What Happens to Solar Power When Batteries Are Full?
Whether living off-grid or as a full-time RV camper, a renewable energy source makes life easier. It’s an excellent option for environmentalists, survivalists, and pragmatists who know that having an alternative power source isn’t just a luxury—it’s a necessity.
Solar power generators use batteries to store the electricity they generate for later use. But what happens to that power when the batteries are full? Does it go to waste?
Here, we look at how solar power systems work and the critical role that their batteries play in storing power. Whether you keep that power on standby, sell it to the grid, or float it to other devices, here’s what you can do when your battery is at maximum capacity.
What Happens When Solar Power Batteries Are Full?
Solar power systems use batteries to store solar energy. However, if the power generated exceeds the solar battery’s capacity, it can overcharge the system. An overcharged solar system can severely damage a battery’s life.
As soon as a solar battery reaches full charge, the inverter and charge controller must step in to mitigate risks by handling excess power. They can do this in three ways: push it back into the panels for power loss, back into the grid for credits, or force a dump load.
Off-grid systems typically include solar panels, charge controllers, battery monitoring systems, and batteries. Solar panels collect energy, which passes through a charge controller to batteries. Battery monitoring displays the battery bank’s charge level.
The charge controller protects batteries and solar panels by managing the energy flow. Battery charge controllers stop electricity flow when they signal that batteries are full.
Many solar power systems incorporate inverters and charge controllers to ensure trickle charging and redistribute excess charges. However, you can also return power to the grid. Surplus energy fed back into the grid is available for use by community members who cannot access solar panels or other renewable energy sources.
A New Way to Stay Charged—EcoFlow DELTA Pro Smart Battery
The DELTA Pro Smart Battery from EcoFlow mitigates the risks outlined above by giving you control of your battery charge levels and recharge rate. With this extra Smart battery, not only can you double the capacity of your DELTA Pro Solar Generator from 3600Wh to 7200Wh, but you can also prevent overcharging issues.
The DELTA Pro Smart battery connects to the DELTA Pro portable power station or solar generator. Connect two, and you can achieve up to 10.8kWh for a robust off-grid home backup or full-time RV living. A sleek LCD screen lets you check the battery’s charge percentage, recharge time, and more. Plus, you can use the EcoFlow app to check the battery’s status, no matter where you are. Once you charge it to maximum capacity, the battery will hold its charge for up to one year after a full charge. Power doesn’t get more convenient or reliable.
How to Know When Your Solar Batteries Are Fully Charged
Several options are available to check the charge level of a battery within a solar energy system.
Intelligent energy storage solutions like the EcoFlow Smart Battery feature display screens that indicate the battery’s charge based on its voltage.
Some inverters display the battery’s charge level on their screen, so you can tell if it’s charging or full. Inverters without display screens may have a warning or indicator system to tell you the battery status.
You can also purchase meters to check the charge level. Look for a voltmeter, hydrometer, and multimeter.
- Voltmeters are instruments that measure electric potential. To check the charge of a battery, connect your voltmeter to the red and black ports. If you want an accurate reading, the battery shouldn’t have delivered electricity for the last few hours.
- Hydrometers are only used for flooded lead-acid batteries since it requires measurements from the liquid inside.
- A multimeter can measure voltage, current, resistance, and many other things about your battery’s condition.
What to Do if Your Batteries Regularly Become Full
If you find that your solar batteries are regularly becoming full, you can offset that extra power and put it to good use.
Sell One of Your Panels
You may be connecting too many solar panels for your energy needs. You can sell excess panels in many marketplaces and local swap pages. There is no doubt that solar panels hold their value well, and you might be surprised at how quickly people will snatch them up. In many cases, worn or outdated solar panels can be recycled or reused.
Purchase Additional Batteries or a Higher Capacity Solar Generator
Purchasing a higher storage capacity solar generator will also help store more power. For example, EcoFlow’s DELTA Pro Solar Generator stores significantly more energy than the generators from EcoFlow’s River 2 series. The River 2 series is intended for camping and other off-grid activities where portability is crucial, while the DELTA Pro is an ideal home backup power solution.
Many solar generators also allow you to purchase extra batteries to increase your solar power storage capacity.
Ignore It
It’s possible to do nothing with your full battery until you need the extra power. Downsizing or upsizing may not be worthwhile if excess power is only available during the sunniest days.
Compare your power usage with the capacity of your battery bank. It may be best to keep the setup unchanged if they are well-matched. On rainy or overcast days, you may need that extra energy.
Use Power
You can use extra power for future needs, such as:
- Charging tools
- Cooking food
- Refrigerating food
- Dehydrate food for storage
- Run an AC unit for longer
Where Does Excess Solar Power Go When Batteries Are Full?
The direction of the power depends on your setup and whether you have a grid or an off-grid system.
An on-grid solar system sends AC power to your appliances first. If the home doesn’t have enough load to use all the electricity, it’ll feed the remaining power back into the grid.
In off-grid applications, the inverter receives extra electricity and converts DC into AC power. Any appliance connected to the circuit can then use this power. With EcoFlow solar generators, the battery will stop absorbing energy once the battery has reached full capacity to prevent any possible damage.
Where Can I Float Excess Energy?
There are two ways to handle excess power. You can let it discharge from your battery, wasting the power and potentially damaging your battery in the long run, or you can float it to appliances and devices to reduce your on-grid power consumption.
Refrigeration
Typically, solar panels generate power for devices and appliances that require electricity immediately but not continuously. If you’re generating enough solar power that your battery consistently reaches capacity, consider using the excess energy to run ice and refrigeration systems.
The Electrical Grid
With many fixed solar power systems, you can send excess energy to the electrical grid if your solar panels have collected enough energy to power your home and charge your battery. For many people, this is a significant reason they use solar energy.
The electrical grid distributes electricity to homes and businesses. Without solar panels, your home depends on the electrical grid.
Owning portable solar panels and a solar generator allows you to live on or off the grid. You don’t have to worry about running out of solar power while on the grid. Electrical grids serve as backups when an on-grid solar system fails.
You can install a net meter on the grid to record your solar energy use. Excess solar energy is directed back to the grid through this meter. Homeowners can earn credits for the extra energy they generate, which can be used on a future bill, saving them some money.
Air Compression
Air compression machines are the next dump load for an excess charge. Intelligent on-grid solar panel systems will send excess power to air compression devices to store energy for later use.
Heating
Depending on how much additional energy your solar system generates, you can use it to assist with home heating. Both heated air and heated water are ways to expend extra energy. For example, you’ll want to use the heater more frequently in the winter to keep the home warm and cozy.
Conclusion
Some solar batteries are at risk of igniting and overheating — or at the very least reducing their lifespan — when overcharged.
Select a solar system that takes the hard work out of monitoring battery performance, adding additional capacity, and efficiently handling excess energy. Shop EcoFlow today for solar energy that’s Smart and efficient.
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.
Battery Charge Controller
For many people, building their own solar panel system and living off-grid is becoming a reality instead of a dream. Connecting the solar panels directly to a single battery or bank of batteries for charging may work, but is not a good idea. What’s needed is a battery charge controller to safely charge and discharge your deep cycle battery for a longer lifespan.
A standard 12 volt solar panel which can be used to recharge a battery, could actually be putting out nearly 20 volts at full sun, much more voltage than the battery needs. This difference in voltage between the required 12 volts need for the battery and actual 20 volts being generated by the solar panel translates into a greater current flow into the battery.
This results in too much unregulated solar generated current overcharging the battery which could cause the electrolyte solution within the batteries to overheat and evaporate off, resulting in a much shortened battery life and ultimately, complete battery failure.
Then the quality of the charging current will directly affect the life of any connected deep cycle battery, so it is extremely important to protect batteries of a solar charging system from being overcharged, or even undercharged, and we can do just that using a battery charge regulation device called a Battery Charge Controller.
A battery charge controller, also known as a battery voltage regulator, is an electronic device used in off-grid systems and grid-tie systems with battery backup. The charge controller regulates the constantly changing output voltage and current from a solar panel due the angle of the sun and matches it too the needs of the batteries being charged.
The charge controller does this by controlling the flow of electrical power from the charging source to the battery at a relatively constant and controlled value.
Thus maintaining the battery at its highest possible state of charge while protecting it from being overcharged by the source and from becoming over-discharged by the connected load. Since batteries like a steady charge within a relatively narrow range, the fluctuations in output voltage and current must be tightly controlled.
Solar Battery Charge Controller
Then the most important functions of battery charge controllers used in an alternative energy system are:
- Prevents Battery Over-charging: This is too limit the energy supplied to the battery by the charging device when the battery becomes fully charged.
- Prevents Battery Over-discharging: Automatically disconnect the battery from its electrical loads when the battery reaches a low state of charge.
- Provides Load Control Functions: Automatically connect and disconnect the electrical load at a specified time, for example operating a lighting load from sunset to sunrise.
Solar panels produce direct or DC current, meaning the solar electricity generated by the photovoltaic panels flows in only one direction only. So in order to charge a battery, a solar panel must be at a higher voltage than the battery being charged. In other words, the voltage of the panel must be greater than the opposing voltage of the battery under charge, in order to produce a positive current flow into the battery.
When using alternative energy sources such as solar panels, wind turbines and even hydro generators, you will get fluctuations in output power. A charge controller is normally placed between the charging device and the battery bank and monitors the incoming voltage from these charging devices regulating the amount of DC electricity flowing from the power source to the batteries, a DC motor, or a DC pump.
The charge controller turns-off the circuit current when the batteries are fully charged and their terminal voltage is above a certain value, usually about 14.2 Volts for a 12 volt battery. This protects the batteries from damage because it doesn’t allow them to become over-charged which would lower the life of expensive batteries. To ensure proper charging of the battery, the regulator maintains knowledge of the state of charge (SoC) of the battery. This state of charge is estimated based on the actual voltage of the battery.
During periods of below average insolation and/or during periods of excessive electrical load usage, the energy produced by the photovoltaic panel may not be sufficient enough to keep the battery fully recharged.
When the batteries terminal voltage starts to drop below a certain value, usually about 11.5 Volts, the controller closes the circuit to allow current from the charging device to recharge the battery bank again.
In most cases a charge controller is an essential requirement in any stand-alone PV system and should be sized according to the voltages and currents expected during normal operation. Understanding your batteries and their charging requirements is also a must for any battery based solar system.
Any battery charge controller must be compatible with both the voltage of the battery bank and the rated amperage of the charging device system. But it must also be sized to handle expected peak or surge conditions from the generating source or required by the electrical loads that may be connected to the controller.
There are some very sophisticated charge controllers available today. Advanced charge controllers use pulse-width modulation, or PWM. Pulse width modulation is a process that ensures efficient charging and long battery life. However, the more advanced and expensive controllers use maximum power point tracking, or MPPT.
Maximum power point tracking maximizes the charging amps into the battery by lowering the output voltage allowing them to easily adapt to different battery and solar panel combinations such as 24v, 36v, 48v, etc. These controllers use DC-DC converters to match the voltage and use digital circuitry to measure actual parameters many times a second to adjust the output current accordingly. Most MPPT solar panel controllers come with digital displays and built-in computer interfaces for better monitoring and control.
Choosing the Right Solar Charge Controller
We have seen that the primary function of a Battery Charge Controller is to regulate the power passing from the generating device, be it a solar panel or wind turbine to the batteries. They assist in properly maintaining the solar power system batteries by preventing them from being overcharged or undercharged, thus offering long life to batteries.
The solar current being regulated by a battery charge controller not only charges batteries but can also be passed to inverters for converting the direct DC current to alternating AC current to supply the utility grid.
For many people who want to live “off grid”, a charge controller is a valuable piece of equipment as part of a solar panel or wind turbine power system. You will find numerous charge controllers manufactures online, but choosing the right one can sometimes be quite confusing and to add to your worries they are not cheap either, so finding a good quality solar charge regulator really matters.
It’s best not to go for those low quality cheaper ones, as they may actually harm the battery life and increase your overall expense in the long run. For a little peace of mind then why not Click Here and check out some of the better battery charge controllers available from Amazon and learn more about the different types of solar charge controllers available as part of your solar power system helping you to save money and the environment.
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- Energy Storage
- Deep Cycle Batteries
- Understanding Batteries
- Connecting Batteries Together
- The Deep Cycle Battery
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Комментарии и мнения владельцев already about “ Battery Charge Controller ”
Hi. Im considering a combination of wind and solar power generation for my boat kept on mooring. I think a combination would be good as Scotland not blessed with lots of sun and my mooring is a bit sheltered with harbour wall. Can i plug output from 2amp wind turbine into a Renogy mppt regulator (20 amp), would it manage the power to my batteries in same way as with a solar panel?
MPPT controllers have been used for photovoltaic (solar) power for a long time, but can also be used for wind turbines. In real life the wind speed is not constant, but changes continuously, thus the ideal rotor RPM for maximum torque will also change. What is important to remember is that there is an optimum RPM for each wind speed, and that is where we want to run the wind turbine to achieve MPPT. However, to work properly the controller needs an MPPT power curve that is specific for the wind turbine that you want to hook up to the controller. So check the MPPT’s manual if you can connect it to a wind turbine. If not, then it is not advisable since unlike PV, a wind turbine can output much higher open circuit input voltages (Voc) when it is not loaded up or your batteries are full.
I have a 730 W, 76 V solar panels system charging 24 V battery set up using a Morning Star MPPT charge controller in an OFF GRID set up. Which is the best suited APC or LUMINOUS UPS/Inverter that is solar compatible that can be used.
Hello, I have read your site with interest. We have a large dwelling with a business operating from it. Our standing load without all onsite is around 4KW This is a combination of servers and IT equipment, freezers, fridges etc. When all onsite with heating lighting TV’s etc. this can reach 10KW our energy costs are spiralling out of control. We have a large paddock approx 50m from the nearest 240V electrical connection into the site wiring that is in a barn. We are looking at taking a step into solar. Our initial aim is to simply power the office load using purely solar Generated energy whenever it is operating and obviously use the grid for any shortfall. We know the property will consume all of the power generated. We had a couple of thoughts. 1) Simple system. Setup an array that can generate approx 3KW and connect it to a Solar inverter and simply connect that into the property wiring system as an input. Whatever it produces should be consumed first before we need to get energy from the grid. Is this assumption correct assuming we have a local load at or exceeding the solar-generated capacity? 2) As an expansion of 1) above. We would look to build a larger array and connect that to a battery bank (this looks like the black magic area) that has enough capacity to provide a stable supply to an inverter that would then be connected as before into the property wiring systems that would provide a variable load of between 4 and 10KW we have seen peaks of 12KW on our monitor that is clamped onto the incoming 100A 240V Grid connection. How would we size the array and battery system and corresponding Invertor etc. Are higher voltage panels better than lower voltage panels? Are higher string voltages better than lower voltages from a power conversion point of view. e.g. is it more efficient to convert from 48V to 240V rather than 12 or 24V to 240V If I have a string of 24V 1000Ah made up of a series connected 2 x parallel 12V strings of 5 x 12V 200Ah batteries giving me 24V 1000Ah of capacity or in theory 24KWh what size inverter would I need to provide power into the property and would my system use the power I have before going to the grid? I am sure some of these questions are a bit basic but we are very DIY-orientated people and want to build this ourselves. Any help in understanding this would be great. I am sure there is much left out of my note. Like cable sizing etc. Logically I think we know what we think is happening, but, that doesn’t make it so! Like will we consume all we have before taking anything from the grid? I apologise for any typos or grammer. Cheers Tony
There are a number of good points raised here, and we will attempt to answer them. Firstly, an inverter fed grid-connected, or grid-tied system is basically a bunch of solar panels (or turbines) connected to a single inverter (or a collection of small inverters) feeding power directly to the utility grid. Generally, PV inverters operate as current sources injecting electric current into the utility grid in-phase with the grid voltage. It is commonly assumed that ALL the power generated by the PV panels (array) is consumed at the point of generation but this is not always the case. Power consumed is both active (real) and reactive. PV panels generate active power only. If your average power consumption is, for example, 10kWh per day, and you generate 12kWh for the 4 hours of full sun that day, then some of the inverters output power maybe autoconsumed and some may flow into the utility grid. Equally 100% inverter current may flow into the grid and you may consume 100% from the grid, just slowing down your energy meter in the process. On average PV panels generate maximum power for 4 to 5 hours of full sun per day as they do not consistently generate power 24 hours per day at their nominal output wattage rating. Oversizing an inverter by having more DC input power than the inverters AC output power, may increase power output in lower light conditions, thus extending the 5 hours. As would solar tracking. Connecting a battery bank would allow for more autonomy but at a cost and an increased array size, as now the array has to charge batteries for 5 hours plus feed the grid. Then the size and type of grid-connected system would ultimately depend on how many hours of autonomy you require and how much you are willing to pay upfront. Higher string voltages are better providing everything stays within tolerance at worst case conditions. As P = VI, a higher voltage (V) means a lower current (I) for a given power (P) and therefore smaller diameter cabling so cheaper. PV panel voltage depends on the wattage (100W or 400W) of the panel. Higher PV wattages means physically bigger panels, which means more m 2 of installation area.
the article states the controller should stop charging a 12V battery at approx 14.2V, what about 6 volt batteries – same?
No of course not. A single 3-cell 6 volt rechargeable battery should have a fully charged terminal voltage of about 6.35 volts. To correctly charge a wet battery, the output voltage of the charging system needs to be slightly higher than the batteries fully charged terminal voltage, to ensure that the charging current flows in the direction from charger to battery. A constant voltage equal to between 2.35 to 2.45 volts per cell is recommended for charging storage batteries. Thus for a 12 volt, 6-cell battery this is between 14.1 and 14.7 volts, so the charge controller should stop charging the battery once this voltage level is reached, or switch to a low current float charge. For a 6 volt, 3-cell battery this voltage level is between 7.05 and 7.35 volts.
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January 7, 2022 Jason Svarc
Best mid-range MPPT solar charge controllers up to 40A
In this article, we review six of the most popular, mid-level MPPT solar charge controllers commonly used for small scale solar power systems up to 2kW. These are more affordable, lower voltage (100-150V) units, which are generally designed for 12V or 24V battery systems, although several can be used on 48V batteries. A number of these charge controllers also feature inbuilt load control terminals for basic DC lighting and other loads.
In this review, we don’t list simple PWM controllers used for DC lighting and basic systems since there are many sites already covering these entry-level PWM controllers. For high-performance MPPT solar charge controllers with higher input voltages up to 300V and current ratings from 60A to 100A, see our high-power MPPT solar charge controllers review.
What is a solar charge controller?
A solar charge controller, also known as a solar regulator, is a battery charge regulator connected between the solar array and battery. Its job is to regulate the solar output to ensure the battery is charged correctly and not overcharged. DC coupled solar charge controllers been around for decades and are used in most small scale off-grid solar power systems.
Top 6 Solar Charge Controllers
Mid-level solar controllers up to 40A
Smaller capacity MPPT solar charge controllers with a current rating from 20A to 40A are used for many different applications including off-grid cabins and homes, RV’s, boats, caravans, telecommunications and remote site backup. These mid-range MPPT solar charge controllers are available from many different manufacturers, but this review will FOCUS on the most popular and best quality charge controllers from the most reputable manufacturers which have been on the market for several years.
| 1 | Victron SmartSolar MPPT | 35 A | 150V | 12V 24V 36V 48V | 350 to 480 | |
| 2 | EPever TRIRON Series | 40 A | 150V | 12V 24V | 150 to 250 | |
| 3 | Morningstar ProStar MPPT | 40 A | 120V | 12V 24V | 460 to 540 | |
| 4 | EPever XTRA Series | 40 A | 150V | 12V 24V 36V 48V | 130 to 190 | |
| 5 | Renogy Rover | 40 A | 100V | 12V 24V | 150 to 190 | |
| 6 | EPever BN Series | 40 A | 150V | 12V 24V | 170 to 250 |
Comparison Criteria
In this review, we rank the various charge controllers according to a number of important criteria including build quality, MPPT tracking speed, battery voltage range, operating temperature range (heat dissipation), monitoring, real-world performance and price. In our reviews, we generally rank performance and quality over affordability, so in this case, we rate the unit price lower than other criteria. This may come across as bias towards the more expensive models, but based on real-world results, testing and performance monitoring, the higher-end controllers have proven to out-perform the cheaper models.
Read more about selecting and correct sizing a solar charge controller in the MPPT solar charge controllers explained article.
Victron SmartSolar
Victron Energy is considered a world leader in power electronics and specialise in manufacturing equipment required for off-grid and stand-alone power systems including, inverters, batteries, chargers, monitors and of course, solar charge controllers. Based in the Netherlands, Victron manufacture many products in India and have become well known for producing quality, reliable off-grid battery inverter/chargers and a wide range of quality MPPT solar charge controllers.
Victron offer a huge range of solar charge controllers, from small 10A PWM models, to high-performance 100A MPPT varieties with high voltage inputs up to 250V. The MPPT 150V models appear very simple in design, and may not have a display or load control terminals like many others, however, where Victron out performs the competition is in MPPT tracking performance, communications and monitoring.
Victron have by far the most advanced system monitoring with inbuilt Bluetooth connection offering easy programming and configuration, plus remote firmware updates which add extra features and options. The display-less design may not please all users, but the fast, accurate MPPT tracking, high build quality, and V.E. Smart networking options are stand-out features.
Smartsolar MPPT 150V 35A
- Fast MPP Tracking
- 150V max Voc
- 12V, 24V or 48V batteries
- Compatible with LiFePO4 Lithium batteries
- Very advanced monitoring app
- Wide operating temperature up to 60°C
- Inbuilt temp sensor
- Optional wireless battery sensor
- Easy remote firmware updates
- 5 Year warranty
See the detailed Victron Energy Review
EPever TRIRON Series
EPever was founded in 2007 and has grown rapidly to become one of the largest Chinese manufacturers of cost-effective power products including a wide range of MPPT solar charge controllers. The Triron series is the next evolution to the well-known Tracer series of MPPT’s.
The TRIRON series from EPever is a much more advanced and user-friendly version of the original AN series of charge controllers. The TRIRON controllers have a unique swappable display module as well as a swappable interface module with an RS485 communication option that can be used for a number of different applications. Note, maximum PV voltage is either 100V or 150V depending on the model. The 5 button display module is very easy to use and provide all the important information you need about the PV, battery and load. Wireless access is available via the eBox-BLE Bluetooth adapter or the Wi-Fi adapter is available for remote monitoring.
TRIRON Series MPPT 150V 40A
- Fast MPP Tracking
- 150V max Voltage Voc (TRIRON 3215N 4215N)
- Easy to use with a large clear display
- Compatible with Lead-acid and Lithium batteries
- 40A Load control
- Swappable display and interface modules
- RS485 Interface for communications and remote control
- USB Port and relay control options
- Optional Temp sensor
Morningstar Prostar MPPT
Morningstar are a well-established company based in the US with 25 years of experience in engineering and manufacturing high-performance solar charge controllers. Morningstar is widely recognized as developing some of the best quality products on the market with high levels of protection against extreme environments, lightning surges and high operating temperatures.
The Prostar range of MPPT charge controllers are available in 25A and 40A versions with a 120V input voltage limit. The extremely fast MPP tracking can perform a full voltage sweep in less than 1 second using the Trakstar technology. The device features good size terminals protected under a front cover, including load control output terminals rated up to 30A, plus a clear backlit LCD display and can easily programmed using the 4 large buttons. However, the very high price tag means the Prostar MPPT series is out of reach for many users.
Prostar MPPT 120V 40A
- Very fast MPP Tracking
- 120V max Voc
- Compatible with LiFePO4 Lithium batteries
- Wide operating temp up to 60°C
- 30A Load control
- High surge protection
- Optional Battery sensor
- 5 Year warranty
EPever XTRA Series
EPever, also known as EPsolar, was founded in 2007 in Beijing, China and has grown rapidly to become one of the largest manufacturers of cost-effective solar power products including a wide range of MPPT charge controllers. The XTRA series of MPPT’s released in early 2018, have only recently become more popular due to the low cost, easy setup, and lithium battery compatibility.
The XTRA series is available in 10 different options with 3 display types, current ratings from 10 to 40A, battery voltages from 12V to 48V, and input voltage limit up to 150V. In comparison to the older AN series which had a 100V input limit, the XTRA series features lithium battery compatibility and a higher input 150V voltage (Voc) on the 30 and 40A models, plus a modern look and concealed screw terminals. Note, the two-button version with LCD is basically the older AN series controller in a modern package.
XTRA Series MPPT 40A
- Good MPP Tracking
- Three display options with a clear simple LCD
- Compatible with most Lithium LiFePO4 batteries
- 40A Load control
- Optional MT50 display
- Optional Temp sensor
- Optional Wi-Fi and Bluetooth module
- Low cost
5. Renogy Rover
Renogy, founded in the US in 2014, recently became a very popular choice for solar enthusiasts across the world due to the low-cost, easy setup and good MPPT tracking. Renogy manufacture a wide range of affordable inverters, DC converters and solar charge controllers in China.
The Rover series from Renogy is a feature packed MPPT controller with a clear inbuilt display, plus a low-cost (optional) Bluetooth adapter which provides a great, easy to use interface with many configuration options. Load control terminals are built-in, although the output is limited to 20A. The overall build quality is quite good, however there are some area’s which could be improved, most notably the cable terminals which are far too small for a 40A controller.
Rover MPPT 100V 40A
- Good MPP Tracking
- Clear Simple display
- Compatible with Lithium (12.8V LiFePO4)
- 20A Load control
- Advanced Bluetooth app and user settings
- Temp sensor included
- Low cost
6. Outback BN series by EPever
The Outback Power Flexmax40 is made by EPever and is commonly known as the Tracer BN series which is a well known affordable MPPT controller.
EPever one of the leading manufacturers of cost-effective power products including a wide range of solar charge controllers. The well-known Tracer and TRIRON series of MPPT’s are a very popular choice for solar enthusiasts across the world due to the easy setup, good MPPT tracking, and low cost.
The first generation AN series is the best-known MPPT in the range, being a low-cost 100V unit with an inbuilt display. However, the BN series is the more expensive higher-performance version with many extra features including a 150V input voltage limit, heavy-duty robust design, large heatsink, and huge input terminals which can accept a cable size up to 50mm2 (1 AWG).
The obvious feature lacking from the BN series is the display. However, monitoring and configuration is available via the additional remote MT50 display which features a good clear LCD screen showing all the basic information required. Wireless access is also available via the eBox-BLE Bluetooth adapter.
Tracer BN Series MPPT 150V 40A
- Very large screw terminals
- Large heatsink and wide operating temperature range
- 12V, 24V batteries
- 150V max Voc
- Wide MPP voltage range
- 20A Load control
- Remote MT50 display with settings and load control
- Optional Temp sensor
What is a solar charge controller and why are they important?
As the name suggests, a solar charge controller is a component of a solar panel system that controls the charging of a battery bank. Solar charge controllers ensure the batteries are charged at the proper rate and to the proper level. Without a charge controller, batteries can be damaged by incoming power, and could also leak power back to the solar panels when the sun isn’t shining.
Solar charge controllers have a simple job, but it’s important to learn about the two main types, how they work, and how to pair them with solar panels and batteries. Armed with that knowledge, you’ll be one step closer to building an off-grid solar system!
Find out how much you can save by installing solar
Key takeaways
- Solar charge controllers allow batteries to safely charge and discharge using the output of solar panels.
- A charge controller is needed any time a battery will be connected to the direct current (DC) output of solar panels; most often in small off-grid systems.
- The two kinds of charge controllers are pulse-width modulation (PWM) and maximum power point tracking (MPPT).
- PWM charge controllers are less expensive, but less efficient, and are best suited for small off-grid systems with a few solar panels and batteries.
- MPPT charge controllers are more expensive and more efficient, and are good for larger off-grid systems that can power a small home or cabin.
- The top off-grid charge controllers are made by brands like Victron, EPEVER, and Renogy, but non-brand-name charge controllers can be just fine if you know what to look for.
Who needs a solar charge controller?
A charge controller is necessary any time a battery bank will be connected to the direct current (DC) output of solar panels. In most cases, this means a small off-grid setup like solar panels on an RV or cabin. If you’re looking for information on how to use solar and batteries off the grid, you’re in the right place!
There are also charge controllers aimed at providing battery backup for an existing grid-tied solar system that is on the roof of a home or business. This application requires a high-voltage charge controller and usually involves rewiring the system to direct a portion of the solar output through the charge controller.
How does a solar charge controller work?
Fair warning before we get started: we’re about to discuss voltage, amperage, and wattage. If you need a refresher on how these things work together, check out our article on watts, kilowatts, and kilowatt-hours.
A solar charge controller is connected between solar panels and batteries to ensure power from the panels reaches the battery safely and effectively. The battery feeds into an inverter that changes the DC power into AC to run appliances (aka loads).
How a charge controller works within an off-grid solar system.
The four main functions of a solar charge controller are:
- Accept incoming power from solar panels
- Control the amount of power sent to the battery
- Monitor the voltage of the battery to prevent overcharging
- Allow power to flow only from the solar panels to the batteries
As a battery charges, its voltage increases, up to a limit. The battery can be damaged if an additional charge is applied past this limit. Therefore, the ability of a battery to provide or accept power can be measured by its voltage. For example, a typical 12-volt AGM lead-acid battery will show a voltage of 11.8 volts at 10% charged to 12.9 volts at 100% charge.
The main function of a solar charge controller is to ensure the amount of power that is sent to the battery is enough to charge it, but not so much that it increases the battery voltage above a safe level. It does this by reading the voltage of the battery and calculating how much additional energy is required to fully charge the battery.
Another important function of the charge controller is to prevent current from traveling back into the solar panels. When the sun isn’t shining, the solar panels aren’t producing any voltage. Because electricity flows from high voltage to low voltage, the power in the battery would flow into the solar panels if there was nothing in place to stop it. This could potentially cause damage. The charge controller has a diode that allows power to flow in one direction, preventing electricity from feeding back into the panels.
How solar power gets from panels to batteries
As we mentioned above, power flows from high voltage to low. So, to add energy to the battery, the output voltage of a solar panel must always be a little higher than the voltage of the battery it’s charging. Thankfully, solar panels are designed to put out more voltage than a battery needs at any given time.
Here’s an example: Say you have a single 100-watt solar panel and a 12-volt battery. Remember from above that a 12-volt battery is actually able to charge up to about 12.9 volts. 12 volts is what is called its “nominal voltage,” while the actual voltage of the battery depends on how charged it is. It might sink to 11.8 volts at low charge, and 12.9 volts when full.
The 100-watt solar panel can put out a maximum of 18 volts, which is a little too high for the battery to accept safely. Leaving it connected to the battery too long could result in a dangerous situation, eventually causing pressure to build up inside the battery and vent out the side as chemical steam.
You need a charge controller in between the solar panel and the battery to limit the voltage available to the battery. But it’s not just about the voltage. it also has to withstand a certain amount of current (amperage) flowing through it. That’s where the amperage rating of the charge controller comes in.
Charge controller amperage rating
The number of amps of current a charge controller can handle is called its “rating.” Exceeding the amperage rating can cause damage to the wiring within the charge controller. Let’s consider a charge controller rated to handle 30 amps of current. The single 100- watt solar panel described above puts out 5.5 amps of current at 18 volts. That amperage is much lower than the charge controller’s maximum of 30 amps, so the charge controller can easily handle the output of the singular solar panel.
In fact, it could handle the output of multiple solar panels wired in parallel (which increases current output). But there’s an important rule about charge controller ratings to consider: always make sure your charge controller is rated to handle 25% more amps than your solar panels are supposed to put out. That’s because solar panels can exceed their rated current output under especially bright sun, and you don’t want to fry your charge controller on the rare occasion when that happens.
Keeping that rule in mind, the 30-amp charge controller in our example could accept a nominal output of up to 24 amps. You could wire as many as four of those 5.5-amp solar panels in parallel to create a solar array capable of putting out 22 amps, staying under the charge controller’s rating plus the 25% cushion. If you think you might expand the size of your solar array in the future, get a charge controller rated for 50% more amps than your immediate needs.
Matching voltages
Another consideration when choosing a charge controller is the voltage of the battery bank you want to charge. Wiring batteries in series increases the voltage they can deliver and accept. For example, two 12-volt batteries wired in series will operate at 24 nominal volts. There are charge controllers on the market that can pair with battery banks of 12, 24, 36, and 48 volts. You need to make sure the charge controller you purchase can pair with the voltage of the battery bank.
Battery charging stages
There are three stages of charging a battery: bulk, absorption, and float. They correspond to how full the battery is.
- Bulk: When a battery charge is low, the charge controller can safely push a lot of energy to it, and the battery fills up with charge very quickly.
- Absorption: as the battery nears its full charge (around 90%), the charge controller reduces its current output, and the battery charges more slowly until it’s full.
- Float: when the battery is full, the charge controller lowers its output voltage just a bit to maintain the full charge.
Think of it like pouring water from a pitcher into a cup with a very slow leak: when the cup is empty, you start pouring and quickly increase the amount of water being poured until the cup is nearly full. Then you reduce the flow until the cup is full. In order to keep the cup full despite the leak, you pour just a trickle to keep it topped off.
The bulk/absorption/float process was developed for lead-acid deep cycle batteries. Some newer lithium batteries allow for higher current up until they’re quite full, meaning a charge controller paired with a lithium battery can be set to shorten or eliminate the absorption stage.
Types of charge controller
There are two main ways to control the flow of power to a battery, and they correspond to the two types of charge controller: pulse-width modulation (PWM) and maximum power point tracking (MPPT).
Pulse-width modulation (PWM)
Pulse-width modulation is the simplest and cheapest automatic way to control the flow of power between solar panels and a battery. There are PWM charge controllers on the market for between about 15 to 40.
A PWM charge controller ensures the battery never charges to more than its maximum voltage by switching the power flow on and off hundreds of times per second (i.e. sending “pulses” of power) to reduce the average voltage coming from the solar panels. The width of the pulses reduces the average output voltage.
Here’s an image to illustrate how the pulses work:
For example, if the charge controller accepts 18 volts from the solar panel, it might adjust the pulses so they’re on 82% of the time, and off 18% of the time. This would reduce the average voltage by 18%, down to about 14.8 volts, which can be used to charge a half-full AGM battery. As the battery gets close to a full charge, a PWM charge controller shortens the pulses even further, down to around 77% of the time, or 13.8 volts, to prevent the battery from overcharging.
Unfortunately, the excess energy produced by solar panels is wasted to reduce the output voltage. In our example, the charge controller would average around 80% efficiency. This means it’s very important to make sure the output voltage of the solar panels is not too much higher than the voltage of your battery bank with a PWM charge controller to minimize wasted energy. If your solar array outputs a much higher voltage, the PWM charge controller will cut that voltage down to what the battery can accept, and waste the rest.
Something like 80% efficiency is fine for small off-grid applications like a few solar panels hooked up to a couple of batteries, especially at the low cost of a PWM charge controller. For larger systems with much higher output, it is generally preferable to use the other kind of charge controller technology known as maximum power point tracking, or MPPT.
Maximum power point tracking (MPPT)
An MPPT solar charge controller operates by converting the incoming power from solar panels to match the theoretical highest-efficiency output at the right input voltage for the battery. The charge controller does this by calculating the point at which the maximum current can flow at a voltage the battery can accept, then converting the solar panel output to that mixture of voltage and current.
The major advantages of MPPT charge controllers are greater efficiency and compatibility with higher voltage solar arrays. This means that you can charge a 12V battery bank with a larger solar array wired in series, as long as you stay within the limits of the controller’s amperage rating. You can calculate this limit by taking the total wattage of the solar array and dividing it by the voltage of the battery bank to get the maximum possible output in amps.
Let’s use the same example numbers as before. The solar panel is putting out 100 watts, or about 5.5 amps into 18 volts. The MPPT charge controller converts the output to 14.8 volts but loses about 5% of the power in the conversion process. So the MPPT controller’s output current is about 6.4 amps, times the 14.8 volts, or 95 watts.
Theoretically, in an hour of full sun, the MPPT charge controller will have delivered 95 amp-hours of energy to the batteries, compared to the PWM charge controller’s energy output of about 80 amp-hours. In practice, it isn’t quite that simple, as solar pro Will Prowse discovered in this video:
Common features and settings on a charge controller
The basic features of the simplest PWM charge controller include the ability to set the type of battery and battery bank voltage, and lights indicating the phase of charging (bulk, absorption, and float). advanced PWM and MPPT models come with a small LCD display for programming and data display, a heat sensor port to monitor battery temperature, and a communications port to connect the charge controller to an external display or computer. The most advanced charge controllers offer Bluetooth connectivity and an app for customizing settings.
Recommended prodcuts
There are tons of fine charge controllers available on the market. Search any solar supply or online marketplace like Amazon and you’re bound to turn up dozens of results.
The cheapest PWM charge controllers can be had for around 15, and are often rebranded versions of the same design. These lack many features but are relatively reliable for how inexpensive they are. expensive PWM charge controllers built with better quality materials can be had for under 50, while full-featured MPPT charge controllers are priced anywhere from 100 to 200.
Below are a few of our recommended charge controllers at different price points for a medium-sized off-grid setup.
Renogy Wanderer 30A 12V PWM
The Renogy Wanderer 30A PWM charge controller is a solid choice for a smaller off-grid setup. It can handle up to 30A of current at 12V, so it’s not meant for a large system.
It doesn’t have a screen, but it does pair with the three main kinds of lead-acid batteries as well as lithium ones. It has a connector port for an optional temperature sensor and includes an RS232 port that can be used to program the charge controller or even to add Renogy’s BT-1 Bluetooth module for connecting to the Renogy app on your smartphone.
The Wanderer can be had for about 40 from Amazon or Renogy direct.
EPEVER Tracer BN 30A 12V/24V MPPT
The EPEVER Tracer BN MPPT 30A charge controller is not the cheapest MPPT charge controller on the market, but it’s a very good one. With a die-cast aluminum body, sturdy connectors, and a DC output to power loads like DC appliances or LED lights, the Tracer BN is a robust piece of equipment perfect for handling solar charging of lead-acid batteries in 12- and 24-volt banks. It can accept an incoming power output of up to 2,340 watts of solar panels (that’s equal to three parallel strings of four 60-cell solar panels wired in series). The Tracer can be programmed to charge lithium batteries, but it doesn’t come with a preset charging profile for them.
This EPEVER Tracer BN kit at Amazon includes a temperature sensor, mounting hardware, and a separate screen for programming and monitoring the health and state of charge of your battery system. Price at the time of publishing was 179.99.
Victron Energy SmartSolar 30A 100V MPPT
Victron is one of the most trusted solar brands in the world, and its technology is now becoming more widely available in the United States. This 30A, 100V charge controller is known as one of the best on market. Just like the EPEVER controller, it works with 12- or 24-volt battery banks but allows for slightly lower voltage solar input. To stay under this charger’s rating, you could run as many as three parallel strings of three 60-cell solar panels in series to achieve an output of 90 volts at around 20 amps (1,800 watts of solar output).
It’s made with quality components, calculates maximum power point quickly and with high efficiency, and is very easy to use. The SmartSolar line of charge controllers all come with Bluetooth connectivity on board and can connect to the VictronConnect app on Android, iOS, macOS, and Windows for easy programming. Perhaps most importantly, you get a 5-year limited warranty that protects you against defects in materials and workmanship.
The SmartSolar 30A is the most expensive product on our list at around 225 on Amazon, but reading the reviews from its users, you can see why the expense might be worth it.
Solar charge controllers: are they right for you?
All the information above should give you a good basis of knowledge about how solar charge controllers work and how to pair them with solar panels and batteries, but there’s no substitute for practical, hands-on experience! If you have a few bucks to spend, you can set up a pretty simple off-grid solar “generator” using a single solar panel, a charge controller, a battery, and a cheap inverter. Choosing a charge controller that’s oversized for a small application gives you a chance to increase the size of the solar array and battery bank as you gain experience or find new ways to use the stored solar energy.
Now go out there and start making solar and batteries work for you!
Solar Charge Controllers Battery Charging
Hey, do you know what solar charge controllers are? They’re devices that regulate the voltage and current coming from your solar panels to your batteries. They prevent overcharging, over-discharging, and reverse current flow. They’re pretty important if you want to keep your solar system running smoothly and efficiently. There are different types of solar charge controllers, such as PWM (pulse width modulation) and MPPT (maximum power point tracking). PWM controllers are cheaper and simpler, but they waste some of the solar power by reducing the voltage. MPPT controllers are more expensive and complex, but they can adjust the voltage and current to match the optimal power point of the solar panel. So, depending on your budget and needs, you might want to choose one or the other. Or maybe you want to have both, just in case. You never know when you might need some extra juice from the sun, right?
Charge Controllers
Midnite Classic 150
Midnite Classic 200
Midnite Classis 250
Midnite Hawkes Bay
Why a charge controller?
Proper Battery Charging prevent excessive overcharge of the batteries within a battery based power system. Unlike other types of generators, solar panels can be short circuited or open circuited without causing damage to them. Controllers contain a relay that opens the charging circuit, terminating the charge at a pre-set high voltage and, once a pre-set low voltage is reached, closes the circuit, allowing charging to continue. Manage your battery life, Get the amp needed using mppt
Charge controllers are the gizmo that goes between the solar array and the batteries and are sized to the systems they protect by the short circuit array current and watts matched to the battery voltage. Most common are 12, 24 and 48 volts. Because of cold temperatures and the “edge of Cloud effect”, sporadically increased current levels are not uncommon. For these and other reasons, the size of a controller’s amperage should be increased by a minimum of twenty five percent of the peak solar array current rounded up. You can also use the manufactures string calculator to correctly size the right charge controller for your battery based system for your zip code.
What Size do I Need?
Take the number of panels x watts to get the total watts of the solar array. You then divide it by the voltage of your battery bank to get amps, add 25% to allow for cold temperatures and as always, round up. Example: 2. 140 watt solar panels in series = 280 watts / 12 VDC battery bank 25% = 29.18 amps. You would choose a 30 amp, 12 VDC charger in this example. Another example would be 4. 250 watt solar panels = 1,000 watts / 24V battery bank = 41.7 amps 25% = 52.09 rounded up = 60 amp controller. Note; Solar charge controllers are rated and sized by the solar panel array current and system voltage. These examples are simple calculations for small systems. If you have a larger system with muliple strings you are considering, you should look at our Off-Grid Living page for some preconfigured systems that include the right sized charge controller or consult the charge controllers manufactures string calculator.
MidNite Solar
Midnite Solar is an American manufacture that produces a wide range of alternative energy products primarily used in off-grid battery applications. MidNite’s Classic series of Maximum Power Point Tracking (MPPT) charge controllers are the most powerful, full featured controllers on the market as well as being the only ETL listed controllers designed to work with Solar, Wind, and Micro Hydro Electric systems.
The typical solar string for battery based systems is three common 60 cell solar panels in series. Throughout North America, 3 in series is a safe string for MPPT most controllers. The higher voltage Midnite Classic controllers may accept strings of 4 or even 5, depending on the solar panels and the local climate.
On a cold clear morning if your solar panel or string of panels Voc exceeds the controller’s limit, the charge controller will protect itself by refusing to turn on. If you grossly exceed the Voc for example by wiring a large string of panels in series or miss-match your single panel to the controller for instance, you’ll get smoke. Smoke coming our of your charge controller is a bad thing.
Most MPPT charge controllers work with higher array voltages, which can greatly reduce the required wire size between the array and the charge controller. While more expensive than PWM controllers, MPPT charge controllers can boost system performance by up to 30% making them very cost effective.
Pulse Width Modulation (PWM) is an effective means to achieve constant voltage battery charging by switching (or pulse) the charge controller’s power devices. When in PWM regulation, the current from the solar array tapers according to the battery’s condition and recharging needs. The PWM charge controller constantly checks the state of the battery to determine how fast to send the electrical pulses, and how long the pulses will be. In a fully charged battery with no load, it may just tick every few seconds and send a short pulse to the battery. In a discharged battery, the pulses would be very long and almost continuous. The charge controller checks the state of charge on the battery between pulses and adjusts itself each time.
Maximum Power Point Tracking (MPPT). A solar panels ideal voltage is that at which it can put out maximum power. Maximum power point, also called peak power voltage abbreviated Vpp is the maximum energy produced. Maximum power point tracking (MPPT) is a electronic design that charge controller manufactures use to get the maximum possible power from a solar panel. The cells that make up a solar panel have a complex relationship between solar irradiation, temperature and resistance that produces a non-linear output efficiency known as the I-V curve. It is the purpose of the MPPT controller to sample the output of the cells and apply the proper load to obtain maximum power for any given environmental conditions. Essentially, this defines the current that the inverter should draw from the solar panel in order to get the maximum possible power, as power equals voltage times current. MPPT controllers are more effective that PWM controllers and save considerable money on larger systems since they provide 16% to 30% more power to the battery.
Charge Controllers, Off-Grid, Deep Cycle Battery Chargers.
Charge controllers are solid-state electronic devices used in nearly every solar and wind energy system that uses batteries. A charge controller is often times used in off-grid solar systems with 12 volt to 48 volt battery banks to keep the voltage to the batteries within acceptable limits. A charge controller automatically tapers, stops, or diverts electrical power when systems batteries become fully charged. Charge controller capacities range from 4 to 80 A and multiple charge controllers can be used in parallel for larger solar battery systems. Some charge controllers offer additional features, like charge status display, data logging, automatic battery equalization charging and generator starting.
The simplest charge controllers cut the power when the battery reaches a set voltage, and turn it on when a low voltage set point is reached. Pulse width modulated (PWM) charge controllers turn on and off very rapidly, maintaining the batteries at full charge with whatever power is available. Maximum power point tracking (MPPT) charge controllers optimize the voltage of the PV array to maximize total power output then convert that to the correct voltage to charge the battery. This process significantly increases the power from a solar array, particularly in low temperatures when battery voltage is significantly below the PV array voltage. Most MPPT charge controllers work with higher array voltages, enabling the use of larger solar modules, which can be more economical on a cost per watt basis. A higher voltage solar array also minimizes the required AWG wire size between the solar panels and the charge controller. While more expensive than PWM controllers The Charge controllers Blue Pacific Solar sells employ the latest in power electronics to regulate the battery charge by controlling the charging voltage and current from a solar panel array. Charge controllers regulate the charge of the battery, but also prevent the battery from being over discharged which can damage the battery bank.
Charge controllers have multiple stages of control it uses to regulate different voltage and current levels. The voltage and current of a battery varies over the different stages of battery charge. Though the amount can vary, the bulk charge usually is approximately 80%, the absorption charge is 10% with the float charge representing the balance of the battery charging process. The bulk charging stage of the charge controllers process is the first stage to used to bring the battery depth of discharge (DOD) back to 100%. The bulk charge stage happens first in in the morning after the batteries DOD has drained down since sunset the previous day. The bulk charging stage pushes as many amps into the battery bank as possible from the solar panels and gets the voltage up in the process. The effect of a charge controller is not unlike trying to fill a glass of water from a faucet. You first turn the faucet on full while the glass if filling, then slowly taper off the pressure until the glass is full. When the battery bank reaches a predetermined level known as the bulk voltage set-point, the charge is then substantially slowed. Because the bulk voltage set point is determined by the type of battery you are using, many charge controllers have to be pre-set to the type of battery which will dictate the rate of charge.
The second state of charge a charge controller employs is the absorption stage. After a battery system has been brought up to the bulk voltage set point, the charge controller slows down the charge rate because the battery bank cannot accept the same Rapid charging pace without overheating and damaging the battery bank. At the absorption stage a battery bank is only about 80% full. The absorption charge is the function level in the process that tops off the battery bank. During the absorption stage, the charge controller holds the battery volts constant and reduces the amount of current sent into the battery. When the absorption stage is complete, the battery bank is fully charges.
The final step a charge controller performs is the float charge. Typically a charge controller enters into a float charge state when the other charge levels of the battery bank has been achieved. When the number of peak sun hours is limited, a solar charge controller may not be able to get the battery bank back to the float stage before the next cycle begins.
MorningStar, Outback and Xantrex are adding new and updated charge controllers technology everyday. Various new charge controller models are released every year making what seems like a dilemma at first, but is actually a better solution. There is in fact a right charge controller for every off-grid solar application. Blue Pacific Solars’ consultants can help you sort through the different challenges of matching the right charge controllers to your battery bank.