Wiring Solar Panels In Series vs Parallel: What’s The Difference Free Calculator
Are you unsure if wiring solar panels in series vs parallel is best? Use our solar panel series and parallel calculator discover the ideal way to wire your solar panels for an optimized camper solar setup. Our comprehensive guide provides practical step-by-step guidance, using clear diagrams and personal experience.
In this post, you’ll learn the various methods for wiring multiple solar panels together to optimize your camper solar setup.
We’ve got you covered with an interactive solar panel calculator to help you determine the ideal configuration for your solar array.
Our guide starts with easy-to-follow diagrams outlining the different wiring configurations and explains how each affects the necessary components.
We’ll even tackle the complexities of mismatched multiple solar panels.
As seasoned, full-time RVers who have experienced hiccups while setting up our RV solar system, we created this post to help you avoid these mistakes.
Consider this post a vital part of our series on RV solar panel systems.
If you’re new to electrics or van builds, start with our beginner’s guide to camper van electrics.
Solar Panel Series and Parallel Calculator
Depending on the number of panels and sizes, your set up could have many different configuration options.
This calculator allows you to enter up to three different panel specs and as many of those panels as you choose.
Enter the details, and we’ll calculate the total power output, voltage and current they could produce when wired:
- in series
- in parallel
- and in a combination, with each panel spec wired in series, then all series groups wired together in parallel,
- and in a combination, with each panel spec wired in parallel, then all parallel groups wired together in series.
It’s important only to enter each spec on one line or your calculations will be skewed.
Aim to choose a configuration that balances the least loss of total power output and a high enough voltage to charge the batteries all day. Calculations are rounded.
We aim to get the best combination of watts (power out) and voltage, so we can spend more time off-grid and make our batteries last longer.
Suppose you’d prefer to wire your mix of panels without losses. In that case, you must wire each panel variant with a dedicated solar charge controller.
We’d need an MPPT controller to handle the string of 95w panels and another for the 130w panel with our setup.
It becomes an expensive pastime, so best to install matching products wherever possible.
Use our other electrical calculators to help size your camper’s electrical system.
Ways of Wiring Multiple Solar Panels
There are three different ways of wiring multiple solar panels on your RV camper:
We’ll look at each of these in turn before comparing.
Solar Panels Wired in Series
Each solar panel has a positive and a negative terminal. A series connection is created when one panel’s positive terminal is connected to the negative terminal of another.
When solar panels are wired in series, the array’s voltage is added together while the current (or amps) stays the same.
In the diagram above, 4 x 100w panels, each with a rated voltage of 17.9 and current of 5.72A, wired in series could produce 71.6 volts and 5.72 amps – a total of 409 watts.
Note, solar panels’ wattage is rated under standard test conditions. So, for example, these 100w panels will provide 100w then but slightly more in colder temperatures.
Solar Panels Wired in Parallel
A parallel connection is created when the positive terminal of one panel is connected to the positive terminal of another, and the negative terminals are connected to each other.
The connections are made with branch connectors.
When solar panels are wired in parallel, the array’s voltage stays the same while the current (or amps) are added together.
In the diagram above, 4 x 100w panels, each with a rated voltage of 17.9 and current of 5.72A, wired in parallel could produce 17.9 volts and 22.8 amps – a total of 409 watts.
Solar Panels Wired in a Combination of Series Parallel
There are no surprises for figuring out what wiring solar panels in a combination of series and parallel means.
Taking the same 4 x 100 watt panels, you’d wire a pair in one string (i.e. in series), the 2nd pair in another string, then wire the two strings in parallel.
When solar panels are wired in a combination of series and parallel, the voltage in each string is added together while the current (or amps) stays the same.
Then, the two strings’ voltage stays the same while the current (or amps) are added together.
In the diagram above, 4 x 100w panels, each with a rated voltage of 17.9 and current of 5.72A:
- The 1st pair of panels wired in series could produce 35.8 volts and 5.72 amps
- The 2nd pair of panels wired in series could produce 35.8 volts and 5.72 amps
- These two strings wired in parallel could produce 35.8 volts and 11.44 amps – a total of 409 watts.
When the solar panels in the array are all the same, the power output is the same regardless of how they are wired (at least mathematically), but the current and voltage differ.
But there are two caveats to all of this.
- Firstly, the calculations only hold when all the solar panels in the array are the same.
- Secondly, the power output calculations are based on optimal operating conditions.
The following sections look at each of these in turn.
Mismatched Solar Panels How Best to Wire Them
Ideally, your camper solar setup will consist of identical solar panels.
They’ll all be the same brand, type, and wattage, so operating currents and voltages will all be the same.
But we don’t live in an ideal world.
Perhaps you have a few mismatched solar panels to kick off a budget solar setup.
What if you’re on the road, living in your van full-time, and need to replace an existing solar panel or want to add another to your setup but can’t source the same panels?
Can you add a different panel?
Yes, you can but determining how best to configure the system isn’t as straightforward.
The calculations explained above for series, parallel, and series and parallel combinations still hold.
When wired in series, the lowest amp rating of all the panels is used in the calculation.
Parallel wiring uses the lowest voltage.
When a solar array uses a mix of panels with different ratings, the power output is no longer the same across all configurations.
Let’s take an example, which happens to be an identical setup to that on Baloo, our Sprinter van conversion:
We have 2 x 95w panels, each rated at 4.5A and 21.1 volts, and a 130w panel rated at 7.5A and 17.3 volts.
Wired in series, we add the volts together and use the lowest current rating. So we get 21.1v 21.1v 17.3v = 59.5v at 4.5A.
We can get a total of 267.75 watts from our 320 watt panels – a loss of over 16%.
Wired in parallel, we add the amps together and use the lowest voltage rating. So we get 4.5A 4.5A 7.5A = 16.5A at 17.3v.
We can get a total of 285.45 watts from our 320 watt panels – a loss of over 11%.
Or we can wire them in a combination of series and parallel. We’ll wire the 95 watt panels in one string because they are identical and keep the 130 watt panel in a string.
At this point we have a further three options. We can either:
- wire the 2 identical panels in series, then connect them to the third panel in parallel, or
- wire the 2 identical panels in parallel, then connect them to the third panel in series, or
- use 2 solar charge controllers so we have two solar arrays with no mismatched panels.
And it makes a difference to how much power the panels can produce. So, let’s take a look.
Wire Identical Panels in Series Connect to a Third Panel in Parallel
- The 95w panels wired in series could produce 42.2 volts and 4.5 amps
- The 130w panel could produce 17.3 volts and 7.5 amps
- Combined, these two strings wired in parallel could produce 17.3 volts and 12 amps – a total of 207 watts, a loss of 35%.
Wire Identical Panels in Parallel Connect to a Third Panel in Series
- The 95w panels wired in parallel could produce 21.1 volts and 9 amps
- The 130w panel could produce 17.3 volts and 7.5 amps
- Combined, these two strings wired in series could produce 38.4 volts and 7.5 amps – a total of 288 watts, a loss of 9%.
Install 2 Solar Charge Controllers Separate the Solar Panels
We can see from the above scenarios, that mixing mismatched panels in any combined configuration inevitably leads to a loss of power.
But you can avoid any losses by separating the different solar panels into a solar with no mismatched panels, each with a dedicated solar charge controller.
Using our example of two 95w panels and a 130w panel, we could wire the two 95 panels in series or parallel, and connect them to a solar charge controller.
Separately, we can install the single 130w panel and connect it to a different solar charge controller.
Now the battery bank is being charged from two separate solar arrays, and neither has a mismatched panel. As a result, there is no power loss. Result!
Watts vs. Volts vs. Amps
This might be confusing and out of topic, but in reality, it is the main core of the topic, and you should understand it very well.
Electricity is divided into three big boys that you should know who they are. First is the power, which is responsible for the wattage or watts (W). So when you say this solar panel is 300 watts, you are referring to the first big boy, the power.
The second big boy is the voltage, and it’s responsible for the volts (V). So when you say this battery is 12 volts, you are calling him. And lastly is the current, which is responsible for the amperage or amps (A).
These three big boys are related. And this is the relation between them:
So when you are asking about how much current your solar panel produces, you must first know exactly which current are you talking about. Are you referring to the one that is coming out of the panel wires? Or maybe you are referring to the one that is being fed by the panel to the battery. You might also be asking this question to know how many amps will this panel provide for your house.
Those are all different questions that deserve different answers, but first, let’s explain how different are those currents and what is DC current and AC current? Let’s go with the current flow and analyze it at every location.
From the Panel Wires
Current is first supplied through your solar panel from the harvested sun rays as DC current and then through the wires to your solar charge controller. This power that is coming out of your solar panel wires is specified behind your panel with a data sheet sticker.
You will also find the currents and voltages, and they will be named as “rated current,” “optimum current,” “operating current,” or “maximum power current,” NOT the “short circuit current. This is the amount of current produced by your panel at a specified power and voltage. For example, take a look at the following 200W solar panel specs from Renogy:
This shows the power of the panel (at perfect conditions) as 200 watts, the optimum voltage as 22.6 volts, and the optimum current as 8.85 amps. Now let’s apply the relationship between the three big boys to see if the current we got is correct:
The current that is fed to your batteries by the solar charge controller will be different than that from the solar panel wires. You ask why? Simply because the solar controller will regulate the voltage coming from the panels to be suitable for your battery bank. So this means that the 22.6 volts coming from the panels will be changed, and accordingly, the 8.85 amps will also change. However, the power will remain the same (neglecting power loss for now).
Let’s say you have a 12-volt battery bank, so how do we know the current that is fed to the batteries? Easily using the same relation:
The inverter will take the power supplied from your panel to the controller to the battery and will convert it to AC current. This is the current type that most of the appliances in your house use. The inverter will change the current from DC (direct current) to AC (alternating current) and will also change the voltage that is supplied by the batteries or the controller, which in this case is 12 volts.
The new voltage depends on the inverter you bought, the appliances you have, and most importantly, the place you live in. For example, if you live in the US or Canada, the voltage will be 120v. However, if you live in Europe, your voltage supply from the grid will be 230v. You can check what voltage is used in your country by visiting this website.
For the sack of example, let’s say we are in the US, and the voltage is 120 volts. This means that the inverter will change the voltage to 120v, and accordingly, the current will also change:
This means you will have 1.67A of AC current supplied to your house, which could power a 40-inch LED TV, a laptop, and even some led bulb lights.
Losses Should NOT be Neglected
Losses are present in every part of the solar power system, and these losses should never be neglected (as we have done in the previous section of the article). For example, losses occur in the solar controller, the batteries, the wires, and the inverter.
- 90% Inverter efficiency = 10% loss
- 95% Solar controller efficiency = 5% loss
- 2% Wiring losses
- 5% Environmental losses (Temperature, dust, shading, etc…)
This adds up to 22% power loss, which could vary depending on your place, inverter controller efficiency, and even wiring thickness.
Now we will consider these losses when finding the currents for different types of solar panels.
How Many Amps Does a 200-watt Solar Panel Produce?
A 200-watt solar panel will produce 1.3 amps of AC current in the US with 120 volts. However, if you live in a place with 230 volts AC grid, then this same panel will produce 0.68 amps of AC current.
Considering 22% losses = 78 % efficiency (100% – 22%) :
I = 200w / 120v 0.78 = 1.3A in the US
I = 200w / 230v 0.78 = 0.68A in Europe
Now considering the current the panel produces directly, without passing through the solar controller or the inverter, it depends solely on the panel itself. Your panel could be 22 volts with 9.09 amps, and it could also be 6 volts with 33.33 amps. You should look at the specifications sticker on the panel’s back for this information.
How Many Amps Will a 200-watt Solar Panel Supply to the Battery?
A 200-watt solar panel will charge a 12-volt battery at a rate of 14.67A every hour at the maximum power point of the day with 12% losses (controller environmental wiring). If your battery bank voltage is different, the current supplied will change:
Considering 12% losses = 88 % efficiency (100% – 12%) :
I = 200w / 12v 0.88 = 14.67A for 12 volt battery bank
I = 200w / 24v 0.88 = 7.33A for 24 volt battery bank
I = 200w / 48v 0.88 = 3.67A for 48 volt battery bank
This is how you could calculate precisely how many amps your solar panel produces and where this amount of current goes. This will now make much more sense to you. However, these calculations might be hard to perform for some people; for this reason, we have created the following calculator that will ask you for your solar panel rated power (200w, 300w, 400w, etc…) and will have a default 22% losses as we mentioned. Still, you could edit these numbers according to your system and losses. The calculator output will be the current supplied to batteries at any voltage you specify and the AC current supplied to your house according to your country’s voltage rating.
How Many Amps Does a 100-watt Solar Panel Produce?
A 100-watt solar panel will produce 0.65 amps of AC current in the US with 120 volts or 0.34 amps in places with 230 volts AC grid (like Europe). In addition, it will supply your 12-volt battery bank with 7.3 amps, 3.67 amps for the 24-volt battery bank, 2.44 amps for the 36-volt battery bank, and 1.83 amps for the 48-volt battery bank. All this while taking into consideration 22% losses.
Solar Integration: Inverters and Grid Services Basics
An inverter is one of the most important pieces of equipment in a solar energy system. It’s a device that converts direct current (DC) electricity, which is what a solar panel generates, to alternating current (AC) electricity, which the electrical grid uses. In DC, electricity is maintained at constant voltage in one direction. In AC, electricity flows in both directions in the circuit as the voltage changes from positive to negative. Inverters are just one example of a class of devices called power electronics that regulate the flow of electrical power.
Fundamentally, an inverter accomplishes the DC-to-AC conversion by switching the direction of a DC input back and forth very rapidly. As a result, a DC input becomes an AC output. In addition, filters and other electronics can be used to produce a voltage that varies as a clean, repeating sine wave that can be injected into the power grid. The sine wave is a shape or pattern the voltage makes over time, and it’s the pattern of power that the grid can use without damaging electrical equipment, which is built to operate at certain frequencies and voltages.
The first inverters were created in the 19th century and were mechanical. A spinning motor, for example, would be used to continually change whether the DC source was connected forward or backward. Today we make electrical switches out of transistors, solid-state devices with no moving parts. Transistors are made of semiconductor materials like silicon or gallium arsenide. They control the flow of electricity in response to outside electrical signals.
A 1909 500-kilowatt Westinghouse “rotary converter,” an early type of inverter. Illustration courtesy of Wikimedia.
If you have a household solar system, your inverter probably performs several functions. In addition to converting your solar energy into AC power, it can monitor the system and provide a portal for communication with computer networks. Solar-plus–battery storage systems rely on advanced inverters to operate without any support from the grid in case of outages, if they are designed to do so.
Toward an Inverter-Based Grid
Historically, electrical power has been predominantly generated by burning a fuel and creating steam, which then spins a turbine generator, which creates electricity. The motion of these generators produces AC power as the device rotates, which also sets the frequency, or the number of times the sine wave repeats. Power frequency is an important indicator for monitoring the health of the electrical grid. For instance, if there is too much load—too many devices consuming energy—then energy is removed from the grid faster than it can be supplied. As a result, the turbines will slow down and the AC frequency will decrease. Because the turbines are massive spinning objects, they resist changes in the frequency just as all objects resist changes in their motion, a property known as inertia.
As more solar systems are added to the grid, more inverters are being connected to the grid than ever before. Inverter-based generation can produce energy at any frequency and does not have the same inertial properties as steam-based generation, because there is no turbine involved. As a result, transitioning to an electrical grid with more inverters requires building smarter inverters that can respond to changes in frequency and other disruptions that occur during grid operations, and help stabilize the grid against those disruptions.
Grid Services and Inverters
Grid operators manage electricity supply and demand on the electric system by providing a range of grid services. Grid services are activities grid operators perform to maintain system-wide balance and manage electricity transmission better.
When the grid stops behaving as expected, like when there are deviations in voltage or frequency, Smart inverters can respond in various ways. In general, the standard for small inverters, such as those attached to a household solar system, is to remain on during or “ride through” small disruptions in voltage or frequency, and if the disruption lasts for a long time or is larger than normal, they will disconnect themselves from the grid and shut down. Frequency response is especially important because a drop in frequency is associated with generation being knocked offline unexpectedly. In response to a change in frequency, inverters are configured to change their power output to restore the standard frequency. Inverter-based resources might also respond to signals from an operator to change their power output as other supply and demand on the electrical system fluctuates, a grid service known as automatic generation control. In order to provide grid services, inverters need to have sources of power that they can control. This could be either generation, such as a solar panel that is currently producing electricity, or storage, like a battery system that can be used to provide power that was previously stored.
Another grid service that some advanced inverters can supply is grid-forming. Grid-forming inverters can start up a grid if it goes down—a process known as black start. Traditional “grid-following” inverters require an outside signal from the electrical grid to determine when the switching will occur in order to produce a sine wave that can be injected into the power grid. In these systems, the power from the grid provides a signal that the inverter tries to match. advanced grid-forming inverters can generate the signal themselves. For instance, a network of small solar panels might designate one of its inverters to operate in grid-forming mode while the rest follow its lead, like dance partners, forming a stable grid without any turbine-based generation.
Reactive power is one of the most important grid services inverters can provide. On the grid, voltage— the force that pushes electric charge—is always switching back and forth, and so is the current—the movement of the electric charge. Electrical power is maximized when voltage and current are synchronized. However, there may be times when the voltage and current have delays between their two alternating patterns like when a motor is running. If they are out of sync, some of the power flowing through the circuit cannot be absorbed by connected devices, resulting in a loss of efficiency. total power will be needed to create the same amount of “real” power—the power the loads can absorb. To counteract this, utilities supply reactive power, which brings the voltage and current back in sync and makes the electricity easier to consume. This reactive power is not used itself, but rather makes other power useful. Modern inverters can both provide and absorb reactive power to help grids balance this important resource. In addition, because reactive power is difficult to transport long distances, distributed energy resources like rooftop solar are especially useful sources of reactive power.
A worker checks an inverter at the 2MW CoServ Solar Station in Krugerville, Texas. Photo by Ken Oltmann/CoServ.
Types of Inverters
There are several types of inverters that might be installed as part of a solar system. In a large-scale utility plant or mid-scale community solar project, every solar panel might be attached to a single central inverter. String inverters connect a set of panels—a string—to one inverter. That inverter converts the power produced by the entire string to AC. Although cost-effective, this setup results in reduced power production on the string if any individual panel experiences issues, such as shading. Microinverters are smaller inverters placed on every panel. With a microinverter, shading or damage to one panel will not affect the power that can be drawn from the others, but microinverters can be more expensive. Both types of inverters might be assisted by a system that controls how the solar system interacts with attached battery storage. Solar can charge the battery directly over DC or after a conversion to AC.
Learn more about the solar office’s systems integration program.
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