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electrical:solar:panels [2022/01/15 03:03]
princess_fluffypants [Efficiency] |
electrical:solar:panels [2024/05/28 16:38] (current)
frater_secessus [Portable] |
| 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. |
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| [[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. |
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| 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. |
| * 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 |
| * 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 |
| ==== Portable ==== | ==== Portable ==== |
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| While most panels are hard mounted horizontally on the roof of the van, portable folding portable solar panels have dropped in price and have some advantages. | While most panels are hard mounted horizontally on the roof of the van, portable solar panels((folding, briefcase, framed or otherwise)) may have some advantages. |
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| [[https://www.amazon.com/portable-solar-panel/s?k=portable+solar+panel|Amazon search]] | [[https://www.amazon.com/portable-solar-panel/s?k=portable+solar+panel|Amazon search]] |
| * Questions exist about long-term durability | * Questions exist about long-term durability |
| * Possibility of panels getting stolen | * Possibility of panels getting stolen |
| | * not all portables are weatherproof |
| | * can be blown over by wind |
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| | Note that regular framed panels can also be carried as portables. To make storage/placement easier they are usually 100x times however many you need. |
| | ==== half-cut ==== |
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| ---- | 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. |
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| | {Secessus reminds us we should avoid [[electrical:solar:shading|shade]] in the first place} |
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| * **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 |
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| 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. |
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| 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. |
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| 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]]. | 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 ===== | |
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| | ===== efficiency ===== |
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| | 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). |
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| 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. |
| 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. |
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| 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. |
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| | ===== longevity ===== |
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| | Framed panels are often warranted to make 80% of their rated output for 25+ years. |
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| | 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) |
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| > At zenith, sunlight provides an irradiance of just over 1 kilowatt per square meter at sea level. Of this energy, 527 watts is infrared radiation, **445 watts is visible light**, and 32 watts is ultraviolet radiation. -- [[https://en.wikipedia.org/wiki/Infrared|wikipedia]] | |
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| Mono panels can capture about 20-22% of this energy. Poly panels capture 13-16%, and film panels capture 9%. | |
| ===== Specifications ===== | ===== Specifications ===== |
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| 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**. |
| * **Maximum Power Voltage (Vmp)**: 28.60 Vmp <- voltage at which max power is generated in lab conditions | * **Maximum Power Voltage (Vmp)**: 28.60 Vmp <- voltage at which max power is generated in lab conditions |
| * **Maximum Power Current (Imp)**: 6.64 Imp <- Amps at Vmp in lab conditions | * **Maximum Power Current (Imp)**: 6.64 Imp <- Amps at Vmp in lab conditions |
| | * **Temperature coefficient**; see below. |
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| Note that in this example the Power (W) rating is 190, which is the Vmp x Imp (28.60 x 6.64 = 189.904W). | Note that in this example the Power (W) rating is 190, which is the Vmp x Imp (28.60 x 6.64 = 189.904W). |
| In real world conditions [[electrical:solar:output|power output will likely be less]] than under optimal lab conditions and the Vmp may not be at the voltage given on the label. Vmp will vary due to local conditions like temperature, shade, and sunshine. An [[electrical:solar:charge_controller|MPPT charge controller]], if present, will sweep the range of voltages regularly to find Vmp under the existing conditions. | In real world conditions [[electrical:solar:output|power output will likely be less]] than under optimal lab conditions and the Vmp may not be at the voltage given on the label. Vmp will vary due to local conditions like temperature, shade, and sunshine. An [[electrical:solar:charge_controller|MPPT charge controller]], if present, will sweep the range of voltages regularly to find Vmp under the existing conditions. |
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| Panels will get closest to their rated output at ambient temperatures around 32f/0f when the panels will be running about 85F. By the time ambient temperatures are 90F panel temps will rise to 145F and power output will drop about 18.45%.((http://digivation.com.au/solar/tempderate.php)) | ==== temperature coefficient ==== |
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| | Panel voltage //decreases// as cell temperature //increases//. Ramifications: |
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| | - since panels are rated by Vmp x Imp, anything that reduces voltage will reduce power.((PWM are generally not affected since they are not using that higher voltage anyhow)) |
| | - the Vmp your MPPT controller finds in human-comfortable temps will likely be lower than rated Vmp |
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| | Example: panels will get closest to their rated output at ambient temperatures around 32f/0f when the panels will be running about 85F. By the time ambient temperatures are 90F panel temps will rise to 145F and power output will drop about 18.45%.((http://digivation.com.au/solar/tempderate.php)) |
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| | The actual amount of drop is dictated by the **temperature coefficient**, expressed as -0.X%/ºC. In other words, the Vmp will go down by X% per degree celsius of cell temp above 25C. Since |
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| | This coeffcient ranges from 0.3% to -0.5%. Crystalline panels average around -0.44% and thin-film lower (in the thirties). The general pattern seems to be that cell chemistries with higher Vmp tend to experience greater heat-related losses. "Mind the [air]gap". |
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| | Let's consider three different panels in 80F ambients: |
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| | * 100w mono, rated 19Vmp, -0.445%/ºC((https://www.researchgate.net/profile/Abdelhamid-Rabhi/publication/274373712/figure/fig3/AS:667621221478403@1536184711417/MPP-thermal-coefficient-for-mono-and-poly-crystalline-PV-module-varying-with-power.png)) == **14.65w** lost @ 16.22Vmp |
| | * 100w poly, rated 18Vmp, -0.440%/ºC == **14.48w** lost @ 15.39Vmp |
| | * 100w CIGS((not really, trying for apples-to-apples here)), rated 18.66Vmp, -0.36%/ºC == **11.85w** lost @ 16.45Vmp |
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| ==== STC and NOCT ==== | ==== STC and NOCT ==== |
| 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. | 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. |
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| | >> 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/)) |
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| | **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 ===== | ===== Diodes ===== |
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