The Ultimate Buyer's Guide for Purchasing 30 Amp Solar Controller

A solar charge controller is a regulator for your solar battery that prevents it from overcharging. Batteries are rated for reasonable volts and voltage capacity, and exceeding that voltage can lead to permanent battery damage and loss of functionality over time. Solar charge controllers act as a gateway to your battery storage system, making sure damage doesn't occur from overloading it.

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Charge controllers are only necessary in a few specific cases. Most commonly, you will want to look into charge controllers if you are trying to install an off-grid solar system ' from rooftop systems to smaller setups on RVs or boats. If you're a homeowner looking to install a solar array with a battery that is connected to the electric grid, there's no need for a charge controller ' once your battery is full, excess energy will be directed to the grid automatically instead, helping you avoid overloading your battery. This is known as load control.

To help you find the best match, we created a list of the best portable solar products of . Many of these include built-in solar charge controllers for ease of use.

For the majority of solar shoppers, there's no need to worry about charge controllers. Rooftop or ground-mount solar installations with a battery backup are almost always linked to the electric grid, and in the case that your battery is completely charged, your excess solar energy will automatically reroute there.

If you're interested in installing a small off-grid solar energy system with battery backup, you might need to look into a charge controller to ensure that your battery is safely charged. For relatively small batteries paired with low-output 5-10 watt (W) solar panels, a PWM charge controller should do the job. For more complex DIY solar projects with higher output panels, you may want to consider an MPPT charge controller.

If you want to use solar to go completely off-grid, there are two types of charge controllers to consider: PWM controllers and MPPT controllers.

Pulse width modulation solar charge controllers

PWM solar charge controllers are the standard type of charge controller available to solar shoppers. They are simpler than MPPT controllers and generally less expensive. PWM controllers work by slowly reducing the amount of power going into your battery as it approaches capacity. When your battery is full, PWM controllers maintain a state of "trickle," which means they supply a tiny amount of power constantly to keep the battery topped off.

With a PWM controller, your solar panel system and your home battery need to have matching voltages. In larger solar panel systems designed to power your whole home, panel and battery voltage aren't typically the same. As a result, PWM controllers are more suited for small DIY solar systems with a couple of low-voltage panels and a small battery.

Maximum Power Point Tracking solar charge controllers

MPPT solar charge controllers are a more expensive and complex charge controller option, often coming with items like lcd displays and bluetooth. They provide the same switch-like protection that a PWM controller does and will reduce the power flowing to your home battery as it nears capacity.

Unlike PWM controllers, MPPT charge controllers can pair non-matching input voltages from panels and batteries. MPPT controllers adjust their input to bring in the maximum power possible from your solar array and can also vary their output power to match the attached battery. This means that MPPT charge controllers are more efficient than PWM controllers and more effectively utilize the full power of your solar panels to charge a home battery system.

If efficiency were the only concern in purchasing a controller, an MPPT controller would be the best choice every time. But it's not always practical. Selecting the right solar charge controller involves several factors beyond just efficiency.

PWM vs. MPPT solar charge controller comparison

To determine what controller is right for you, answer these questions:

What type of panels do you have?

Most off-grid solar panels are 36-cell panels designed for 12-Volt battery charging current and amperage ratings of typically around 30 amps. These systems work well with PWM controllers and lithium batteries. 60-cell and 72-cell panels are typically used with a grid-tie solar panel system and have a higher voltage (24-volt systems or more), thus requiring an MPPT controller.

How big is your system?

A PWM controller works with any system size as long as the voltage between the solar power system and home battery are matched, even at low voltage 'though typically, they don't match in larger systems, making a PWM ideal for smaller setups. MPPT controllers are less efficient unless your array is at least 170 W.

What temperatures can you expect?

MPPT controllers work better than PWM controllers when it gets colder. As the temperature drops, the voltage increases, and an MPPT controller can capture the excess voltage. In warm climates where the temperature doesn't typically get very low, there isn't extra voltage and an MPPT controller isn't necessary. Temperature sensors are another additional feature that could be added.

What is your budget for a controller?

In general, MPPT charge controllers are more expensive than PWM controllers due to their higher charging efficiency. An MPPT controller can reach up to 20 percent higher efficiency ' this is due to its four-stage charging method, which is healthier for your battery life. PWM solar charge controllers are more versatile and more easily installed, but their lower efficiency usually means lower prices.

Renogy

Renogy produces DIY-friendly products for off-grid projects of all sizes. Their offerings include solar panels, batteries, inverters, and more. Their line of charge controllers is ideal for small projects that require a PWM charge controller or larger projects that need the more robust MPPT charge controller. Each type of charge controller comes in different sizes, so you can match your system's requirements.

BougeRV

BougeRV is a reliable resource for RV travelers and others seeking off-grid power solutions. Both their PWM and MPPT chargers are well-rated and have size and compatibility options to make them work with your system. BougeRV also develops other outdoor appliances and power solutions, which is great if you are concerned about overall system compatibility.

Victron Energy

Victron Energy offers a wide range of off-grid energy supply and storage solutions. The company has been in the industry for 45 years and continues to develop new products to meet changing consumer needs. The amp MPPT charge controller linked above is just one of many they have at different sizes and price points to suit your system requirements.

On the EnergySage Marketplace, you can register your property to begin receiving quality quotes for solar installations. If you are interested in storage solutions to pair with your panels, you can simply indicate your interest on your profile for installers to see. Connecting your solar project to the grid (even with battery backup) is a smart move, as it provides a second backup for your system, and in the case that your battery storage capacity isn't enough, you won't simply run out of power to use.

Goto KINGSUN to know more.

While going completely off-grid with a DIY solar project may work in some cases, if your main concern is saving money, hiring a qualified installer to help you go, solar is still a sound financial decision. What's more, having a professional installer work on your solar project ensures that you are getting the expertise you need to have a functional and effective solar system. Installers also offer warranties and protections for their products that you can't always get with a DIY project. If you want to see how much you can save by going solar, check out our Solar Calculator for an instant estimate based on your unique property.

Why Do I Need a Solar Charge Controller?

A solar charge controller (frequently called a regulator) is similar to a regular battery charger, i.e. it regulates the current flowing from the solar panel into the battery bank to avoid overcharging the batteries. (If you don't need to understand the why's, scroll to the end for a simple flow chart). As with a regular quality battery charger, various battery types are accommodated, the absorption voltage, float voltage can be selectable, and sometimes the time periods and/or the tail current are also selectable. They are especially suited for lithium-iron-phosphate batteries as once fully charged the controller then stays at the set float or holding voltage of around 13.6V (3.4V per cell) for the remainder of the day.

The most common charge profile is the same basic sequence used on a quality mains charger, i.e. bulk mode > absorption mode > float mode. Entry into bulk charge mode occurs at:

• sunrise in the morning
• if the battery voltage drops below a defined voltage for more than a set time period, e.g. 5 seconds (re-entry)

This re-entry into bulk mode works well with lead-acid batteries as the voltage drop and droop is worse than it is for lithium-based batteries which maintain a higher more stable voltage throughout the majority of the discharge cycle.

Lithium Batteries

Lithium batteries (LiFePO4) do not benefit from re-entry into a bulk mode during the day as the internal impedance of the lithium batteries increases at high (and low) states of charge as indicated by the orange vertical lines in the chart below and it is only necessary to occasionally balance the cells which can only be done around the absorption voltage. A related reason is to avoid the rapid and large variation in voltage that will occur in these regions as large loads are switched on and off.

Lithium batteries do not have a defined 'float voltage', and therefore the 'float voltage' of the controller should be set to be at or just below the 'charge knee voltage' (as indicated in the chart below) of the LiFePO4 charge profile, i.e. 3.4V per cell or 13.6V for a 12V battery. The controller should hold this voltage for the remainder of the day after bulk charging the battery.

The Difference Between PWM and MPPT Solar Charge Controllers

The crux of the difference is:

• With a PWM controller, the current is drawn out of the panel at just above the battery voltage, whereas
• With an MPPT solar charge controller the current is drawn out of the panel at the panel 'maximum power voltage' (think of an MPPT controller as being a 'smart DC-DC converter')

You often see slogans such as 'you will get 20% or more energy harvesting from an MPPT controller'. This extra actually varies significantly and the following is a comparison assuming the panel is in full sun and the controller is in bulk charge mode. Ignoring voltage drops and using a simple panel and simple math as an example:

• Panel maximum power current (Imp) = 5.0A
• Panel maximum power voltage (Vmp) = 18V

Battery voltage = 13V (battery voltage can vary between say 10.8V fully discharged and 14.4V during absorption charge mode). At 13V the panel amps will be slightly higher than the maximum power amps, say 5.2A

With a PWM controller, the power drawn from the panel is 5.2A * 13V = 67.6 watts. This amount of power will be drawn regardless of the temperature of the panel, provided that the panel voltage remains above the battery voltage.

With an MPPT controller the power from the panel is 5.0A * 18V = 90 watts, i.e. 25% higher. However this is overly optimistic as the voltage drops as temperature increases; so assuming the panel temperature rises to say 30°C above the standard test conditions (STC) temperature of 25°C and the voltage drops by 4% for every 10°C, i.e. total of 12% then the power drawn by the MPPT will be 5A * 15.84V = 79.2W i.e. 17.2% more power than the PWM controller.

In summary, there is an increase in energy harvesting with the MPPT controllers, but the percentage increase in harvesting varies significantly over the course of a day.

The Differences in PWM and MPPT Operation:

PWM:

A PWM (pulse width modulation) controller can be thought of as an (electronic) switch between the solar panels and the battery:

• The switch is ON when the charger mode is in bulk charge mode
• The switch is 'flicked' ON and OFF as needed (pulse width modulated) to hold the battery voltage at the absorption voltage
• The switch is OFF at the end of absorption while the battery voltage drops to the float voltage
• The switch is once again 'flicked' ON and OFF as needed (pulse width modulated) to hold the battery voltage at the float voltage

Note that when the switch is OFF the panel voltage will be at the open-circuit voltage (Voc) and when the switch is ON the panel voltage will be at the battery voltage + voltage drops between the panel and the controller.

The best panel match for a PWM controller:

The best panel match for a PWM controller is a panel with a voltage that is just sufficiently above that required for charging the battery and taking temperature into account, typically, a panel with a Vmp (maximum power voltage) of around 18V to charge a 12V battery. These are frequently referred to as a 12V panel even though they have a Vmp of around 18V.

MPPT:

The MPPT controller could be considered to be a 'smart DC-DC converter', i.e. it drops the panel voltage (hence 'house panels' could be used) down to the voltage required to charge the battery. The current is increased in the same ratio as the voltage is dropped (ignoring heating losses in the electronics), just like a conventional step-down DC-DC converter.

The 'smart' element in the DC-DC converter is the monitoring of the maximum power point of the panel which will vary during the day with the sun strength and angle, panel temperature, shading, and panel(s) health. The 'smarts' then adjust the input voltage of the DC-DC converter ' in 'engineering speak' it provides a matched load to the panel.

The best panel match for an MPPT controller:

1. The panel open circuit voltage (Voc) must be under the permitted voltage.
2. The VOC must be above the 'start voltage' for the controller to 'kick in'
3. The maximum panel short circuit current (Isc) must be within the range specified
4. The maximum array wattage - some controllers allow this to be 'over-sized', e.g the Redarc Manager 30 is permitted to have up to 520W attached

Choosing the Right Solar Controller/Regulator

The PWM is a Good Low-Cost Option:

• for smaller systems
• where the efficiency of the system is not critical, e.g trickle charging
• or solar panels with a maximum power voltage (Vmp) of up to 18V for charging a 12V battery (36V for 24V battery, etc).

The MPPT Controller is Best:

• For larger systems
• where the additional 20%* or more energy harvesting is worthwhile
• When the solar array voltage is substantially higher than the battery voltage e.g. using house panels, for charging 12V batteries

*An MPPT controller will yield higher returns compared with a PWM controller as the panel voltage increases. I.e. a 160W panel using 36 conventional monocrystalline cells with a maximum power amp of 8.4A will provide around 8.6A at 12V; while the 180W panel having 4 more cells will provide the same amperage but 4 additional cells increases the panel voltage by 2V. A PWM controller will not harvest any additional energy, but an MPPT controller will harvest an additional 11.1% (4 / 36) from the 180W panel. For the same principle, all panels using SunPower cells with more than 32 cells require an MPPT charge controller otherwise a PWM controller will harvest the same energy from 36, 40, 44 cell panels as it does from a 32 cell panel.

Solar Charge Controller Features and Options

Victron SmartSolar Controllers have a built-in Bluetooth to monitor your MPPT remotely by pairing it with a smartphone or other device through the Victron app.

Boost MPPT Controllers

'Boost' MPPT charge controllers allow batteries to be charged that has a higher voltage than the panel.

Contact us to discuss your requirements of 30 Amp Solar Controller. Our experienced sales team can help you identify the options that best suit your needs.