RV and vandwellers wiki

User Tools

Site Tools

Trace:
opinion:solar:sizing

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Both sides previous revision Previous revision
Next revision 		Previous revision
Last revision Both sides next revision
opinion:solar:sizing [2022/11/08 19:29]
frater_secessus [solar panels] 		opinion:solar:sizing [2023/12/26 11:54]
frater_secessus [battery bank]
Line 40: Line 40:
       * if you have undersized solar       * if you have undersized solar
       * you have lead-chemistry battery bank       * you have lead-chemistry battery bank
 +      * if charging is time-limited and you want maximal harvest from the alternator, shore, or other high-current charging source.  **Example: ** If battery specs say you can constant-charge at [[electrical:12v:battery_capacity|0.2C]] (20A per 100Ah of capacity) then((all other things being equal)) a 100Ah bank could take 20A, 200Ah could take 40A, and 300Ah could take 60A.  
  
 You will need **somewhat less Ah capacity** You will need **somewhat less Ah capacity**
Line 62: Line 63:
 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: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((due to inversion losses, typically at least 10%))     * 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]]
Line 79: Line 80:
     * 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:solar:pvwatts|average insolation sun power available at the time/place]];  in the northern hemisphere full-timers base this on December since it's the lowest-yield month.  For part-timers, it will be the month of lowest insolation you will camp in.
 +  * the contribution of any other charging sources
 +  * minimum charging current requirements, if any.   (we can ballpark 0.2C for AGM and 0.1C for FLA.  Lithium has no minimums)
 +
 +Let's assume a 200Ah AGM bank depleted to 50% SoC, wintering in [[camping:snowbirding:quartzsite|Quartzsite]] with an MPPT-based solar config and flat-mounted panels.  
 +
 +  - 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:solar:pvwatts|In December in Quartzsite]], a panel will receive an daily average of **3.08 hours of full sun equivalent**
 +  - 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:12v:dailypowerrequirements|actual daily power requirements]].  You may find it easier in the long-term to model this kind of thing in a spreadsheet. 
 +
 +
 +**Note**:  the numbers are for //average// yields, including average seasonal weather.  Individual days may be better or worse.  **If you have non-negotiable power requirements** you may want to oversize your array to account for days of locally-poor harvest. 
 ==== solar charge controller ==== ==== solar charge controller ====
  
Line 104: Line 130:
 [[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).  
  
-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]].
  
 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. 
Line 113: Line 139:
   * 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]]
  
  
opinion/solar/sizing.txt ยท Last modified: 2023/12/26 11:57 by frater_secessus

Page Tools

Except where otherwise noted, content on this wiki is licensed under the following license: CC Attribution-Noncommercial-Share Alike 4.0 International

affilliate disclosure

CC Attribution-Noncommercial-Share Alike 4.0 International Donate Powered by PHP Valid HTML5 Valid CSS Driven by DokuWiki