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electrical:solar:sizing [2019/10/01 13:00]
frater_secessus [usable capacity in Amp-hours] 		electrical:solar:sizing [2022/01/15 03:10]
princess_fluffypants [voltage]
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 Words of Wisdom:  "I'd say 500 watts is the minimum for the [Pacific Northwest] in winter and you would be better off with [750 watts] if you can get it on the roof."  akrvbob((http://www.cheaprvliving.com/forums/Thread-One-large-solar-panel-or-several-small-ones?pid=101801#pid101801)) Words of Wisdom:  "I'd say 500 watts is the minimum for the [Pacific Northwest] in winter and you would be better off with [750 watts] if you can get it on the roof."  akrvbob((http://www.cheaprvliving.com/forums/Thread-One-large-solar-panel-or-several-small-ones?pid=101801#pid101801))
 +
 +
  
 ====== Sizing a solar installation ====== ====== Sizing a solar installation ======
  
 Sizing **residential off-grid solar configurations** is relatively easy: calculate power needs in the worst case scenario (December in a particular geographical area)((https://web.archive.org/web/20110906013732/http://www.solarpowerforum.net/forumVB/solar-energy/1793-basic-off-grid-solar-design.html)) and pay for it.  Sizing **residential off-grid solar configurations** is relatively easy: calculate power needs in the worst case scenario (December in a particular geographical area)((https://web.archive.org/web/20110906013732/http://www.solarpowerforum.net/forumVB/solar-energy/1793-basic-off-grid-solar-design.html)) and pay for it. 
 +
 +Campervan solar configurations have a more variables:
  
   - worst case scenario [[electrical:12v:loads|loads]] (the max loads you will apply in any 24hr period((or at any given time, if you plan to run heavy loads)))   - worst case scenario [[electrical:12v:loads|loads]] (the max loads you will apply in any 24hr period((or at any given time, if you plan to run heavy loads)))
-  - worst case scenario sunlight, usually December in your geographical area due to shortest daylight hours+  - worst case scenario sunlight, usually December in your geographical area due to shortest daylight hours, but also affected by tree canopies, mountains, "urban canyons", or other forms of [[electrical:solar:shading|shading]]
   - days of reserve (ie with no solar charging) you want   - days of reserve (ie with no solar charging) you want
   - whether or not you have access to other forms of charging: [[electrical:shore_power|shore power]], [[electrical:12v:alternator|alternator]], [[electrical:generator|generator]]   - whether or not you have access to other forms of charging: [[electrical:shore_power|shore power]], [[electrical:12v:alternator|alternator]], [[electrical:generator|generator]]
-  - These factors will tell you size of the system needed.  If the system you need will not physically fit on/in your vehicle, you will have to take [[electrical:solar:sizing#maxxed_system|a different approach]]. +  - the kind of [[electrical:12v:deep_cycle_battery|battery chemistry]] - some((lithium, for example)) charge more efficiently than others 
- +  - the kind of camping you do.  Full-timers will need more robust systems.  Weekenders can [[https://mouse.mousetrap.net/blog/2020/07/04/agm-for-weekenders/|"get by" then recharge batteries fully at home]].  
- +    
- +These factors will dictate the system capactity you will need.  If the system you need will not physically fit on/in your vehicle, you will have to take [[electrical:solar:sizing#maxxed_system|a different approach]].
- +
- +
- +
- +
- +
- +
  
  
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 Before you dig in, consider that it is far **easier and cheaper to [[electrical:solar:rationing|use less power]]** than it is to make more power. Before you dig in, consider that it is far **easier and cheaper to [[electrical:solar:rationing|use less power]]** than it is to make more power.
  
-Power requirements are usually expressed in Amp-hours needed every day (Ah/day).  There are two different kinds of loads 'dwellers usually run, [[electrical:shore_power|AC (110v)]] and [[[electrical:12v:intro|DC (12v)]].  +Power requirements are usually expressed in Amp-hours needed every day (Ah/day), although thinking in Watt-hours (Wh) might be simpler less complicated.   
 + 
 +There are two different kinds of loads 'dwellers usually run, [[electrical:shore_power|AC (110v)]] and [[electrical:12v:intro|DC (12v)]]. Appliances run off an inverter will incur additional efficiency penalties (see below).  
  
 ==== how much power does stuff use? ==== ==== how much power does stuff use? ====
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   * [[http://gpelectric.com/tools/GoPowerCalculator.htm?state=RvDiv|GoPower calculator]]   * [[http://gpelectric.com/tools/GoPowerCalculator.htm?state=RvDiv|GoPower calculator]]
   * [[http://www.rvsolarsystemsonline.com/wattage-calculator/|RVSSO calculator]]   * [[http://www.rvsolarsystemsonline.com/wattage-calculator/|RVSSO calculator]]
 +
 +Also see [[https://re.jrc.ec.europa.eu/pvg_tools/en/tools.html#SA|the EU PVGIS modeler]].
  
 ===== your reserve needs ===== ===== your reserve needs =====
 +
 +> ...one that really [effed] with me was running out of power or spending a few days in the dark cause the weather is bad. -- hellexual((https://www.reddit.com/r/vandwellers/comments/er4gf7/whered_you_get_your_van/ff1i66p/))
 +
 Solar power is highly dependent on local conditions like weather, season, and latitude.  One cannot assume getting a full charge every day in every condition. Solar power is highly dependent on local conditions like weather, season, and latitude.  One cannot assume getting a full charge every day in every condition.
  
-To account for this decide how many reserve days of power you need if there is little [[https://www.wholesalesolar.com/solar-information/sun-hours-us-map|solar power available]].  You may need few in desert regions and many more in the Pacific Northwest.  Long stretches of little solar charging may necessitate +To account for this decide how many reserve days of power((https://duckduckgo.com/?q=days+of+autonomy&t=ffab&ia=web)) you need if there is little [[https://www.wholesalesolar.com/solar-information/sun-hours-us-map|solar power available]].  You may need few in desert regions and many more in the Pacific Northwest.  Long stretches of little solar charging may necessitate 
 [[electrical:solar:rationing|rationing solar power]]. [[electrical:solar:rationing|rationing solar power]].
  
-Reserve days of power is also known as //days of autonomy//.((https://duckduckgo.com/?q=days+of+autonomy&t=ffab&ia=web))+
  
 It is safest and simplest for solar newbies to assume a day of poor solar harvest = zero solar harvest.  In actuality zero harvest is highly unlikely; more experienced or risk-tolerant RVers can run with [[electrical:solar:slim reserve|less reserve or no reserve at all]].  It is safest and simplest for solar newbies to assume a day of poor solar harvest = zero solar harvest.  In actuality zero harvest is highly unlikely; more experienced or risk-tolerant RVers can run with [[electrical:solar:slim reserve|less reserve or no reserve at all]]. 
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 A rule of thumb is flooded lead acid batteries in offgrid scenarios should be charged between C/10 and C/8.  For a 200AH bank this would be 20A-25A.  Charging at lesser rates may result in not getting fully charged each day.  Charging at greater rates may result in increased outgassing and the need for a lengthier Absorption stage. A rule of thumb is flooded lead acid batteries in offgrid scenarios should be charged between C/10 and C/8.  For a 200AH bank this would be 20A-25A.  Charging at lesser rates may result in not getting fully charged each day.  Charging at greater rates may result in increased outgassing and the need for a lengthier Absorption stage.
 +
 +=== reserve ===
 +
 +
 +
 +
 +
 +
 +
 +|  **total**|  91|
 +| | |
 +|  Minimum battery bank((except lithium))|  182|
 +
 +
 +and that's just to get through a 24hr period **with good sun**.  If you want to get through a day (or more) of terrible solar yield (rain, snow, fog) it requires even more battery capacity (//reserve//), money, and cargo capacity. These numbers are both very rough but will illustrate the pattern:
 +
 +| |  **Rated Ah**|  **cost (flooded)**|  **cost (AGM)**|  **weight in lbs**|
 +|  **Minimum battery bank((except lithium))
 +0 days of reserve**|  182|  $182.00|  $364.00|  91|
 +| | | | | |
 +|  **1 day of reserve**|  364|  $364.00|  $728.00|  182|
 +|  **2 days of reserve**|  546|  $546.00|  $1,092.00|  273|
 +|  **3 days of reserve**|  728|  $728.00|  $1,456.00|  364|
 +
 +
 +
 +==== charging efficiency ====
 +
 +Lead batteries take something like ~13% more amps to charge from 50% DoD than were consumed.  So if you need to replace 50A it will take ~56.5A the next day to replace it.  //While// you are running your normal loads.
  
  
 +Lithium batteries have very high charging efficiency, so 50A consumed will take ~50A to recharge.  
  
-==== voltage ====+==== Voltage ====
  
 Most camper solar installs run at [[electrical:12v:electrical_notation|nominal]] [[electrical:12v:intro|12v]].  Because of this most accessories are 12v.   Most camper solar installs run at [[electrical:12v:electrical_notation|nominal]] [[electrical:12v:intro|12v]].  Because of this most accessories are 12v.  
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 ===== solar panel array ===== ===== solar panel array =====
  
-Pick a solar panel array output on battery bank capacity.  A common **rule of thumb for matching panels to battery bank** is that there should be 1-2 panel watts per amp-hour of nominal bank capacity.  +Pick a solar panel array output on battery bank capacity.  A common **rule of thumb for matching panels to battery bank** is that there should be **at least** 1 panel watt per amp-hour of nominal bank capacity.  
  
 > "...the person draining their batteries to the 50% range regularly would do much better with a 2 watts to 1Ah ratio, or even 3 to 1." -- SternWake((http://www.cheaprvliving.com/forums/Thread-How-much-solar-do-I-need?pid=278438#pid278438)) > "...the person draining their batteries to the 50% range regularly would do much better with a 2 watts to 1Ah ratio, or even 3 to 1." -- SternWake((http://www.cheaprvliving.com/forums/Thread-How-much-solar-do-I-need?pid=278438#pid278438))
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     * deep cycling with [[electrical:solar:sizing#augmenting_solar|augmented charging]] in the morning     * deep cycling with [[electrical:solar:sizing#augmenting_solar|augmented charging]] in the morning
   * **2:1** - deep cycling and charging from solar only   * **2:1** - deep cycling and charging from solar only
-  * **3:1** - deep cycling and charging from solar only in areas with low insolation like the Pacific Northwest (PNW)+  * **3:1** - deep cycling and charging from solar only in [[opinion:frater_secessus:panelsizesforinsolation|areas with low insolation]] like the Pacific Northwest (PNW)
  
 A **crude rule of thumb for panel output per day** is a horizontally mounted panel on a sunny day will generate Ah (amp hours) roughly equal to Rated Wattage / 3.((http://www.cruisersforum.com/forums/f14/current-strategies-in-solar-power-42602.html#post473854)) \\  A **crude rule of thumb for panel output per day** is a horizontally mounted panel on a sunny day will generate Ah (amp hours) roughly equal to Rated Wattage / 3.((http://www.cruisersforum.com/forums/f14/current-strategies-in-solar-power-42602.html#post473854)) \\ 
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 There are two general rules: There are two general rules:
   - voltage from panels must not exceed controller voltage, ever.   - voltage from panels must not exceed controller voltage, ever.
-  - controller rating should be the panels' output plus a safety margin, unless you are [[electrical:solar:overpaneling|overpaneling]] on purpose.+  - controller rating should be the panels' output plus a safety margin, unless you are [[electrical:solar:overpaneling|overpaneling]] an [[electrical:solar:charge_controller#mppt|MPPT controller]] on purpose.
  
 ===== augmenting solar ===== ===== augmenting solar =====
electrical/solar/sizing.txt · Last modified: 2023/08/31 19:54 by princess_fluffypants

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