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electrical:solar:charge_controller [2019/09/02 23:53]
frater_secessus [shunt] holding Vans all day |
electrical:solar:charge_controller [2020/08/15 21:26]
frater_secessus [MPPT] |
| [[http://amzn.to/2iD3WKf|{{ https://images-na.ssl-images-amazon.com/images/I/51bi9IjcsRL._AC_US160_.jpg}}]] | [[http://amzn.to/2iD3WKf|{{ https://images-na.ssl-images-amazon.com/images/I/51bi9IjcsRL._AC_US160_.jpg}}]] |
| **MPPT** (maximum power point tracking) controllers have two defining abilities: | **MPPT** (maximum power point tracking) controllers have two defining abilities: |
| | |
| - discover (track) and utilize various power points along [[http://samlexsolar.com/learning-center/solar-panels-characteristics.aspx|the panel's power curve]]. Sometimes this is the maximum power point (MPP); often in a 'dweller context the system needs less power and the controller runs the panels at some other power point. It might be more accurate to call them PPT controllers. | - discover (track) and utilize various power points along [[http://samlexsolar.com/learning-center/solar-panels-characteristics.aspx|the panel's power curve]]. Sometimes this is the maximum power point (MPP); often in a 'dweller context the system needs less power and the controller runs the panels at some other power point. It might be more accurate to call them PPT controllers. |
| - DC-DC downconvert excess voltage to amps | - DC-DC downconvert excess voltage to amps - this is possible because MPPT decouples panel voltage (Vpanel) from charging voltage (Vbatt) |
| | |
| When maximum power is required((in Bulk or at other time when loads + charging >= panel output)) the controller will run the panels at Vmp (the maximum power point). At other times the controller will find a less-than-maximum power point to match panel output to system needs. | When maximum power is required((in Bulk or at other time when loads + charging >= panel output)) the controller will run the panels at Vmp (the maximum power point). At other times the controller will find a less-than-maximum power point to match panel output to system needs. |
| [[http://amzn.to/2yP01Ob|{{https://images-na.ssl-images-amazon.com/images/I/512x3hbc6jL._AC_US160_.jpg }}]] | [[http://amzn.to/2yP01Ob|{{https://images-na.ssl-images-amazon.com/images/I/512x3hbc6jL._AC_US160_.jpg }}]] |
| Since panel voltage at a given power point is usually too high for system needs((particularly with higher than nominal 12v panels )) the controller performs a DC-DC conversion to bring the voltage down to a directly usable level. Because **current through a conductor is directly proportional to voltage**((https://en.wikipedia.org/wiki/Ohm%27s_law)) this downconversion effectively turns excess voltage into increased amps.(minus conversion losses). | |
| | Since panel voltage at a given power point is usually too |
| | high for system needs((particularly with higher than nominal 12v panels )) the controller performs a DC-DC conversion to bring the voltage down to a directly usable level. Because **current through a conductor is directly proportional to voltage**((https://en.wikipedia.org/wiki/Ohm%27s_law)) this downconversion effectively turns excess voltage into increased amps.(minus conversion losses). |
| This ability to decouple panel and bank voltage can result in 10%-30% more power harvested from 12v nominal panels than with a PWM controller. Marketers like to call this "boost" or "gains" but it really just full capture of whatever power the panel[s] can provide under given conditions. | This ability to decouple panel and bank voltage can result in 10%-30% more power harvested from 12v nominal panels than with a PWM controller. Marketers like to call this "boost" or "gains" but it really just full capture of whatever power the panel[s] can provide under given conditions. |
| | |
| === "boost" effect === | === "boost" effect === |
| {{ https://media.licdn.com/mpr/mpr/AAEAAQAAAAAAAAwtAAAAJGJhNjE1OGY3LTM3OWQtNGQ2Mi05NWEwLTI2Mzc3MGY3MDk3MA.png?150}}When compared apples-to-apples on identical systems with //only the controller being different//, the "boost" effect is most pronounced: | {{ https://media.licdn.com/mpr/mpr/AAEAAQAAAAAAAAwtAAAAJGJhNjE1OGY3LTM3OWQtNGQ2Mi05NWEwLTI2Mzc3MGY3MDk3MA.png?150}}When compared apples-to-apples on identical systems with //only the controller being different//, the "boost" effect is most pronounced: |
| * during bulk stage and the early part of absorption stage when the battery can take in the most power | * during bulk stage and the early part of absorption stage when the battery can take in the most power |
| | * anytime the system is fully loaded down (charging and/or loads) |
| * when the battery is most depleted (ie lowest resting voltage). This is the result of a cascade of factors: | * when the battery is most depleted (ie lowest resting voltage). This is the result of a cascade of factors: |
| * When a battery is deeply discharged it will go into Bulk charging mode until it reaches the Absorption voltage (Vabs). For the purpose of illustration we will assume the bank is depleted to 12.2v (~50% [[electrical:depth_of_discharge|state of charge]]), a commonly recommended lower limit for deep cycle batteries. | * When a battery is deeply discharged it will go into Bulk charging mode until it reaches the Absorption voltage (Vabs). For the purpose of illustration we will assume the bank is depleted to 12.2v (~50% [[electrical:depth_of_discharge|state of charge]]), a commonly recommended lower limit for deep cycle batteries. |
| * PWM controllers can only run the panel at whatever voltage they are charging at right now. In our example that is 12.2v. | * PWM controllers can only run the panel at whatever voltage they are charging at right now. In our example that is 12.2v. |
| * Nominal 12v panels usually have max power output (Vmp) around 17v.((https://www.altestore.com/howto/solar-panels-pv-and-voltages-a98/)) | * Nominal 12v panels usually have max power output (Vmp) around 17v.((https://www.altestore.com/howto/solar-panels-pv-and-voltages-a98/)) |
| * when a typical 100w panel((Iop = 5.6A)) is run at 12.2v in lab conditions it puts out **~68.32W**. The same panel run at Vmp (~17v) would put out **100W**. **MPPT is capturing more power than the PWM when the battery needs it most**.((there are minor inefficiencies not considered here)) | * when a typical 100w panel((Iop = 5.6A)) is run at 12.2v in lab conditions it puts out **~68.32W**. The same panel run at Vmp (~17v) would put out **100W**. **MPPT is capturing more power than the PWM when the battery needs it most**.((there are minor inefficiencies not considered here)) |
| * during times of greatest PV efficiency((i.e. highest voltage)) (clear, cold weather) | * during times of greatest PV efficiency((i.e. highest voltage)) (clear, cold weather) |
| * during times of low irradience (low light levels due to low angle or overcast conditions)((this is a function of higher input voltages))((https://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf Section 7.3)) | * during times of low irradience (low light levels due to low angle or overcast conditions)((this is a function of higher input voltages))((https://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf Section 7.3)) |
| There are //DC-DC converting charge controllers// (DDCCC) appearing on the market that claim to be MPPT but do not actually track power points (maximum or otherwise). They do downconvert some excess voltage into amperage. See [[https://boondockplan.wordpress.com/2017/12/15/backchannel-dc-dc-converting-charge-controllers/|this blog post]]. | There are //DC-DC converting charge controllers// (DDCCC) appearing on the market that claim to be MPPT but do not actually track power points (maximum or otherwise). They do downconvert some excess voltage into amperage. See [[https://boondockplan.wordpress.com/2017/12/15/backchannel-dc-dc-converting-charge-controllers/|this blog post]]. |
| ==== how to choose ==== | ==== how to choose ==== |
| **PWM is the default choice** in most situations because they get the job done in most scenarios and are inexpensive. PWM controllers can cost half or a third of their MPPT workmates for any given rated output.((10A, 20A, 40A, etc)) | **PWM is a reasonable default choice** in most situations((12v house power, 12v panels)) because they work well enough and are inexpensive. PWM controllers can cost half or a third of their MPPT workmates for any given rated output.((10A, 20A, 40A, etc)) |
| If more power is needed (and there is physical space) additional PV can be added to match the charging output of an MPPT charger, often at a lower cost. [There are no prizes for fanciest or most expensive charge controller! Do what is best for you -- frater secessus] | If more power is needed (and there is physical space) additional PV can be added to match the charging output of an MPPT charger, often at a lower cost. [There are no prizes for fanciest or most expensive charge controller! Do what is best for you -- frater secessus] |
| MPPT controllers also tend to consume more power to run themselves than PWM models due to additional processing and electronic components. | |
| **MPPT may be a better fit** when: | There are also edge cases((low altitude, high temperature, Absorption)) where PWM can actually make more power than MPPT on poly [[electrical:solar:panels|panels]] during Absorption stage in very hot weather, due to MPPT DC-DC conversion losses and [[electrical:solar:output#panel_temperature|temperature derating]]. |
| * battery banks are cycled deeply on a regular basis so more time is spent in Bulk | |
| * nominal 12v panels have a relatively high Vmp (>=18v) for [[https://www.reddit.com/r/vandwellers/comments/bmlosu/is_vandwelling_a_frugal_lifestyle/emz5lsf/?context=1|reasons discussed here]]. | |
| * [[https://www.wholesalesolar.com/solar-information/sun-hours-us-map|areas of low insolation]] | |
| * high latitudes | |
| * overcast or rainy weather | |
| * if the camper will be used in areas of partial shade((http://forum.solar-electric.com/discussion/comment/250936#Comment_250936)) | |
| * canyon or "urban canyon" areas | |
| * forested areas | |
| * if temperatures are very low (greater harvest) | |
| * the increase in cost is not an undue burden | |
| **MPPT is effectively required** when: | **MPPT is effectively required** when: |
| * using panels with nominal voltages higher than 12v | * using panels with nominal voltages higher than 12v ((more prescisely, when panel nominal voltage exceeds house bank nominal voltage)) |
| * space available for panels is limited, as on a sailboat or small vehicle | * space available for panels is limited, as on a sailboat or small vehicle |
| | * daytime loads are hampered by [[electrical:solar:pwm_tweaking|PWM Vbatt hobbling]] |
| * [[#overpaneling|overpaneling]] | * [[#overpaneling|overpaneling]] |
| * making [[electrical:converter#diy_converters|DIY converters]] | * making [[electrical:converter#diy_converters|DIY converters]] |
| We say "effectively required" because one //can// use 24v panels with PWM and 12v banks -- it just doesn't work very well. The 24v panels will be run at 12v voltages, yielding about half the power you would get with MPPT. | We say "effectively required" because one //can// use 24v panels with PWM and 12v banks -- it just doesn't work very well. The 24v panels will be run at 12v voltages, yielding about half the power you would get with MPPT. |
| **Shunt controllers are useful for [[electrical:solar:shallow_cycling|shallow-cycling configurations]]** or for battery chemistries that are not damaged by [[electrical:depth_of_discharge|partial state of charge (PSoC)]]. Their relative inexpense makes them useful for even very small systems and test configurations. | |
| Their simple ON and OFF setpoints may also make them useful for charging [[electrical:12v:lifepo4_batteries_thread|lithium]] chemistries. | |
| Further reading: | Further reading: |
| [[https://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf|an excellent and readable whitepaper by Victron]] (PDF). | [[https://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf|an excellent and readable whitepaper by Victron]] (PDF). |
| | |
| | **MPPT may be a better fit** when: |
| | |
| | * the existing PWM system is not providing enough output |
| | * using monocrystalline panels, as the higher Vmp and lower Imp further reduces PWM output. |
| | * battery banks are cycled deeply on a regular basis so more time is spent at low Vbatt where PWM struggles. |
| | * nominal 12v panels have a relatively high Vmp (>=18v) for [[https://www.reddit.com/r/vandwellers/comments/bmlosu/is_vandwelling_a_frugal_lifestyle/emz5lsf/?context=1|reasons discussed here]]. |
| | * if multiple panels will be used in areas of [[electrical:solar:shading|partial shade]] |
| | * if temperatures are very low (rising Vmp means increasing output which PWM could not capture) |
| | * the increase in cost is not an undue burden |
| | |
| | **Shunt controllers** are extremely inexpensive, making them useful for even very small systems, test configurations, and backups. |
| | |
| | Shunts with a configurable charge setpoint((effectively Vabs)) will likely charge deeply cycled batteries better than a more $$$ PWM controller that lacks configuratble setpoints. See [[electrical:solar:shunt_tweaking|shunt tweaking]]. |
| | |
| | * [[electrical:solar:shallow_cycling|shallow-cycling configurations]] |
| | * battery chemistries that are not damaged by [[electrical:depth_of_discharge|partial state of charge (PSoC)]]. |
| | * Their simple ON and OFF setpoints may also make them useful for charging [[electrical:12v:deep_cycle_battery#lithium_chemistries|lithium]] chemistries. |
| | |
| | |
| ===== multiple charge controllers ===== | ===== multiple charge controllers ===== |
| [[electrical:12v:multipoint_charging|Multiple controllers (with separate arrays) can be used to charge a common bank]]. The controllers should be configured with similar charging setpoints for the greatest efficiency.((http://www.morningstarcorp.com/parallel-charging-using-multiple-controllers-separate-pv-arrays/)) | [[electrical:12v:multipoint_charging|Multiple controllers (with separate arrays) can be used to charge a common bank]]. The controllers should be configured with similar charging setpoints for the greatest efficiency.((http://www.morningstarcorp.com/parallel-charging-using-multiple-controllers-separate-pv-arrays/)) |
| ===== sizing your charge controller ===== | ===== sizing your charge controller ===== |
| As with [[electrical:inverter|inverters]], sizing the controller correctly will help system efficiency. An oversized CC will have unnecessarily high parasitic drains as it powers itself. An undersized CC will not be able to put all the rated solar wattage to use and will leave no room for expansion. | As with [[electrical:inverter|inverters]], sizing the controller correctly will help system efficiency and save money. An oversized CC will have unnecessarily high parasitic drains as it powers itself and will cost more. An undersized CC will not be able to put all the rated solar wattage to use and will leave no room for expansion. |
| For PWM controllers, the formula is something like (panel wattage / 13) * (1.2 oversize for safety) = charge controller amps.((https://www.altestore.com/howto/sizing-pwm-solar-charge-controllers-a91/)) | For PWM controllers, the formula is something like (panel wattage / 13) * (1.2 oversize for safety) = charge controller amps.((https://www.altestore.com/howto/sizing-pwm-solar-charge-controllers-a91/)) |
| MPPT controllers have more leeway in sizing since they can control the output of the panels independently of battery voltage. | MPPT controllers have more leeway in sizing since they can control the output of the panels independently of battery voltage. |
| > Inductive loads can generate large voltage spikes that may damage the controller’s lightning protection devices.((http://www.morningstarcorp.com/wp-content/uploads/2014/02/TS.IOM_.Operators_Manual.04.EN_1.pdf)) | > Inductive loads can generate large voltage spikes that may damage the controller’s lightning protection devices.((http://www.morningstarcorp.com/wp-content/uploads/2014/02/TS.IOM_.Operators_Manual.04.EN_1.pdf)) |
| although an exception is made for the SunSaver MPPT which "Handles inductive loads without problems."((http://support.morningstarcorp.com/wp-content/uploads/2014/07/SunSaverMPPT-FeaturesBenefits.pdf)) | although an exception is made for the SunSaver MPPT which "Handles inductive loads without problems."((http://support.morningstarcorp.com/wp-content/uploads/2014/07/SunSaverMPPT-FeaturesBenefits.pdf)) |
| | |
| One can run loads heavier than the controller is rated for (or inductive/capacitive loads) by connecting those load[s] to a relay((http://support.morningstarcorp.com/wp-content/uploads/2014/07/ALL.DIG_.Load_Control_Using_A_Relay.01.EN_.pdf)), which is in turn connected to the LOAD output. This still allows for Low Voltage Disconnect because the CC will turn off power to the LOAD output, which turns off power to the relay, which turns power off to the load. | One can run loads heavier than the controller is rated for (or inductive/capacitive loads) by connecting those load[s] to a relay((http://support.morningstarcorp.com/wp-content/uploads/2014/07/ALL.DIG_.Load_Control_Using_A_Relay.01.EN_.pdf)), which is in turn connected to the LOAD output. This still allows for Low Voltage Disconnect because the CC will turn off power to the LOAD output, which turns off power to the relay, which turns power off to the load. |
| | |
| You may also be able to use the LOAD output to create a [[electrical:solar:nonessential|separate 12v circuit for non-essential ("opportunity") loads]]. | You may also be able to use the LOAD output to create a [[electrical:solar:nonessential|separate 12v circuit for non-essential ("opportunity") loads]]. |
| | |
| Note: in wind and hydro power applications the output can be sequenced so that LOAD is activated only when batteries are fully charged. This is called a "dump load" because those power sources need to be able to "dump" excess current to prevent damage to themselves. Dump loads are not necessary in solar because panels can be open- or short-circuited without damage. | Note: in wind and hydro power applications the output can be sequenced so that LOAD is activated only when batteries are fully charged. This is called a "dump load" because those power sources need to be able to "dump" excess current to prevent damage to themselves. Dump loads are not necessary in solar because panels can be open- or short-circuited without damage. |
| ===== positive ground controllers ===== | ===== positive ground controllers ===== |
