Author: Jasmeen Aneja

If you’ve added solar panels to your boat or are thinking about it, you’ve probably come across the terms PWM and MPPT. These refer to the two types of charge controllers that regulate the power coming from your solar panels before it reaches your batteries. While both prevent overcharging and ensure safe charging, they work very differently. And the right choice can make a big difference in how much power you get from your solar investment. Let’s break it down in a way that makes sense for real-world boating.

Why You Need a Charge Controller

Solar panels don’t send a steady, battery-friendly voltage. Their output fluctuates based on sunlight, temperature, and shading, meaning they can produce much more voltage than your batteries need—or sometimes not enough. A charge controller acts as a gatekeeper, making sure that your batteries receive the right amount of power without getting damaged.

There are two main types of solar charge controllers: PWM (Pulse Width Modulation) and MPPT (Maximum Power Point Tracking). They both do the same job, but the way they do it—and the results you get—are very different.

PWM Controllers: Simple and Affordable

PWM controllers are the more basic and affordable option. Think of them as a simple switch—they connect your solar panels directly to your battery and regulate the charging process by pulsing the connection on and off as the battery voltage rises. While this sounds effective, there’s a major downside. If you have a 12V battery bank, a PWM controller forces your solar panels to match that voltage—usually around 12 to 14 volts. The problem? Most solar panels produce higher voltages (around 18V for a “12V” panel). Since a PWM controller can’t use that extra voltage, it simply goes to waste.

A PWM controller works well in small-scale setups, such as a single 12V panel charging a 12V battery, where the panel’s voltage closely matches the battery voltage. It’s a cost-effective solution for modest energy needs, such as powering lights or a small fridge during mooring. However, for larger systems or in conditions where panels produce significantly higher voltages, PWM controllers fall short in efficiency.

MPPT Controllers: Get More Power from Your Panels

MPPT controllers are a game-changer for boaters who want to maximize solar efficiency. Instead of forcing the solar panel to match the battery’s voltage, MPPT controllers adjust the voltage and current to ensure you’re getting the most power possible from your panels. Think of it like an automatic transmission that optimizes speed and torque depending on driving conditions.

Here’s a practical example: Your 12V panel is producing 18V at 5.5A, which equals 99W of power. A PWM controller will drop the panel voltage to 12V but keep the current the same, so the power reaching your battery is only about 66W.  An MPPT controller, however, will step down the voltage to 12V but increase the current to around 8.25A, ensuring your battery receives close to 99W instead of 66W.

The result? Up to 30% more power harvested from your solar panels. Over time, that adds up to significantly more stored energy, meaning more time using your fridge, electronics, and other onboard systems without running the engine.

Marine environments demand resilience and adaptability, and this is where MPPT controllers excel. They thrive in conditions with partial shading, fluctuating sunlight, and high panel voltages. MPPT controllers also allow you to wire panels in series to produce higher voltages, reducing losses from long wiring runs—a common challenge on larger boats.

Battery Voltage and Controller Size

Here’s something many boat owners miss: The voltage of your battery bank directly impacts how much solar power your MPPT controller can handle. The higher the battery voltage, the more panels you can connect. For example, A 60A MPPT can handle up to 800W with a 12V battery bank. This capacity doubles to 1,600W with a 24V battery bank and increases to 3,200W with a 48V system.

This means if you have a 24V system, you can install twice as many panels with the same controller compared to a 12V system. That’s why many serious boaters upgrade to higher voltage battery banks—they allow for a more efficient and scalable solar setup.

The Bottom Line

Your boat’s solar setup is only as good as its charge controller. Making the right choice now will ensure you get the most power, the best efficiency, and the longest-lasting performance from your solar investment. For small, low-power setups, PWM controllers are budget-friendly and can get the job done. But if you want maximum efficiency, better performance in varying conditions, and the ability to expand your solar setup, an MPPT controller is a highly recommended choice.

Ready to begin your solar journey? Explore Xantrex’s marine-grade solar panels or reach out to our team for personalized solar system design.

Solar panels are an excellent energy source for boats, but understanding their real-world output is essential to designing a reliable system. While panels may be rated for a specific wattage under ideal conditions, various factors such as sunlight hours, efficiency losses, and wiring configurations can significantly impact the actual wattage delivered to your battery bank. This guide unpacks the details behind how wattage is calculated, the role of MPPT controllers, and how to optimize your solar setup to maximize efficiency.

Solar Panel Wattage and Peak Sun Hours

The wattage of a solar panel is based on standard test conditions (STC), typically 1,000W/m² of sunlight at 25°C. For instance, a 100W panel produces 100 watts under perfect sunlight with no shading or inefficiencies. However, real-world conditions rarely match STC. Solar output depends on your location, season, weather, and panel placement, which are collectively measured in peak sun hours (PSH).

Peak sun hours represent the total equivalent hours of full sunlight your panels receive in a day. For example:

Miami averages 5.5 PSH in summer, so a 100W panel produces 100×5.5=550 Wh/day.

Boston, with 4 PSH in winter, sees a drop in output to 100×4=400 Wh/day.

Check the Peak Sun Hours for your city here.

Factors such as shading from masts or sails can further reduce the PSH, sometimes by as much as 50%. To combat this, careful placement of panels and the use of multiple panels on both port and starboard side is crucial.

The Role of MPPT Efficiency

Solar panels produce variable voltage and current throughout the day, influenced by sunlight intensity and shading. A Maximum Power Point Tracking (MPPT) charge controller optimizes this by adjusting the panel’s voltage and current to match the battery’s charging needs while minimizing losses. Unlike simpler PWM controllers, MPPT controllers increase system efficiency, especially when panel voltage is much higher than battery voltage.

How MPPT Controllers Work:

An MPPT controller adjusts the higher voltage from solar panels into usable current for the battery. For example:

A 100W panel generating 20V and 5A in ideal conditions would output 20V×5A=100W

If connected to a 12V battery bank, an MPPT converts the 20V to 12V and increases the current proportionally, delivering approximately 12V×8.3A=100W, minus minor conversion losses.

MPPT controllers are not 100% efficient. Typical conversion efficiencies range from 92% to 97%, so the actual output would be closer to 100W×0.95=95W.

Voltage Requirements and Minimum Thresholds

For an MPPT controller to operate effectively, the input voltage from the solar array must exceed the battery’s voltage by a specific margin, known as the voltage threshold. Most MPPT controllers require at least 5V above the battery’s nominal voltage to function. For example:

A 12V battery requires at least 17V from the solar array to initiate charging.

For a 24V battery bank, the minimum solar array voltage is approximately 29V.

If the panel voltage drops below this threshold due to shading, poor weather, or improper wiring, the MPPT cannot produce any wattage, and the system will idle. This is why wiring panels in series are preferred, however it is critical to understand panel wiring implications to achieve adequate voltage across MPPT.

Check this blog to understand the impact of Series, Parallel, and Mixed Solar Wiring on Efficiency

Understanding Wattage Ratings of MPPT Controllers

The maximum solar panel wattage an MPPT controller can handle is closely tied to the voltage of your battery bank. A 60A MPPT, for instance, can manage up to 800W when paired with a 12V battery bank, but this capacity doubles to 1,600W with a 24V bank and increases further to with a 48V bank. This scaling happens because as the battery voltage rises, the controller is able to process the same current delivering more power.

This relationship is a crucial consideration when designing your solar system, as higher battery voltages allow you to connect more panels or higher-wattage arrays to the same MPPT. However, exceeding the MPPT’s maximum input wattage is not recommended as it can lead to system instability, or even failure.

Refer to your manufacturer’s specifications for the maximum PV input rating to avoid the risks of under-sizing or overloading the system.

Losses in a Solar Setup

In addition to MPPT inefficiencies, other factors can reduce solar output:

Shading: Even partial shading on one panel can significantly reduce the output of the entire array in series connections. In parallel configurations, shading affects only the shaded panel but may reduce the voltage below the MPPT’s threshold.

Heat: Solar panels lose efficiency as they heat up. Every degree above 25°C typically reduces panel efficiency by 0.5%. For example, on a hot deck at 40°C, a 100W panel may only produce around 92.5W.

Wiring Losses: Voltage drops across long wires can reduce output, especially in high-current parallel setups. It is suggested to mount MPPTs close to the panels, alternatively opt for series set-up to minimize copper losses.

Check out this blog to discover the best panel placement strategies for your boat’s design and ensure minimal impact from shading.

Do I need more than one MPPT?

If your boat has multiple solar panels, instead of connecting all panels to a single MPPT, multiple controllers allow each group of panels to work independently, making the system more efficient.

Take, for example, a boat with panels on both the port and starboard sides. By connecting each side to its own MPPT, shading on one side won’t impact the other. On the other hand, if panels are combined into a single MPPT using a series-parallel setup, the system’s output can drop to match the weakest performing string, reducing overall efficiency. With multiple MPPTs, each panel group operates at its best giving maximum Ah to your battery bank.

How to Calculate Actual Solar Output for Your Boat

To estimate the real-world wattage from your solar panels, use the following formula:

Actual Output (W)= Panel Wattage × Peak Sun Hours × MPPT Efficiency × System Efficiency

Example Calculation:

Panel Wattage: 400 W

Peak Sun Hours: 5h

MPPT Efficiency: 95%=0.95

System Efficiency (wiring, heat, etc.): 90%=0.90

Actual Output in a day   = Panel Wattage x Peak Sun Hours x MPPT Efficiency x System Efficiency = 400×5×0.95×0.90 = 1710 Wh/day

With this calculation, you can now determine your solar system’s watt-hours (Wh) and evaluate additional loads can be powered with solar energy.

Maximizing wattage out of your solar investment requires understanding of sun hours, MPPT efficiency, panel locations and wiring configurations. Whether you’re designing a small setup or a complex multi-panel system, the right planning and components will ensure you make the most of your solar investment.

Ready to begin your solar journey? Explore Xantrex’s marine-grade solar panels or reach out to our team for personalized solar system design.

Solar panels are increasingly popular for powering boats, offering a clean and efficient energy source. However, their performance depends heavily on how they are wired. The choice between series, parallel, or a combination of both impacts the system’s voltage, current, and overall power output. Each method has unique implications, especially in the marine environment, where shading, space constraints, and wiring complexity play critical roles. Let’s dive into these configurations to help you make an informed decision for your boat.

Series Connections: When Voltage Matters

In a series connection, the positive terminal of one panel connects to the negative terminal of the next. This setup adds the voltage of each panel while keeping the current constant. For example, if you have four panels, each rated at 100W (20 volts and 5 amps), wiring them in series will produce 80 volts and 5 amps, resulting in a total power output of 400W.

Series wiring is ideal for systems where higher voltage is beneficial, such as when the panels are installed far from the charge controller. Higher voltage reduces energy loss over long wiring runs, making this configuration particularly efficient for installations where panels are located on the stern or cabin roof, with the charge controller placed near the battery bank.

However, the advantages of series wiring come with trade-offs. In a marine environment, shading is a significant concern. If one panel is shaded, the entire string acts as an open circuit and stops producing power, which could leave you without energy during critical moments. This makes series wiring more suitable for locations on the boat where sunlight exposure is consistent, and shading is minimal. This is why port and starboard side panels are usually connected in series and not connected with each other.

Parallel Connections: Resilience to Shading

In a parallel connection, the positive terminals of both panels are connected, as are the negative terminals. This configuration keeps the voltage the same as that of a single panel, while adding the current of each panel. Using the same four panels rated at 100W (20 volts and 5 amps), wiring them in parallel produces 20 volts and 20 amps, resulting in a total output of 400W.

Parallel wiring is well-suited for boats where shading is unavoidable. Unlike series wiring, a shaded panel affects only its own performance, while the other panel continues operating at full capacity. This makes parallel wiring a practical choice for setups with panels installed on areas prone to shading, such as near rigging, antennas, or sails.

Despite its advantages, parallel wiring comes with its own challenges. If one panel’s voltage drops due to degradation or shading, the entire system operates at the voltage of the weakest panel. For example, if one panel drops to 18 volts, the array produces 18 volts at 20 amps, or 360W—a noticeable loss in power. Additionally, the higher current in parallel systems requires thicker wiring to handle the load safely, which can increase installation complexity and cost, particularly on boats with limited wiring space.

Balancing Voltage and Current with Series-Parallel Connections

A combination of series and parallel wiring offers a balance between the benefits of both methods. This configuration involves wiring panels in series to increase voltage and then connecting those series strings in parallel to add current. For example, two pairs of panels wired in series (each producing 40 volts and 5 amps) can be connected in parallel to produce 40 volts and 10 amps, maintaining the total output of 400W.

This setup is especially beneficial in sailboats as the panels are exposed to varying sunlight conditions throughout the day. The panels on the port side may receive more sunlight in the morning, while those on the starboard side perform better in the afternoon. Wiring these groups separately allows you to maximize performance under changing conditions.

However, series-parallel configurations require careful planning. Panels within the same series string should have similar voltage and current ratings to avoid inefficiencies. Mixed panels with mismatched ratings can lead to significant power losses, as the system’s output is limited by the weakest panel in the string (check example below).

Properly grouping panels and using separate MPPT controllers can help mitigate these issues and optimize overall performance.

When it comes to wiring decisions, it must account for shading to maximize power output. Panels installed on opposite sides of the boat are often wired into separate MPPT controllers to ensure optimal performance under different sunlight conditions. This approach prevents shading on one side from impacting the panels on the other. Additionally, using corrosion-resistant wiring and connectors is essential for withstanding the harsh saltwater environment. Fuses or circuit breakers should be installed for each series string to protect against potential failures and short circuits, adding an extra layer of safety to the system.

Choosing the right wiring configuration for your solar panels depends on your boat’s layout, shading conditions, and energy requirements. By understanding different configurations and their implications, you can design a reliable solar system that meets your energy needs and withstands the challenges of the marine environment.

Ready to begin your solar journey? Explore Xantrex’s marine-grade solar panels or reach out to our team for personalized suggestions.

Solar power has become an increasingly valuable energy solution for boaters, offering a cleaner, quieter, and more reliable alternative to traditional power sources. As the marine industry moves toward more sustainable practices, solar panels are proving to be an effective way to enhance energy independence while reducing environmental impact. But what solar is right for your boat? Choosing the best solar panels involves understanding your energy needs, your boat’s layout, and the trade-offs between different options out there. Let’s explore all the options to choose the right solar for your boat.

Why Solar?

The appeal for Solar energy goes beyond sustainability—although using renewable energy is certainly a major advantage. Solar panels operate silently and have a long life. Once installed, solar panels require very little maintenance, allowing boaters to focus more on the journey and less on upkeep.

However, the switch to solar isn’t without its challenges. Space on a boat is often limited, and finding the right location for solar panels can be tricky. Shading from masts, sails, or rigging can reduce efficiency, and the upfront cost of a solar system might give pause. Yet, for many, the long-term benefits far outweigh the initial hurdles. Solar power enables energy independence, reduces reliance on marinas, and offers peace of mind that comes with a reliable power source.

What to Consider When Choosing Solar Panels

One of the first decisions in your solar journey is choosing between glass panels and flexible panels. Each has its strengths, making the choice a matter of understanding your boat and how you intend to use the system. Glass panels are highly efficient and incredibly durable, designed for permanent installations on flat surfaces like decks or hardtops. However, their rigidity can be a drawback for boats with limited or uneven space.

Flexible panels, on the other hand, offer unmatched versatility. Lightweight and bendable, they can adapt to curved surfaces, such as Biminis or canvas covers, making them ideal for space-constrained installations. They are also easier to install and remove, giving you more options for placement. While they may not last as long as their rigid counterparts, advancements in technology are narrowing the gap in efficiency and durability.

Durability is non-negotiable in the marine environment. Saltwater, constant movement, and UV exposure put any equipment to the test, and solar panels are no exception. Look for panels specifically designed for marine use, with corrosion-resistant materials and warranties that reflect their reliability. Finally, think about your energy needs. Consider how you’ll use the system. Are you powering a few lights and a fridge, or running a more complex array of electronics? Understanding your requirements ensures you don’t over- or under-invest in your solar setup.

Mounting Solar Panels: Finding the Right Fit

Where and how you mount your panels can be just as important as the type you choose. Decks and hardtops are popular for rigid panels, offering a stable, open surface for installation. Flexible panels, with their lightweight design, can be mounted on Biminis or canvas covers, making them a smart choice for boats with unconventional layouts. For those looking to maximize exposure to the sun, pole or rail mounts are an excellent option. These adjustable systems allow you to angle the panels throughout the day, although they may require more complex installation.

No matter the mounting method, the goal is the same: find a location that balances efficiency, accessibility, and durability. It’s worth taking the time to assess your boat’s layout and consider how the panels will fit into your overall energy plan.

How Solar Power Enhances Life on Water

The right solar panels can improve your boating experience. With a reliable power source, you can venture further and stay off-grid longer. Solar panels allow you to run essential systems like navigation equipment and refrigerators without worrying about draining your batteries. They reduce your reliance on fuel and generators, cutting costs and eliminating noise and fumes. And perhaps most importantly, they align with the values of eco-conscious boaters, providing a sustainable way to enjoy the beauty of the water.

Adding solar panels to your boat is about more than just energy, it’s about minimizing your impact on the environment, and creating a smoother, quieter journey. While challenges like space and shading require careful planning, the benefits of solar power make it an option worth exploring. Whether you’re considering rigid glass panels or flexible ones, the key is finding the solution that best suits your boat’s unique needs.

Ready to begin your solar journey? Explore Xantrex’s marine-grade solar panels and take the first step toward powering your adventures sustainably.