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--- electrical:solar:pvwatts [2023/06/16 13:04]
frater_secessus
+++ electrical:solar:pvwatts [2023/06/16 13:50]
frater_secessus [choose a location]
@@ Line 5: / Line 5: @@
 You can use [[https://pvwatts.nrel.gov/index.php|PVWatts]] to find solar harvest estimates for a particular place, month, array size, etc.  You can use this info to
- - find out how much power your
+  - find out how much panel is required to make a certain amount of Watt-hours (Wh) daily; or
+  - find out how much power your existing solar setup can make
-===== how much energy can my system harvest? =====
+===== how much panel do I need to make X watt-hours? =====
-==== choose a location ====
+==== GET STARTED ====
-First, pick a location using the search bar:
+First, [[https://pvwatts.nrel.gov/index.php|pick a location]] using the search bar:
 {{https://img.mousetrap.net/misc/pvwatts0.jpg}}
@@ Line 19: / Line 20: @@
 ==== SOLAR RESOURCE DATA ====
+This page shows you the location it selected.  Accept the default unless it needs correcting.
+==== SYSTEM INFO ====
+Accept the defaults on this page, as it won't make a difference in this case.  All we want is Hours of **F**ull **S**un **E**quivalent (FSE), which will be given on the next page.
+==== RESULTS ====
+The results has three columns:  month, solar radiation (aka FSE), and AC Energy.  We want that middle column.  We will use the lowest FSE for any month we will be camping. For fulltimers this will usually be December.
+==== using the results ====
+Run the arithmetic below, using 0.85 for overall system efficiency with MPPT and 0.7 with PWM.
+    Wh required / "Solar Radiation" (FSE) / overall system efficiency
+==== example ====
+[[https://img.mousetrap.net/misc/stuttgartFSE.jpg|{{ https://img.mousetrap.net/misc/thumbs/stuttgartFSE.jpg}}]]
+You need 900Wh/day.  You live in Stuttgart, Germany and the lowest FSE in a month you will be camping is 2.37 October.  You have an MPPT [[electrical:solar:charge_controller|solar charge controller]].
+So 900Wh / 2.37 / 0.85 = **446.76w** of flat-mounted panel. Round up to 450w or 500w, whatever is available.
+===== how much energy can my system harvest? =====
+==== GET STARTED ====
+First, pick a location using the search bar:
+{{https://img.mousetrap.net/misc/pvwatts0.jpg}}
 ==== system info ====
-We need to make a couple changes here
+We need to make a couple changes to the defaults here:
   * your array size in **kW**.  A kilowatt is 1,000w, so a 200w = 0**.**2kW (zero-point-two)((the calculator is set up like this because it is designed to model large residential and commercial installations that are measured in kW))
@@ Line 39: / Line 93: @@
 ==== results ====
-The first column is kWh/square meter/**day**, AKA Hours of Full Sun Equivalent (FSE).
+The second column is kWh/square meter/**day**, AKA Hours of Full Sun Equivalent (FSE).
-The second column is kWh harvested per **month**. To find average maximal harvest per day divide this figure by the number of days in that month.
+The third column is kWh harvested per **month**. To find average harvest per day divide this figure by the number of days in that month.
 Example:  In January in this location the system could make 17kWh.  17 divided by 31 days = 0.548kWh/day,  (**548Wh/day**).
@@ Line 48: / Line 102: @@
 {{https://img.mousetrap.net/misc/pvwatts2-annotated.jpg}}
-Note:  the 2nd column is //rounded to whole numbers//.  This makes little difference with large residential installs but can distort the result with our small systems.  You can use the FSE number to do the math for your setup directly:
+Note:  the 3rd column is //rounded to whole numbers//.  This makes little difference with large residential installs but can distort the result with our small systems.  You can use the FSE number to do the math for your setup more accurately:
   FSE x array wattage x ((100 - system losses) / 100)
-...which gives a more precise **605Wh/day**.  You may want to plug that formula into a spreadsheet for easy re-use.The system losses will be 14.08 or 30.0 as above, depending on the controller.
+...which gives a more precise **605Wh/day**.  You may want to plug that formula into a spreadsheet for easy re-use.  The system losses will be 14.08 or 30.0 as above, depending on the controller.
-===== how much panel do I need to make X watt-hours? =====
-This is simpler because you can pick your location as above then accept the defaults.  We only care about Hours of FSE, the 2nd column which is called "Solar Radiation".  Since we want to know the worst-case scenario, pick the month with the lowest FSE when you will be camping.  For full-timers this usually means December.
-The formula is
-    Wh required / FSE / overall system efficiency
-System efficiency will be 0.85 for MPPT and 0.7 for PWM.

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