newbies typically think their power needs are small]] until they sit down to read those power labels on the stuff that want to run. D'oh! |
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| Most people will do best with much more panel-to-battery depending on battery chemistry, [[opinion:frater_secessus:panelsizesforinsolation|geography]] and use patterns. | Most people will do best with much more panel-to-battery depending on battery chemistry, [[opinion:frater_secessus:panelsizesforinsolation|geography]] and use patterns. |
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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. |
| * if you want to run more [[electrical:12v:loads|loads]] | * if you want to run more [[electrical:12v:loads|loads]] |
| * if you live offgrid full time (FT) | * if you live offgrid full time (FT) or spend long periods [[camping:dispersed|boondocking]] |
| * to run things off [[electrical:inverter|inverter]] rather than 12v | * to run things off [[electrical:inverter|inverter]] rather than 12v((due to inversion losses, typically at least 10%)) |
| * to charge a bigger [[electrical:12v:deep_cycle_battery|battery bank]] | * to charge a bigger [[electrical:12v:deep_cycle_battery|battery bank]] |
| * to charge lead-chemistries (FLA, AGM, Gel) rather than lithium | * to charge lead-chemistry (FLA, AGM, Gel) banks |
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| You will **need somewhat less solar** | You will **need somewhat less solar** |
| * 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:12v:alt_and_solar|augment solar]] with [[electrical:generator|generator]], [[electrical:12v:alternator|isolator]], etc | * if you [[electrical:12v:alt_and_solar|augment solar]] with [[electrical:generator|generator]], [[electrical:12v:alternator|isolator]], [[electrical:converter|shore power]] etc |
| * if you live in the vehicle part time (PT) and can charge consistently from [[electrical:converter|shore power]] when not camping. | * if you live in the vehicle part time (PT) and can charge consistently from [[electrical:converter|shore power]] when not camping. |
| * 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:solar:nonessential|excess power]] is available | * if you time-shift loads to periods like the afternoon when [[electrical:solar:nonessential|excess power]] is available |
| | * to charge lithium banks |
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| ==== solar charge controller ==== | ==== solar charge controller ==== |
| [[electrical:solar:charge_controller|Controllers]] are rated by the Amps they can pump out. A 20A controller can handle up to 20 Amps (about 250w incoming power, depending on battery voltage). | [[electrical:solar:charge_controller|Controllers]] are rated by the Amps they can pump out. A 20A controller can handle up to 20 Amps (about 250w incoming power, depending on battery voltage). |
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| A common **rule of thumb for sizing PWM controllers** is to divide [[electrical:solar:panels|panel]] wattage by 10; 300w((rated power)) of panel on a 30A PWM controller. They are cheap enough that a little oversizing is not a big deal, and they need a bit of headroom since they do not throttle incoming current to protect themselves.((they do use PWM switching to throttle current to hold a given setpoint)) | A common **rule of thumb for sizing PWM controllers** is to divide [[electrical:solar:panels|panel]] wattage by 10; 300w((rated power)) of panel on a 30A PWM controller. They are cheap enough that a little oversizing is not a big deal, and they need a bit of headroom since they do not throttle incoming current to protect themselves.((they do use PWM switching to throttle current to hold a given setpoint)) See [[https://mouse.mousetrap.net/blog/2023-06-13-backchannel---comments-on-solar-advice.html#fn:amps|these examples]]. |
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| MPPT sizing is less straightforward. These tend to cost 2-3x as much for a given rating as PWM, so oversizing can get $$$. MPPT have the ability to [[electrical:solar:overpaneling#vs_charge_controller|clip power]] during unusually-high harvest to limit current to their rated capacity. For this reason they are often **sized to the power the panels make under normal circumstances** rather than the panels' lab rated power. | MPPT sizing is less straightforward. These tend to cost 2-3x as much for a given rating as PWM, so oversizing can get $$$. MPPT have the ability to [[electrical:solar:overpaneling#vs_charge_controller|clip power]] during unusually-high harvest to limit current to their rated capacity. For this reason they are often **sized to the power the panels make under normal circumstances** rather than the panels' lab rated power. |
| * 300w of panel might make 249w under good conditions. 25A controllers are rare, so they might be put on a 20A mppt controller | * 300w of panel might make 249w under good conditions. 25A controllers are rare, so they might be put on a 20A mppt controller |
| * 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://mouse.mousetrap.net/blog/2023-06-13-backchannel---comments-on-solar-advice.html#sizing-an-mppt-controller|more examples with explanation]] |
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| * disadvantages - in-place camping makes DC-DC charging less cost-effective. Entire life must be powered, not just recreational loads while camping. [[electrical:solar:sizing#your_reserve_needs|Days of autonomy]] == forever. | * disadvantages - in-place camping makes DC-DC charging less cost-effective. Entire life must be powered, not just recreational loads while camping. [[electrical:solar:sizing#your_reserve_needs|Days of autonomy]] == forever. |
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| This isn't a game or vacation anymore; //this is your life//. You need power every day and under all conditions. The most reliable way to do this is by [[electrical:solar:overpaneling|overpaneling]] (having massive solar to account for all weather conditions), although you could do it with smaller solar [[electrical:12v:alt_and_solar|combined with]] a [[electrical:generator|generator]]. | FT boondocking game or vacation anymore; //this is your life//. You need power every day and under all conditions. The most reliable way to do this is by [[electrical:solar:overpaneling|overpaneling]] (having massive solar to account for all weather conditions), although you could do it with smaller solar [[electrical:12v:alt_and_solar|combined with]] a [[electrical:generator|generator]]. |
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| 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. |
