Are you looking for a solar charge controller for your main or backup solar power system?
You’ve come to the right place.
A solar charge controller is an essential part of a solar charging system. It stands between the solar panels and the battery bank where it regulates the amount of voltage and current reaching the batteries.
A solar charge controller protects your batteries by preventing an electrical overload or excessive discharging. It also optimizes the performance of your solar system.
A solar charge controller also helps you monitor the state of your system. You can check how much power the solar panel is generating or how quickly the batteries are charging or discharging.
What’s in This Buying Guide
In this in-depth buying guide, we review the best solar charge controllers available in the market, including standard PWM controllers and the more advanced MPPT controllers.
It will help you choose the best one for your needs and budget.
As you compare different solar charge controllers, make sure you know the requirements for your solar panels and battery bank.
Pick a controller that is compatible with your system.
If you have any doubts about what specs to look for (voltage, amps, etc.), contact your solar panel installer or the manufacturer for advice.
If you are also looking for a solar generator backup system, read our guide to the best solar backup generators for the home.
Best Solar Charge Controllers 2021
EPEVER 40A MPPT
- Best overall
12V/24V lead acid and lithium batteries
EPEVER 100A MPPT
- Best for large solar systems
12V-48V lead acid and lithium batteries
ALLPOWERS 20A PWM
- Best for small solar systems
12V/24V lead acid and lithium batteries
EPEVER Dual Battery
- Best for RVs and boats
12V/24V lead acid and lithium batteries
- Best for campers
12V lead acid batteries
OOYCYOO 60A MPPT
- Best value
12V/24V lead acid and lithium batteries
Outback Flexmax 80
- Best performance
12V-60V lead acid and lithium batteries
- Best for outdoor use
12V/24V lead acid and lithium batteries
SmartSolar 30A MPPT
- Best Bluetooth-connectivity
12V/24V lead acid and lithium batteries
The EPEVER 40A MPPT solar charger is the best choice for most homes as well as some RVs and boats.
It’s compatible with small and medium-size solar systems and can support four types of batteries, including lithium-ion.
For an MPPT solar charger, the price is not too bad. It’s one of the more affordable medium size MPPT solar chargers you can get.
1. Ideal for Small and Medium Size Arrays
With a max input limit of 100V, the EPEVER 40A charge controller is ideal for use with small and medium size arrays.
You can wire up to four 12V solar panels in series (12V solar panels usually exceed that voltage, hence the limit of 4).
If you have eight 100W 12V panels, you can set them up as two parallel sets to avoid going over the voltage limit.
2. MPPT Technology with 99.5% Efficiency
MPPT technology greatly increases the performance of your solar system. With an efficiency of over 99%, the EPEVER charge controller ensures your batteries get the most out of the solar panels.
This charges the batteries faster and maintains good performance on cloudy days.
3. Supports Lithium and Lead Acid Batteries
The EPEVER solar charge controller is compatible with both lead-acid and lithium-ion batteries.
Compatible lead acid batteries are sealed, gel, and flooded.
These three plus lithium ion cover most of the deep cycle batteries used in homes.
4. Load Output with Multiple Control Modes
The load output allows you to control a load, usually lighting, manually or automatically.
The EPEVER solar charge controller has four control options: a simple light on/off switch, manual control, a timer mode, and a test mode.
5. Temperature Compensation
High temperatures can reduce the efficiency of a solar system and even cause damage from excess voltage.
The EPEVER is designed to compensate for temperature changes to protect your battery system and maximize charging performance.
But to take advantage of this feature, you’ll need to buy a temperature sensor separately.
The display can be difficult to read in some lighting conditions.
It’s small and doesn’t have backlighting.
Other than that, this charge controller works great.
Best for a Large solar system:
The EPEVER 100A solar charge controller from the Tracer 10420AN series is perfect for large solar systems at home or an institution.
It can handle plenty of current from the solar panels (up to 100A) and charge high-voltage batteries as well (up to 48V).
1. High Tracking and Conversion Efficiency
This solar charge controller utilizes the Multiphase Synchronous Rectification Technology (MSRT) algorithm powered by a dual-core processor to improve efficiency, increase response speed, and ensure reliability.
The charge controller can easily keep up with demanding residential and industrial systems.
It quickly responds to changes in temperature and cloud cover, adapting the system load to maximize the amps going into your battery.
Similar to most MPPT charge controllers, the EPEVER controller can achieve a very high conversion efficiency of up to 98.6% whether there is a full sun out or it’s cloudy.
This ensures your system is at peak performance all the time.
2. Ideal for Large Systems
With a maximum current limit of 100A and input voltage limit of 200V, the EPEVER solar charge controller can handle a large high-output solar system without a problem.
It’s great for completely off-grid homes that need to generate a lot of solar power, especially during winter.
3. Four Battery Options
The solar charge controller is compatible with batteries ranging between 12V and 48V, another reason why it’s the best for large systems with large batteries.
It can charge four types of batteries: Gel, Flooded, Sealed, and User-defined (you can set your battery parameters. Ideal if you have a lithium-ion battery).
4. Easy to Use LCD display
You can track basic information on the small LCD display, including battery level, voltage, and temperature.
Two LED indicators show the system working status and alert you to a fault alarm.
Using two buttons under the display, you can browse and set some parameters, configure load relay, select your type of battery, change temperature unit and clear faults.
5. MT50 Remote Meter and PC Monitoring Cable
The solar charge controller comes with an MT50 remote meter that provides advanced control and monitoring of various parameters.
The meter displays much more data and gives you more control than the basic LCD display on the charge controller.
Another way to monitor your system is to hook up the charge controller to your laptop using the RS485PC Monitoring Cable.
Note: The system is compatible only with Windows OS devices.
The only downside of the 100A EPEVER solar charge controller is the price tag.
But it’s understandable considering its current and voltage limits. At least, it comes with all the accessories you need, including the MT50 remote meter, temperature sensor, and PC cable.
Best for a Small Solar System:
If you have a small solar system, whether it’s in your home or RV, there is no need to invest in an expensive MPPT solar charge controller.
A PWM controller like this one from ALLPOWERS works just as well. As a bonus, it’s cheap too.
The charge controller protects your battery from over-charging and short-circuiting while keeping it topped off for best performance.
Note that the ALLPOWERS solar charge controller is only compatible with lead-acid batteries, including flooded, AGM, and gel.
1. An Affordable Solar Charge Controller for Small Systems
If you are looking for a low-cost solar charge controller for your small solar system, we highly recommend the ALLPOWERS PWM controller.
With a max input voltage of just 50V and current input limit of 20A, it’s far from some of the powerful MPPT systems available online.
But it’s perfect for use with small solar panels.
Just make sure the total voltage doesn’t go beyond 50V, and the current at maximum power is less than 20A.
For instance, you can wire two 100W 12V panels in series (max total peak power will be around 36V) or three in parallel (total amps will be around 17A).
2. 4-stage PWM Technology
PWM (pulse with modulation) technology is less sophisticated than MPPT. But it’s good enough for small to mid-size systems that don’t require very high conversion efficiency.
The ALLPOWERS controller uses a 3-stage process to protect your battery and keep it topped off.
In the bulk stage, the controller delivers maximum voltage and current to the battery for a quick recharge. It kicks in when your batteries are low.
When the battery gets close to full, the controller goes into ABS or absorption stage. It will reduce the current to the battery to top it off slowly without overheating or overcharging it.
In float stage, the controller delivers a trickle current to the battery to keep it charged.
3. Battery Protection
The ALLPOWERS solar charge controller extends the life of your battery by delivering just the right amount of voltage and current.
There is no risk of overcharging or overheating, which can degrade your battery.
The controller also prevents short-circuiting and provides reverse current protection at night or when the solar panels are shaded.
4. Easy to Use Display
The display shows essential data and indicates the status of the system. At a glance, you can check your battery voltage, how much power is coming in, and the controller stage.
You can also configure various parameters and switch between modes.
5. USB Ports
The dual 5V/3A USB ports on the controller come in handy if you are using it in your RV or boat. They are also great for campers.
You can directly charge small devices while still charging your battery.
The obvious limitation here is power.
You can only use the ALLPOWERS charge controller with small systems. And even then, it cannot charge a depleted battery (below 8V).
It’s also not compatible with lithium-ion batteries.
Best for RVs, Boats, and Vehicles:
If you have two batteries in your RV, boat, or truck, it can be difficult to keep both of them fully charged using solar power.
Most people resort to using two separate solar panels wired to each battery.
But that adds more costs to your setup.
The EPEVER dual battery solar charge controller allows you to charge both batteries using the same connection from your solar panel or panels.
The dual solar charge controller comes with a remote meter that lets you monitor the state of each battery and the amount of power they are receiving.
1. Dual Battery Solar Charging
The charge controller regulates the voltage and current going to each battery. Instead of setting up a separate solar panel for each battery, you can charge both from a single panel.
Note that the two batteries can be of different capacities but must be the same type and voltage.
For instance, you can connect it to a 20Ah 12V sealed battery and a 200Ah 12V sealed the battery.
But you cannot connect it to a 12V sealed battery and a 24V sealed battery or a 12V flooded battery and a 12V sealed battery.
This is a PWM controller, so it lacks the high efficiency and advanced technology of an MPPT controller. But it still provides the same solid protection to your batteries from overcharging, overheating and short-circuiting.
It also prevents reverse charging, which can drain your batteries.
2. Remote Meter
The charge controller comes with a remote meter plus a 32ft communication cable.
The meter displays lots of status information about the solar panels and your batteries. You can also configure various parameters.
3. Remote Temperature Sensor
In addition to the meter, you also get a remote temperature sensor designed specifically for the dual controller.
The sensor feeds temperature data to the controller, which then compensates for temperature changes to increase performance and protect the batteries.
4. Compatible with Three Battery Types
You can select from one of three types of batteries: sealed, flooded and gel.
The EPEVER dual solar charge controller is not compatible with lithium-ion batteries.
The EPEVER dual solar charge controller is designed for small solar systems such as those typically used in RVs, boats, and trucks.
If you are looking for a high-capacity PWM solar charge controller, this is not it.
Best for Campers:
ZEALLIFE 12V 8A Solar Panel Charge Controller
For avid campers who rely on solar energy, the ZEALLIFE solar charge controller is perfect.
It’s a cheap addition to your solar kit.
It can’t handle much power, 8A max current, and 12V max voltage, but it’s good enough for most 12V solar panels that campers use.
Just make sure your panel’s wattage is between 20W and 130W.
If your solar panel does not have the wattage specified, calculate it by multiplying the maximum current in amperes by the maximum voltage (16V-20V) for 12V solar panels.
1. Great For Camping
The ZEALLIFE makes it easy to monitor your solar system when camping.
It works with most 12V solar panels as long as the total input current is 8A or lower and the wattage is between 20W and 130W.
The controller’s small footprint makes it perfect for campers short on space.
2. PWM Charge Management Technology
This is a PWM charger. It doesn’t make sense to use MPPT technology for small solar systems.
The ZEALLIFE charge controller uses a 3-stage process to increase charging efficiency and protect the batteries.
The three stages include bulk, absorption, and float.
An intelligent microprocessor automatically switches the controller between modes depending on the battery status.
This prevents overcharging, reverse charging, and short-circuiting.
It also keeps the battery’s voltage from going too low, which can prevent it from recharging. Some buyers bought it to keep the battery in a rarely driven car from dying.
3. LCD Display
As expected, the display is tiny. But it fits all the information you need to know.
At a glance, you can see how much current is going into the battery and the battery’s voltage.
The display is not backlit, making it a bit difficult to see the small numbers.
4. Easy Setup
Unlike most solar charge controllers where all the ports are located on the same side, the ZEALLIFE separates the three ports.
This makes it super easy to connect all the wires without messing up. It also makes for a neater setup.
In addition to three conveniently placed ports, the controller also includes a USB port where you can charge your smartphone and other gadgets.
5. Compatible with Three Battery Types
The ZEALLIFE solar charge controller is compatible only with AGM, gel, and flooded batteries.
It cannot charge lithium-ion batteries.
This solar charge controller is only ideal for very small solar systems. In most cases, you can only connect it to a single solar panel.
If you need more power, you’ll have to buy extra controllers and connect each to a solar panel.
MPPT solar charge controllers can be expensive, especially those designed for large solar systems.
The OOYCYOO MPPT solar charge controller is an exception. It can handle a maximum current of 60 amps and a max voltage of 100V.
That’s not too bad considering the price tag.
If you are looking for an affordable but powerful MPPT solar charge controller, the OOYCYOO controller is a great choice.
1. MPPT Technology
The OOYCYOO solar charge controller uses MPPT charge management technology to draw the maximum power from your solar array at all times.
By quickly tracking the maximum power from the solar panels, it can change the voltage to deliver maximum energy to the batteries.
This increases the performance of your system by 30%-40%.
In addition to increasing your system’s performance and efficiency, the controller also protects your batteries from overloading and short-circuiting.
It switches from delivering a high current to a trickle current to a floating charge depending on the status of the battery.
2. Ideal for Medium Size Systems
The OOYCYOO controller takes up to 60amps in current and up to 100V in voltage.
As for wattage, you can use a max 720 watts array if you have a 12V battery or a max 1440 watts array if you are charging a 24V battery.
The controller is good enough for most residential solar systems.
3. LCD Display
The decently sized display shows you real-time information. You can check the battery voltage, the amount of power coming from the solar panels, and the status of external loads.
You can also configure various parameters such as the type of battery you are using and the load timer.
Note: Battery options are sealed, gel, and flooded. This controller doesn’t support lithium batteries.
4. Aluminum Heat Sink and ABS Housing
An aluminum heat sink allows the OOYCYOO charge controller to dissipate heat faster and more efficiently. This maintains high performance and prolongs its life.
The heat and impact resistant ABS housing also ensure the controller works at its best and lasts for years.
Most MPPT solar charge controllers support lithium-ion batteries. So it’s a bit disappointing to see that the OOYCYOO controller is only compatible with lead-acid batteries.
The Outback Flexmax is not quite as powerful as the EPEVER 100A controller we recommended for large systems, but it’s one of the highest performance solar charger controllers.
It has a maximum current rating of 80 amps, a maximum voltage of 150V and can charge batteries between 12V and 60V (the EPEVER controller goes up to 48V).
So if you have a high-voltage battery bank, this is the best solar charge controller.
1. Ideal for Large Systems
The Outback Flexmax is a great choice for homes using a large solar array to charge a large battery bank.
The controller can handle an input power of up to 5,000 watts (for 60V batteries) and current up to 80 amps.
2. MPPT Technology
The Flexmax automatically tracks how much power the solar panel is generating and adjusts the voltage to deliver maximum power to the batteries.
This increases the efficiency of your array in all weather conditions.
The controller also monitors the status of the batteries to keep them from overcharging or short-circuiting.
It’s compatible with the most common types of lead-acid batteries and can also be hooked to lithium-ion batteries.
However, if you are charging a lithium-ion battery bank, you have to adjust various voltage parameters to maximize charging performance.
3. Intelligent Thermal Management
The Flexmax solar charge controller can operate in temperatures as high as 104F thanks to an intelligent thermal management system that keeps it cool.
For the best cooling performance, the manufacturer recommends buying an external temperature sensor.
4. Backlit Display
The display is quite small. So it displays only basic data.
It only displays current flow in and out of the batteries. You can also see performance data from the last 128 days and configure various settings.
If you want to monitor your battery voltage and other parameters, you’ll need a separate meter.
Flexmax 80 is one of the most expensive solar charge controllers you can buy.
If you are looking for a budget MPPT solar charge controller, this is not it.
Best for Outdoor Use:
Most of the solar charge controllers you’ll come across can only be used indoors. That’s okay because most people use them indoors anyway.
But for the few who need to set it up outside, we recommend the Renogy Voyager. It is waterproof, meaning you can use it outside or inside.
The Renogy Voyager has an IP65 rating.
That means it can withstand rain and snow without any damage. It’s also designed to keep out dust and other particles.
2. Advanced 5-stage PWM Charge Controller
The Voyager uses PWM technology to keep your batteries safe and maximize charging performance.
It can switch between five stages depending on the state of the battery. They are a soft start, bulk, boost, float, and equalization.
By selecting the right stage, the controller prevents the batteries from over-charging and overheating. It also prevents reverse polarity, which could discharge the batteries.
3. Backlit LCD and LED Bar
For easy viewing, even in bright sunlight, the LCD display is backlit. It displays basic information about the battery and power flow.
Below the display is a row of LED indicators that you can check to determine charge and battery status quickly.
4. Compatible with Seven Battery Types
It is one of the most versatile PWM solar charge controllers you’ll find.
5. Temperature Compensation
The charge controller compensates for an ambient temperature around the battery to ensure the system stays efficient in all weather conditions.
It receives temperature readings from the included temperature sensor that you are supposed to connect near the battery.
This is a solid charge controller overall.
The only complaint from customers is that the contacts are a bit too close. This makes it tedious to connect thicker wires and raise concerns about how well the contacts are insulated from each other.
Another limitation is that the Voyager only works with 12V batteries. No support or 24V systems.
Best Bluetooth-Connected Solar Charge Controller:
If you’d like to check your battery or power flow status without having to look at the display on the charge controller or a connected meter, we recommend the SmartSolar Bluetooth-connected MPPT charge controller.
As long as you are within range, you can easily check important metrics on your smartphone.
The solar charger controller itself is rated at 30amps and 100V, making it ideal or small and medium-size systems.
1. Remote Smartphone Monitoring
Instead of trying to squint at a tiny display with small numbers, you can use your smartphone to monitor your battery and check the power flow.
The app displays the battery voltage, current, and state (bulk, absorption, or float).
You can also check how much charge your battery contains, how much charge you have consumed, and how much time is remaining before it is fully charged.
It’s much more information than you get on a standard charge controller display.
It’s also easier and more convenient than a meter (you can still connect a meter if you want).
The app stores information for the last 30 days in case you want to check past performance data.
2. MPPT Technology
This is an MPPT solar charge controller.
It greatly increases the efficiency and performance of your solar system, allowing your batteries to charge faster and more efficiently in all weather conditions.
It also ensures your batteries do not overcharge or overheat.
3. Temperature Compensation
An internal temperature sensor measures ambient temperature. The controller then compensates for temperature changes throughout the day to maintain charging efficiency.
The controller has no display of any kind; just three indicators to show the current state.
The only way to check the status of the system is by using your smartphone. This is probably not an issue for many people but can be a limitation for those who’d love a backup option.
Another issue is that the charge controller does not come with an external battery temperature sensor, and there doesn’t seem to be one available separately on Amazon or the manufacturer website.
I’m not sure whether it is compatible with other temperature sensors.
What is a Solar Charge Controller?
A charge controller is an electronic device that monitors and controls the amount of power – current and voltage –going to the battery from a solar panel.
It’s an essential part of most solar systems.
Without a solar charge controller, your batteries would get damaged and wouldn’t last long because of too much or too little power.
A charge controller does several important things to protect your batteries and improve performance:
Prevents overcharging: The charge controller monitors the voltage of the battery and reduces current or stops it completely when it gets to a certain point.
Prevents extremely low voltage: If your battery’s voltage gets too low, it will struggle to recharge again and can deteriorate if such voltage drops happen frequently. A charge controller can prevent this by automatically turning off the load when the battery drops to a certain voltage.
Prevents overheating: Some charge controllers come with a temperature sensor that you install near the battery. If the battery temperature rises, the controller lowers the voltage input to prevent overheating.
Prevents reverse charging: At night, your battery can discharge because of the voltage difference between the solar panel and the battery. A charge controller prevents this.
Increases performance: An MPPT solar charge controller allows your battery bank to charge faster and more efficiently, even in cloudy weather.
Types of Solar Charge Controllers
There are three types of solar charge controllers: simple shunt controllers, PWM controllers, and MPPT controllers.
The first type, shunt controllers, are outdated and are not used anymore. They work by simply switching a shunt on or off to allow or block current to the battery.
They are ideal if you don’t want any electromagnetic interference.
Since you are unlikely to find a shunt solar charge controller, we’ll focus on the other two.
PWM Solar Charge Controllers
PWM stands for Pulse Width Modulation.
It works by sending a series of pulses to the battery rather than a single continuous output.
When the battery level is low, the pulses will be long and far between; an almost continuous flow.
As the battery fills up, the pulses become shorter and quicker until they become just a trickle to maintain the full battery.
This keeps the batteries from overcharging.
PWM solar charge controllers are great for small systems where efficiency is not essential. They are common in RV, boat, and camping solar systems.
They do a great job protecting the battery but they ‘waste’ some power.
A 12V solar panel will typically output 16V-18V of power depending on the weather. But to charge a 12V battery, the charge controller has to step down that voltage to match that of the battery.
If you want to capture this lost power, get an MPPT controller.
MPPT Charge Controllers
MPPT stands for Maximum Power Point Tracking.
An algorithm in the controller constantly checks the maximum amount of power the solar array is delivering.
The controller then adjusts the voltage to maximize the amount of power going into the batteries.
An MPPT controller will still step down the 16-18 volts to a safe 12V for the battery. But it doesn’t let the remaining voltage go to waste. It converts it into amps.
Your battery bank receives more current and charges faster.
A good MPPT solar charge controller can increase your system efficiency by 30% or more.
What to Consider When Buying a Solar Charge Controller
PWM vs. MPPT: which one should you go for?
The answer depends on your needs.
If you have a small or medium size solar system for your RV, boat, or small home, a PWM controller will do.
But for most residential solar systems, an MPPT solar controller is far more efficient.
2. Max Voltage and Current
The next thing to check is the controller’s capacity – how much voltage and current can it handle.
Max voltage ranges from as little as 12V for the smallest controllers to as high as 150V for powerful MPPT charge controllers.
Make sure the open circuit voltage of your solar array does not go beyond the set limit.
When calculating the total voltage from your solar panels, don’t forget to add a 25% margin. Most solar panels often produce a higher voltage than the one specified.
Do the same when calculating the total current.
Maximum input current ranges from as little as 8A for RV and truck charge controllers to 80A for high capacity charge controllers.
3. Battery Compatibility
Check what battery voltage the charge controller is compatible with.
Most can be connected to 12V or 24V batteries. Some are 12V only while others can charge any battery up to 60V.
In addition to the voltage, check the battery type requirement.
Most PWM charge controllers are only compatible with lead-acid batteries (gel, sealed and flooded) while MPPT controllers can also support lithium batteries.
But you can still find PWM controllers that are compatible with lithium batteries and MPPT controllers that are ideal for lead-acid batteries only.
4. Load Control
Charge controllers turn off the output load automatically if the battery gets too low. This prevents extreme discharging, which can reduce the lifespan of your battery.
If you’d like to be able to turn off the load at any time, look for a charge controller with manual load control. This will usually be a switch you can press or toggle.
Some controllers also have a timed on/off feature. You can set the load to go on or off at a specific time.
This is handy for applications such as outdoor lights.
5. Temperature Compensation
Check whether your solar charge controller has a temperature compensation feature. It’s especially useful if you live in a hot area.
The controller will reduce the voltage if it detects the battery temperature is rising.
Overheating can damage your battery and reduce its lifespan.
If the charge controller has that feature, it will likely come with an external temperature sensor, or you’ll need to buy one separately.
6. System Monitoring and Control
One of the biggest advantages of a charge controller that I haven’t mentioned yet is that it allows you to monitor and control your solar system.
You can easily check the status of your battery, how much power the solar panel is producing, and other performance data.
Most solar charge controllers come with a simple integrated display where you can see basic details and configure various parameters.
For easier monitoring and more advanced control, look for a charge controller that comes with a remote meter or is compatible with one.
Alternatively, get a Bluetooth-connected charge controller that you can monitor from your smartphone.
Frequently Asked Questions
Can a solar charge controller work with a wind turbine?
No. Solar charge controllers are designed specifically for use with solar panels. If you have a wind turbine, look for a charge controller specifically for wind power.
How do solar charge controllers work?
PWM solar charge controllers detect the voltage of the battery and then decide how much power to send.
MPPT solar charge controllers detect the maximum power generated by the solar panels and turn the excess voltage into amps to charge the batteries faster and more efficiently.
How do I choose a solar charge controller?
Check the voltage and current produced by your solar panels and add 25% to both. Then look for a solar charge controller with maximum current and voltage above the figures you get.
What size solar panel do I need to charge a 12v battery?
Look for a solar panel that produces at least 13.6V in the worst-case scenario. Most solar panels can do this.
When do I need a solar charge controller?
Not everyone using solar panels needs a charge controller. Generally, a charge controller is essential in situations involving a significant amount of current, which could overcharge or damage the battery.
But if you are using small solar panels that output a limited amount of current and voltage, you likely don’t need a solar charge controller.
To check whether you need a charge controller, compare your battery amp hours with your solar panel max power. You generally don’t need a charge controller if the solar array puts out less than five watts of powerfor every 100 amp hours of battery capacity.
For example, you can safely charge a 40,000 mAh (40 Ah) power bank with a mini 2W solar panel.