What is Pulse Width Modulation (PWM) Solar Charge Controller?
What is Pulse Width Modulation Or A PWM Charge Controller?
A PWM (Pulse Width Modulation) controller is an (electronic) transition between the solar panels and the batteries:
The solar charge controller (frequently referred to as the regulator) is identical to the standard battery charger, i.e., it controls the current flowing from the solar panel to the battery bank to prevent overcharging the batteries. As in a standard battery charger, it can accommodate different types of batteries.
The absorption voltage can select the float voltage, and it can often also set the time and tail current. They are best suitable for lithium-iron-phosphate batteries since when the controller is in full charge, it remains at the fixed float or maintains a voltage of about 13.6V (3.4V per cell) for the rest of the day.
The most popular charging profile is the same simple sequence found on a quality mains adapter, i.e., bulk mode – absorption mode – float mode. Entry to bulk charging mode happens at:
- Sunrise in the morning
- If the battery voltage drops down the specified voltage for longer than a specified period, e.g., 5 seconds (re-entry)
This re-entry into bulk mode works better for lead-acid batteries since the voltage drop and drop are more significant than lithium-based batteries, which retain a higher, more stable voltage for the rest of the discharge period.
In the solar charge controller:
- The switch is ON while the charger mode is in bulk charging mode.
- The switch is ON and off when required (pulse width modulated) to keep the absorption’s battery voltage.
- It is OFF at the end of the absorption when the battery voltage decreases to the float voltage.
- The switch is ON and OFF again as required (pulse width modulated) to keep the battery voltage at the float voltage.
Notice that when the switch is off, the panel voltage will be at the open-circuit voltage (Voc). When the button is on the panel, the voltage will be at the battery voltage the voltage decreases between the board and the controller.
The best match for a PWM controller:
The best matching panel for a PWM controller is a panel with a voltage just above provided for charging the battery and taking into account the temperature, usually, a board with a Vmp (maximum voltage) of about 18V to charge a 12V battery. They are sometimes referred to as a 12V row even though they have a Vmp of about 18V.
Below is the block diagram of a typical PWM solar charge controller.
PMW 3 Stage Charging
Bulk Charge: The bulk charging level is where the PV device continues much of the battery’s charge. The device will charge the battery with a high current and voltage when the voltage is down. When the voltage at the end of the battery is more significant than this maintenance value while setting, direct charging should stop.
Absorb Charge: Usually, after the first step of charging, the battery will wait for a period to allow the voltage to decrease naturally and then reach the balanced charging stage. The stage is also called constant voltage charging.
Float Charge: It is the last stage of 3-stage charging, known as Trickle charging. The trickle is a slight charging current to the battery at a low rate and steady. Most rechargeable batteries lose power when entirely powered due to self-discharge. If the charging stays at the same low current as the self-discharge rate, it can sustain the charge capacity.
PWM Solar Controller Pros:
- The PWM Regulator has matured and established techniques.
- Simple structure and cost-effective
- Easy deployment of the PWM regulator
- The lower budget on a small initiative
PWM Solar Charge Controller Cons:
- Low conversion rate
- Input voltage must balance the bank voltage of the battery.
- Less scalability for device development
- Less Loading Mode
- Less protection;
The Function of the Solar Charge Controller:
The central charge controller essentially regulates the unit’s voltage and opens the circuit, stopping the charge as the battery voltage rises to a certain amount. charge controls used a mechanical relay to open or shut off the course, stop or start power from the electrical storage unit.
Generally, 12V batteries are for solar power applications. Solar panels can convey much more voltage than the battery needs to charge. The charge voltage will be maintained at the highest possible level while the time taken to set the electrical storage equipment entirely is minimal. It helps the solar systems to run continuously optimally. The wires ‘ power dissipation is significantly low by running a higher voltage in the solar panels’ cables to the charge controller.
Solar charge controllers can also control the flow of reverse electricity. The charge controllers will discern whether there is no power coming from the solar panels and open the circuit separating the solar panels from the battery devices and stopping the reverse current flow.
Types of solar Charger controller:
Three types of the solar charge controller
1) Simple 1 or 2 Phase Controls: has switched transistors to regulate the voltage in one or two steps.
2) PWM (pulse width modulated): this is the traditional form of the charge controller, e.g., xantrex, Blue Sky, and so on. It is the industry norm at the moment.
3) Maximum power point tracking (MPPT): MPPT identifies the optimum operating voltage and amperage of the solar panel display and matches that of the electrical cell bank.
Sizing a PWM Solar Charge Controller
PWM controllers are not able to restrict their current performance. They’re just using the current collection. Therefore, if the solar array will generate 40 amps of current and the charge controller you are using is only rated at 30 amps, the controller could be impaired. It is essential to ensure that your charge controller is parallel, compliant with, and correctly sized for your panels.
When looking at a charge controller, many items are looked at in the list of features or tags. A PWM controller would have an amp read with it, e.g., a 30 amp PWM controller. It reflects how many amps the controller can accommodate, in the above example, 30 amps. In general, the amperage and voltage rating are the two things you want to look at in a PWM control.
Next, we want to look at the nominal device voltage. It would inform us what voltage the controller’s battery banks are compliant with. You may use 12V or 24V battery banks in this situation. The controller would not be able to operate on anything higher, such as a 48V battery bank.
Second, the rated current of the battery is important. In this case, let’s assume that you have a 30-amp rating charge controller. A protection ratio of at least 1.25 is recommended, which means that you can average the current from the panels by 1.25 and then equate it to 30 amps. E.g., five 100 watt panels will be 5.29 x 5 = 26.45 amps in parallel. 26.45 Amps x 1.25 = 33 amps, and that will be too much for the controller. The panel will encounter more current than what is valued when exposure to sun rays is above 1000 watts/m^2.
Thirdly, we should look at the maximum input of solar energy. It shows you how many volts you can get to the controller. This controller cannot tolerate more than 50 volts. It is taking a look at making 2 x 100 Watt panels in series with a total of 22.5V (open-circuit voltage) x 2 = 45 volts. In this case, it’s going to be ok to wire these two panels in series.
Fourthly, we should have a look at the terminals. Each controller will typically have the maximum size of the terminal gauge. It is critical when buying wiring for your machine.
Finally, look at the type of battery. It tells us which batteries are compliant with the charge controller. It is essential to verify as you don’t want to get batteries that the controller device cannot power.
Let see the following another basic example for sizing a PWM solar charge controller.
What is the suitable size of PWM solar charge controller for a 100W, 12V solar panel having ISC (Short Circuit current) of 8A?
We will have to add the safety factor of 25% current i.e. 1.25 x ISC to find the appropriate size of solar charge controller.
This way; 8A x 1.25 = 10A.
Hence, you can safely use a 10A, 12V of solar charge controller for this basic solar panel system.
Another way, if the total connected DC load is 12V, 95W.
Nominal load current = Total DC load / Nominal System Voltage = 95W / 12V
Nominal load current = 7.91 A
Safety Factor x Nominal load current
1.25 x 7.91 = 9.9A
Finally, a basic power formula method i.e. P = V x I
Note that you will have to apply the same formula for series and parallel connected solar panels and batteries according to voltage and current ratings. You may See more solved example for sizing PWM and MMPT Charge controller in the previous post.
The Discrepancy between PWM and MPPT Solar Load Controllers
The crux of the difference is:
- With the PWM controller, the current is drawn out of the panel at just above the battery level while
- With the MPPT controller, the current draws out of the panel at the “maximum power voltage” button (think of the MPPT controller as a “Smart DC to DC converter“).
You also see slogans such as “you’re going to get 20% or more energy harvesting from an MPPT controller.” This extra also differs significantly, and the following is a reference to whether the panel is in full sunlight and the controller is in bulk charge mode. Ignoring voltage decreases, using a simple panel and simple math as an example:
The charger’s voltage = 13V (battery voltage can vary between, say, 10.8V fully discharged and 14.4V during absorption charge mode). At 13V, the panel amp would be marginally higher than the total power amp, say 5.2A.
With a PWM controller, the output from the panel is 5.2A13V = 67.6 watts. This sum of power would be drawn regardless of the panel temperature, provided that the panel voltage stays above the battery voltage.
With an MPPT controller, the panel’s power output is 5.0A18V = 90 watts, i.e., 25 percent higher. However, this is excessively ambitious as the voltage decreases as the temperature increases; thus, assume that the panel temperature rises to 30°C above the normal test conditions (STC) temperature of 25°C. The voltage drops by 4 percent at every ten °C, i.e., a total of 12 percent, the output of the MPPT would be 5A15.84V = 79.2W, i.e., 17.2 percent more power than the PWM controller.
So, there is an increase in energy harvesting for the MPPT controls, but the percentage increase in harvesting differs considerably over the day.
Advantages of PWM Charger
Charging a solar-powered battery is a unique and challenging challenge. In the old days, essential on-off regulators were used to reduce the battery from gas when the solar panel provided excess electricity. However, as the solar systems evolved, it became apparent how much these simplistic instruments had messed with the charging process.
On-off regulators’ experience has been early battery errors, rising load disconnects, and increasing consumer frustration. PWM has recently emerged as the first breakthrough in the charging of solar batteries. PWM solar chargers use hardware similar to most modern, high-quality battery chargers.
As the battery voltage exceeds the control limit, the PWM algorithm slowly decreases the charging current to prevent the battery from being heated and gaseous, while charging begins to return the total amount of energy to the battery in the shortest time possible. It results in better charging efficiency, fast recharging, and a long-lasting battery at maximum power.
Also, this new way of charging solar batteries offers some very fascinating and unusual PWM pulsation advantages.
- Ability to restore reduced battery power and dissipate the battery
- Dramatically boost the approval of the battery charge.
- Retain high overall battery capacity (90 percent to 95 percent) relative to on-off controlled state-of-charge ranges usually between 55 percent and 60 percent.
- Equalize the drift cells of the battery.
- Limit the heating and gasification of the battery.
- Automatically compensate for the age of the battery.
- Self-regulation of voltage rises and temperature effects in solar systems
Choosing the Best Solar Controller
The PWM is a decent low-cost option:
- For smaller devices
- Where the reliability of the device is not essential (the charging process)
- For solar panels with a nominal voltage (Vmp) of up to 18V for charging a 12V battery (36V for 24V battery, etc.)
- The MPPT controller is ideally suited for:
- For more extensive networks where an additional 20% or more energy harvesting is worthwhile;
- Where the solar array voltage is considerably more significant than the battery voltage, e.g., using house panels, for charging 12V batteries;
In recent days, the method of producing electricity from sunlight has become more common than other alternative sources, and photovoltaic panels are free of emissions and do not require high maintenance. Here are few examples where we are using solar energy.
- Street lamps use photovoltaic cells to transform sunlight to DC electrical charge. This machine uses a solar charge device to store DC in the batteries and uses it in several locations.
- Home systems use the PV module for house-holding purposes.
- The hybrid solar panel uses various energy sources to provide full-time backup supplies to other sources.
Note: This Article is published by www.electricaltechnology.org
A/20A/30A PWM Solar Charge Controllers
These PWM Solar Battery Charge Controllers automatically manage and regulate the voltage and current to the battery from the solar panel(s). They incorporate short-circuit, open-circuit, reverse polarity, and overload protection in order to ensure that the batteries are not overcharged and that power isn’t discharged from the batteries to the solar panels during shaded or dark conditions and drain the batteries. They come with USB ports to charge your phone and other electronic devices directly from the controller.
The maximum input charging current from the solar panel is 10A, 20A or 30A depending upon the model chosen. The maximum panel output current should be about 25% less than the controller’s maximum input current rating.
For example, with a single 6A 100W panel, use the 10A model. Two 6A panels (12A total) should use the 20A model. If in doubt, use the higher current model, i.e. if the maximum panel output current is 9A, use the 20A model rather than the 10A model.
Maximum Input Voltage:
12V batteries should be used with solar panels capable of generating 18V-25VWith 12V batteries, the maximum panel voltage must not exceed 25V
24V batteries should be used with solar panels capable of generating 36V-50VWith 24V batteries, the maximum panel voltage must not exceed 50V
Maximum Input Power:
10A Model 12V: 120W (MAX), 24V: 240W (MAX)20A Model 12V: 240W (MAX), 24V: 480W (MAX)30A Model 12V: 360W (MAX), 24V: 720W (MAX)
Maximum Discharge Current / Power:
The maximum discharge current to the load is 10A. Therefore with 12V batteries, the maximum power is 120 Watts. With 24V batteries, it is 240 Watts.
Connection to the Battery, Solar Panel and Load:
This charge controller uses the battery voltage to operate its onboard circuitry, including its self-protection and control circuitry. If the controller is not powered on, connecting a live solar panel to it may damage the unit.
Do not connect your solar panel to the controller until the battery is first connected and the LCD is turned on.
- Connect the battery to the charge controller first. The controller’s LCD should turn on. Do not proceed if the LCD display does not turn on! The controller needs about 10V to operate. If the LCD does not turn on it is usually because the battery cannot provide at least 10V. Charge it using an external battery charger before proceeding.
- Connect the photovoltaic module to the charge controller.
- Connect your load (the device(s) you are going to power) to the charge controller.
Reverse these steps when disconnecting or uninstalling the controller.
There are three icons along the bottom of the display for the panels, the battery, and the load. If the battery is charging, there will be an arrow between the panel and the battery. See the attached image. If the LCD arrow is on, it is charging. If it is off, it is not charging. If it is flashing, it is maintaining the float voltage.
Referring to the buttons below the display, the left button is the “Menu” button (also used to Set and Select), the middle is the “Up” button and the right button is the “Down” button.
Tapping the Menu button will scroll through the different parameters.
The sequence of the display is:
- Battery Voltage (V)
- Float Voltage (V)Adjustable, sets the battery voltage at which the panel is disconnected from the battery to prevent overcharging of the battery)
- Discharge Voltage Reconnection Level (V)Adjustable, sets the battery voltage at which the solar panel is reconnected to the battery to initiate charging
- Low Voltage Disconnection (Discharge Stop) (V)Adjustable, the voltage at which the battery is disconnected from the load to protect the battery from over-discharge
- Load Working Mode (H)Adjustable: 24H = the load output is on 24 hours per day1-15H = The load output is on from sunset for the number of hours programmed0H = The load output is on from dusk to dawn
- Battery TypeAdjustable:b1 = Lead Acidb2 = AGM (Absorbent Glass Mat)b3 = Gel
Operating and Programming The Controller:
Tap the Menu (left) button to cycle through the interface and parameters.
To change a parameter:
- Cycle through the display until the parameter you want to change is displayed
- Long press the menu button for about 3 seconds to enter the programming mode. The value will begin flashing.
- Use the Up and Down buttons the change the value
- Tap the Menu button to save the setting. Tape it again to continue cycling through the parameters
|Charge icon not on when sunny||Solar panel opened, disconnected or reversed||Reconnect the solar panel|
|Load icon off||Mode setting wrongBattery Low||Set the Mode againRecharge the battery|
|Load icon slow flashing||Over loadShort circuit||Reduce load wattageRemove short circuit, automatic recover after ~1 minute|
|Power off||Battery too low or reversed||Check battery and recharge if needed, check the connection|
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What is a solar charge controller?
A solar charge controller, also known as a solar regulator, is basically a solar battery charger connected between the solar panels and battery. Its job is to regulate the battery charging process and ensure the battery is charged correctly, or more importantly, not over-charged. DC-coupled solar charge controllers have been around for decades and are used in almost all small-scale off-grid solar power systems.
Modern solar charge controllers have advanced features to ensure the battery system is charged precisely and efficiently, plus features like DC load output used for lighting. Generally, most smaller 12V-24V charge controllers up to 30A have DC load terminals and are used for caravans, RVs and small buildings. On the other hand, most larger, more advanced 60A MPPT solar charge controllers do not have load output terminals and are specifically designed for large off-grid power systems with solar arrays and powerful off-grid inverter-chargers.
Solar charge controllers are rated according to the maximum input voltage (V) and maximum charge current (A). As explained in more detail below, these two ratings determine how many solar panels can be connected to the charge controller. Solar panels are generally connected together in series, known as a string of panels. The more panels connected in series, the higher the string voltage.
- Current Amp (A) rating = Maximum charging current.
- Voltage (V) rating = Maximum voltage (Voc) of the solar panel or string of panels.
MPPT Vs PWM solar charge controllers
There are two main types of solar charge controllers, PWM and MPPT, with the latter being the primary FOCUS of this article due to the increased charging efficiency, improved performance and other advantages explained below.
PWM solar charge controllers
Simple PWM, or ‘pulse width modulation’ solar charge controllers, have a direct connection from the solar array to the battery and use a basic ‘Rapid switch’ to modulate or control the battery charging. The switch (transistor) opens until the battery reaches the absorption charge voltage. Then the switch starts to open and close rapidly (hundreds of times per second) to modulate the current and maintain a constant battery voltage. This works ok, but the problem is the solar panel voltage is pulled down to match the battery voltage. This, in turn, pulls the panel voltage away from its optimum operating voltage (Vmp) and reduces the panel power output and operating efficiency.
PWM solar charge controllers are a great low-cost option for small 12V systems when one or two solar panels are used, such as simple applications like solar lighting, camping and basic things like USB/phone chargers. However, if more than one panel is needed, they will need to be connected in parallel, not in series (unless the panels are very low voltage and the battery is a higher voltage).
MPPT solar charge controllers
MPPT stands for Maximum Power Point Tracker; these are far more advanced than PWM charge controllers and enable the solar panel to operate at its maximum power point, or more precisely, the optimum voltage and current for maximum power output. Using this clever technology, MPPT solar charge controllers can be up to 30% more efficient, depending on the battery and operating voltage (Vmp) of the solar panel. The reasons for the increased efficiency and how to correctly size an MPPT charge controller are explained in detail below.
As a general guide, MPPT charge controllers should be used on all higher power systems using two or more solar panels in series, or whenever the panel operating voltage (Vmp) is 8V or higher than the battery voltage. see full explanation below.
What is an MPPT or maximum power point tracker?
A maximum power point tracker, or MPPT, is basically an efficient DC-to-DC converter used to maximise the power output of a solar system. The first MPPT was invented by a small Australian company called AERL way back in 1985, and this technology is now used in virtually all grid-connect solar inverters and all MPPT solar charge controllers.
The functioning principle of an MPPT solar charge controller is relatively simple. due to the varying amount of sunlight (irradiance) landing on a solar panel throughout the day, the panel voltage and current continuously vary. In order to generate the most power, an MPPT sweeps through the panel voltage to find the sweet spot or the best combination of voltage and current to produce the maximum power. The MPPT continually tracks and adjusts the PV voltage to generate the most power, no matter what time of day or weather conditions. Using this clever technology, the operating efficiency greatly increases, and the energy generated can be up to 30% more compared to a PWM charge controller.
PWM Vs MPPT Example
In the example below, a common 60 cell (24V) solar panel with an operating voltage of 32V (Vmp) is connected to a 12V battery bank using both a PWM and an MPPT charge controller. Using the PWM controller, the panel voltage must drop to match the battery voltage and so the power output is reduced dramatically. With an MPPT charge controller, the panel can operate at its maximum power point and in turn can generate much more power.
Best MPPT solar charge controllers
See our detailed review of the best mid-level MPPT solar charge controllers used for small scale off-grid systems up to 40A. click on the summary table below. Also see our review of the most powerful, high-performance MPPT solar charge controllers used for professional large-scale off-grid systems here.
Battery Voltage options
Unlike battery inverters, most MPPT solar charge controllers can be used with a range of different battery voltages. For example, most smaller 10A to 30A charge controllers can be used to charge either a 12V or 24V battery, while most larger capacity, or higher input voltage charge controllers, are designed to be used on 24V or 48V battery systems. A select few, such as the Victron 150V range, can even be used on all battery voltages from 12V to 48V. There are also several high voltage solar charge controllers, such as those from AERL and IMARK which can be used on 120V battery banks.
Besides the current (A) rating, the maximum solar array size that can be connected to a solar charge controller is also limited by the battery voltage. As highlighted in the following diagram, using a 24V battery enables much more solar power to be connected to a 20A solar charge controller compared to a 12V battery.
Based on Ohm’s law and the power equation, higher battery voltages enable more solar panels to be connected. This is due to the simple formula. Power = Voltage x Current (P=VI). For example 20A x 12.5V = 250W, while 20A x 25V = 500W. Therefore, using a 20A controller with a higher 24V volt battery, as opposed to a 12V battery, will allow double the amount of solar to be connected.
- 20A MPPT with a 12V battery = 260W max Solar recommended
- 20A MPPT with a 24V battery = 520W max Solar recommended
- 20A MPPT with a 48V battery = 1040W max Solar recommended
Note, oversizing the solar array is allowed by some manufacturers to ensure an MPPT solar charge controller operates at the maximum output charge current, provided the maximum input voltage and current are not exceeded! See more in the oversizing solar section below.
Solar panel Voltage Explained
All solar panels have two voltage ratings which are determined under standard test conditions (STC) based on a cell temperature of 25°C. The first is the maximum power voltage (Vmp) which is the operating voltage of the panel. The Vmp will drop significantly at high temperatures and will vary slightly depending on the amount of sunlight. In order for the MPPT to function correctly, the panel operating voltage (Vmp) must always be several volts higher than the battery charge voltage under all conditions, including high temperatures. see more information about voltage drop and temperature below.
The second is the open-circuit voltage (Voc) which is always higher than the Vmp. The Voc is reached when the panel is in an open-circuit condition, such as when a system is switched off, or when a battery is fully charged, and no more power is needed. The Voc also decreases at higher temperatures, but, more importantly, increases at lower temperatures.
Battery Voltage Vs Panel Voltage
For an MPPT charge controller to work correctly under all conditions, the solar panel operating voltage (Vmp), or string voltage (if the panels are connected in series) should be at least 5V to 8V higher than the battery charge (absorption) voltage. For example, most 12V batteries have an absorption voltage of 14 to 15V, so the Vmp should be a minimum of 20V to 23V, taking into account the voltage drop in higher temperatures. Note, on average, the real-world panel operating voltage is around 3V lower than the optimum panel voltage (Vmp). The String Voltage Calculator will help you quickly determine the solar string voltage by using the historical temperature data for your location.
In the case of 12V batteries, the panel voltage drop due to high temperature is generally not a problem since even smaller (12V) solar panels have a Vmp in the 20V to 22V range, which is much higher than the typical 12V battery charge (absorption) voltage of 14V. Also, common 60-cell (24V) solar panels are not a problem as they operate in the 30V to 40V range, which is much higher.
In the case of 24V batteries, there is no issue when a string of 2 or more panels is connected in series, but there is a problem when only one solar panel is connected. Most common (24V) 60-cell solar panels have a Vmp of 32V to 36V. While this is higher than the battery charging voltage of around 28V, the problem occurs on a very hot day when the panel temperature increases and the panel Vmp can drop by up to 6V. This large voltage drop can result in the solar voltage dropping below the battery charge voltage, thus preventing it from fully charging. A way to get around this when using only one panel is to use a larger, higher voltage 72-cell or 96-cell panel.
When charging 48V batteries, the system will need a string of at least 2 panels in series but will perform much better with 3 or more panels in series, depending on the maximum voltage of the charge controller. Since most 48V solar charge controllers have a max voltage (Voc) of 150V, this generally allows a string of 3 panels to be connected in series. The higher voltage 250V charge controllers can have strings of 5 or more panels which is much more efficient on larger solar arrays as it reduces the number of strings in parallel and, in turn, lowers the current.
Note: Multiple panels connected in series can produce dangerous levels of voltage and must be installed by a qualified electrical professional and meet all local standards and regulations.
Solar panel voltage Vs Temperature
The power output of a solar panel can vary significantly depending on the temperature and weather conditions. A solar panel’s power rating (W) is measured under Standard Test Conditions (STC) at a cell temperature of 25°C and an irradiance level of 1000W/m2. However, during sunny weather, solar panels slowly heat up, and the internal cell temperature will generally increase by at least 25°C above the ambient air temperature; this results in increased internal resistance and a reduced voltage (Vmp). The amount of voltage drop is calculated using the voltage temperature co-efficient listed on the solar panel datasheet. Use this Solar Voltage Calculator to determine string voltages at various temperatures.
Both the Vmp and Voc of a solar panel will decrease during hot sunny weather as the cell temperature increases. During very hot days, with little wind to disperse heat, the panel temperature can rise as high as 80°C when mounted on a dark-coloured rooftop. On the other hand, in cold weather, the operating voltage of the solar panel can increase significantly, up to 5V or even higher in freezing temperatures. Voltage rise must be taken into account as it could result in the Voc of the solar array going above the maximum voltage limit of the solar charge controller and damaging the unit.
Panel Voltage Vs Cell Temperature graph notes:
- STC = Standard test conditions. 25°C (77°F)
- NOCT = Nominal operating cell temperature. 45°C (113°F)
- (^) High cell temp = Typical cell temperature during hot summer weather. 65°C (149°F)
- (#) Maximum operating temp = Maximum panel operating temperature during extremely high temperatures mounted on a dark rooftop. 85°C (185°F)
Voltage increase in cold weather
Example: A Victron 100/50 MPPT solar charge controller has a maximum solar open-circuit voltage (Voc) of 100V and a maximum charging current of 50 Amps. If you use 2 x 300W solar panels with 46 Voc in series, you have a total of 92V. This seems ok, as it is below the 100V maximum. However, the panel voltage will increase beyond the listed Voc at STC in cold conditions below 25°C cell temperature. The voltage increase is calculated using the solar panel’s voltage temperature coefficient, typically 0.3% for every degree below STC (25°C). As a rough guide, for temperatures down to.10°C, you can generally add 5V to the panel Voc which equates to a Voc of 51V. In this case, you would have a combined Voc of 102V. This is now greater than the max 100V Victron 100/50 input voltage limit and could damage the MPPT and void your warranty.
Solution: There are two ways to get around this issue:
- Select a different MPPT solar charge controller with a higher input voltage rating, such as the Victron 150/45 with a 150V input voltage limit.
- Connect the panels in parallel instead of in series. The maximum voltage will now be 46V 5V = 51 Voc. Note this will only work if you use a 12V or 24V battery system; it’s unsuitable for a 48V system as the voltage is too low. Also note, in parallel the solar input current will double, so the solar cable should be rated accordingly.
Note: Assuming you are using a 12V battery and 2 x 300W panels, the MPPT charger controller output current will be roughly: 600W / 12V = 50A max. So you should use a 50A MPPT solar charge controller.
Guide only. Use the new String Voltage Calculator to determine panel voltages accurately.
The charge controller Amp (A) rating should be 10 to 20% of the battery Amp/hour (Ah) rating. For example, a 100Ah 12V lead-acid battery will need a 10A to 20A solar charge controller. A 150W to 200W solar panel will be able to generate the 10A charge current needed for a 100Ah battery to reach the adsorption charge voltage provided it is orientated correctly and not shaded. Note: Always refer to the battery manufacturer’s specifications.
Advanced Guide to off-grid solar systems
Before selecting an MPPT solar charge controller and purchasing panels, batteries or inverters, you should understand the basics of sizing an off-grid solar power system. The general steps are as follows:
- Estimate the loads. how much energy you use per day in Ah or Wh
- Battery capacity. determine the battery size needed in Ah or Wh
- Solar size. determine how many solar panel/s you need to charge the battery (W)
- Choose the MPPT Solar Charge Controller/s to suit the system (A)
- Choose an appropriately sized inverter to suit the load.
Estimate the loads
The first step is to determine what loads or appliances you will be running and for how long? This is calculated by. the power rating of the appliance (W) multiplied by the average runtime (hr). Alternatively, use the average current draw (A) multiplied by average runtime (hr).
- Energy required in Watt hours (Wh) = Power (W) x Time (hrs)
- Energy required in Amp hours (Ah) = Amps (A) x Time (hrs)
Once this is calculated for each appliance or device, then the total energy requirement per day can be determined as shown in the attached load table.
Sizing the Battery
The total load in Ah or Wh load is used to size the battery. Lead-acid batteries are sized in Ah while lithium batteries are sized in either Wh or Ah. The allowable daily depth of discharge (DOD) is very different for lead-acid and lithium, see more details about lead-acid Vs lithium batteries. In general, lead-acid batteries should not be discharged below 70% SoC (State of Charge) on a daily basis, while Lithium (LFP) batteries can be discharged down to 20% SoC on a daily basis. Note: Lead-acid (AGM or GEL) batteries can be deeply discharged, but this will severely reduce the life of the battery if done regularly.
For example: If you have a 30Ah daily load, you will need a minimum 100Ah lead-acid battery or a 40Ah lithium battery. However, taking into account poor weather, you will generally require at least two days of autonomy. so this equates to a 200Ah lead-acid battery or an 80Ah lithium. Depending on your application, location, and time of year, you may even require 3 or 4 days of autonomy.
Sizing the Solar
The solar size (W) should be large enough to fully charge the battery on a typical sunny day in your location. There are many variables to consider including panel orientation, time of year shading issues. This is actually quite complex, but one way to simplify things it to roughly work out how many watts are required to produce 20% of the battery capacity in Amps. Oversizing the solar array is also allowed by some manufacturers to help overcome some of the losses. Note that you can use our free solar design calculator to help estimate the solar generation for different solar panel tilt angles and orientations.
Solar sizing Example: Based on the 20% rule, A 12V, 200Ah battery will need up to 40Amps of charge. If we are using a common 250W solar panel, then we can do a basic voltage and current conversion:
Using the equation (P/V = I) then 250W / 12V battery = 20.8A
In this case, to achieve a 40A charge we would need at least 2 x 250W panels. Remember there are several loss factors to take into account so slightly oversizing the solar is a common practice. See more about oversizing solar below.
Solar Charge controller Sizing (A)
The MPPT solar charge controller size should be roughly matched to the solar size. A simple way to work this out is using the power formula:
Power (W) = Voltage x Current or (P = VI)
If we know the total solar power in watts (W) and the battery voltage (V), then to work out the maximum current (I) in Amps we re-arrange this to work out the current. so we use the rearranged formula:
Current (A) = Power (W) / Voltage or (I = P/V)
For example: if we have 2 x 200W solar panels and a 12V battery, then the maximum current = 400W/12V = 33Amps. In this example, we could use either a 30A or 35A MPPT solar charge controller.
Selecting a battery inverter
Battery inverters are available in a wide range of sizes determined by the inverter’s continuous power rating measured in kW (or kVA). importantly, inverters are designed to operate with only one battery voltage which is typically 12V, 24V or 48V. Note that you cannot use a 24V inverter with a lower 12V or higher 48V battery system. Pro-tip, it’s more efficient to use a higher battery voltage.
Besides the battery voltage, the next key criteria for selecting a battery inverter are the average continuous AC load (demand) and short-duration peak loads. Due to temperature de-rating in hot environments, the inverter should be sized slightly higher than the load or power demand of the appliances it will be powering. Whether the loads are inductive or resistive is also very important and must be taken into account. Resistive loads such as electric kettles or toasters are very simple to power, while inductive loads like water pumps and compressors put more stress on the inverter. In regards to peak loads, most battery inverters can handle surge loads up to 2 x the continuous rating.
Inverter sizing example:
- Average continuous loads = 120W (fridge) 40W (lights) TV (150W) = 310W
- High or surge loads = 2200W (electric kettle) toaster (800W) = 3000W Considering the above loads, a 2400W inverter (with 4800 peak output) would be adequate for the smaller continuous loads and easily power the short-duration peak loads.
ATTENTION SOLAR DESIGNERS. Learn more about selecting off-grid inverters and sizing solar systems in our advanced technical off-grid system design guide.
MPPT Solar Oversizing
Due to the various losses in a solar system, it is common practice to oversize the solar array to enable the system to generate more power during bad weather and under various conditions, such as high temperatures where power derating can occur. The main loss factors include. poor weather (low irradiation), dust and dirt, shading, poor orientation, and cell temperature de-rating. Learn more about solar panel efficiency and cell temperature de-rating here. These loss factors combined can reduce power output significantly. For example, a 300W solar panel will generally produce 240W to 270W on a hot summer day due to the high-temperature power de-rating. Depending on your location, reduced performance will also occur in winter due to low solar irradiance. For these reasons, oversizing the solar array beyond the manufacturers ‘recommended or nominal value’ will help generate more power in unfavourable conditions.
Oversizing by 150% (Nominal rating x 1.5) is possible on many professional MPPT solar charge controllers and will not damage the unit. However, many cheaper MPPT charge controllers are not designed to operate at full power for a prolonged amount of time, as this can damage the controller. Therefore, it is essential to check whether the manufacturer allows oversizing. Morningstar and Victron Energy allow oversizing well beyond the nominal values listed on the datasheets as long as you don’t exceed the input voltage and current limits. Victron MPPT controllers have been successfully used with 200% solar oversizing without any issues. However, the higher the oversizing, the longer the controller will operate at full power and the more heat it will generate. Without adequate ventilation, excess heat may result in the controller overheating and derating power or, in a worst-case scenario, complete shutdown or even permanent damage. Therefore always ensure adequate clearance around the controller according to the manufacturer’s specifications, and add fan-forced ventilation if required.
Warning. you must NEVER exceed the maximum INPUT voltage (Voc) or maximum input current rating of the solar charge controller!
IMPORTANT. Oversizing solar is only allowed on some MPPT solar charge controllers, such as those from Victron Energy, Morningstar and EPever. Oversizing on other models could void your warranty and result in damage or serious injury to persons or property. always ensure the manufacturer allows oversizing and never exceed the maximum input voltage or current limits.
about Solar Sizing
As previously mentioned, all solar charge controllers are limited by the maximum input voltage (V. Volts) and maximum charge current (A – Amps). The maximum voltage determines how many panels can be attached (in series), and the current rating will determine the maximum charge current and, in turn, what size battery can be charged.
As described in the guide earlier, the solar array should be able to generate close to the charge current of the controller, which should be sized correctly to match the battery. Another example: a 200Ah 12V battery would require a 20A solar charge controller and a 250W solar panel to generate close to 20A. (Using the formula P/V = I, then we have 250W / 12V = 20A).
As shown above, a 20A Victron 100/20 MPPT solar charge controller together with a 12V battery can be charged with a 290W ‘nominal’ solar panel. Due to the losses described previously, it could also be used with a larger ‘oversized’ 300W to 330W panel. The same 20A Victron charge controller used with a 48V battery can be installed with a much larger solar array with a nominal size of 1160W.
Compared to the Victron MPPT charge controller above, the Rover series from Renogy does not allow solar oversizing. The Rover spec sheet states the ‘Max. Solar input power’ as above (not the nominal input power). Oversizing the Rover series will void the warranty. Below is a simple guide to selecting a solar array to match various size batteries using the Rover series MPPT charge controllers.
20A Solar Charge Controller. 50Ah to 150Ah battery
- 20A/100V MPPT. 12V battery = 250W Solar (1 x 260W panels)
- 20A/100V MPPT. 24V battery = 520W Solar (2 x 260W panels)
- 40A/100V MPPT. 12V battery = 520W Solar (2 x 260W panels)
- 40A/100V MPPT. 24V battery = 1040W Solar (4 x 260W panels)
Remember that only selected manufacturers allow the solar array to be oversized, as long as you do not exceed the charge controller’s max voltage or current rating. always refer to manufacturers’ specifications and guidelines.
solar charge controller Price guide
The older, simple PWM, or pulse width modulation, charge controllers are the cheapest type available and cost as little as 40 for a 10A unit. In contrast, the more efficient MPPT charge controllers will cost anywhere from 80 to 2500, depending on the voltage and current (A) rating. All solar charge controllers are sized according to the charge current, which ranges from 10A up to 100A. Cost is directly proportional to the charge current and maximum voltage (Voc), with the higher voltage and current controllers being the most expensive.
A general guide to the cost of different size solar charge controllers:
- PWM 100V Solar controllers up to 20A. 40 to 120
- MPPT 100V Solar controllers up to 20A. 90 to 200
- MPPT 150V Solar controllers up to 40A. 200 to 400
- MPPT 150V Solar controllers up to 60A. 400 to 800
- MPPT 250V Solar controllers up to 80A. 800 to 1200
- MPPT 300V Solar controllers up to 100A. 900 to 1500
- MPPT 600V Solar controllers up to 100A. 1600 to 2800
About the Author
Jason Svarc is a CEC-accredited off-grid solar power system specialist who has been designing and building off-grid power systems since 2010. During this time, he also taught the stand-alone power systems design course at Swinburne University (Tafe). Living in an off-grid home for over 12 years and having designed, installed and monitored dozens of off-grid systems, he has gained vast experience and knowledge of what is required to build reliable, high-performance off-grid solar systems.
This is to be used as a guide only. Before making any purchases or undertaking any solar/battery related installations or modifications, you must refer to all manufacturer’s specifications and installation manuals. All work must be done by a qualified person.
What Is a Solar Charge Controller, and Do You Need It?
Installing solar panels requires understanding the workings of many components: solar batteries, inverters wiring, conduit bending… If you’re going the DIY route, you could practically work as an electrician once you finish the installation!
The charge controller is one component of a solar power system that confuses many people. A solar charge controller is necessary for most residential PV panel installations. Let’s explore what exactly a solar charge controller does and whether or not you’ll need one for your setup.
What Is a Solar Charge Controller?
A solar charge controller is a device that regulates the energy that travels from the solar panels into the battery. Solar generators convert and store power in a battery, with the electrical capacity recharged by the solar panels. A solar charge controller regulates the electrical current to prevent the battery from electrical surges that can damage it and reduce its lifespan.
A solar charge controller is essential if your PV solar array feeds a battery bank. If you are on a grid-tied system, you probably don’t need a solar charge controller.
How Does a Solar Charge Controller Work?
A solar charge controller regulates the voltage transmitted from the solar panels to the batteries.
Solar panels for a 12V battery system are usually rated for 17V. It may seem counterintuitive, but there is a good reason for it.
Solar panels rarely output their full power rating due to clouds, dirt on the panels, or other environmental factors. So, if they were only rated at 12V, they would always be putting out less power — which a 12V battery cannot accept.
A 12V battery at rest is around 12.7V, and a charging battery is around 13.6 to 14.4V. So, a solar panel must generate at least this much electrical output.
A solar charge controller takes the electricity from the solar panel — around 16 to 20V — and downregulates it to the voltage the battery currently needs. This amount can range from 10.5V to 14.6V depending on the battery’s current charge, the temperature, and the controller’s charging mode.
Charge controllers ultimately protect against battery damage. Inconsistencies in the electrical output, power surges, and other external factors can overcharge and damage a solar battery.
Types of Solar Charger Controllers
There are two main types of charge controllers: PWM and MPPT. Neither is necessarily “better” than the other — each has advantages depending on climate, array size, and system components.
While MPPT controllers typically cost more than PWM, the difference is negligible considering the total solar installation cost. Always choose a controller because it is the right tool for the job — not because it is cheaper.
PWM Charge Controllers – PWM (Pulse Width Modulation) controllers are generally smaller and less expensive than MPPT controllers. PWM controllers often come standard with small solar systems, such as RV and small cabin setups.
When using a PWM controller, the voltage from the array needs to match the battery voltage. Off-grid solar panels (those rated at 17-18V) are required when using PWM controllers, which sometimes cost more than grid-tied panels (often rated at 37V).
PWM controllers work best in “ideal” conditions — warm, sunny weather. When the weather becomes colder, batteries operate at less efficient rates.
A PWM controller is not able to adjust voltages. Instead, it shuts on and off as the voltage from your solar array inevitably varies — this auto shut-off also results in some loss of power.
MPPT Charge Controllers – MPPT (Maximum Power Point Tracking) controllers are more expensive than PWM, but they are significantly more efficient in many circumstances.
MPPTs draw out the current at a rate based on the panel’s maximum voltage. They can utilize a higher-voltage array with lower-voltage batteries. You can use the mass-produced, lower-cost PV modules standard on residential homes.
An MPPT controller can accept and modulate varying voltages. They harness excess power that a PWM would otherwise waste.
Who Needs a Solar Charge Controller?
All off-grid solar systems require a solar charge controller to regulate the energy moving to and from the batteries.
You won’t usually need a solar charge controller for grid-connected renewable energy systems. The utility company gathers any excess energy produced and utilizes the electricity.
When Should You Use a Solar Charge Controller?
Almost all solar systems that utilize batteries will require a solar charge controller. Tiny solar setups are the only exception — 5-watt trickle chargers and similar devices will not need one.
For example, many golf cart owners will keep their batteries charged over winter with a small panel. This setup does not need a charge controller between the panels and the golf cart batteries.
If you are hooking up a full array of 400W panels, you will need an adequate solar charge controller (likely of the MPPT variety).
Some solar solutions already have a built-in charge controller, such as the EcoFlow Portable Power Stations. The controller, batteries, inverter, power outlets, and everything else are part of the power station — you just need to add the solar panels.
How to Size Charge Controllers Correctly?
Solar charge controllers come in various sizes for arrays of varying voltages and currents. Choosing the wrong one can lead to power loss and inefficiency.
First, you’ll want to check the voltage rating on the charge controller. Most PWM controllers are rated for 12 or 24V, while MPPT controllers can handle 12, 24, 36, and 48V systems. Robust off-grid energy solutions like EcoFlow’s Power Kits come with an MPPT charge controller and 48V battery (or batteries) built-in.
Most charge controllers have an “amps” rating. Smaller PWM controllers may be rated at 10, 20, or 30 amps. MPPT controllers are often rated at higher amps — 80 or 100 amps are common — to accommodate larger PV arrays.
To determine the potential amps that a solar array can output, we need to make a simple calculation:
Let’s say we have an 800-watt array running at 12 volts. We can plug these numbers into our equation:
Amps = 800 watts / 12 volts = 66.67 amps
The system could produce up to 66.67 amps. A charge controller rated below this amount can overload and malfunction. For this example, you would want a charge controller rated at 70 amps.
You’ll also want to check that your batteries are compatible with the charge controller. Lithium-ion and lead-acid batteries utilize different technology. Most controllers are designed for one battery type or the other.
Control Set Points vs. Battery Types
Most charge controllers operate at different voltages depending on the current state of the battery. For instance, a PWM controller may charge the battery most of the way, then reduce the voltage for a final trickle charge. The level at which the controller changes voltage is called a control set point.
Different battery types require varying methods of charging. Lithium-ion batteries utilize a three-stage charging system: precharge, constant current, and supplementary.
The precharge stage uses a low current for batteries that are nearly dead. Then, the constant current stage provides a steady supply at full power. Finally, the supplementary stage keeps the lithium battery at maximum charge.
Lead-acid batteries utilize three main charging stages: bulk, absorption, and float. The bulk stage sends maximum power to the batteries until they hit around 80-90% capacity. For the absorption stage, the current begins to drop. Finally, the float stage provides a trickle charge to keep the batteries topped off.
Why Are Displays and Metering Important?
Many solar charge controllers now feature an LCD. The display allows the user to monitor essential system vitals, such as battery charge percentage, current voltage, and time remaining on the battery at the current load. Some basic controllers for smaller systems will omit the LCD screen as the information may be unnecessary.
Other systems like the EcoFlow DELTA 2 have intelligent monitoring and Smart app control. The in-built metering system lets you see the input and output levels of the battery and other critical information, including the battery’s vitals, charge time, and more, all on the smartphone app.
Understanding Control Set Points vs. Temperature
The temperature has a significant effect on battery charging. The energy in batteries flows with more ease while in warm temperatures. The battery has a harder time moving energy around as it gets colder.
Most control set points are set for room temperature operation. Temperature compensation is featured in most charge controllers to adjust the voltage for various temperatures. Some controllers have built-in temperature sensors, while others utilize a remote sensor.
Some charge controllers even allow for custom set points based on temperatures. Battery manufacturers each recommend a different adjustment based on the temperature, so this feature enables the homeowner to dial in their system.
Common Features and Settings on a Charge Controller
Charge controllers for residential applications will almost always have an LCD to convey essential information. Many controllers will allow custom set points to work well with your battery bank and climate.
Most charge controllers have built-in protection against reverse polarity, overload, short-circuiting, and other standard electrical issues.
Advanced technologies integrated into premium controllers will even allow remote monitoring on a smartphone and Bluetooth operation. Software like the EcoFlow Smart app enables you to manage these features from a smartphone.
Building your solar system can be challenging, as it requires you to understand the basics of electricity. However, putting the system together is manageable once you learn the essentials.
A solar charge controller is at the center of your solar system. It bridges the gap between your PV array and your battery bank. Make sure you choose the correct controller to prevent any issues down the line.
All-in-one solutions can be helpful if the electrical jargon is too much for you. The EcoFlow Solar Generators and Power Kits are a great way to switch to solar, with a built-in MPPT controller and Smart app to make metering and regulating your energy use even easier.
Frequently Asked Questions
You always need a solar charge controller if you are installing an off-grid solar system with batteries. Only the smallest panels — such as 1 or 5-watt trickle chargers — can operate without a controller. You do not need a solar charge controller for grid-tied residential systems. Instead, the utility grid regulates the electricity flow and absorbs the excess power.
A 100W panel needs a solar charge controller if it is supplying a battery. Many small solar systems utilize just one 100-watt panel and a single battery. This system would require a charge controller to regulate the current that travels into the battery.
A 7-watt solar panel does not require the use of a charge controller. These panels allow low-voltage trickle charging, which does not need regulation of the electrical flow.
EcoFlow is a portable power and renewable energy solutions company. Since its founding in 2017, EcoFlow has provided peace-of-mind power to customers in over 85 markets through its DELTA and RIVER product lines of portable power stations and eco-friendly accessories.