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opinion:frater_secessus:panelsizesforinsolation [2021/12/30 15:18]
frater_secessus [Amount of solar wattage required per 100Ah of Pb] |
opinion:frater_secessus:panelsizesforinsolation [2024/03/20 00:01] (current)
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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| 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. | 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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| ^ 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]] ^ | ^ 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]] ^ |
| | Seattle - avg | 280w | 329w | 140w | 103w | | | Seattle - avg | 280w | 329w | 140w | 103w | |
| | Seattle - Dec | 921w | 1056w | 528w | 388w | | | Seattle - Dec | 921w | 1056w | 528w | 388w | |
| Assumptions: | 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 | * **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 | * 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]]. |
| * [[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. | * [[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. |
| * [[electrical:solar:output#panel_temperature|temperature-related derating]] baked in based on monthly average high temperatures | * [[electrical:solar:output#panel_temperature|temperature-related derating]] baked in based on monthly average high temperatures |
| * due to internal resitance differences, the **contributions from alternator/generator** on lithium will be //increased//, and therefore may reduce panel requirements. Those contributions on flooded lead-acid (FLA) will be //decreased//, and therefore may increase panel requirements.((This is a function of how quickly the battery rises to Vabs, at which point alt/genny charging is discontinued as stipulated.)) | * 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 15% less panel than lead due to better charging efficiency. Lithium can be charged successfully off alternator/generator only so no panel would be required. | * 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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| | * factors affecting [[electrical:solar:output|solar harvest]] |
