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opinion:solar:sizing [2022/05/08 11:13]
frater_secessus [solar panels]
opinion:solar:sizing [2022/05/24 15:18] (current)
frater_secessus [fulltime boondocking]
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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)) [[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))
  
-====== solar sizing - the Big Picture ======+====== 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.  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.
  
  
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 In general, bigger systems (higher wattage panels, bigger controllers, bigger battery banks) cost less per-watt-harvested. In general, bigger systems (higher wattage panels, bigger controllers, bigger battery banks) cost less per-watt-harvested.
  
-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.+
 ==== days of reserve ==== ==== days of reserve ====
  
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 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.  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 =====
  
-===== solar panels =====+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.  
  
-The bare-bones minimum for solar, assuming everything goes exactly right,((shallow discharge, excellent solar conditions, well-designed system))  is [[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!  +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. 
  
-Most people will do best with much more panel-to-battery depending on battery chemistry, [[opinion:frater_secessus:panelsizesforinsolation|geography]] and use patterns.  
  
 +After figuring your rough capacity requirements, consider these factors:
  
 +You will **need somewhat more Ah capacity**
 +
 +      * if you have undersized solar
 +      * you have lead-chemistry battery bank
 +
 +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]]
 +    * 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** You will **need somewhat more solar**
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-===== solar charge controller =====+==== solar charge controller ====
  
-==== controller choice ==== 
  
 +=== controller choice ===
  
-Most people do fine with a PWM controller.  Folks who live off-grid with lead-chemistry batteries can get by with [[electrical:solar:shunt_tweaking|a $10 cheapie]].  +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**: You may **want an MPPT controller**:
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-==== controller sizing ====+=== 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).   [[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).  
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- 
-===== battery bank ===== 
-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, it is better to have an undersized bank you can charge //fully and consistently// rather than a bigger bank you cannot charge.  
- 
-You will **need somewhat more Ah capacity** 
- 
-      * if you have undersized solar 
- 
-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]] 
  
  
 ===== alternator charging ===== ===== alternator charging =====
  
-For most people living in vehicles [[electrical:12v:alt_and_solar|alternator charging + modest solar]] will be the best-performing system for the dollar. +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** You will need **some kind of alternator charging**
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   * you have a voltage-sensitive battery like gel or 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]].
  
  
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   * 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.   * 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.
  
-This isn't a 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]]. +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.   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.  
opinion/solar/sizing.1652022810.txt.gz · Last modified: 2022/05/08 11:13 by frater_secessus