- key electrical terms to understand solar panel wiring
- basics of solar panel wiring (aka stringing)
- information you need to determine how to place solar panels
- basic rules on how to place solar panels
- explore other options
- key points
Solar panel wiring (also known as stringing) and how to attach solar panels is a critical topic for any solar installer. It’s important to understand how different wiring configurations affect a solar panel’s voltage, current, and wattage so you can select a suitable inverter for your panel and ensure the system works effectively.
The stakes are high. if your array voltage exceeds the inverter’s maximum, output will be limited by what the inverter can output (and depending on the measurement, the inverter’s lifespan may be reduced). If the array voltage is too low for the inverter you have chosen, the system will also have insufficient output because the inverter will not run until its “start voltage” has been reached. this can also happen if you don’t consider how shade will affect system voltage throughout the day.
Fortunately, modern solar software can handle this complexity for you. for example, aurora’s autochaining feature will automatically tell you if your chain lengths are acceptable, or even chain the system for you. If you’re looking for a reliable and easy way to plot your solar setup, Aurora’s auto-chaining functionality allows you to virtually chain solar panels together.
Click here, or on the image below, for a free demo and see how aurora can panelize for you.
However, as a solar professional, it is still important to understand the rules that guide string sizing. Solar panel wiring is a complicated topic and we won’t go into all the details in this article, but whether you’re new to the industry and learning the principles of solar design, or looking for a refresher, we hope this manual provides a helpful overview of some of the key concepts.
In this article, we will review the basics of daisy chaining 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
To understand the rules for wiring solar panels, you need to understand some key electrical terms (in particular, voltage, current, and power) and how they relate to each other. To understand these concepts, a helpful analogy is to think of electricity as water in a tank. To extend the analogy, having a higher water level is like having a higher voltage: there is more chance of something happening (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 several factors. first is the amount of sunlight (irradiation) on the array. As you might guess, the higher the irradiance on the panels, the higher the voltage.
Temperature also affects voltage. as temperature increases, the amount of power a panel produces decreases (see our discussion of temperature coefficients for a more detailed discussion on this). On a cold, sunny day, a solar panel’s voltage can be much higher than normal, while on a very hot day, the voltage can drop significantly.
what is an electric current?
Electric current (represented as “i” in the equations) is defined as the rate at which charge flows.
In our example above, the water flowing through the pipe out of the tank is comparable to the current in an electrical circuit. electrical current is measured in amps (short for amps).
what is electrical energy?
power (p) is the rate at which energy is transferred. it is equivalent to voltage times current (v*i = 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 panel into AC power for use at home and on the grid, is to maximize the power output of the panel by varying the current and the voltage. .
For a more technical explanation of how current, voltage, and power interact in the context of a solar PV system, see our article on maximum power point tracking (mppt).
In it, we look at current-voltage curves (iv) (graphs showing how panel output current varies with panel output voltage) and power-voltage curves (showing how power varies panel output voltage with the panel output voltage). these curves provide information on the voltage and current combinations at which the output power is maximized.
basics of solar panel wiring (also known as stringing)
To have a functional solar PV system, you need to wire the panels together to create an electrical circuit through which the current will flow, and you also need to connect the panels to the inverter which will convert the DC power produced by the panels. to alternating current that can be used in your home and sent to the network. in the solar industry. this is generally known as “chaining” and each series of panels connected to each other is called a chain.
In this article, we will focus on the string inverter (as opposed to micro-inverters). each string inverter has a range of voltages it can operate on.
serial strings vs. parallel
There are several ways to approach the wiring of solar panels. One of the key differences to understand is stringing solar panels in series versus stringing solar panels in parallel. These different string configurations have different effects on the electrical current and voltage in the circuit.
connection of solar panels in series
stringing solar panels in series involves connecting each panel to the next in a line (as illustrated on the left side of the diagram above).
Just like a typical battery you may be familiar with, solar panels have positive and negative terminals. when connected in series, the wire from the positive terminal of one solar panel connects to the negative terminal of the next panel, and so on.
When panels are chained in series, each additional panel adds to the total voltage (v) of the chain, but the current (i) in the chain remains the same.
One drawback to daisy-chaining is that a shaded panel can reduce the current through the entire daisy chain. because the current remains the same throughout the entire string, the current is reduced to that of the panel with the lowest current.
connection of solar panels in parallel
Connecting solar panels in parallel (shown on the right side of the diagram above) is a bit more complicated. instead of connecting the positive terminal of one panel to the negative terminal of the next, when daisy chained in parallel, the positive terminals of all panels in the chain are connected to one wire and the negative terminals are connected to another wire.
When running panels in parallel, each additional panel increases the current (amperage) of the circuit, however, the circuit voltage remains the same (equivalent to the voltage of each panel). Because of this, a benefit of paralleling is that if one panel is heavily shaded, the rest of the panels can function normally and the current for the entire string will not be reduced.
information you need to determine how to place solar panels
There are several important pieces of information about your inverter and solar panels that you need before you can determine how to connect your solar panel.
You will need to understand the following inverter specifications (these can be found in the product manufacturer’s data sheet):
- maximum dc input voltage (vinput, max) – the maximum voltage the inverter can receive
- minimum or “start” voltage (vinput, min) – the voltage level required for the inverter to operate
- max input current: how much power can the inverter handle before it breaks down
- how many maximum power point trackers (mppts) does it have?
what are mppt?
As stated above, one function of inverters is to maximize power output as environmental conditions in the panels vary. They do this through Maximum Power Point Trackers (MPPTs) that identify the current and voltage at which power is maximized.
however, for a given mppt, the conditions across the panels must be relatively consistent or efficiency will be reduced (for example, differences in shading levels or panel orientation).
It is also important to note that if the inverter has multiple mppts, 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 will also need the following information about your selected panels:
- open circuit voltage (voc): the maximum voltage the panel can produce in its no load condition
- short circuit current (isc): the current through the cell when the voltage is at zero (although we won’t delve into the actual calculations in this article)
One important thing to understand about these values is that they are based on the performance of the module under what are called standard test conditions (stc).
stc includes an irradiance of 1000 watts per square meter and 25 degrees centigrade (~77 degrees f). These specific laboratory conditions provide consistency in testing, but the real-world conditions a PV system experiences can be very different.
As a result, the actual current and voltage of the panels may vary significantly from these values.
You will need to adjust your calculations based on the expected minimum and maximum temperatures where the panels will be installed to ensure that the string lengths are adequate for the conditions that the PV system will encounter, as we will see below.
basic rules on how to lay solar panels
1. make sure the minimum and maximum voltage is within the range of the inverter
Do not allow the strings you are connecting to the inverter to exceed the maximum input voltage or maximum current of the inverter, or drop below its minimum/start voltage.
make sure the maximum voltage meets the code requirements in the area where you are designing.
in the usa In the US, the National Electrical Code limits the maximum allowable voltage to 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 can intuitively assume that you can determine the design voltage of our proposed PV system and whether it is within the inverter’s recommended range by multiplying the panels voltage by the number in a series string. You might also guess that you could determine the system current by adding the current in each parallel string (which would be equal to the current in the panels multiplied by the number in the parallel string).
However, as discussed above, since stc values reflect the performance of modules under very specific conditions, the actual voltage of panels under real conditions can be quite different.
so the simplified calculations taken from the stc values only give you an initial rough estimate; you must consider how the system voltage will change depending on the temperatures you may experience in the area where it is installed. at cooler temperatures, the system voltage can be much higher; at higher temperatures, it can be much lower.
To ensure that the temperature-adjusted string voltage is within the inverter’s input voltage window, a more complicated formula will be required, such as the following:
If these equations seem a bit inconsistent, don’t worry, aurora solar design software automatically performs these calculations and alerts you while you design if string lengths are too long or too short given the conditions. temperatures expected at the site. (For more information on creating strings in aurora, see this help center article.)
aurora also performs a variety of other validations to ensure the system works as expected and does not violate codes or equipment specifications; this can prevent costly performance issues. (For a detailed description of these validations, see this page in our help center.)
an example of low performance photovoltaic systems
To see a real-world example of why it’s so important to accurately account for how environmental conditions will affect your PV system’s voltage, read our analysis of an underperforming system in Cathedral City, California. in that case, a solar designer’s failure to account for shading caused the system to frequently drop below the inverter’s starting voltage and thus produce much less power than anticipated.
2. make sure chains have similar conditions, or connect chains with different conditions to different mppt ports
once you have determined that your strings are of acceptable lengths for the inverter specifications, another key consideration is that the strings have the same conditions (e.g., same azimuth/bearing, same tilt, same irradiance) if they are connected to the same mppt inverter.
mismatches in string conditions will reduce the efficiency and power output of your solar design. For a discussion of why mismatches in shading, yaw, or azimuth result in power loss, see the fourth article in our series on PV System Losses: Tilt & orientation, incidence angle modifier, ambient conditions and inverter losses & trim.
if you are designing for a site where it is necessary to have panels on different faces of the roof, or some areas of the array will get more shade than others, you can ensure that panels with different conditions are separated into their own strings, and then connect those strings to different mppts of the inverter (as long as your chosen inverter has more than one mppt).
This will allow the inverter to ensure that each string is running at the point where it produces maximum power.
3. advanced considerations to optimize your design
The above rules will ensure that your wiring configuration meets your inverter specifications and that system power output is not adversely affected by discrepancies in panel conditions.
However, there are additional factors that a solar designer may consider to arrive at the optimal design (ie, the design that maximizes energy output and minimizes costs). These factors include inverter clipping, the use of module-level power electronics (MLPE), devices including microinverters and DC optimizers, and design efficiency provided by software tools.
Sometimes it can make sense to oversize the solar array you are connecting to the inverter, leading to a theoretical maximum voltage slightly higher than the inverter maximum. this can allow your system to produce more power (because there are more panels) when it is below its maximum voltage, in exchange for reduced (“trimmed”) output during times when the array’s dc voltage exceeds the maximum of the array. investor.
If production gains exceed production lost from 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 must be made carefully and with a clear understanding of how much production will be cut 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 by clipping so you can make an informed decision about whether this makes sense. For a detailed explanation of inverter saturation and when a system with inverter saturation makes sense, see our blog article on the subject.
string inverters are not the only inverter option. Microinverters, which are inverters that connect to each individual panel (or a pair), allow each panel to operate at its maximum power point, regardless of the conditions of the other panels. in this arrangement, one need not worry about ensuring that panels on the same chain 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 get the optimal layout the first time, so it can be useful to evaluate a few different options. however, for this to be efficient, you’ll need a process where you can evaluate multiple designs quickly. this is where solar software, like aurora, can be particularly valuable.
let the solar software do the strings for you
finally, technology like aurora’s autochains functionalitycan do the chains for you! will take into account the considerations discussed here and will present you with an ideal string setup.
Schedule a demo to see how the software can help you design your solar systems.
- You can put solar panels in series or in parallel, which is better depends on the specific situation. in general, when there are potential shading issues, parallel is the best option.
- don’t forget the essential information you’ll need:
- maximum dc input voltage
- start voltage
- max input current
- number of mppts
- open circuit voltage
- short circuit current
Understanding the principles of solar panel wiring allows you to 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 the software can help you design your solar systems.
frequently asked questions
Here are some quick answers to frequently asked questions about the basics of solar panel wiring.
what wiring is required for solar panels?
Solar panels require wiring that is protected for outdoor use and rated to handle the amperage of the system. Most modern solar panel installations use single-conductor photovoltaic (PV) cable, between 10 and 12 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 in parallel?
In terms of energy production, it is better to connect solar panels in a parallel circuit rather than in series. Parallel solar wiring allows for more independent power production between panels, but also increases upfront system costs for materials and installation. To maximize electricity production without exceeding the inverter’s voltage ratings, some solar power 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 their rated power. For example, if you have a 5,000 watt inverter, you can connect about 5,000 watts (or 5 kW) of solar panels. Using 300W solar panels, it could connect about 17 solar panels (5000W / 300W 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. Since solar energy is generated at different 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 the storage bank maximizes system production and protects the battery from overcharging, damage, and malfunction.
can i use solar panels and inverter without battery?
Yes, as battery technology improves, many homeowners are looking at battery storage as an addition to their solar system. but, traditionally, most grid-tied solar systems did not have battery storage. While it is impossible to run an off-grid photovoltaic (PV) system without battery storage, licensed and professionally installed solar panels and inverters safely produce solar energy that is distributed throughout the home and fed into the home. public power grid.