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electrical:solar:panels [2021/07/19 22:18]
frater_secessus [Table]
electrical:solar:panels [2024/01/04 16:54] (current)
frater_secessus [STC and NOCT] compare
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 To avoid overcharging,((a bit of an oversimplification, admittedly)) a [[electrical:solar:charge controller|charge controller]] is placed between the PV and the battery bank. To avoid overcharging,((a bit of an oversimplification, admittedly)) a [[electrical:solar:charge controller|charge controller]] is placed between the PV and the battery bank.
  
-[[electrical:solar:output|Many factors]] will affect output; and panels will rarely generate power equal to their laboratory rating. +[[electrical:solar:output|Many factors]] will affect output; and panels will rarely generate power equal to their laboratory rating.  As a general rule, expect panels to put out much less than their rated wattage under normal conditions.  
  
 There are several types of PV widely available on the market, and many more in research stages.  PV are described by how each panel's cells are constructed. There are several types of PV widely available on the market, and many more in research stages.  PV are described by how each panel's cells are constructed.
  
 +----
  
-===== types of panels =====+===== Types of panels =====
  
-==== monocrystalline ====+==== Monocrystalline ====
  
 //Mono// or //single crystal// cells are made from complete slices of silicon crystal.  Mono cells have rounded edges because they were cut from a single cylindrical crystal.((http://energyinformative.org/best-solar-panel-monocrystalline-polycrystalline-thin-film/)) \\  //Mono// or //single crystal// cells are made from complete slices of silicon crystal.  Mono cells have rounded edges because they were cut from a single cylindrical crystal.((http://energyinformative.org/best-solar-panel-monocrystalline-polycrystalline-thin-film/)) \\ 
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     * slightly better than poly in uniform low light     * slightly better than poly in uniform low light
     * theoretically greater longevity than poly, much better longevity than thin film     * theoretically greater longevity than poly, much better longevity than thin film
-    * slightly higher [[electrical:12v:electrical_notation|Vmp]] than poly((https://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf Section 7.4))+    * slightly higher [[electrical:12v:electrical_notation|Vmp]] than poly((https://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf Section 7.4)), for situations in which that could be a benefit
     * slightly better performance in higher temps than poly, possibly due to higher Vmp     * slightly better performance in higher temps than poly, possibly due to higher Vmp
   * CON   * CON
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-==== polycrystalline ====+==== Polycrystalline ====
  
 //Poly// cells are made up of smaller pieces of slices.  Poly cells are rectangular.((http://energyinformative.org/best-solar-panel-monocrystalline-polycrystalline-thin-film/)) //Poly// cells are made up of smaller pieces of slices.  Poly cells are rectangular.((http://energyinformative.org/best-solar-panel-monocrystalline-polycrystalline-thin-film/))
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-==== flexible ====+==== Flexible ====
  
 Flexible panel configurations place unusual demands on the materials.  Framed panels use extremely durable glass encapsulation((wrapping, basically)) but this would not work for flex panels.  One challenge is to come up with encapsulation that is transparent, strong, and durable.   Flexible panel configurations place unusual demands on the materials.  Framed panels use extremely durable glass encapsulation((wrapping, basically)) but this would not work for flex panels.  One challenge is to come up with encapsulation that is transparent, strong, and durable.  
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 The other challenge is to make solar cells that can slightly flex. The other challenge is to make solar cells that can slightly flex.
  
-=== crystalline ===+=== Crystalline ===
  
 While the flex panel market has largely gone to poly/mono crystalline, there are obvious issues related to making flexible objects out of brittle silicon crystals.  It is not clear why the market went that direction.   While the flex panel market has largely gone to poly/mono crystalline, there are obvious issues related to making flexible objects out of brittle silicon crystals.  It is not clear why the market went that direction.  
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 Handle with care, and bend as little as possible. Handle with care, and bend as little as possible.
  
-=== thin film ===+=== Thin film ===
  
 [Note:  actual thin-film panels are rarer as of 2018.  The market has gone to flexible mono or poly((which do not have the benefits described below))] [Note:  actual thin-film panels are rarer as of 2018.  The market has gone to flexible mono or poly((which do not have the benefits described below))]
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     * semi-flexible so it can be applied to curved shapes     * semi-flexible so it can be applied to curved shapes
     * least affected by high temps     * least affected by high temps
-    * least affected by shading+    * least affected by shading due to cell construction 
 +    * least affected by cloudy/hazy conditions, due to increased sensitivity at the blue end of the light spectrum((https://www.academia.edu/32974503/Investigating_the_Effect_of_Spectral_Variations_on_the_Performance_of_Monocrystalline_Polycrystalline_and_Amorphous_Silicon_Solar_Cells)),((overcast light is blue-shifted))
     * very light     * very light
   * CON   * CON
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     * lower Vmp     * lower Vmp
  
-===== portable =====+==== Portable ====
  
-While most panels are hard mounted horizontally, some are mounted on tilt panels to increase yield, and some are portable.+While most panels are hard mounted horizontally on the roof of the vanportable folding portable solar panels have dropped in price and have some advantages.
  
-PRO+[[https://www.amazon.com/portable-solar-panel/s?k=portable+solar+panel|Amazon search]] 
 + 
 +  * **PRO**
   * no mounting costs   * no mounting costs
   * can be stored securely in the camper   * can be stored securely in the camper
   * can collect sunlight while the camper stays in the shade   * can collect sunlight while the camper stays in the shade
 +  * Can be angled and moved follow the sun and collect maximum power
 +  * Sometimes have USB charging ports directly on the back of them, allowing charging of small devices directly without the use of a charge controller and battery setup.
  
  
-CON+  * **CON**
   * animals may damage or pee on the panels((http://www.cheaprvliving.com/forums/showthread.php?tid=28505&pid=358926#pid358926))   * animals may damage or pee on the panels((http://www.cheaprvliving.com/forums/showthread.php?tid=28505&pid=358926#pid358926))
   * long wiring runs can cause voltage drop   * long wiring runs can cause voltage drop
   * deployed panels can make [[camping:safety|quick getaways]] impractical   * deployed panels can make [[camping:safety|quick getaways]] impractical
   * it is easy to get lazy and not put out the panels every time   * it is easy to get lazy and not put out the panels every time
 +  * Questions exist about long-term durability
 +  * Possibility of panels getting stolen
  
  
  
 +==== half-cut ====
  
 +Some panels are "half-cut" which means the cells are cut in half and wired to make 2x as many cells.   This can result in better harvest in some partial shade conditions with some increase in complexity and expense.  
  
 +{Secessus reminds us we should avoid [[electrical:solar:shading|shade]] in the first place}
  
  
-===== panel voltage =====+ 
 +===== Panel voltage =====
  
 12V panels are not really 12V;  they are called that because they charge 12V battery banks (which aren't really 12v either!).  Since they are called 12V we say //nominal// (ie, "named") 12v.  [yes, it's confusing.  -- frater secessus] 12V panels are not really 12V;  they are called that because they charge 12V battery banks (which aren't really 12v either!).  Since they are called 12V we say //nominal// (ie, "named") 12v.  [yes, it's confusing.  -- frater secessus]
  
  
-  * **Nominal 12v panels** have 36 cells.  They will generally have max power (Vmp) around 18v and open circuit (Voc) around 21v.((https://www.altestore.com/howto/solar-panels-pv-and-voltages-a98/))  These are commonly found on mobile and portable installations.+  * **Nominal 12v panels** have 36 cells.  They will generally have max power (Vmp) around 18v and open circuit (Voc) around 21v.((https://www.altestore.com/howto/solar-panels-pv-and-voltages-a98/))  These are commonly found on mobile and portable installations.  \\ Note:  there are some "12v" panels that actually have 40 cells.((nominal 13v?))  Example:  [[https://amzn.to/3Pcrcsi|Renogy 200w "12v"]] panels, with Vmp of 22.6v and Voc 27v.  The extra voltage //cannot be harvested by PWM// so MPPT is effectively required with these.
   * **Nominal 20v panels** have 60 cells.  They will generally have max power (Vmp) around 30v and open circuit (Voc) around 36v.((https://www.altestore.com/howto/solar-panels-pv-and-voltages-a98/))  These are commonly found in residential rooftop installations.   * **Nominal 20v panels** have 60 cells.  They will generally have max power (Vmp) around 30v and open circuit (Voc) around 36v.((https://www.altestore.com/howto/solar-panels-pv-and-voltages-a98/))  These are commonly found in residential rooftop installations.
-  * **Nominal 24v panels** have 72 cells.  They will generally have max power (Vmp) around 36v and open circuit (Voc) around 42v.((https://www.altestore.com/howto/solar-panels-pv-and-voltages-a98/))  These are commonly found in commercial or residential ground level installations.  Due to internal construction (actually 2 36-cell segments in parallel)((https://youtu.be/ofo1HQyGG8s?t=1m22s)) they can be more resistant to partial shading.+  * **Nominal 24v panels** have 72 cells.  They will generally have max power (Vmp) around 36v and open circuit (Voc) around 42v.((https://www.altestore.com/howto/solar-panels-pv-and-voltages-a98/))  These are commonly found in commercial or residential ground level installations.  
 +  * even higher cell counts (and voltages) can be present in very large panels, like >400w.
  
  
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 higher voltage panels are more common on the used market, as people upgrade residential/commercial installations higher voltage panels are more common on the used market, as people upgrade residential/commercial installations
  
-MPPT [[electrical:solar:charge_controller|controllers]] do a DC-DC downconversion that is quite efficient. If Vmp isn't required most will move PV voltage away from Vmp to prevent power from ever getting to the CC.+MPPT [[electrical:solar:charge_controller|controllers]] do a DC-DC downconversion that is quite efficient. If Vmp isn't required they will move PV voltage away from Vmp to prevent power from ever getting to the CC.
  
 Higher voltage panels can reduce wire costs; amps are cut in half for the same amount of wattage. Higher voltage panels can reduce wire costs; amps are cut in half for the same amount of wattage.
-They more likely to stay above charging setpoints in poor insolation or high heat.+They are more likely to stay above charging setpoints in poor insolation or high heat
 + 
 +Panel voltage((more precisely, the relationship between panel voltage and battery voltage)) is an important factor when [[electrical:solar:charge_controller#how_to_choose|selecting a solar charge controller]].
  
  
 ===== efficiency ===== ===== efficiency =====
 +
 +The formula for panel efficiency is simply rated watts / square meter.  A 20% efficient panel will make 200w per square meter under lab conditions (ie, 20% of the lab's 1000w standard).
 +
  
 Higher efficiency doesn't mean the panel makes more power;  it means it makes more power from a given area.  100w is 100w, but you might be able to fit a 110w panel high-efficiency panel in the same space as a regular-efficiency panel.  Higher efficiency doesn't mean the panel makes more power;  it means it makes more power from a given area.  100w is 100w, but you might be able to fit a 110w panel high-efficiency panel in the same space as a regular-efficiency panel. 
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 In general, mono has higher efficiency than poly, and poly has higher efficiency than thin film. In general, mono has higher efficiency than poly, and poly has higher efficiency than thin film.
  
-The cost of higher efficiency panels typically outstrips the increase power, so unless you are tight for space they typically aren't a good value for money.  If you are tight for space and need the power then pony up the cash and enjoy the premium product+The cost of higher efficiency panels typically outstrips the increase power, so unless you are tight for space they typically aren't a good value for money.  If you are tight for space and need the power then higher efficiency panels might be worth the premium. 
 + 
 + 
 + 
 +===== longevity =====
  
 +Framed panels are often warranted to make 80% of their rated output for 25+ years.  
  
 +There is [[https://web.archive.org/web/20220703094223/https://www.sciencedirect.com/science/article/pii/S2211379716301280|some evidence]] that panels with a load connected degrade slower than those stored unconnected (open circuit)
  
  
  
  
-===== specifications =====+===== Specifications =====
  
 PV are generally rated by several criteria((http://www.kg4cyx.net/solar-panel-specifications-explained/)) PV are generally rated by several criteria((http://www.kg4cyx.net/solar-panel-specifications-explained/))
-  * **Power (W)**: 190 Watts.  <- rated power in Watts under lab conditions.  You can derive **price-per-watt** by dividing $/watts.+  * **Power (W, or Pmax)**: 190 Watts.  <- rated power in Watts under lab conditions.  You can derive **price-per-watt** by dividing $/watts.
   * **Open Circuit Voltage (Voc)**: 36.00 Voc  <- Volts in full sun with no load.  In practice you will likely not see Voc when hooked to the controller, but **all parts of your solar installation need to be able to cope with the theoretical Voc**.  In serial arrays the Voc ratings are added.   * **Open Circuit Voltage (Voc)**: 36.00 Voc  <- Volts in full sun with no load.  In practice you will likely not see Voc when hooked to the controller, but **all parts of your solar installation need to be able to cope with the theoretical Voc**.  In serial arrays the Voc ratings are added.
   * **Short Circuit Current (Isc)**: 7.42 Isc  <- Amps in full sun when shorted.  Also theoretical, but **connectors and cables need to be sized to handle Isc**.   * **Short Circuit Current (Isc)**: 7.42 Isc  <- Amps in full sun when shorted.  Also theoretical, but **connectors and cables need to be sized to handle Isc**.
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 To help consumers understand output outside the lab (Standard Test Conditions - STC) some producers also publish specs for conditions that might be more applicable to actual use (Normal Operating Cell Temperature - NOCT).  Here is how they differ:((https://solardesignguide.com/stc-and-noct-solar-panel-test-conditions-explained/)) To help consumers understand output outside the lab (Standard Test Conditions - STC) some producers also publish specs for conditions that might be more applicable to actual use (Normal Operating Cell Temperature - NOCT).  Here is how they differ:((https://solardesignguide.com/stc-and-noct-solar-panel-test-conditions-explained/))
  
-^                  ^ STC                   | **NOCT**              | +^                  ^ STC                                                   | **NOCT**              | 
-| **Irradience**   | 1000W / square meter  | 800W / square meter   | +| **Irradience**   | 1000W / square meter                                  | 800W / square meter   | 
-| **temperature**  | //cell// temp 25C     | //ambient// temp 20C  | +| **temperature**  | //cell// temp 25C((which would be about 0C ambient))  | //ambient// temp 20C  | 
-| **wind speed**   | n/a                   | 1m/s                  |+| **wind speed**   | n/a                                                   | 1m/s                  |
  
  
-With NOCT the sunlight is not as strong, and the panels are assumed to be much warmer((therefore Vmp and Pmax reduced)) though some cooling from ambient breezes is present.((panels are installed with an airgap to let breezes cool the underside))+We can see that with NOCT the sunlight is not as strong, and the panels are assumed to be much warmer((therefore Vmp and Pmax reduced)) though some cooling from ambient breezes is present.((panels are installed with an airgap to let breezes cool the underside))
  
- +While NOCT may be useful for gauging normal harvests, STC is used for system component((like controllers)) sizing because the panels really can make STC power((or even more)) in some real world conditions.  The system needs to be sized to deal with high-output situations, particularly overly high panel voltages.  
 + 
 +>> NOCT is useful for comparing two panels **[that have] the same STC rating**. A panel with a higher rated power at NOCT for example, will generally result in a higher performing panel.((https://solardesignguide.com/stc-and-noct-solar-panel-test-conditions-explained/))
  
-===== diodes =====+**PTC** ([[https://www.osti.gov/servlets/purl/93997-mpCvkV/webviewable/|PVUSA]] Test Conditions)((https://solarmazd.com/stc-ptc-noct-what-do-they-mean-and-how-to-use-them/)) is a rarer standard. 
 +===== Diodes =====
  
 > A diode is designed to let current flow in one direction.... [it] is the electrical equivalent of a [plumbing] check valve. -- Amy@AltE((https://www.youtube.com/watch?v=5rYy0gHZepI)) > A diode is designed to let current flow in one direction.... [it] is the electrical equivalent of a [plumbing] check valve. -- Amy@AltE((https://www.youtube.com/watch?v=5rYy0gHZepI))
electrical/solar/panels.1626747511.txt.gz · Last modified: 2021/07/19 22:18 by frater_secessus