Solar Panels Connected in Series/Parallel
In this information blog, we will try and help you understand how to connect solar panels together, in parallel or series, as both have very different outcomes regarding the voltage and current output from the solar panels. Several solar panels connected together is known as a PV array.
Please note: This blog is more technical than previous blogs but we will try and break it down.
Here we go
Before we start the technical bit you need to know the following:
Solar panels can be connected in series or parallel to increase voltage or current depending on the battery configuration charging requirements.
Connecting in series basically means you connect the panels together in a single line i.e. the positive of the first panel is connected to the negative of the next and so on. This increases the final voltage.
Connecting in parallel is where you have all the positives together from your solar panels connected as one to your controller and also all the negatives connected as one to your controller. This increases the final current.
We measure the solar panel output in Watts (W) or Watt hours (Wh), this is the amount of energy in Watts the solar panel can generate in an hour in standard test conditions (STC)
A point to note: No matter which way you connect your panels they won’t give you any more than the rated power for that panel.
Technical / Mathematical bit
By connecting your panels in series or parallel you will keep the original Watt hour rating the same. So if four 100w panels are connected in series or in parallel the energy produced (Watts in this case 4 x 100w = 400w) will remain the same.
The Watt hour rating is a product of volts multiplied by amps (Vmp x Imp) on the solar panel data plate (normally found on the back of your solar panel) you will find the Vmp (Voltage maximum peak) and Imp (Current maximum peak) these figures are taken at STC (Standard test conditions) and once multiplied together will give you the watts of that panel.
You will also find on the data plate Voc (Voltage open circuit) and Isc (Current short circuit) the solar panel rating (Watts) cannot be calculated by multiplying Voc and Isc, these values are not generated in practical working conditions.
However we do used them when designing a system to understand what the max voltage, and current available from the solar panels could be when deciding what solar controller you will require.
The connection principle is the same as the connection of batteries wired for series or parallel.
The system voltage can be increased by connecting in series, the current production can be increased by connecting in parallel.
The charge controller you choose will need to be rated to tolerate higher voltages and currents depending on how you’re looking at connecting them together.
As a general rule of thumb, all panels in the installation are best to be rated at the same voltage, wattage, and preferably the same brand as each other. Varying panels can be used, but unequal voltage and wattage ratings may lead to inefficient energy production and poor battery charging.
All cables and links need to be the same cross-sectional (CSA) area and length, and of a sufficient CSA to carry the current this will ensure that the circuit resistance, (Installation circuit impedance) and system losses will be kept to a minimum.
Solar Panels connected in Series
Fig 1 shows four solar panels connected in series; this will increase the system voltage. The solar panel Voc multiplied by the number of panels connected in series; this can be termed as a string voltage.
As can be seen in Fig 1, four solar panels with a Voc of 23.76 connected in series will give a system voltage of 95.04V (23.76 x 4) The current Isc will remain at 5.45
Fig.1. Four solar panels connected in Series
Solar Panels connected in Parallel
Fig 2 shows the same four solar panels connected in parallel, this will multiply the amount of current produced.
Four solar panels with a Voc of 23.76 connected in parallel will give a system voltage of 23.76 (23.76 x 1) The current Isc will increase to 21.8 (5.45 x 4)
Fig.2. Four solar panels connected in Parallel
So, I hear you ask, what is the best way for me to connect up my panels on the roof of my caravan/ motorhome/ boat etc.?
Well this all depends on many different things but the type of charge controller you have (yes we will do a blog on that one day) is the main reason to choose your connection method.
If you have an MPPT charge controller that can cope with the higher voltage, use the serial way to connect up your panels. If you have a PWM charge controller, it can’t efficiently utilize the extra voltage so as long as it has a current rating that can cope with the extra current, use the parallel way to wire up your system.
Personally from my point of view the series way of connecting the panels is generally the best if you have an MPPT charge controller that can cope with the higher voltage.
What this means is the higher voltage of connected panels will keep your controller alive and charging the battery more often than not. I.e. the controller isn’t hitting its low voltage point as early and shutting down the charging of the batteries.
If you have any questions about this blog or just want to understand more about solar panels, then contact us.
Connecting Multiple Solar Panels – Series vs. Parallel
To design a solar PV system for any household, it is necessary to consider several parameters like the available solar resource, amount of power to be supplied by the system, solar panel efficiency, autonomy of the system (off-grid or connected to the grid) as well as the selection of components like inverters, batteries and controllers.
Beyond the analysis of these components, there is another element that can deeply influence the total power output of the system and can also affect the overall cost of the solar installation. It is the connection of solar panels.
We often hear the installers talking about the connection of solar panels in series or parallel, but many of us not related to the technical terms do not understand the difference between these designs, and therefore, do not understand the impact our decision has on the overall life-cycle of the system.
In this article we will help you determine the best way to connect solar panels and describe general design options of the series and parallel connection of solar panels with their advantages and disadvantages.
The first thing that you must know is that in any power system the variable that matters the most is the active power (expressed in watts). Why? Because all electrical devices consume the active power to function.
The equation that determines this variable is P=VI, where ‘V’ is related to the voltage and ‘I’ is related to the current. These are the only variables that allow to modify the power output of a solar system, keep this in mind as it will be important later.
To obtain the desired active power, there are three ways of connecting multiple solar panels together to create a power system that provides solar electricity to your house.
- connection in parallel
- connection in series
- a combination of the two (series-parallels)
The decision of one or another solar panel connection will depend on the desired output and application of the system.
Connecting solar panels in parallel
Wiring solar panels in parallel implies connecting positive terminals of each panel together and wiring the negative terminals of each panel together as well. Then, they are connected to the charge controller or to the inverter of the solar system.
When solar panels are connected in parallel (known as arrays) they all share the same voltage, and the current that each one of them provides is summed up.
The main advantage of this configuration is reliability. In case when one or more solar panels are affected either by shading or by other damage caused during the manufacture or along the life-cycle of the system, the performance of other solar panels in the array is not affected because the wiring connection makes every single unit independent from the other one.
On the other hand, there are some disadvantages of this connection type. Low voltages denote higher current values, which translates into higher electrical losses (power losses are related to the square values of current), and therefore, lower efficiency performance of your solar photovoltaic system.
Besides, increasing the current is not desirable either because it implies an increase of wire gauges in order to have better capacities for enduring higher ampere values (associated with higher temperatures and therefore security issues). In the end, this translates into higher installation costs due to the bigger size of the cables and also due to an increase in the length of the cables to be able to perform the connection .
When should the installation be done in parallel connection?
The answer is relative, but in most cases, we assume that the system is very small and is meant to supply low loads, or has a battery set to a low voltage design (12 Volts, for example).
Connecting solar panels in series
The series connection is done by wiring the positive terminal of each panel to the negative terminal of the next panel (a connection similar to the ones of the Christmas lights) until the final panel is connected to the charge controller or inverter.
In the series connection the voltages of all solar panels are summed up and the current is maintained the same for all the panels. The set of solar panels connected in series is known as a string.
As stated before: lower voltages imply higher currents and higher voltages imply lower currents.
This statement is very important for series connection, because as this configuration increases voltage values with every added panel, then, the overall current provided by the system will be lower.
This translates in savings due to lower wire sizes and cable length, and also in higher efficiency of the PV system (lower electrical losses).
However, the main disadvantage of this configuration is low reliability of the system when connected in series. In other words, as the whole system is connected by one single cable, if the cable fails then all the system will be affected.
When one of the solar panels in the string is shaded, whether by a tree or a Cloud, the overall performance and efficiency of the system is affected.
Shading can even become a bigger problem in this configuration because a shaded part creates resistance in the current flow. This effect creates so called hotspots. Hotspots are sections with increased temperature, and depending on the wiring and the system size can even represent a security problem.
When should the series connection be used?
Generally, when higher voltages are desired, the logical solution is the series connection.
Besides, when the distance between an inverter or charge controller and solar panels is long (20 feet or more), it is advisable to use the connection in series because this type of connection allows to increase the voltage of the system to meet the voltage input of the inverter.
The series connection has its issues as stated before, but the shading and efficiency problem can be solved by using one of these two considerations:
- The first one is related to the efficiency. Selecting a micro-inverter for each panel provides the best solution to achieve maximum efficiency, as every panel will be independent from the other one . Therefore, shading of one panel will not affect the overall power output.
- The second option is to buy solar panels with a bypass diode. This diode acts as a wall that blocks or isolates the shaded area of the panel in order to avoid efficiency losses of the rest of the same panel, and therefore of the entire power system .
Unfortunately, the reliability issue cannot be solved, as it is an intrinsic property of the connection itself.
We have described the advantages and disadvantages of the series and parallel connections of solar panels, but what happens when we combine them together?
It is often necessary to establish the connection according to the voltage and the current input range of an inverter or a charge controller.
But in some cases it is not possible to achieve the required voltage and current range through the implementation of a series or parallel connection on its own.
In case of series connection, voltage limit could be exceeded. And in the parallel connection, current limit could be exceeded while at the same time not supplying the maximum possible active power of the configuration .
That is when a combination of the two connection types is needed.
The idea is to establish strings (series connection of two or more panels) and connect them in parallel with other strings (creating arrays of strings). This allows to obtain the advantages of the series connection (lower electrical losses and lower costs) and the benefits of the parallel connection (reliability).
In other words, each string of panels will add a current and will also be independent from the performance of another string, while at the same time obtaining higher active power with higher voltage and lower current values (desirable due to security measures).
In this configuration creativity is the rule of thumb, as with the same number of panels, multiple design options can be created that adjust to the purposes of the homeowner or to the specific requirements of the power components.
Combining solar panels with different electrical characteristics
There is another important topic related to the selection of one or another type of connection in the solar PV system.
Do your solar panels share the same electrical characteristics?
So far we have assumed that your system contains a set of very similar or equal solar panels, meaning the same manufacturer, same electrical efficiency and characteristics (voltage, current and active power).
But what happens if you decide to connect different solar panels?
Remember the intrinsic characteristics of each type of connection, the parallel connection forces all the system to have the same voltage and the series connection forces all the system to have the same current.
Consider having a set of four solar panels: three panels of 12V and 3A and one panel of 9V and 1A.
If you connect these four panels in parallel, all of them must have the same voltage, and therefore, will generate at the maximum possible voltage for one of the panels, which means 9V.
Ptot = P1 P2 P3 P4 = 9V (3A 3A 3A 1A) = 90W.
When you take a look at the expression P=VI, you realize that the input of each panel will be dropped in voltage (instead of the output voltage 12V, you obtain only 9V output for each one). This phenomenon influences directly the overall efficiency of your PV system, because you are underutilizing the total capacity of the panels and therefore increasing the marginal cost of your system.
Now, let’s suppose that you connect the same panels in series, the same problem is presented. You will sum up the voltages but the current will be the lower one.
Ptot = P1 P2 P3 P4 = (12V 12V 12V 9V) (1A) = 45W.
As you can see, the obtained power output is very different from one configuration to the other, and if solar panels had been selected equally, then, the total active power would had been Ptot= 144W for any of the two configurations.
Therefore, it is not advisable to combine solar panels with different specifications, because low performance and underutilization will affect the system.
Even selecting solar panels from different manufacturers with the same electrical characteristics is not advisable because besides the rated power, each panel has its specific power degradation percentage which is never the same among different manufacturers. In the long term, you will have some panels degrading at different rate than other. This presents instability and could also lead to higher electrical losses.
But always remember that the major decision makers to establish the type of connection that your system should have are:
As you can see, the selection of one or another connection type is supported by the deep technical analysis, and the range of possibilities can be very wide if the system is large enough.
Series vs. Parallel connection of solar panels, how do you choose?
When you choose the solar system to generate electricity, you have many solar panels in your hand. Suppose you want these panels to generate electricity efficiently for your house, RV, or other electrical equipment. How do you choose the connection method? You should know that different connection methods will bring different power generation effects. However, when multiple solar panels are connected, you have two choices: series connection and parallel connection. Deciding which way to join depends on the conditions and environment under which you use the solar system. Next, let’s see which method is most suitable for you.
Series connection of solar panels
What is the series connection of solar panels?
A significant point: when solar panels are connected in series, their voltages are added together, and the current remains constant. Here is a simple example:
What conditions are solar panels connected in series?
Suppose you are in an environment with sufficient light intensity, and the solar panels are less likely to be blocked. In that case, consider connecting them in a series. Because in series mode, each meeting will affect the whole system’s power output.
In addition, the series connection is also a good choice if you want a low-current system. Because the solar panels are connected in series, the current is constant. The lower current allows you to use smaller wires, which are cheaper and more accessible.
Finally, when you connect the solar panels in series, an additional important tool is the MPPT charging controller. It is mainly used to adjust the voltage and current of the solar panel, adjust the current to a suitable size, and prevent sacrificing the power of the solar charging panel.
Parallel connection of solar panels
What is the parallel connection of solar panels?
A significant point : when solar panels are connected in series, their current is added together, and the voltage remains unchanged. Here is a simple example:
What conditions are solar panels connected in parallel?
Suppose you are in an environment where the sunlight is occasionally blocked, and the solar panels often work under mixed light. In that case, the parallel connection mode is your best choice. Because similar solar panels work independently, the remaining solar panels will continue to generate electricity as expected when the shadow covers one or two meetings. Like the series connection of solar panels, the parallel connection of solar panels also has an essential tool, the PWM controller. It can control the low-voltage system in a low-cost way so that the output voltage of your solar charging panel matches the standard battery charging voltage.
Series. Parallel connection of solar panels
What is the series and parallel connection of solar panels?
Generally, the solar panel array will be affected by many factors, especially the charging controller used. The design of the charging controller only accepts a certain amount of current intensity and voltage. For larger solar energy systems, the series-parallel connection design must be adopted at the same time to maximize the power of the solar energy system. We must keep the current and voltage within the appropriate range for this creative connection. Similarly, take a simple example:
- In the above figure, 4 x 100w panels, each with a rated voltage of 17.9V and a current of 5.72A
- The first pair of panels in the series can produce 35.8 volts and 5.72 amps.
- The second pair of panels in the series can produce 35.8 volts and 5.72 amps.
- The two lamp strings in parallel can produce a voltage of 35.8 volts and a current of 11.44 amperes. 409 watts in total.
When the solar panels in the array are identical, no matter how they are wired (at least mathematically), the power output is the same, but the current and voltage are different.
What conditions are solar panels connected in series-parallel?
As mentioned above, when your solar system is extensive, it is not most effective to use solar panels only by using a series or parallel connection. In reality, it is a standard method to connect multiple solar cells in series and parallel, which can make the current and voltage critical balance, thus giving full play to the best performance of the solar system.
At this time, the series connection will increase the voltage, allowing you to use smaller wires. Your MPPT charging controller will be more effective and valuable. The parallel connection will increase the current, requiring larger wires, which can prevent the power generation efficiency of the solar panel from being affected due to insufficient light intensity.
In a word, no matter how you connect multiple solar panels, the simple considerations can be summarized as voltage, current, and the size of the solar system. Suppose you encounter problems during the connection process. In that case, you must seek professional help, and the best advice, and BougeRV’s after-sales team will continue to help.
What is the difference between series and parallel solar panels?
Let’s imagine a scene: the Christmas lights in the Christmas tree suddenly have a bulb burned out for some reason, and the whole string of lights will not light up at this time. This is because these lights are connected in series. You must find the defective bulb and replace it.
However, today’s Christmas lights are all connected in parallel, which means that even if one is broken, other bulbs can work as usual. This is the parallel connection method.
If one panel in a series fails, the entire circuit will fail. In contrast, the defective solar panels in parallel will not affect the output of other solar panels.
Another essential thing to remember is that connecting solar panels in series will increase the voltage. In contrast, the parallel connection will increase the current. When designing a solar system, professionals will consider the voltage, current, system size, and the inverter most suitable for you.
In most cases, professional solar installers will design a system shared in series and parallel, enabling the system to generate power at the most appropriate voltage and current so as not to overload the inverter so that your solar charging panel can output power at the best state.
Should your solar panels be connected in series or in parallel?
The choice of series connection or parallel connection for your solar charging panel mainly depends on the demand of your electrical equipment and the surrounding environment. For general ships and RVs, the parallel connection of solar charging panels can provide more efficient wiring and public voltage.
However, for large applications with a power of more than 3000w, it may be better to use the series connection mode to obtain higher voltage. Before choosing, you should understand the operating conditions and working principles of various wiring devices to ensure that you determine the most appropriate way and confidently install the solar charging panel.
If your solar charging panel is not covered by shadows most of the time, connecting multiple solar panels in series will be your first choice. This will make your solar charging panel system more efficient and perform better in the daytime and on cloudy days.
In a word, there is no solution for everyone. There should be a corresponding solution for specific problems and conditions. If you are unsure how many shadows your panel will receive, consider using the parallel method. Of course, you can also communicate with the after-sales team of bougeRV, and we will do our best to help you.
Suggestions for efficient use of solar charging panels
Pay attention to any object on the roof that may cast shadows on the panel, such as an antenna, satellite, vent, etc.
In the whole solar system, use solar panels of the exact specification as much as possible.
Using a hybrid panel. you can connect them in series through appropriate wires to configure the maximum current.
Remove the damaged panels in the solar system to avoid affecting the power output of other boards.
Make the specifications of the solar panels as close as possible. Don’t put panels with significant differences in specifications together for use. For example, put 50w 3A 18v and 200w 9A 21v together.
When the RV uses the solar energy system. it usually adopts the series connection method.
Avoid parking your RV in an utterly fantastic place to maximize the solar system’s efficiency.
Solar panel wiring basics: How to string solar panels
Solar panel wiring (also known as stringing), and how to string solar panels together, is a fundamental topic for any solar installer. It’s important to understand how different stringing configurations impact the voltage, current, and power of a solar array so you can select an appropriate inverter for the array and make sure that the system will function effectively.
The stakes are high. If the voltage of your array exceeds the inverter’s maximum, production will be limited by what the inverter can output (and depending on the extent, the inverter’s lifetime may be reduced). If the array voltage is too low for the inverter you’ve chosen, the system will also underproduce because the inverter will not operate until its “start voltage” has been reached. This can also happen if you fail to account for how the shade will affect system voltage throughout the day.
Thankfully, modern solar software can manage this complexity for you. For example, Aurora’s auto-stringing functionality will automatically advise you on whether your string lengths are acceptable, or even string the system for you. If you are looking for a reliable and easy way to map out your solar configuration, Aurora’s auto-stringing functionality enables you to virtually string solar panels.
However, as a solar professional, it’s still important to have an understanding of the rules that guide string sizing. Solar panel wiring is a complicated topic and we won’t delve into all of the details in this article, but whether you’re new to the industry and just learning the principles of solar design. or looking for a refresher, we hope this primer provides a helpful overview of some of the key concepts.
In this article, we’ll review the basic principles of stringing in systems with a string inverter and how to determine how many solar panels to have in a string. We also review different stringing options such as connecting solar panels in series and connecting solar panels in parallel.
Key electrical terms for solar panel wiring
In order to understand the rules of solar panel wiring, it is necessary to understand a few key electrical terms—particularly voltage, current, and power—and how they relate to each other. To understand these concepts, a helpful analogy is to think of electricity like water in a tank. To expand the analogy, having a higher water level is like having a higher voltage – there is more potential for something to happen (current or water flow), as illustrated below.
What is voltage?
Voltage. abbreviated as V and measured in volts. is defined as the difference in electrical charge between two points in a circuit. It is this difference in charge that causes electricity to flow. Voltage is a measure of potential energy, or the potential amount of energy that can be released.
In a solar array, the voltage is affected by a number of factors. First is the amount of sunlight (irradiance) on the array. As you might assume, the more irradiance on the panels, the higher the voltage will be.
Temperature also affects voltage. As the temperature increases, it reduces the amount of energy a panel produces (see our discussion of Temperature Coefficients for a more detailed discussion of this). On a cold sunny day, the voltage of a solar array may be much higher than normal, while on a very hot day, the voltage may be significantly reduced.
What is an electrical current?
Electric current (represented as “I” in equations) is defined as the rate at which the charge is flowing.
In our example above, the water flowing through the pipe out of the tank is comparable to the current in an electrical circuit. Electric current is measured in amps (short for amperes).
What is electric power?
Power (P) is the rate at which energy is transferred. It is equivalent to voltage times current (VI = P) and is measured in Watts (W). In solar PV systems, an important function of the inverter — in addition to converting DC power from the solar array to AC power for use in the home and on the grid — is to maximize the power output of the array by varying the current and voltage.
For a more technical explanation of how current, voltage, and power interact within the context of a solar PV system, check out our article on Maximum Power Point Tracking (MPPT).
In it, we discuss current-voltage (IV) curves (charts that show how the panel output current varies with panel output voltage), and power-voltage curves (which show how panel output power varies with panel output voltage). These curves offer insight into the voltage and current combination(s) at which power output is maximized.
Basic concepts of solar panel wiring (aka stringing)
To have a functional solar PV system, you need to wire the panels together to create an electrical circuit through which current will flow, and you also need to wire the panels to the inverter that will convert the DC power produced by the panels to AC power that can be used in your home and sent to the grid. In the solar industry. This is typically referred to as “stringing” and each series of panels connected together is referred to as a string.
In this article, we’ll be focusing on string inverter (as opposed to microinverters ). Each string inverter has a range of voltages at which it can operate.
Series vs. parallel stringing
There are multiple ways to approach solar panel wiring. One of the key differences to understand is stringing solar panels in series versus stringing solar panels in parallel. These different stringing configurations have different effects on the electrical current and voltage in the circuit.
Connecting solar panels in series
Stringing solar panels in series involves connecting each panel to the next in a line (as illustrated in the left side of the diagram above).
Just like a typical battery that you may be familiar with, solar panels have positive and negative terminals. When stringing in series, the wire from the positive terminal of one solar panel is connected to the negative terminal of the next panel and so on.
When stringing panels in series, each additional panel adds to the total voltage (V) of the string but the current (I) in the string remains the same.
One drawback to stringing in series is that a shaded panel can reduce the current through the entire string. Because the current remains the same through the entire string, the current is reduced to that of the panel with the lowest current.
Connecting solar panels in parallel
Stringing solar panels in parallel (shown in the right side of the diagram above) is a bit more complicated. Rather than connecting the positive terminal of one panel to the negative terminal of the next, when stringing in parallel, the positive terminals of all the panels on the string are connected to one wire and the negative terminals are all connected to another wire.
When stringing panels in parallel, each additional panel increases the current (amperage) of the circuit, however, the voltage of the circuit remains the same (equivalent to the voltage of each panel). Because of this, a benefit of stringing in parallel is that if one panel is heavily shaded, the rest of the panels can operate normally and the current of the entire string will not be reduced.
Information you need when determining how to string solar panels
There are several important pieces of information about your inverter and solar panels that you need before you can determine how to string your solar array.
You’ll need to understand the following inverter specifications ( these can be found in the manufacturer datasheet for the product):
- Maximum DC input voltage (V input, max ): the maximum voltage the inverter can receive
- Minimum or “Start” Voltage (V input, min ): the voltage level necessary for the inverter to operate
- Maximum Input Current: how much energy the inverter can handle before breaking
- How many Maximum Power Point Trackers (MPPTs) does it have?
What are MPPTs?
As noted above, a function of inverters is to maximize power output as the environmental conditions on the panels vary. They do this through Maximum Power Point Trackers (MPPTs) which identify the current and voltage at which power is maximized.
However, for a given MPPT, the conditions on the panels must be relatively consistent or efficiency will be reduced (for instance, differences in shade levels or the orientation of the panels).
It is also important to note that, if the inverter has multiple MPPTs then strings of panels with different conditions can be connected to a separate MPPT.
Solar panel information
In addition to the above information about your selected inverter, you’ll also need the following data on your selected panels:
- Open circuit voltage (V oc ) : the maximum voltage that panel can produce in its no-load condition
- Short circuit current (I sc ): the current running through the cell when the voltage is at zero (although we won’t delve into current calculations in this article)
An important thing to understand about these values is that they are based on the module’s performance in what is called Standard Test Conditions (STC).
STC includes an irradiance of 1000W per square meter and 25 degrees Celsius (~77 degrees F). These specific lab conditions provide consistency in testing but the real-world conditions a PV system experiences may be very different.
As a result, the actual current and voltage of the panels may vary significantly from these values.
You’ll need to adjust your calculations based on the expected minimum and maximum temperatures where the panels will be installed to ensure that your string lengths are appropriate for the conditions the PV system will encounter, as we’ll discuss below.
Basic rules for how to string solar panels
Ensure the minimum and maximum voltage are within the inverter range
Do not allow the strings you are connecting to the inverter to exceed the inverter’s maximum input voltage or maximum current, or to fall below its minimum/start voltage.
Ensure that the maximum voltage complies with code requirements in the area where you are designing.
In the U.S., the National Electrical Code caps the maximum allowable voltage at 600V for most residential systems. In Europe, higher voltages are allowed.
Pro Tip: Don’t use STC values alone to determine voltage range
We know that voltage is additive in series strings while current is additive in parallel strings. As such, you might intuitively assume that you can determine the voltage of our proposed PV system design and whether it falls within the recommended range for the inverter by multiplying the voltage of the panels by the number in a series string. You might also assume that you could determine the current of the system by adding the current of each parallel string (which would be equal to the current of the panels multiplied by the number in the parallel string).
However, as we discussed above, since STC values reflect the modules’ performance under very specific conditions, the actual voltage of the panels in real-world conditions may be quite different.
Thus the simplified calculations taken from STC values only give you an initial rough estimate; you must account for how the voltage of the system will change depending on the temperatures it may experience in the area where it is installed. At colder temperatures, the voltage of the system may be much higher; at higher temperatures, it may be much lower.
To ensure that the temperature-adjusted string voltage is within the input voltage window of the inverter it will require a more complicated formula, like the ones below :
If these equations look a bit like gibberish, don’t worry, Aurora solar design software automatically performs these calculations and alerts you as you are designing if your string lengths are too long or too short given the expected temperatures at the site. (For more information on stringing in Aurora, see this help center article.)
Aurora also performs a variety of other validations to ensure that the system will operate as expected and not violate codes or equipment specifications — this can prevent costly performance issues. (For a detailed overview of these validations see this page in our help center.)
An example of underperforming PV systems
For a real-world example of why it is so important to accurately account for how environmental conditions will impact the voltage of your PV system, read our analysis of an underperforming system in Cathedral City, California. In that case, a solar designer’s failure to account for the presence of shade resulted in the system frequently falling below the inverter’s start voltage and therefore producing significantly less energy than forecasted.
Ensure strings have similar conditions — or connect strings with different conditions to different MPPT ports
Once you’ve determined that your strings are acceptable lengths for the inverter specifications, another key consideration is that the strings have the same conditions (e.g. same azimuth/orientation, same tilt, same irradiance) if they are connected to the same inverter MPPT.
Mismatches in the conditions on the strings will reduce the efficiency and power output of your solar design. For a discussion of why mismatches in shading. orientation, or azimuth result in lost power output see the fourth article in our PV system losses series : Tilt Orientation, Incident Angle Modifier, Environmental Conditions, and Inverter Losses Clipping.
If you are designing for a site where it’s necessary to have panels on different roof faces, or some areas of the array will get more shade than others, you can ensure that the panels with different conditions are separated into their own strings, and then connect those strings to different MPPTs of the inverter (provided your chosen inverter has more than one MPPT).
This will allow the inverter to ensure each string operates at the point where it produces the maximum power.
Advanced considerations to optimize your design
The above rules will ensure that your stringing configuration will comply with the specifications of your inverter and that the energy production of the system won’t be negatively affected by mismatches in the conditions on the panels.
However, there are additional factors that a solar designer can consider to arrive at the optimal design (that is, the design that maximizes energy production while minimizing cost). These factors include inverter clipping, the use of module-level power electronics (MLPE) — devices which include microinverters and DC optimizers, and design efficiency provided by software tools.
Sometimes it may make sense to oversize the solar array that you are connecting to the inverter leading to a theoretical maximum voltage that is slightly higher than the inverter max. This may allow your system to produce more energy (because there are more panels) when it is below its maximum voltage, in exchange for reduced (“clipped”) production during the times when the DC voltage of the array exceeds the inverter’s maximum.
If the production gains exceed the production lost to inverter clipping, then you can produce more power without paying for an additional inverter or one with a higher voltage rating.
Of course, this decision should be made with care and a clear understanding of how much production will be clipped compared to how much additional production will be gained at other times.
In its system loss diagram. Aurora indicates how much energy will be lost to clipping so that you can make an informed decision about whether this makes sense. For a detailed explanation of inverter clipping and when a system with inverter clipping makes sense, see our blog article on the subject.
String inverters are not the only inverter option. Microinverters, which are inverters that are attached to each individual panel (or a couple), allow each panel to operate at its maximum power point regardless of the conditions on other panels. In this arrangement, one need not worry about ensuring panels on the same string have the same conditions. Microinverters can also make it easier to add more panels in the future.
Explore a few different options to find the best one
As you can see, there are many considerations when it comes to stringing your panels and finding the inverter and stringing configuration that is best for the customer.
You may not arrive at the optimal design the first time around so it can be helpful to evaluate a few different options. In order for this to be efficient, however, you’ll need a process where you can evaluate multiple designs quickly. This is where solar software, like Aurora, can be particularly valuable.
Let solar software do the stringing for you
Finally, technology like Aurora’s autostringing functionality can do the stringing for you! It will take into account the considerations discussed here and present you with an ideal stringing configuration.
Schedule a demo to see how software can help you design your solar systems.
- Maximum DC input voltage
- Start voltage
- Maximum input current
- Number of MPPTs
- Open circuit voltage
- Short circuit current
Understanding the principles of solar panel wiring lets you ensure optimal designs for your solar customers. To learn more about how solar works, how to size a solar system, how to mitigate shading losses, and more, check out PV Education 101: A Guide for Solar Installation Professionals.
Schedule a demo to see how software can help you design your solar systems.
Here are a handful of quick answers to frequently asked questions about solar panel wiring basics.
What wiring is required for solar panels?
Solar panels require wiring that is protected for outdoor use and rated to handle the system’s amperage. Most modern solar panel installations use single-conductor Photovoltaic (PV) wire, between 10 and 12 gauge AWG. Wiring is required to connect the solar panels to the charge controller, inverter, and battery (in an off-grid system).
Is it better to wire solar panels in series or parallel?
In terms of power production, it is better to wire solar panels in a parallel circuit rather than a series. Parallel solar wiring allows for more independent power production between the panels but also increases the system’s upfront costs for materials and installation. To maximize electricity production without exceeding inverter voltage ratings, some solar energy systems use a combination of series and parallel wiring connections. Technology such as solar optimizers and microinverters can also help maximize system efficiency.
How many solar panels can I connect to my inverter?
The number of solar panels you can connect to your inverter is identified by its wattage rating. For example, if you have a 5,000 W inverter, you can connect approximately 5,000 watts (or 5 kW) of solar panels. Using 300 W solar panels, you could then connect roughly 17 solar panels (5000 W / 300 W per panel).
Can I connect solar panels directly to a battery?
Although the answer is technically yes, you should never connect a solar panel directly to a battery. As solar power is generated at various intensities throughout the day, charge controllers (or regulators) modify the energy so that it can be efficiently stored in the battery. Using a charge controller between the solar panels and storage bank maximizes the system’s production and protects the battery from overcharging, damages, and malfunctions.
Can I use solar panels and an inverter without a battery?
Yes, as battery technology improves, many homeowners are considering battery storage as an addition to their solar system. But, traditionally, most grid-connected solar systems didn’t have battery storage. While it is impossible to run an off-grid photovoltaic (PV) energy system without battery storage, professionally permitted and installed solar panels and inverters safely produce solar power that is distributed throughout a home and fed into the utility electrical grid.
Understand the difference between wiring your solar panels in series vs parallel.
You want your solar panels to deliver the maximum amount of energy possible, right? But did you know how your solar panels are connected within the electrical wiring of your house makes a difference in how well they work? Connecting your solar panel in series vs parallel affects current flow and is dictated by your installation’s setup.
OK, now that the disclaimer is out of the way, we’re ready!
What is a circuit?
Before we get into whether solar panels are better connected in series or in parallel, let’s talk a little about wiring basics, starting with circuits. An electronic circuit is simply a path electrons can flow through. The simplest circuit is a battery, wires, and light bulb.
As electrons move through a circuit, they create voltage — the difference in charge between two points (measured in volts) — and current — the rate at which charge is flowing (measured in amps). Check out this great 5 minute video to understand the difference between voltage and current – it’s going to come in handy later on!
Each electrical component in a circuit affects current flow by changing its electrical properties. For example, resistors dissipate energy, while capacitors store electrical charge. Conductive wires enable current to flow. The configuration, or placement, of these components within the electrical circuit affects the flow of current and its electrical power.
What does “in series” and “in parallel” even mean?
Components connected in series looks like a string of Christmas lights – each piece is placed in a line, one after another, with each piece connected only to the one before and after. Since all the components are connected in a single line, the electrical current can only travel in one direction. If a circuit is disconnected at any point, current will not be able to flow through it. This will halt electrical activity in the entire circuit.
You experience this each year when you take those Christmas lights out of storage, then have to check every bulb to find the one that’s burnt out and preventing the entire strand from lighting.
Fortunately, this isn’t how the wiring in your house works. Most household electrical circuits are parallel circuits. Each component is connected to every other component. A parallel circuit will continue to work even if it contains a broken component because it has multiple paths for current to travel.
A broken component reduces the overall current, but the other components will stay operational. This why you can have 5 lights connected to the same circuit in your home, but choose which ones to turn on or off without affecting any of the others.
How does this apply to solar panels?
Just like the examples above, you can choose whether to connect your solar panels in series or in parallel. Let’s go over the pros and cons of each as well as how to choose between the two.
Connecting in series
When installing solar panels in series, the voltage adds up, but the current stays the same for all of the elements. For example, if you installed 5 solar panels in series – with each solar panel rated at 12 volts and 5 amps – you’d still have 5 amps but a full 60 volts.
There are some major benefits to connecting solar panels in series. First, it allows you to get away with smaller wiring (since the current stays the same), which saves you quite a bit of expense and effort during the installation.
And second, you can have very long wire runs (from your solar panels on your roof to the inverter on the side of your house, for instance) without losing too much electricity. For these reasons, most solar panels on homes today are, at least partially, connected in series.
There is one issue with connecting in series, however. If you remember our Christmas lights example from above, you can imagine the drawbacks to wiring your solar panels in a similar way. If one solar panel goes out or is shaded, then the entire system’s production drops drastically.
Shading decreases production in any system and that’s why installers typically avoid areas of your roof where nearby trees, shrubs, buildings, satellites, chimneys, or anything else could get in the way.
Connecting in parallel
Solar cells can also be arranged in parallel, where each solar panel is connected to every other panel in the circuit. Unlike connecting in series, connecting in parallel allows the voltage to stay the same, but the current adds up. In fact, it’s the exact opposite of connecting in series!
Using our same example of 5 panels, each rated at 12 volts and 5 amps, if you connected them in parallel, you’d still have 12 volts but now 25 amps!
Connecting panels in parallel requires heavier wire to handle the higher current (25 amps vs 5 amps in the examples above) and you need more wire to make all the connections to the different panels. It’s more difficult and costly to run these large wires to connect your solar panels to a distant inverter (like is typically found in residential situations).
Off-grid systems have a bit more flexibility and solar owners will sometimes connect their panels in parallel to meet their battery needs (12 volt solar system to charge a 12 volt battery, for example).
It is also possible to install solar as a combination of series and parallel circuits to try and maximize the advantages of both types of wiring. This combination can also help you achieve a desired amount of voltage or current depending on what your needs are.
As we mentioned, most grid-connected homes use solar panels that are connected in series. Smaller systems can get away with a single string of panels, but larger systems typically need 2 or more strings to safely accommodate the number of panels in play and many inverters these days accommodate this need.
If you want to bypass the whole issue of whether to connect your solar panels in series vs parallel, you could always just install microinverters, which optimize each panel individually – no need to worry about shading or anything like that!
Should I install my solar panels in series vs parallel?
How you choose to wire your solar panels depends on your installation design (where the panels and inverter be installed), whether you’re connected to the grid or not, and the size of your installation.
Keep in mind that there are positives and negatives to each system. While it may be easier to wire your solar panels in series, a disruption to one of the elements will disrupt the entire circuit, so it is less reliable. On the other hand, panels connected in parallel need larger, more expensive wire (and more of it).
Ideally, your solar energy plan should include some type of optimization tracking such as MPPT in addition to any modifications made to the solar cell itself, as it may be more beneficial to perform energy tracking rather than modify the wiring of your solar panels. And don’t forget about avoiding this whole issue entirely and going with microinverters!