Solar panels have become an increasingly popular choice for off-grid power. They are silent, environmentally friendly, and have never been more affordable. However, learning about solar panels can be an intimidating task. The numbers and technical jargon can become overwhelming quickly, and the task of setting up even a basic solar power system can seem like a daunting task.
Luckily, solar panels and their associated components are quite simple, and setting up a solar array can be a surprisingly easy task. Books could be written about the technical specifications and physics behind each of these components. However, we believe that a brief overview of the basics is an important first step in learning about solar power. Here’s what you need to know.
How Do Solar Panels Work?
The operation of solar panels is incredibly simple. At their most basic, they are simply a panel that produces an electrical current when exposed to light. You may hear solar panels referred to as “photovoltaic” or “PV” panels, but these are simply different terms for the same device.
Unlike a gas generator, solar panels cannot power devices directly. Because the direction and intensity of the sun are not consistent, the output of a solar panel is accordingly unpredictable. Thus, a solar generator system is not just a solar panel. Rather, it is a charging circuit that provides power to a battery bank that you can then use to power your devices.
Explain The Numbers
There are a few key terms you need to know to fully understand the capabilities of a solar panel. The first is “watts.” A watt is a unit of power used to describe the intensity of an electric current, similar to how horsepower describes the output of a car’s engine.
Just as more horsepower will make a car move faster, more watts will make a battery charge faster. In the context of generators, the term “kilowatt” is also commonly used. This is merely a shorthand way of saying 1,000-watts.
Volts x Amps = Watts
If you delve deeply into solar panel specifications, you may also see their output described in terms of “volts” or “amps.” It is not necessary to get bogged down on the nuances here. Just remember that multiplying volts times amps results in watts. So if you see a solar panel listed as “20 volts and 2 amps”, you can immediately know it is a 40-watt panel.
The other consideration is “watt-hours”, which is used to describe the capacity of a battery. Going back to our car analogy, the “watt-hours” is a way of describing how many gallons of fuel can fit in the tank. The number of watt-hours in a battery is how many watts the battery can output for one hour. If you have a device that draws 100-watts of power, a 100 watt-hour battery could power that device for one hour. If the device only consumes 50-watts, that same battery could power it for two hours.
What Equipment Do I Need?
Now that you know the numbers, let’s take a look at the equipment you’ll need. As I mentioned above, a solar panel alone does not produce much usable power. Rather, the solar panels are the starting point that charges batteries and allows you to use that power to run your devices.
Of course, you will need solar panels for a solar charging system. But how much power can a solar panel generate? Solar panels come in an almost limitless variety of shapes and sizes. The smallest panels can be as small as 5-watts and are typically reserved for powering a few lights or a cell phone. At the other end of the spectrum, the panels that make up a larger solar array are typically between 100 and 200-watts.
Panels of this size are typically fairly large; about 24”x48”, or the size of a cornhole board. A comprehensive off-grid system can easily consist of many of these panels for a total output of 1,000-watts or more. However, it should be noted that the rated output of a panel reflects its maximum output in direct sunlight. Thus, asking “what is the output of a solar panel” will depend on the specific sunlight conditions.
Solar panels come in a few different form factors as well. Although the large glass-fronted “rigid” panels are the most common, flexible solar panels are becoming increasingly popular. Further, foldable panels are a nice option for anyone looking for a more portable setup. Thankfully, all of these designs have similar efficiency, so simply choose the shape and design that is best for you.
Solar Charge Controller
The next component you’ll need in an off-grid solar system is a solar charge controller. This is a device that takes the variable and unregulated power of the solar panels and converts it into a consistent signal that can be used to charge batteries.
These devices range from very simple and inexpensive to quite complex. There are two main types, and the best version for you will depend on your needs and budget.
Pulse Width Modulation (PWM)
The most common form of a solar charge controller is a PWM-style unit. These units are very compact and affordable, often costing less than $20. For a basic solar setup where peak power efficiency is not crucial, these are a fantastic option. However, its efficiency is not ideal.
PWM controllers rely on the entire panel being exposed to even sunlight. If the panel becomes partially shaded or unevenly powered, a PWM controller will only be able to charge at the rate provided by the most shaded portion of the panel. In short, you will always be limited by the weakest link in the chain.
For occasional power, PWM units are more than sufficient. Further, they work well in areas with more direct sunlight and fewer trees, such as many areas in the western United States. However, for shady or cloudy regions, they can pose a significant limitation.
Maximum Power Point Tracking (MPPT)
Maximum power point tracking solar charge controllers represent the most efficient solar charge controllers. As the name would suggest, these controllers can optimize the charging rate based upon the area of the panel that is providing the most power. Thus, even if a panel is partially shaded or dirty, it can continue to produce power at a reasonable rate.
However, they are also a more costly option. If you want to design a system that works in a wider variety of conditions, or that provides power as efficiently as possible, choose an MPPT controller.
The batteries are likely to be the most expensive aspect of your solar power system. However, they are also the component that will likely have the largest impact on the usability of your solar generator system. Thus, it is important to understand the meaning behind different types of batteries and their capacities.
As mentioned above, a battery’s capacity is measured in watt-hours (or amp-hours, depending on the manufacturer.) Your solar system will not be able to actively charge at night or during overcast conditions, so your system will rely entirely on your batteries for power during this time. Therefore, your batteries must provide enough reserve capacity to provide power during these less sunny periods.
A lead-acid battery is the most common type of battery found under the hood of a car. These batteries are inexpensive, but they are heavy and have relatively low capacity given their size. More importantly, they do not respond well to being discharged repeatedly.
Many lead-acid batteries are only capable of being discharged five or six times before being replaced. Further, you can only safely discharge them to 50% of their rated capacity without risking permanent damage. For these reasons, lead-acid is not a good choice for a solar system.
Absorbed Glass Mat (AGM)
AGM batteries are also commonly used as car-starting batteries. However, they use different chemistry which allows them to be discharged more times without damage. Like lead-acid, AGM’s are heavy and have a relatively small capacity. Yet, they are comparatively affordable. If you are designing a system with a strict budget in mind, AGM’s are a good option.
Lithium Ion or Lithium Iron Phosphate
Lithium-Ion or Lithium Iron Phosphate are two distinct types of batteries, but they have similar properties. These batteries are commonly used in cell phones or electric cars. Compared to other options, they are lightweight, capable of many discharge cycles, and have excellent energy density.
The downside is that they are the most expensive option, and they can require an additional battery management system. It is important to do your research to use this style of battery safely. However, if you want the most capable solar system, this is the right choice.
The final component in a solar charging system is the inverter. The inverter is a device that takes the direct current power from the batteries and converts it into 120-volt alternating current (AC) power that can be used by household appliances. Less expensive inverters produce a signal known as a “modified sine wave”, and some electronic devices do not accept this signal. Thus, the best inverters are “pure sine wave” models.
Inverters are available in almost any imaginable size, from 100-watts up to 10,000. However, a 1,000-watt inverter will be sufficient for most purposes. If you intend to run a more energy-hungry device such as an induction cooktop or window air conditioner, consider purchasing at least a 2,000-watt inverter.
How Much Can I Power?
As you would expect, the amount that you can power from a solar charging system depends significantly on the specific components of your setup. If you have a large array of panels but a small battery bank, you may be able to power a lot of devices but only when the sun is out. Solar energy requires careful monitoring of your consumption and the capacities of your system.
However, it is fairly simple to calculate your needs. Create a list of all the devices you anticipate powering, and determine how many watts they consume. If the power consumption is not listed on the device, it is easy to find a “power consumption table” on the internet. Then, multiply the wattage of the device by how many hours per day you intend to use it. Some devices, like a cooktop, require a lot of power but may only be used for a few minutes a day. Thus, simply knowing the wattage doesn’t paint a complete picture.
Let’s Look At The Limits Of A Few Common Setups
25-Watts of Solar
Many small solar systems have 25-watt solar panels and around 150 watt-hours of battery storage. With this setup, you would be able to charge a cell phone, run several LED lights.
100-Watts of Solar
The most common size of a solar panel is a 100-watt unit. Let’s assume a simple and affordable set up by coupling a 100-watt panel with a single AGM battery, providing about 500 watt-hours of storage With this setup, you would be able to reliably power a small 12-volt refrigerator, a laptop, several LED lights, and a small TV.
500-Watts of Solar
Many larger RV or van setups have around 500-watts of solar panels, with around 1200 watt-hours of battery storage, typically from lithium batteries. With this setup, you would be able to reliably run an induction cooktop, a coffee maker, and as many laptops, phones, lights, and gadgets as you would like.
Is There an Easier Way?
Building your own solar system can be a good way of having a system that perfectly suits your needs, but it can also be a complex endeavor. Thus, all-in-one solar generators are becoming increasingly common. There are many brands of these, including Goal Zero, Jackery, Bluetti, and many more.
These devices combine a solar charge generator, batteries, and an inverter, allowing you to have a one-stop solution. By simply adding solar panels, you can have a simply off-the-shelf device that handles the entire process for you.
As you can see, answering the question “how much power can a solar panel generate?” can be a difficult question to answer. The panels are simply the first step in a chain of energy storage and conversion, and the amount of power you can produce depends on the interaction of each component.
Thus, by knowing the solar panels power output, you will know how quickly your batteries can recharge, but not necessarily how many devices you can power. Thankfully, the systems become fairly simple once you know the basics, and many all-in-one solar generators are available to ease the process.