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--- electrical:solar:sizing [2021/06/21 14:11]
frater_secessus [charge controller]
+++ electrical:solar:sizing [2024/07/16 10:58] (current)
frater_secessus [your reserve needs]
@@ Line 14: / Line 14: @@
   - whether or not you have access to other forms of charging: [[electrical:shore_power|shore power]], [[electrical:12v:alternator|alternator]], [[electrical:generator|generator]]
   - the kind of [[electrical:12v:deep_cycle_battery|battery chemistry]] - some((lithium, for example)) charge more efficiently than others
-  - 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 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]].
@@ Line 68: / Line 70: @@
 ==== calculators ====
+  * Unbound Solar [[https://unboundsolar.com/solar-information/offgrid-calculator|offgrid calculator]]
+  * AltE [[https://www.altestore.com/store/calculators/off_grid_calculator/|offgrid calculator]]
   * [[https://www.batterystuff.com/kb/tools/calculator-sizing-a-battery-to-a-load.html|BatteryStuff 12v load calculator]]
   * [[http://gpelectric.com/tools/GoPowerCalculator.htm?state=RvDiv|GoPower calculator]]
@@ Line 75: / Line 79: @@
 ===== your reserve needs =====
+[see also [[electrical:autonomy|days of autonomy]]]
 > ...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/))
@@ Line 80: / Line 86: @@
 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((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
+To account for this decide how many reserve days of power(("days of autonomy")) 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]].
@@ Line 99: / Line 105: @@
 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))
+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 ====
@@ Line 107: / Line 138: @@
 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.
+Some installations utilize 24v electrical systems. This is common in boats, and occasionally some very large commercial RVs.  The common theme of an advantage to 24v is that you're using half the amperage to transfer the same amount of power, which can result in cheaper components
 You may want to consider running a 24v system if:
-    * your panels are rated at 600w or higher - Ohm's law tells us that 600w / 12v = 50A but 600w / 24v = 25A.  A 24v system can use a much smaller/cheaper charge controller and small/cheaper wiring to handle the same amount of power.
+    * You have a //lot// of solar, like 600w or more.
-    * the run from panels to charge controller is lengthy
+      * Ohm's law tells us that 600w / 12v = 50A but 600w / 24v = 25A.  Therefor, you can use much smaller (and cheaper) wiring to connect your solar panels to the charge controllor
-    * you will be using inverters heavily - inversion from 24vdc to 110vac is more efficient than inversion from 12vdc.
+    * You will be using inverters heavily
+      * Inversion from 24vdc to 110vac is more efficient than inversion from 12vdc.
+    * You have large, power-hungry appliances that can run natively off of 24v
+      * Some [[food:refrigeration|DC refrigerators]] and induction cooktops can run off of both 12v or 24v, and are slightly more efficient when running off of 24v.
+      * [[hvac:solar_ac|Off-grid Air Conditioning]] can be slightly more efficient with 24v native systems, and will allow smaller wires to be used.
+    * You have a lot of long, large cable runs
+      * 24v doesn't have as much voltage drop as 12v over a similar distance, and can use smaller/cheaper cables.
+    * A 24v system can use a much smaller/cheaper charge controller
-There are downsides to 24v, however.  There are fewer 24v accessories, and you cannot use a chassis ground as it is already grounded to the coach's 12v system.
+There are downsides to 24v, however.  There are fewer 24v accessories, and you cannot use a chassis ground as it is already grounded to the coach's 12v system.  It can also make alternator charging difficult, as [[https://www.amazon.com/Hyuduo-Converter-Voltage-Regulator-Stabilizer/dp/B07NM52VV5|DC-DC boost converters]] get quite expensive when they are sized to handle the required loads.
@@ Line 122: / Line 162: @@
 ===== 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 **at least** 1 panel watt per amp-hour of nominal bank capacity.
+Pick a solar panel array output on daily power requirements and  battery bank capacity.  A common **rule of thumb for matching panels to battery bank** is that //at a minimum// there should be 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))

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