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--- opinion:solar:sizing [2023/12/26 16:57]
frater_secessus [battery bank]
+++ opinion:solar:sizing [2025/06/05 14:02] (current)
frater_secessus [solar panels]
@@ Line 3: / Line 3: @@
 ====== 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.
+This article focuses on designing a DIY power system from scratch.   See [[opinion:solar:sizing.walkthrough|this article]] for a sample walkthrough of how it might be applied for a given use case.
-See [[opinion:solar:sizing.walkthrough|this article]] for a sample walkthrough of the numbers.
+Also see [[opinion:more_power|making more power from an existing system]].
@@ Line 25: / Line 25: @@
 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 or [[electrical:12v:battery_capacity|limits on charging current]]. Sitting in the dark at night with no fan is less fun than it sounds.
-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 early replacement.  Because lead batteries need frequent and full charging, it may be better in the long run an "undersized" bank you can charge rather than a bigger bank you cannot.
-Having an **oversized lead bank** for your charging ability results in [[electrical:batterycide|battery murder]] and replacement.  Having an **oversized lithium bank** is $$$ and can strain the alternator if [[electrical:12v:b2b|a current-limiting isolator]] isn't used.
+Having an **oversized lithium bank** is $$$ and can [[electrical:12v:alternator_details#current|strain the alternator]] if [[electrical:12v:b2b|a DC-DC charger]] or other [[electrical:12v:directcharginglfp#tweaking_current_with_resistance|current-limiting approaches]] are not taken.((this can also happen with large lead banks))
-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.
@@ Line 89: / Line 88: @@
   * 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.
+  * [[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. Typically June in the southern hemisphere.  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)

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