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opinion:frater_secessus:panelsizesforinsolation [2021/12/30 13:48] frater_secessus [Amount of solar wattage required per 100Ah of Pb] |
opinion:frater_secessus:panelsizesforinsolation [2024/03/20 00:01] frater_secessus [Amount of solar wattage required per 100Ah of Pb] |
This page is a rough attempt to show how geographical location and meteorological conditions affect the amount of solar wattage one needs. | This page is a rough attempt to show how geographical location and meteorological conditions affect the amount of solar wattage one needs. |
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**Reminder:** available sunlight ([[electrical:solar:output#insolation|insolation]]) is expressed in Hours of Full Sun Equivalent (FSE) compared to lab conditions. So an entire cloudy day might provide only 2 hours of FSE, meaning it would be the same amount of sunlight as 2 hours of full sunlight under lab conditions. Historical weather info is also used to calculate FSE, so good/bad weather is already baked into the average. | **Reminder:** available sunlight ([[electrical:solar:output#insolation|insolation]]) is expressed in Hours of **Full Sun Equivalent (FSE)** compared to lab conditions. So an entire cloudy day might provide only 2 hours of FSE, meaning it would be the same amount of sunlight as 2 hours of full sunlight under lab conditions (1000w/sq meter). Therefore **2 hours of FSE = 2kWh**.((and 7.2MJ (megajoules) for our metric friends)) Multiply [FSE for the time/place] x [rated panel wattage] to see what see how many watts your system would harvest on average if it were perfectly efficient.((hint: it's not)). Example: 4 hours of FSE x 200w = 800Wh, or 0.8kWh, before various losses.((see Assumptions section at bottom for typical losses)) |
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| Historical weather info is also used to calculate FSE, so good/bad weather is already baked into the average. |
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Ambient temperatures also affect panel output, and that is silently factored into the bottom table. | |
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===== Amount of solar wattage required per 100Ah of Pb ===== | ===== Amount of solar wattage required per 100Ah of Pb ===== |
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These figures have [[electrical:solar:output#panel_temperature|temperature-related derating]] baked in, then are rounded off to usable numbers. | These are crude estimates about the panel wattage required to fully charge 100Ah of AGM from 50% DoD each day. See the list of assumptions below the chart. |
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Assumptions:((I think the charging assumptions from alternator and generator are too high; I will revisit at some point and re-evaluate at 50% and 75% charging, respectively -- secessus)) | ^ Location ^ [[electrical:solar:charge_controller#mppt|MPPT]] only ^ [[electrical:solar:charge_controller#pwm|PWM]] only ^ w/ [[electrical:12v:alternator|"isolator"]] ^ w/ [[electrical:12v:b2b|DC-DC charger]] or [[electrical:generator|generator]] ^ |
* battery is discharged to [[electrical:depth_of_discharge|50% DoD]] nightly | | Seattle - avg | 280w | 329w | 140w | 103w | |
| | Seattle - Dec | 921w | 1056w | 528w | 388w | |
| | Seattle - Jul | 163w | 192w | 82w | 60w | |
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| | SLC - avg | 238w | 281w | 119w | 88w | |
| | SLC - Dec | 473w | 556w | 236w | 174w | |
| | SLC - Jul | 156w | 183w | 78w | 57w | |
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| | Phoenix - avg | 200w | 235w | 100w | 73w | |
| | Phoenix - Dec | 369w | 434w | 184w | 135w | |
| | Phoenix - Jul | 149w | 175w | 74w | 55w | |
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| Assumptions: |
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| * panel output is temperature-derated according to daily average high at each time/place |
| * **no other loads** other than charging are present |
| * AGM deep cycle battery is discharged to [[electrical:depth_of_discharge|50% DoD]] nightly and [[electrical:12v:charging|fully charged]] the next day. Charging efficiency 90%. |
* MPPT controller is 95% efficient | * MPPT controller is 95% efficient |
* PWM yields, overall, 85% of MPPT yield. PWM yields will be quite close to MPPT yields when other forms of charging is present, as PWM will no longer be [[electrical:solar:pwm_tweaking|hamstrung by low Vbatt]]. | * PWM yields, overall, 85% of MPPT yield. PWM yields will be quite close to MPPT yields when other forms of charging is present, as PWM will no longer be [[electrical:solar:pwm_tweaking|hamstrung by low Vbatt]]. |
* isolator charging is done in early morning, and discontinued when alternator no longer raises voltage. The chart assumes at that point [[opinion:frater_secessus:charging_faster|~70% of charging will be done]]. | * [[electrical:12v:alternator|isolator charging]] is done in early morning, //every// morning, at ~[[electrical:12v:battery_capacity|C]]/3((~33A, AGM max charging current)), and discontinued when alternator no longer raises voltage.((~14.4v?)) The chart assumes at that point [[opinion:frater_secessus:charging_faster|~50% of charging will be done]]. |
* DC-DC (or generator) charging is is done in early morning, and discontinued when Vabs is achieved. We assume at this point 85% of charging will be done.((adjust as necessary for your charging current)) | * [[electrical:12v:b2b|DC-DC]] (or [[electrical:generator|generator]]) charging is is done in early morning //every// morning, at C/3,((~33A, AGM max charging current)) and discontinued when Vabs is achieved((!4.7v)). We assume at this point 63.3%% of charging will be done. The practical difference between alternator charging and DC-DC or generator charging is the latter will charge all the way to Absorption voltage. |
* wattage listed as ''any'' means "any amount over 100w". | * [[electrical:solar:output#panel_temperature|temperature-related derating]] baked in based on monthly average high temperatures |
* solar-only charging the same number of amps into lithium would require about 15% less panel than lead. Lithium can be charged successfully off alternator/generator only so no panel would be required. | * due to lower internal resistance **lithium will accept more charge from alternator/generator** than AGM by the time it reaches the charging source's voltage setpoint, thereby requiring somewhat less panel wattage. Likewise, flooded batteries will accept //less// than AGM and then require more panel. |
| * solar-only charging the same number of amps into lithium would require about 10% less panel than AGM due to better charging efficiency. Lithium can be charged successfully off alternator/generator only so [[electrical:12v:mandatory_solar|no panel would be required]]. |
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| ===== further reading ===== |
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^ Location ^ [[electrical:solar:charge_controller#mppt|MPPT]] only ^ [[electrical:solar:charge_controller#pwm|PWM]] only ^ w/ [[electrical:12v:alternator|isolator]] ^ w/ [[electrical:12v:b2b|DC-DC charger]] or [[electrical:generator|generator]] ^ | * factors affecting [[electrical:solar:output|solar harvest]] |
| Seattle - avg | 250w | 300w | any | any | | |
| Seattle - Dec | 950w | 1100w | 275w | 150w | | |
| Seattle - Jul | 150w | 175w | any | any | | |
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| SLC - avg | 200w | 250w | any | any | | |
| SLC - Dec | 425w | 500w | 125w | any | | |
| SLC - Jul | 150w | 175w | any | any | | |
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| Phoenix - avg | 175w | 200w | any | any | | |
| Phoenix - Dec | 325w | 400w | any | any | | |
| Phoenix - Jul | 125w | 150w | any | any | | |