RV and vandwellers wiki

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[[lifestyle:words_of_wisdom|Words of Wisdom]]:  "You have to build for winter, and figure out what to do with the extra electricity in summer." -- timselectric((https://diysolarforum.com/threads/less-than-perfect-off-grid-system.35869/post-450655))

====== power system sizing - the Big Picture ======

There are many [[electrical:solar:sizing#calculators|calculators where you can plug in the numbers]].  This page is a 35,000ft view of how choices affect what you will need. 

See [[opinion:solar:sizing.walkthrough|this article]] for a sample walkthrough of the numbers.


===== overall economics =====

Since solar is dependent on local conditions one has to size the system to **the worst conditions** the system is expected to experience:  winter, high latitudes, bad weather.  This means solar is relatively expensive when used alone where solar conditions are poor. [[electrical:12v:alt_and_solar|Adding in another form of charging]] not affected by local conditions means you can downsize your solar to fit **average conditions**, saving money and space. 

In general, bigger systems (higher wattage panels, bigger controllers, bigger battery banks) cost less per-watt-harvested.


==== days of reserve ====


Your **reserve requirements** will profoundly affect the size, complexity, and cost of the system.  
Sizing for an overnight camping trip is easy;  sizing for a three day trip a challenge;  sizing for a long trip or full-time vandwelling is serious business.  See the bottom of this article for example configurations. 

===== battery bank =====

Once you know your daily power and reserve requirements you can spec out a battery  bank.  The capacity and chemistry of the bank will drive much of the charging section below. 

Broadly speaking, lithium chemistries are most cost-effective when the camping experience is expected to last for many years and the batteries stored inside.((Note that it is false economy to pay for 10 years of battery cycling (as with lithium) if one is going to wreck it in 2 years)).  For shorter projects (traveling around the country for  ≤3 years) in an RV with exterior battery trays the standard T-105 style FLA bank((like 2x 6v Trojan T-105 batts in series for 12v)) may be more cost-effective.  For very short installations ( ≤1 year) marginal batteries found at walmart may be fine. I encourage people to do the //$/kWh math for the situation// rather than relying on the latest trends or loudest voices. Horses for courses.

Having an **undersized bank** means //running out of power// at night.  Sitting in the dark at night with no fan.  

Having an **oversized lead bank** for your charging ability results in [[electrical:batterycide|battery murder]] and replacement.  Having an **oversized lithium bank** is $$$ and can strain the alternator if [[electrical:12v:b2b|a current-limiting isolator]] isn't used.

IMO, with lead chemistries((flooded, agm, gel)) it is better to have an undersized bank you can charge //fully and consistently// rather than a bigger bank you cannot charge. 


After figuring your rough capacity requirements, consider these factors:

You will **need somewhat more Ah capacity**

      * if you have undersized solar (lithium banks only)
      * you have lead-chemistry battery bank (50% usable capacity rather than 80% usable)
      * 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**

    * if you run loads in the daytime instead of at night
    * if you have [[electrical:solar:overpaneling|oversized solar]]
    * if you drive often and have [[electrical:12v:alternator|altenator charging]]
    * you have lithium-chemistry battery bank((can be ~0.62% the size of the lead bank, due to deeper [[electrical:depth_of_discharge|DoD]].))


===== solar charging =====


==== solar panels ====



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!  


Most people will do best with much more panel-to-battery depending on battery chemistry, [[opinion:frater_secessus:panelsizesforinsolation|geography]] and use patterns. 

You will **need somewhat more solar**

    * 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 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 charge a bigger [[electrical:12v:deep_cycle_battery|battery bank]]
    * to charge lead-chemistry (FLA, AGM, Gel) banks

You will **need somewhat less solar**

    * 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 [[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 voluntarily reduce your power consumption
    * if you time-shift loads to periods like the afternoon when [[electrical:solar:nonessential|excess power]] is available
    * 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 ====


=== controller choice ===

The [[electrical:solar:charge_controller|controller]]'s job is to sit in between the panels and battery bank and regulate charging.  Counterintuitively, its most important job is to //prevent overcharging//.


Most people do fine with a PWM controller.  Folks who live off-grid with lead-chemistry batteries can get by with even [[electrical:solar:shunt_tweaking|a $10 cheapie]].  Nicer PWM have staged ("smart") charging, more configurabilty, and likely better reliability. 

You may **want an MPPT controller**:

  * if you discharge your batteries deeply overnight((low battery voltage hamstrings PWM))
  * if you have a lithium or AGM bank((they have lower resistance and so come up to voltage more slowly;  see point above)) 


You will **need an MPPT controller**:

  * if your panels are higher voltage than your battery bank (e.g. 24v panels and 12v bank)


=== controller sizing ===

[[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))   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. 

Examples:  

  * A 200w panel might really only make 166W in actual use under good conditions.  This panel might be used with a 15A 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.
  * [[https://mouse.mousetrap.net/blog/2023-06-13-backchannel---comments-on-solar-advice.html#sizing-an-mppt-controller|more examples with explanation]]















===== alternator charging =====

For many people living in vehicles [[electrical:12v:alt_and_solar|alternator charging + modest solar]] will be the best-performing system for the dollar.   The ratio of camping //vs// driving((and to some extent what time of day you are driving)) will affect the solar/isolator/[[electrical:generator|generator]] balance. 

You will need **some kind of alternator charging**

  * if you have no solar
  * if you have insufficient solar <-- very common
  * if you have AGM, which craves a ton of current in Bulk charging

You will **not need alternator charging**

  * if you have [[electrical:solar:overpaneling|a ton of solar]]
  * if you stay on shore power much of the time
  * if have solar and most of your driving happens after noon((the isolator contributes best during Bulk, which typically occurs in the morning))

More expensive [[electrical:12v:b2b|DC-DC chargers]] are warranted when

  * you have no solar
  * current-hungry battery like AGM or lithium threatens your alternator's longevity, or you need to restrict charging rate for lithium. 
  * you have a voltage-sensitive battery like gel or lithium


===== generator charging =====



You may need a generator if:

  * you need to run big loads like A/C
  * you have a lithium battery bank but camp in long stretches with minimal solar.  In this model you would charge the batteries full blast((up to [[electrical:12v:battery_capacity|0.5C]])) for a few hours every few days. 
  * you have enough solar to [[electrical:12v:charging|Absorp/Float your lead batteries but not enough for bulk]].


===== special case:  trailers =====

**Cargo trailers**((aka utility trailers)) have unique advantages and disadvantages

advantages

  * flat roof space for panels, especially cheaper-by-the-watt large panels
  * relatively low, making tiltable arrays more practical since you can reach them

disadvantages

  * charging from alternator can be challenging.  See [[https://diysolarforum.com/threads/ricks-charge-from-the-tv-solution-for-owners-of-mppt-charge-solar-in-the-trailer.20730/|one way]] around the charging limitations of the 7-pin harness.

**RV travel trailers** have additional challenges

  * roofspace often lacks contiguous open spots to mount panels
  * rooftop accessories [[electrical:solar:shading|shade]] panels
  * large parasitic [[electrical:12v:loads|loads]], due to the common assumption they will be hooked up to [[electrical:shore_power|a power pedestal]] at a paid campsite


===== example setups =====


==== overnight camping ====

  * advantages - only 24 hours away from home (and grid power), only need to store power for 24 hours of use.  No need to generate power. 
  * challenges - need to keep battery bank on [[https://amzn.to/3x94mZA|a small charger/maintainer]] at home to avoid sulfation and [[electrical:batterycide|early death]]

The battery is used occasionally and briefly then put back on the maintainer at home.  The battery doesn't have to be particularly good((it will die within a couple years no matter how good or bad we treat it));  it can be [[electrical:12v:deep_cycle_battery#chain_store_batteries|a chain store battery]], often labeled "marine" or "hybrid" or similar.  

It is used to run small fans, LED lights, recharge phones. 


==== weekend camping ====

This is like the scenario above, only with more battery capacity required. 

  * advantages - as above, only stretched to 72 hours
  * disadvantages - more capacity required((200Ah?)).  [[https://amzn.to/2SvH5lT|Bigger charger/maintainer]] required((unless [[electrical:12v:alternator|isolator]] installed))

For a longer discussion Also see blog article [[https://mouse.mousetrap.net/blog/2020/07/04/agm-for-weekenders/|AGM Charging for Weekenders]].


==== overlanding ====

In this scenario you are away from home for long stretches of time, driving daily to the next campsite.  The system needs to be self-sufficient


  * advantages - driving daily makes [[electrical:12v:b2b|DC-DC chargers]] highly effective.
  * disadvantages - rough roads increase likelihood of damage to flooded lead batteries.  Forest camping can make [[electrical:solar:shading|shade]] a challenge.  Fully-provisioned roof racks make mounted solar a challenge.

More expensive chemistries like AGM or lithium are warranted;  plain FLA batteries may experience plate damage from vibration and rough driving. DC-DC charging will do the majority of charging, with a portable panel or two supplementing charging/loads during the day.  

==== stealth camping ====

[[camping:stealth_camping|Stealth camping]] has some similarity to overlanding in that the stealth camper will likely drive every day.  

  * advantages - driving at least a short distance every day for relocation or work commute makes alternator charging effective. 
  * disadvantages - need to remain stealthy limits solar array mounting

The relatively short distances driven by stealthers means that a plain [[electrical:12v:alternator|isolator]] will likely outperform a fancy [[electrical:12v:b2b|DC-DC charger]].  These quick blasts suggest the need for a bank that can suck up power fast:  AGM or lithium. 

The need for stealth suggests smaller (or just more discreet) arrays):  higher-efficiency panels, perhaps with black frames to minimize visual impact to onlookers.  Mounting on OEM racks can help fool the eye. 

The possibility of [[electrical:shore_power|shore power]] charging, even rarely, means the stealther may want to adding a shore power port and [[electrical:converter|converter/charger]].((and carry a long, heavy,  [[https://amzn.to/35clxxG|outdoor-rated extension cord]]!))
==== fulltime boondocking ====

  * advantages - roofspace can be devoted to large solar arrays.  Can choose batteries based on long-term value. 
  * 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.

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]]. 

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.
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