How to Size a Portable Solar Charger

Solar panels give you the benefit to recharge your batteries without being near a power source. As long as you have sunshine you can recharge. This is especially when you camping in the outdoors. But how much power does a portable solar charger produce and which ones can be reliable for what you intend to use them for?

This is a challenging question to answer because the number of watts you need depends on so many factors . We look at what solar charger wattages and voltage actually mean for you. We also look at the other factors you need to look out for when choosing a portable charger and why its important to add a battery pack.

How to Size Solar Panel Power

Power Wattage in the Case of a Solar charger is the expected is Power output from a panel. They are normally rated by the direct current power produced in standard test conditions. The label of the Wattage on the panels is theoretical under ideal testing conditions with our assumption of 100% efficiency. Some are also labeled with the Solar Panels Capacity, Wattage, and Power output. But the power output is the most important to look out for. The STC rating is given by the power wattage given under lab conditions, while PTC is from the manufacturer from the technical equipment specifications. PTC is usually 10-15% lower compared to STC.

Portable Solar Panels range from the Smallest 5 watts to the highest which can go up to 200 watts. This also dictates the price and would range from $20 to $500, depending upon the brand and additional features. The wattage of the panels is indicated and this can guide you in choosing the best use such as heavy-duty or light, mobile, and either single outlet or multiple outlets.

A phone needs 3watts to 5watts of power to charge while an iPad would need around 11 watts. However, if you pick the 5 watts charger for your phone it may not be dependable as this will drop drastically due to inefficiency and won’t fully charge your cellphone on cloudy days. Solar chargers are tested at STC (Standard Test Conditions) at a humidity of around 1.5 and ambient temperature 25 degrees Celsius and are flashed with 100 watts of light. These tests provide a theoretical maximum rating that will not simply work in real-world conditions.

To get the wattage of a Solar Panel you simply multiply the Rated Amperage with the Voltage (This may be accurate in some instances)

Example 3A x 5V = 15 Watts

A solar charger is easy to use and you have just to leave the charger around in the sun to charge. Dispersed light is better for solar panels than direct sunlight or sunlight at an angle and a panel can exceed 30% efficiency with dispersed light. Solar Panels can be used to charge all types of Batteries regardless of Voltage. But when selecting a Solar Panel it is important that you match up Wattage and Voltage in order to get the best results.  


Solar panels should have a higher rated voltage than the battery this is because the panel’s voltage may drop in case of bad weather and may not charge the batteries. For example a 12v battery system this however does not mean that you should get a 12v Solar panel. The A panel rated between 16 and 19.5 volts will ensure the battery is continually charged.  A voltage system below 21 volts also ensures that you avoid electrical shock.

Matching Wattage to Use

Solar panels come in all kinds of shapes, sizes, and weights. The general rule is that the bigger the panel the more that wattage but that’s not necessarily true. Two panels of the same size can have a very different output in the same conditions. This mostly goes down to the technology and efficiency which we’ll discuss later in this article.  

Phone Charger

A solar-powered cell phone charger is a charging system for your phone that operates on solar energy. This type of cell phone charger is easy to use and is portable, so it is great for people who like to travel a lot. There are two types: Direct Charger and the Power bank Charger With a solar charger, you can be sure to have power available to your cell phone whenever you need it. It does not matter how far away from the city and the electricity you get. If you own a solar charger you will be able to power your cell phone at all times. Phones usually come with inbuilt charge controllers so it is safe to use directly.  

Laptop Charger

The handy solar laptop chargers come in different sizes, weights and shapes and even with their cost. This might cost you, but simply think about the help that it could provide for you such as free energy and a long period of employment. A 60 Watt Monocrystalline Solar Charger will be sufficient for this purpose. It is also important to make sure you match the voltage for you laptop. Furthermore, the usage of this charger is not for laptop alone, it can also be use to charge electronic devices like the mobile, GPS systems, iPods, camcorders, PDAs and even to jump start an automobile during emergencies. Using a Laptop on the Outdoors Using this kind of charger is considered as handy due to it has less wiring and cabling. There are two types of solar battery available in the market. Both of these compact and user friendly but the selection will depend on your preference as well as your budget. There is a kind of solar laptop charger that you can also fold and there are ones which is a hard case type and bring it safely. With this kind of solar panel charger, you only need to click the shut button if you are not going to use it. This will surely eliminate the chances of damaging the solar panel itself.  

Solar Panels for Power Stations

Portable power stations are basically large batteries that can be used to charge devices while they’re being used or when they’re not connected to an outlet. They’re great for camping trips or emergency situations where you might need power but don’t want to rely on your car battery or outlets. Solar panels charging a power station The size of solar panel you need to charge your portable power station will depend on the size of the power station itself. If it’s a small one, like the Goal Zero Yeti 400, a 100W solar panel will be enough. If you have a larger one, like the Yeti 1400, then you’ll need something bigger

Battery Chargers

Solar Chargers can be used to charge batteries or to keep them maintained.Simple Solar Chargers can supply constant voltage or current to the battery being charged without altering its output based on time or the charge on the battery. Another solar charger fit for all-day use is a trickle charger that is simple in terms of power consumption. This charger charges a battery slowly so you can leave it for prolonged hours without spoiling it compared to other battery chargers. If you are looking to solar charge an RV or cabin, this is what you want to start with. This package should include a solar panel, Charge Controller, mounting brackets, an adaptor kit and tray cables. This panel can charge a 50Ah Battery from 50% in 3 hours in direct sunlight. Used to charge deep cycle SLA, Gel or flooded batteries.   Other Size considerations for Your Solar Charger  

Width and length

Manufacturers of Solar Panels use standard sizes to build solar panels used in roof systems in homes and businesses. For residential solar panels, you expect to find them measuring about 65 inches by 39 inches and those on the commercial side are a bit longer going up to 77 inches by 39 inches. Though the width and length slightly vary, many organizations manufacture these systems in standard sizes. The size used for the residential connections is 65 inches by 39 inches. On the other hand, for commercial use is 77 inches by 39 inches. Now on the portable solar chargers that are now more popular nowadays, the width and length are up to the discretion of the manufacturer and use of the panel. You can find a 1cm panel on a calculator, or 2 by 2-inch panel on a solar light while most portable solar chargers will come at around 11.1 × 6 inches.


The solar panels’ depth normally ranges between 1.5 inches to 2 inches with portable ones having a depth of 0.71 inches. Again this is also influenced by the technology used.


Solar panels used in roofing systems typically weigh around 40 pounds and some can go up to 50 pounds for a 300 watt panel. This is because of the additional framing used to mount the solar panels to the roof. For a portable system, you can’t be carrying around 40 pounds to use for the outdoors. But typically 50-watt panel would be 3 to 5 pounds. 7.2 Pound Solar Charger

The solar cells numbers

The cells are the electrical devices that convert sunlight into power. To produce a significant amount of power, these cells are together connected to a solar panel. The 60-cell modules are the typical standard for home applications; however, slightly large commercial solar panels have about 72 cells. Sunpower which is a leading manufacturer of Solar Panels uses about 96 cell panels which their panels one of the most efficient in the market. Solar Panel Cells  


All electrical equipment is inefficient and loses power to resist and in the form of heat, but solar panels are notoriously inefficient. And by “efficiency” we the rate at converting sunlight to electricity or the “sunlight conversion rate”. This rate can be anywhere from 5% to 10% but the technology continues to improve with modern solar panels having a sunlight conversion rate of up to 21%.

Thin Film Vs Mono-Crystalline

The most common types of Solar Panels you will find in the market are the thin film and Mono Crystalline types. Thin-film solar panels have better efficiency, occupy less space, and weigh less. Thin-film panels also perform better at high temperatures and can maintain efficiency when it’s hot. Monocrystalline solar panels have a small advantage in colder conditions and shady conditions. They also maintain Efficiency over time while Thin Film Panels tend to decline over time.


A foldable solar panel allows you to save up space – one that folds up to a suitcase with a handle allows you to move around with it just as you would a briefcase.  This allows you to move it around and make sure you mount the panels where there is a lot of sunshine. A Full size 54.4 inches by 19.9 inches 100-Watt solar panel can be folded to half size of 27.2 inches by 19.9 inches. Since the panels are folded up into a case you just need to unpack them from the case, unfold the panels and adjust the tilt legs and set them on the ground facing sunlight.

Add a Power Bank with your Solar Panel Charger

A Power Bank takes the unstable solar panel input and converts it to a more stable DC output which can be used to charge your gadgets with minimal disruptions. Low-capacity power banks, like 5000mAh or even 10000mAh for small devices like mobile phones or tablets. In general, these units are capable of recharging your phone two times from 0% – 100%.

The smaller ones around 2000mAh cannot recharge your device completely but they still contain enough power to give it a bit of energy while on the move. You can easily make out how much battery capacity a power bank contains from its size or weight.

The more powerful ones range from typically around 10,000mAh to 25Ah and upwards. At this level you might be able to charge your laptop with them if it’s not too big of a model (and requires around 55W at most). Some models come with a second USB output to power another device while charging itself via solar panel or wall socket.

You could even use two connected ones in series to get more energy for something like an electric scooter or bicycle, though normally these packs have enough juice already even for bigger applications like laptops.There are also some bigger units with a whopping output of 25000mAh and more. These might be big and heavy but they can definitely handle your laptops, not to mention keeping it running for some hours (not very long if you’re using it at the same time).