Whether you’re an experienced camper or a novice, you likely know that portable solar panels have become essential for most camping trips.
Types of Portable Solar Panels
Before diving into the specifics, let’s explore the different types of solar panels available. Currently, the market offers three main types: hard-frame folding panels, which were the first portable solar options introduced, and the newer mat and blanket-style models.
Hard-Frame Folding Panels
When first introduced, hard-frame folding solar panels were revolutionary, but they were also bulky and inefficient by today’s standards. These panels originally comprised two banks of cells, hinged in the middle for folding, and were encased in a thick aluminum frame with a sheet glass front. This design made them fragile, inflexible, and extremely heavy (over 25 kg).
Modern hard-frame panels are thinner and lighter than their predecessors but still have significant drawbacks. Their relatively large folded size and lack of flexibility make them cumbersome to store and susceptible to damage during travel.
Solar Blankets
Solar blankets gained popularity around 2015, thanks to their innovative design that made portable solar power accessible to a wider range of campers. They remain one of the most popular options today.
Solar blankets are made up of smaller banks of cells, typically arranged in a 2×5 or 3×4 configuration. These cells are coated with durable materials like PET (for cheaper models) or ETFE (for higher-quality models) instead of glass and are stitched into a canvas outer layer.
Weighing less than half of the old hard-frame panels and having a much smaller folded size, solar blankets are easier to transport, set up, and ideal for long-distance travelers where storage space is limited. The absence of glass also makes these panels more resistant to accidental damage.
However, a key disadvantage of solar blankets is the difficulty in positioning them at the optimum angle for maximum solar radiation. Typically, they are placed on a windscreen, bonnet, roof rack, or on the ground. Ideally, the solar cells should be positioned at a 15 to 40-degree angle and rotated throughout the day to ensure they face the sun directly.
Solar Mats
Solar mats are the latest innovation in portable solar technology, combining the best features of both hard-frame panels and solar blankets.
Typically, solar mats consist of 3 to 4 banks of solar cells mounted on a semi-flexible baseboard. Similar to solar blankets, the cells are coated with durable materials like PET or ETFE, allowing them to flex slightly without damage. These cells are also stitched into a canvas outer layer.
The primary difference between solar blankets and solar mats is the folding design. While solar blankets usually have a 2×5 or 3×4 configuration, solar mats fold in only one direction. This design adds some rigidity and makes them more suitable for free-standing setups. To facilitate this, solar mats often come with built-in legs that help achieve the optimal angle for maximum sun absorption.
Solar mats maintain the lightweight characteristics of solar blankets. Although they are a bit bulkier to store, they are far less cumbersome compared to hard-frame panels.
How Do Portable Solar Panels Produce Power?
Portable solar panels generate power by capturing the sun’s rays and converting them into usable energy through a device known as a charge controller or regulator. This controller then connects to a battery to keep it charged.
What Is a Solar Regulator?
A solar regulator ensures that the power generated by a solar panel is efficiently and safely transferred to a battery, taking into account the battery’s chemistry and charge level.
High-quality regulators are programmed with a multi-stage charge algorithm (usually 5 or 6 stages) and offer different programs for various types of batteries. Modern, advanced regulators include specific programs for lithium batteries, whereas many older or more affordable models may only support AGM, Gel, and Wet cell batteries. It is crucial to use the correct program for your battery type.
A good solar regulator also includes a range of electronic protection features to safeguard the battery. These features typically include reverse polarity protection, short circuit protection, reverse current protection, overcharge protection, transient overvoltage protection, and over temperature protection.
Maximum Power Point Tracking (MPPT)
Maximum Power Point Tracking, or MPPT, regulators can convert excess voltage into additional current under optimal conditions.
An MPPT controller continuously monitors the panel’s voltage, which fluctuates based on factors like panel temperature, weather conditions, and the sun’s position. It calculates the optimal combination of voltage and current using the full voltage from the panel, then adjusts (downrates) the voltage to match the battery’s charge voltage, thereby delivering additional current to the battery (since power = voltage x current).
However, there’s a significant caveat that limits the practical effectiveness of MPPT controllers with portable solar panels. To benefit from an MPPT controller, the panel voltage needs to be at least 4-5 volts higher than the battery’s charge voltage. Given that most portable solar panels have a maximum voltage of around 18-20V, which can drop to 15-17V when heated, and most AGM batteries operate between 12-13V and most lithium batteries between 13-14.5V, the voltage differential is often insufficient for MPPT functionality to significantly impact charge current.
Types of Solar Cells
The two most common types of cells used in portable solar products today are polycrystalline and monocrystalline. A third type, amorphous or thin-film, is occasionally seen but much less popular because it requires about double the surface area to produce the same amount of power and tends to be less durable. However, it is more stable at very low and very high temperatures. Here, we’ll focus on the more popular polycrystalline and monocrystalline types.
Polycrystalline
Polycrystalline cells are made from multiple silicon crystal shards that are melted together to form a block or ingot. This block is then sliced into very thin wafers, measuring about 200-350 micrometers in thickness, which form the basis of the solar cell.
If you look closely at a polycrystalline cell, you will notice a ‘metalflake’ appearance where the different crystals have joined. Electrons can become trapped at these joins, reducing the flow of electricity and lowering the panel’s efficiency.
Polycrystalline cells are cheaper than monocrystalline cells but are not recommended for portable solar applications as they require a larger surface area to produce the same amount of power.
Monocrystalline
Monocrystalline cells are made from a single silicon crystal, which is grown into a block and then cut into wafers in the same manner as polycrystalline cells. Because the cell is a single crystal, electrons can flow more freely, significantly increasing the panel’s efficiency.
Monocrystalline cells have a much more uniform appearance, lacking the metalflake characteristic of polycrystalline cells. Due to their higher efficiency, they require less surface area to produce the same amount of power as an equivalent polycrystalline cell.
Additionally, monocrystalline cells tend to have a longer lifespan and perform better at higher temperatures.
What Does the Panel Efficiency Rating Mean?
A solar panel’s efficiency rating indicates how effectively it can convert solar radiation hitting its surface into usable power.
Solar radiation reaching the top of Earth’s atmosphere averages about 1,361W per square meter. As it travels through the atmosphere, it attenuates, resulting in 1,000-1,050W hitting the Earth’s surface at sea level on a clear day.
For example, if a solar panel has an efficiency rating of 20%, it means that under ideal conditions, it can convert 20% (or approximately 200W) of that radiation into power for every square meter of surface area.
In practice, several factors affect the actual percentage of total solar radiation captured by a solar panel. These include the overall quality of the manufacturing process, the quality of anti-reflective coating used, and the angle of the radiation source relative to the panel.
How to Position Solar Panels
Many campers suggest that placing your portable solar panels at a 30-degree angle is optimal. While this is a reasonable approximation in many cases, the correct positioning is a bit more complex. The optimal angle primarily depends on two factors: the latitude of your location and the time of year.
In ideal conditions (i.e., during warmer seasons), the angle of your solar panel should closely match the latitude of your location.
Using Solar Panels in Partial Shade or Cloudy Weather
You can use portable solar panels in cloudy weather or partial shade, but their output will be significantly reduced compared to ideal conditions. A 200W panel might produce up to 11A or more per hour in optimal conditions, but this can drop to 3A per hour or even less in full cloud cover or adverse weather.
Solar as Part of a Dual-Battery System
Portable solar panels are increasingly used as part of dual battery systems. While fixed solar panels mounted on a vehicle’s roof are a popular choice, more campers are opting for portable solar panels. This is because, to maximize the benefit of fixed solar panels, you need to park your vehicle in the sun, which isn’t ideal for comfort. With portable solar panels, you can use an extension lead to position them up to 5-10 meters away from the vehicle, allowing you to park in the shade.
Most modern DC-DC chargers include an input for a solar panel and can intelligently switch between charging from the alternator and charging from solar, depending on whether the vehicle’s ignition is on and if the alternator is delivering sufficient voltage.
One caution: DC-DC chargers usually have their own built-in solar regulator. If your portable solar panel has its own regulator, you must disconnect it before connecting the panel to the DC-DC charger.
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