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--- electrical:solar [2017/05/26 19:16]
frater_secessus [Solar power]
+++ electrical:solar [2020/02/16 11:14]
frater_secessus [weather-related issues]
@@ Line 1: / Line 1: @@
+**Words of Wisdom:** I'm not sure people always grasp the concept of "minimum" either; they tend to think it means "all that you really need" when it fact it means "the least you can get away with provided everything else goes right". After all, the sun does not shine brightly every day. -- Cariboocoot((http://forum.solar-electric.com/discussion/comment/250894#Comment_250894))
 ====== Solar power ======
-Solar (photovoltaic or PV) power is an excellent fit for 'dwellers and especially for boondockers.  It is silent, nearly maintenance-free, and requires no infrastructure or [[electrical:shore_power|grid]].
+[Note:  a [[electrical:solar:gentle intro|gentle introduction to solar]] is also available]
+Solar (photovoltaic or PV) power is an excellent fit for 'dwellers and especially for boondockers.  It is silent, nearly maintenance-free, and requires no infrastructure or [[electrical:shore_power|grid]].  Downsides include expense, bulky panels, and the requirement for access to direct/unshaded sunlight.
 Broadly speaking, **solar power systems consist of** [[electrical:solar:panels|panels]] to collect energy, [[electrical:12v:deep_cycle_battery|house batteries]] to store energy, and [[electrical:solar:charge_controller|charge controllers]] to regulate how those batteries get/stay charged.
-Under normal use solar setups charge during the daytime and discharge at night; the lowest [[electrical:depth_of_discharge|State of Charge]] will likely be just before sunrise.  On a properly-sized [[electrical:12v:deep_cycle_battery|deep cycle]] system the bank will have used no more than 50% of its capacity at this point.  Then the sun comes up and charging begins again.
+Under normal use solar setups charge fully during the daytime and discharge at night; the lowest [[electrical:depth_of_discharge|State of Charge]] will likely be just before sunrise.  On a properly-sized [[electrical:12v:deep_cycle_battery|deep cycle]] system the bank will have used no more than 50% of its capacity at this point.  Then the sun comes up and charging begins again.  'Dwellers running small solar setups (or experiencing poor insolation or heavy loads) may have to [[electrical:solar:rationing|ration their use of solar power]].
+The most difficult part of a solar power system (other than [[electrical:solar:frugal|paying for it]]!) is [[electrical:solar:sizing|sizing it correctly]] for your needs.
+===== do you really need solar? =====
+Maybe not. If any of these conditions are met you probably don't need solar:
+  * you stay in campgrounds or other places with access to [[electrical:shore_power|shore power]]
+  * you have a [[electrical:12v:deep_cycle_battery#lithium_chemistries|lithium]] or [[electrical:12v:carbon foam|carbon foam]] batteries that do not require [[electrical:12v:charging|smart (multistage) charging]]((carbon foam does require smart charging, but only 1x/month or so))
-===== sizing a solar installation =====
-==== amp-hours needed ====
-There are calculators online that will tell you how much panel and battery you need.  That is the easy part.
-The **hardest part is figuring out what your daily power needs really are**.  This based on each load and how long that load is expected to run in a 24hr period.  And it's very often wrong, with
+===== practical considerations =====
-If you are going to be using both 12vdc and 110vac (through an inverter) it may be easier to do the calculation in watts, then convert to Amps DC by dividing by 12.  Otherwise an [[https://www.solar-electric.com/solar/calc/|amp-based calculator]] is fine.
+  * [[electrical:solar:panels|solar panels]] take a lot of room and must not be shaded.  Where will you put them?
+  * panels are coming down in price but are $$$ to ship.  Where will you get them?
+  * wiring from the panels will have to enter the camper body somewhere, and the entry will have to be waterproof
+  * lead acid batteries (flooded, sealed, AGM, etc) are extremely heavy and bulky.  Where will you put them that is out of the way and that will not negatively impact the balance of your camper?  How will you get to them to maintain/inspect them?  How will you vent them?
+  * wiring from power sources will need to be fused or fitted with circuit breakers
+  * how will you ensure your batteries don't run your batteries too low and damage them?
-Note:  remember you can't use all the capacity of a battery;  deep cycles allow for up to 50% discharge.  [[electrical:12v:lifepo4_batteries_thread|LiFePO4]] can use almost all the //nominal// power due to understated specs.
+===== scheduling your use of solar power =====
+//When// you use power from your system can be as important as //how much// power you use.
-=== number of days ===
+There are times (bulk, early absorption) when the system is struggling to charge the lead-chemistry bank; loads should be minimized during these periods.
-Build in capacity for days when there is little solar energy available:  shade, overcast conditions, rain, snow, etc.  Desert dwellers in the southwest may build in no extra days while folks in the rainy northwest may need two or more.  The latter may also want to use LiFePO4 which does not require (or like!) getting to 100% [[electrical:depth_of_discharge|State of Charge]].
+At other times like late absorption and float the system will have [[electrical:solar:nonessential|surplus capacity that can be used to run loads]].
-==== matching panels to controller to battery bank ====
+===== things that affect solar power =====
-A common rule of thumb is that there should be 1-2 panel watts per amp-hour of bank capacity, and a charge controller to handle the panels' maximum current.
+  * Insolation (Intensity of sunlight)
+    * **strongest** when there is least atmosphere between the sun and panels:  sun is overhead (noon, summer), nearer the equator, and at higher elevations.
+    * **weakest** when there is the most atmosphere between sun and panels:  sun is low (morning/afternoon, winter), higher latitudes, and lower elevations.
+  * hours of sun each day - more in southern latitudes and in summer; fewer in northern latitudes and in winter
+  * clouds - panels make more power on sunny days and less on cloudy days, due to increased current (voltage relatively unchanged).
+  * temperature - panels make more power when cold, due to increased voltage (current relatively unchanged)
+  * physical obstruction / shade - as when in forested areas
+  * physical obstruction / covering - as when covered in dust or snow
-For a ~200AH 2x6v golf cart bank this would mean 200w-400w of nominal panel and a charge controller that can handle the panels' peak output.  Some rough scenarios to set expectations:
-^Scenario^Solar^Charge controller^Battery bank^Notes^
-|minimal|200w|20A|2x6v 2p1s|Careful use of electric power.  \\ Loads include 12v compressor refrigerator, LED lighting, charge devices, demand use of roof fan. Minimal use of inverter. |
-|ample|400w|40A|2x6v 2p1s|Pay attention to use of power but don't worry.  \\ Loads mentioned above, plus running TV, extensive use of laptop, extensive use of roof fan. Some use of inverter.|
-|plenty|600w|45A-60A|4x6v 2p2s|Enough power that you usually don't have to think about it except in inclement weather. \\ Loads above, plus use of microwave, coffee maker, etc.|
-Make the most of the power provided by solar by [[electrical:12v:conservation|minimizing power consumption]].
+===== how much solar? =====
+Solar sizing has been moved to [[electrical:solar:sizing|its own page]].
@@ Line 61: / Line 80: @@
 ===== weather-related issues =====
+Weather and [[electrical:solar:shading|shading]] have serious effects on [[electrical:solar:output|solar output]].
 ==== cloudy weather ====
@@ Line 70: / Line 90: @@
     * when the **sun is near the edge of a cloud** you can get spikes in current, called Edge of Cloud Effect (ECE).   Here is a [[https://youtu.be/i5fM8TE1INQ?t=1m50s|youtube video of a charge controller's out during ECE]].  Here is [[https://web.archive.org/web/20150921142259/http://www.digitalwa.net/Temp/Untitled.jpg|a simple drawing illustrating ECE]].  [[https://www.youtube.com/watch?v=yzTtzVu-pWM|Here is a demonstration of why it happens]].
-Rainy weather causes a drop in current due to the cloud cover effect.
+Rainy weather causes a drop in current due to the cloud cover effect.  An upside is it can wash dust off panels.
 Dusty or snowy weather can cause a loss of output due to physical presence on the panels.

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