Solar Photovoltaic Cell Basics
When light shines on a photovoltaic (PV) cell – also called a solar cell – that light may be reflected, absorbed, or pass right through the cell. The PV cell is composed of semiconductor material; the “semi” means that it can conduct electricity better than an insulator but not as well as a good conductor like a metal. There are several different semiconductor materials used in PV cells.
When the semiconductor is exposed to light, it absorbs the light’s energy and transfers it to negatively charged particles in the material called electrons. This extra energy allows the electrons to flow through the material as an electrical current. This current is extracted through conductive metal contacts – the grid-like lines on a solar cells – and can then be used to power your home and the rest of the electric grid.
The efficiency of a PV cell is simply the amount of electrical power coming out of the cell compared to the energy from the light shining on it, which indicates how effective the cell is at converting energy from one form to the other. The amount of electricity produced from PV cells depends on the characteristics (such as intensity and wavelengths) of the light available and multiple performance attributes of the cell.
An important property of PV semiconductors is the bandgap, which indicates what wavelengths of light the material can absorb and convert to electrical energy. If the semiconductor’s bandgap matches the wavelengths of light shining on the PV cell, then that cell can efficiently make use of all the available energy.
Learn more below about the most commonly-used semiconductor materials for PV cells.
Silicon
Silicon is, by far, the most common semiconductor material used in solar cells, representing approximately 95% of the modules sold today. It is also the second most abundant material on Earth (after oxygen) and the most common semiconductor used in computer chips. Crystalline silicon cells are made of silicon atoms connected to one another to form a crystal lattice. This lattice provides an organized structure that makes conversion of light into electricity more efficient.
Solar cells made out of silicon currently provide a combination of high efficiency, low cost, and long lifetime. Modules are expected to last for 25 years or more, still producing more than 80% of their original power after this time.
Thin-Film Photovoltaics
A thin-film solar cell is made by depositing one or more thin layers of PV material on a supporting material such as glass, plastic, or metal. There are two main types of thin-film PV semiconductors on the market today: cadmium telluride (CdTe) and copper indium gallium diselenide (CIGS). Both materials can be deposited directly onto either the front or back of the module surface.
CdTe is the second-most common PV material after silicon, and CdTe cells can be made using low-cost manufacturing processes. While this makes them a cost-effective alternative, their efficiencies still aren’t quite as high as silicon. CIGS cells have optimal properties for a PV material and high efficiencies in the lab, but the complexity involved in combining four elements makes the transition from lab to manufacturing more challenging. Both CdTe and CIGS require more protection than silicon to enable long-lasting operation outdoors.
Perovskite Photovoltaics
Perovskite solar cells are a type of thin-film cell and are named after their characteristic crystal structure. Perovskite cells are built with layers of materials that are printed, coated, or vacuum-deposited onto an underlying support layer, known as the substrate. They are typically easy to assemble and can reach efficiencies similar to crystalline silicon. In the lab, perovskite solar cell efficiencies have improved faster than any other PV material, from 3% in 2009 to over 25% in 2020. To be commercially viable, perovskite PV cells have to become stable enough to survive 20 years outdoors, so researchers are working on making them more durable and developing large-scale, low-cost manufacturing techniques.
Organic Photovoltaics
Organic PV, or OPV, cells are composed of carbon-rich (organic) compounds and can be tailored to enhance a specific function of the PV cell, such as bandgap, transparency, or color. OPV cells are currently only about half as efficient as crystalline silicon cells and have shorter operating lifetimes, but could be less expensive to manufacture in high volumes. They can also be applied to a variety of supporting materials, such as flexible plastic, making OPV able to serve a wide variety of uses.PV
Quantum Dots
Quantum dot solar cells conduct electricity through tiny particles of different semiconductor materials just a few nanometers wide, called quantum dots. Quantum dots provide a new way to process semiconductor materials, but it is difficult to create an electrical connection between them, so they’re currently not very efficient. However, they are easy to make into solar cells. They can be deposited onto a substrate using a spin-coat method, a spray, or roll-to-roll printers like the ones used to print newspapers.
Quantum dots come in various sizes and their bandgap is customizable, enabling them to collect light that’s difficult to capture and to be paired with other semiconductors, like perovskites, to optimize the performance of a multijunction solar cell (more on those below).
Multijunction Photovoltaics
Another strategy to improve PV cell efficiency is layering multiple semiconductors to make multijunction solar cells. These cells are essentially stacks of different semiconductor materials, as opposed to single-junction cells, which have only one semiconductor. Each layer has a different bandgap, so they each absorb a different part of the solar spectrum, making greater use of sunlight than single-junction cells. Multijunction solar cells can reach record efficiency levels because the light that doesn’t get absorbed by the first semiconductor layer is captured by a layer beneath it.
While all solar cells with more than one bandgap are multijunction solar cells, a solar cell with exactly two bandgaps is called a tandem solar cell. Multijunction solar cells that combine semiconductors from columns III and V in the periodic table are called multijunction III-V solar cells.
Multijunction solar cells have demonstrated efficiencies higher than 45%, but they’re costly and difficult to manufacture, so they’re reserved for space exploration. The military is using III-V solar cells in drones, and researchers are exploring other uses for them where high efficiency is key.
Concentration Photovoltaics
Concentration PV, also known as CPV, focuses sunlight onto a solar cell by using a mirror or lens. By focusing sunlight onto a small area, less PV material is required. PV materials become more efficient as the light becomes more concentrated, so the highest overall efficiencies are obtained with CPV cells and modules. However, more expensive materials, manufacturing techniques, and ability to track the movement of the sun are required, so demonstrating the necessary cost advantage over today’s high-volume silicon modules has become challenging.
Learn more about photovoltaics research in the Solar Energy Technologies Office, check out these solar energy information resources, and find out more about how solar works.
Ways to Test Solar Panels: Output, Wattage Amps
Just so you know, this page contains affiliate links. If you make a purchase after clicking on one, at no extra cost to you I may earn a small commission.
This tutorial contains everything you need to know about how to test solar panels.
- How to test a solar panel with a multimeter
- How to test solar panel amps with a clamp meter
- How to measure solar panel output in watts
How to Test a Solar Panel with a Multimeter
Your multimeter is your best friend when testing solar panels.
What You Need
- Multimeter — I recommend getting one that is auto-ranging. Also, a simple voltmeter won’t work here. You need a multimeter that can measure both volts and amps.
Video Walkthrough
Here’s a short video I made of testing solar panels with a multimeter. Check it out and consider subscribing to my YouTube channel for more DIY solar tutorials!
Prep your multimeter to measure DC volts. To do so, plug the black probe into the COM terminal on your multimeter. Plug the red probe into the voltage terminal.
Set your multimeter to the DC voltage setting (and the correct voltage range if yours isn’t auto-ranging). It is indicated by a solid line above a dotted line next to the letter V.
Take your solar panel outside and place it in direct sunlight. For best results, angle it toward the sun.
Locate the positive and negative solar panel cables. The positive cable is typically the one with the male MC4 connector, which has a red Band around it.
Touch the red probe of your multimeter to the metal pin inside the positive MC4 connector. Touch the black probe to the metal pin inside the negative MC4 connector.
Read the voltage on your multimeter and compare it to the open circuit voltage (Voc) listed on the back of your panel. (If your voltage reading is negative, reverse the probes and measure again.)
I measured a Voc of 19.85V on my panel. The claimed Voc for this panel is 19.83V, so we’re spot on.
The voltage you measure with your multimeter should be close to the open circuit voltage listed on the back of the panel. It doesn’t have to be identical, though.
If they’re similar, so far your panel seems to be in good condition. You can move on to the next step — measuring short circuit current.
If the voltage you measure is significantly less than the Voc, try the following then remeasure:
- Make sure it’s a sunny day, the panel is in direct sunlight and it’s angled toward the sun
- Make sure no part of the solar panel is shaded
- Clean the solar panel
If your measurement is still off, your solar panel may be damaged.
Step 2: Measure Short Circuit Current (Isc)
Locate the short circuit current (Isc) on the specs label on the back of the panel. Remember this number for later.
Prep your multimeter to measure amps. To do so, move the red probe to the amperage terminal. Set your multimeter to the amp setting (A), choosing the right limit if yours isn’t auto-ranging.
Take your panel outside and put it in direct sunlight. Throw a towel over it to stop it from generating power.
Touch the red probe of your multimeter to the metal pin inside the positive MC4 connector. Touch the black probe to the metal pin inside the negative MC4 connector.
Remove the towel, read the current on your multimeter, and compare it to the short circuit current (Isc) listed on the back of your panel.
The short circuit current you’re measuring should be close to the one listed on the back of the panel. It doesn’t have to be the same, though.
For instance, I only measured 6.08A but my panel’s claimed Isc is 6.56A. There was a little haze in the sky when I tested, though, plus it was 11AM on a November morning, so I’m fine with these results. On a clear summer day at noon I’d expect it to be nearly identical to the Isc.
If your measurement is similar to the Isc listed on the back of the panel, great! Your panel is working fine.
For most people, measuring open circuit voltage and short circuit current are all you need to do to test that your solar panel is in good working order. You can stop testing if you want.
However, if you want to keep at it, there are more ways to test a solar panel with and without a multimeter. Keep reading to find out how.
If your measurement is pretty far off the claimed Isc, try the following and measure again:
- Make sure it’s a sunny day and the panel is in direct sunlight
- Test the solar panel as close to noon as possible
- Angle the solar panel towards the sun
- Make sure no part of the solar panel is shaded
- Clean the solar panel
Time of year also effects solar panel output. If your measurement doesn’t quite reach the Isc, it may not be your solar panel. It might just be the winter sun.
Step 3: Measure Operating Current (aka PV Current)
Note: You can also measure PV current by connecting the solar panel to a charge controller, which I discuss below in method #2.
That’s right — you can use a multimeter to measure how much current your solar panel is outputting. You’ll need some extra equipment, though:
Connect the solar charge controller to the battery.
Connect adapter cables to the charge controller.
Connect the negative solar cable to the negative adapter cable. DON’T connect the positive solar cable.
Prep the multimeter to measure amps, like you did in step 2. Throw a towel over the solar panel or place it face down on the ground so that it’s not generating any power.
Touch the red multimeter probe to the metal pin on the male MC4 connector (the one connected to the solar panel). Touch the black multimeter probe to the metal pin on the female MC4 connector (the one connected to the charge controller), thereby completing the connection.
Remove the towel from your solar panel (or flip it face up) and read the amperage on your multimeter to see how much current your solar panel is producing. My panel output 4.46A.
You can experiment with the panel’s tilt angle and direction to see how these factors affect output.
You can compare this number to the current at max power (Imp) on the back of the panel to see how close to maximum output your solar panel currently is. For instance, my panel’s Imp is 6.26A, and I measured a current of 4.46A.
While this may seem far off, it’s actually not that bad. Solar panels typically produce 70-80% of their rated power output, only reaching close to 100% in the industry-standard set of test conditions. (Not to mention the haze in the sky at the time of testing, and it being later in the year.)
4.46A is 71% of 6.26A, so this measurement is in line with expectations.
You’ve learned how to test solar panels with a multimeter.
Now it’s time to talk about how to test solar panel amps with a clamp meter. That’s right — you’ll learn how to check how much current your solar panel is producing.
How to Test Solar Panel Amps with a Clamp Meter
A clamp meter, sometimes called an ammeter, can measure the level of current flowing through a wire. You can use one to check whether or not your solar panels are outputting their expected number of amps.
A clamp meter makes solar panel testing incredibly quick and convenient because you don’t have to disconnect your panels in order to check them.
What You Need
- Clamp meter — Get one that can measure AC and DC current; many can only measure AC current.
- A working solar panel system — This testing method assumes your solar panel is already connected to your system and producing power. (If yours isn’t, first set it up.)
Step 1: Prep Your Clamp Meter to Measure DC Amps
Turn the clamp meter’s dial to the correct amps setting. For most people, that will be the lowest amperage setting. For instance, the solar panel I’m testing this time around — the Renogy 100W 12V solar panel — outputs only around 5-6 amps at max power, so I turned mine to the 60A setting.
Some clamp meters default to measuring AC current, so switch to the DC current mode if needed. You also might need to zero out the reading before measuring DC current.
Now your clamp meter is good to go.
Step 2: Measure the Solar Panel’s Current
Open the jaws of the clamp meter, place one of the solar panel’s wires inside, and close the jaws. The solar panel’s current reading will show on the display. Remember this number. I got 5.24 amps when I checked mine.
Sometimes, depending on which way the meter is oriented, you may get a negative current reading. That’s completely normal, just clamp the other wire or point the meter in the opposite direction and then re-clamp the wire.
Tip: When checking solar panel amps with a clamp meter, never clamp more than one wire at a time. If you do, because the current is flowing in opposite directions, it will cancel itself out and you’ll get a reading of zero amps.
Step 3: Compare Your Current Reading to the Panel’s Max Power Current
Look at the label on the back of your solar panel. Find the panel’s current at max power, abbreviated Imp. It may also be called the maximum operating current or something similar. In this example, my panel’s listed Imp is 4.91 amps.
Compare the panel’s Imp to your current reading. Your current reading should be in the ballpark of the panel’s current at max power, but by no means does it have to be identical. The current I measured was 5.24 amps and my panel’s Imp is 4.91 amps, so I know my panel is working properly!
If your current reading is significantly less than the panel’s Imp, try the following and recheck:
- Check that the the clamp meter is set to the DC current setting and the right amperage range. Also, make sure that, before measuring, you zero out the DC current reading, if needed.
- Make sure you’re only clamping one wire with your meter
- Make sure the solar panel is in direct sunlight with no clouds blocking the sun and no shade on the panel
- Check that the solar panel is angled towards the sun
- Clean the solar panel
- Make sure your battery isn’t full charged. If a battery is mostly or full charged, the charge controller will reduce the solar panel’s output. If it is, discharge the battery a bit and then retry.
If you’ve tried the above and your solar panel is still outputting much less current than expected, it may be damaged.
You can repeat these steps for all the solar panels in your system. If you find a panel that is outputting significantly less current than the listed Imp, it’s worth disconnecting and diagnosing that specific panel further.
How to Test Solar Panel Output with a Solar Charge Controller
You can also test solar panels by connecting them to a solar charge controller.
Once connected, you can measure:
Some charge controllers make this easier to do than others.
For instance, some have LCD displays that show system specs such as PV current and PV voltage, which you can use to calculate wattage. Others can be connected via Bluetooth to your phone where you can monitor your system and measure its output.
And some have neither feature — they can’t tell you how much power your solar panel is generating. Avoid these ones.
What You Need
- Solar charge controller — Get one that either displays PV voltage and PV current (e.g. Renogy Wanderer 10A), or has Bluetooth (e.g. Victron SmartSolar MPPT or Renogy Wanderer 30A with Renogy BT-1 Bluetooth Module)
- Battery — e.g. this 12V 33Ah lead acid battery
- Battery to charge controller cables
- Solar panel to charge controller cables
Step 1: Connect the Battery to the Charge Controller
Connect your battery and charge controller.
For my setup, I used the Renogy Wanderer 10A, this 12V 33Ah lead acid battery, and some connector cables.
Step 2: Connect the Solar Panel to the Charge Controller
Next, connect your solar panel to the charge controller.
Step 3: Calculate Power Output
Cycle through the display screens until you find PV voltage. Mine was 15.2V.
Next, find the PV current. Mine was 4.5A.
To calculate the solar panel wattage, simply multiply volts times amps to get watts:
15.2 volts 4.5 amps = 68.4 watts
My solar panel was outputting 68.4 watts. Not bad for a 100 watt solar panel on a hazy November day.
If you have a charge controller with Bluetooth, you can also use the brand’s app to measure solar panel output from your phone.
For example, let’s say you’re using the Renogy Wanderer 30A. As you can see, it doesn’t have an LCD display, so there’s no way of calculating the solar panel output by looking at it.
To find out, we need to use Bluetooth. Some charge controllers, like the Victron SmartSolar MPPT, have Bluetooth built-in.
The Wanderer 30A, on the other hand, has a compatible Bluetooth module you can buy, called the Renogy BT-1. I plugged the BT-1 into my Wanderer 30A and connected the charge controller to my phone using the Renogy DC Home app.
Then I opened up the app and was able to see a slew of system specs, including wattage. The clouds rolled in as I was setting up this system, so my 100 watt solar panel was outputting just 28 watts. (That’s typical for a 100 watt solar panel on cloudy days.)
Using the charge controller’s app is my favorite way of measuring solar panel output. It’s just so convenient. Bluetooth is definitely a worthwhile upgrade in my opinion.
Plus, apps like these automatically track solar energy production over time. Now we’re talking!
If you can’t measure solar panel power output with your charge controller, don’t fret.
How to Measure Solar Panel Output with a Watt Meter
This is a watt meter (aka power meter):
You can find them for cheap on Amazon. Connect one inline between your solar panel and charge controller and it’ll measure voltage, current, wattage, and more.
What You Need
- Solar charge controller — e.g. Renogy Wanderer 30A
- Battery — e.g. this 12V 33Ah lead acid battery
- Watt meter — Get one with MC4 connectors attached to it or be prepared to crimp them on yourself
- Battery to charge controller cables
- Solar panel to charge controller cables
Step 1: Connect Battery to Solar Charge Controller
Connect the battery and charge controller.
Step 2: Connect the Watt Meter to the Adapter Cables
Connect the watt meter inline to the charge controller adapter cables. You can see I crimped the MC4 connectors to one end and a length of wire to the other.
Tip: You can buy this watt meter with MC4 connectors if you don’t want to fuss with crimping wire connectors.
Connect the adapter cables (with watt meter) to the charge controller.
Step 3: Connect the Solar Panel
Connect the solar panel to the charge controller adapter cables.
Step 4: Measure Power Output
Place the solar panel outside in direct sunlight. Once you do, the watt meter will automatically turn on and start measuring your solar panel’s power output.
At this point in the day, the clouds were here to stay, so my watt meter measured an output of 24.4 watts from my 100 watt solar panel.
As you can in the photo, you can also use a power meter to measure solar panel amps (1.86A) and voltage (13.14V). The meter also measures total watt hours, a useful metric for seeing how much energy your solar panel generates in a day.
Note: A watt meter placed in this location automatically turns off when the solar panel stops generating power. When it turns back on, the totals will all be reset to zero. If you want to record your solar panel’s energy production over time, I recommend getting a charge controller with Bluetooth such as the Victron SmartSolar MPPT.
How to wire solar panels in series vs. parallel
As a homeowner who is just learning about solar energy options, it is easy to get confused with all the technical terms you might read or hear about. You may have come across the different ways that solar panels can be wired. And your first thought might be: does this really matter? After all, you just want the panels to produce electricity!
How your solar panels are wired actually does matter. It impacts the performance of your system, as well as the inverter you will be able to use. You want your panels wired so that they give you the best savings possible, and a better return on investment.
Here are answers to a few of the common questions homeowners ask about wiring solar panels that can help you get a better understanding of whether your panels should be wired in series or parallel.
What does it mean to wire solar panels in series?
Just like a battery, solar panels have two terminals: one positive and one negative.
When you connect the positive terminal of one panel to the negative terminal of another panel, you create a series connection. When you connect two or more solar panels like this, it becomes a PV source circuit.
Solar panels are wired in series when you connect the positive terminal of one panel to the negative terminal of another.
When solar panels are wired in series, the voltage of the panels adds together, but the amperage remains the same. So, if you connect two solar panels with a rated voltage of 40 volts and a rated amperage of 5 amps in series, the voltage of the series would be 80 volts, while the amperage would remain at 5 amps.
Putting panels in series makes it so the voltage of the array increases. This is important, because a solar power system needs to operate at a certain voltage in order for the inverter to work properly.
So, you connect your solar panels in series to meet the operating voltage window requirements of your inverter.
What does wiring solar panels in parallel mean?
When solar panels are wired in parallel, the positive terminal from one panel is connected to the positive terminal of another panel and the negative terminals of the two panels are connected together.
The positive wires are connected to a positive connector within a combiner box, and the negative wires are connected to the negative connector. When multiple panels are wired in parallel, it is called a PV output circuit.
With parallel solar panels, the positive terminal from one panel is connected to the positive terminal of another panel and the negative terminals of the two panels are connected together.
Wiring solar panels in parallel causes the amperage to increase, but the voltage remains the same. So, if you wired the same panels from before in parallel, the voltage of the system would remain at 40 volts, but the amperage would increase to 10 amps.
Wiring in parallel allows you to have more solar panels that produce energy without exceeding the operating voltage limits of your inverter. Inverters also have amperage limitations, which you can meet by wiring your solar panels in parallel.
How do solar panels wired in series compare to solar panels wired in parallel?
A charge controller is a determining factor when it comes to solar panel wiring. Maximum Power Point Tracking (MPPT) charge controllers are for wiring solar panels in a series, where Pulse Width Modulation (PWM) charge controllers are used to wire solar panels in parallel.
To understand how wiring in series works in comparison to how parallel wiring works, let’s think for a moment about how Christmas lights used to work.
If a bulb burned out, came loose from its socket or broke, the entire string wouldn’t light up. This was because the lights were wired in a series. You would have to locate the problem bulb and replace it or reseat it to get the string of lights to work again.
Today, most Christmas lights feature a form of parallel wiring that allows for strings of lights to stay lit even when there is one troublemaker in the string.
Circuits wired in series work the same way for solar panels. If there is a problem with the connection of one panel in a series, the entire circuit fails. Meanwhile, one defective panel or loose wire in a parallel circuit will not impact the production of the rest of the solar panels.
In practice, how solar panels are wired today depends on the type of inverter that is being used.
Find out how much solar panels can save you annually
Wiring solar panels when using a string inverter
String inverters have a rated voltage window that they need from the solar panels in order to operate. It also has a rated current that the inverter needs to function properly.
String inverters have maximum power point trackers (MMPT) in them that can vary the current and voltage to produce the maximum amount of power possible.
In most crystalline solar panels, the open circuit voltage is around 40 Volts. Most string inverters have an operational voltage window between 300 and 500 volts. This would mean that when designing a system, you could have between 8 and 12 panels in a series.
Any more than that would exceed the maximum voltage the inverter could handle.
The thing is, most solar panel systems are larger than 12 panels. So, in order to have more panels in the system, you could wire another series of panels, and connect those series in parallel. This allows you to have the right number of panels to meet your home’s energy needs, without exceeding the limits of your inverter.
Which wiring works better – series or parallel?
In theory, parallel wiring is a better option for many electrical applications because it allows for continuous operation of the panels, even if one of the panels is malfunctioning. But, it is not always the best choice for all applications. You also might need to meet certain voltage requirements in order for your inverter to operate.
A critical balance of voltage and amperage needs to be achieved in order for your solar array to perform at its best. So, in most cases, a solar installer will design your solar array with a hybrid of both series and parallel connections.
Can you add more solar panels to your existing system?
Going with a full installation from the start is always best when installing a residential solar system. Using a solar calculator helps estimate your solar system costs and power needs in order to accurately determine how many panels you should have in your system.
However, if you were limited with your budget, or underestimated your future power needs when you installed your PV panels, you could consider adding more panels to your existing system.
If you are thinking about expanding your solar PV system in the future, you should design your system with that in mind. In order to accommodate more panels in the future, you should have an oversized inverter.
Does the use of microinverters or optimizers change how solar panels are wired?
The use of microinverters or optimizers in the design of your solar system can help avoid inverter-size limitations that string inverters have. By having each panel connected to its own microinverter, your system can be expanded one panel at a time.
This can be done with existing string inverters that are maxed out, provided that the additional panels are wired on the AC side of the string inverter.
How do you connect solar panels to the grid?
Another consideration between series wired and parallel wired is the amount of wires that are used to connect the solar system into the grid. A series wired circuit will use a single wire to connect. Meanwhile, a parallel wired system will have multiple wires to connect it into the grid.
Series vs. parallel. why not have both?
The main thing to remember is that wiring in series will increase your voltage, while wiring in parallel will increase your amperage. Both of the voltage and amperage need to be considered when designing your system, especially when it comes to finding an inverter that will work best for you.
Most of the time, a solar installer will choose to design a system with both series and parallel connections. This allows the system to operate at a higher voltage and amperage, without overpowering the inverter, so your solar panels can operate at their best.
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Key takeaways
- The way in which solar panels are wired determines how the system performs and what inverter the system can be paired with.
- When solar panels are wired in series, the positive terminal of one solar module is connected to the negative terminal of another, which increases the voltage of the solar system.
- Solar panels are wired in series to increase the voltage in order to meet the minimum operating requirements of the inverter.
- If solar modules are wired in parallel, the positive terminal of one module is connected to the positive terminal of another module, which increases the amperage of the system.
- Wiring solar panels in parallel allows you to have more solar panels without exceeding an inverter’s voltage limit.
Andrew Sendy
Home Solar Journalist
Andy is deeply concerned about climate change but is also concerned about cost of living pressures on American families. He advocates for solar energy and solar battery storage only to the extent that they make financial sense for homeowners. He is not affiliated with any particular solar company in the United States.
Solar Cells
Solar cells are in fact large area semiconductor diodes. Due to photovoltaic effect energy of light (energy of photons) converts into electrical current. At p-n junction, an electric field is built up which leads to the separation of the charge carriers (electrons and holes). At incidence of photon stream onto semiconductor material the electrons are released, if the energy of photons is sufficient. Contact to a solar cell is realised due to metal contacts. If the circuit is closed, meaning an electrical load is connected, then direct current flows. The energy of photons comes in packages which are called quants. The energy of each quantum depends on the wavelength of the visible light or electromagnetic waves. The electrons are released, however, the electric current flows only if the energy of each quantum is greater than WL. WV (boundaries of valence and conductive bands). The relation between frequency and incident photon energy is as follows:
h. Planck constant (6,626·10.34 Js), μ. frequency (Hz)
Crystalline solar cells
Among all kinds of solar cells we describe silicon solar cells only, for they are the most widely used. Their efficiency is limited due to several factors. The energy of photons decreases at higher wavelengths. The highest wavelength when the energy of photon is still big enough to produce free electrons is 1.15 μm (valid for silicon only). Radiation with higher wavelength causes only heating up of solar cell and does not produce any electrical current. Each photon can cause only production of one electron-hole pair. So even at lower wavelengths many photons do not produce any electron-hole pairs, yet they effect on increasing solar cell temperature. The highest efficiency of silicon solar cell is around 23 %, by some other semi-conductor materials up to 30 %, which is dependent on wavelength and semiconductor material. Self loses are caused by metal contacts on the upper side of a solar cell, solar cell resistance and due to solar radiation reflectance on the upper side (glass) of a solar cell. Crystalline solar cells are usually wafers, about 0.3 mm thick, sawn from Si ingot with diameter of 10 to 15 cm. They generate approximately 35 mA of current per cm 2 area (together up to 2 A/cell) at voltage of 550 mV at full illumination. Lab solar cells have the efficiency of up to 30 %, and classically produced solar cells up to 20 %.
Wafers and crystalline solar cells (courtesy: SolarWorld)
Amorphous solar cells
The efficiency of amorphous solar cells is typically between 6 and 8 %. The Lifetime of amorphous cells is shorter than the lifetime of crystalline cells. Amorphous cells have current density of up to 15 mA/cm 2. and the voltage of the cell without connected load of 0.8 V, which is more compared to crystalline cells. Their spectral response reaches maximum at the wavelengths of blue light therefore, the ideal light source for amorphous solar cells is fluorescent lamp.
Surface of different solar cells as seen through microscope (courtesy: Helmholtz-Zentrum Berlin)
Solar Cell Models
The simplest solar cell model consists of diode and current source connected parallelly. Current source current is directly proportional to the solar radiation. Diode represents PN junction of a solar cell. Equation of ideal solar cell, which represents the ideal solar cell model, is:
IL. light-generated current [1] (A), Is. reverse saturation current [2] (A) (aproximate range 10.8 A/m 2 ) V. diode voltage (V), VT. thermal voltage (see equation below), VT = 25.7 mV at 25°C n. diode ideality factor = 1. 2 (n = 1 for ideal diode)
Thermal voltage VT (V) can be calculated with the following equation:
k. Boltzmann constant = 1.38·10.23 J/K, T. temperature (K) q. charge of electron = 1.6·10.19 As
FIGURE 1: Ideal solar cell model
FIGURE 2: Real Solar cell model with serial and parallel resistance [3] Rs and Rp, internal resistance results in voltage drop and parasitic currents
The working point of the solar cell depends on load and solar irradiation. In the picture, I-V characteristics at short circuit and open circuit conditions can be seen. Very important point in I-U characteristics is Maximum Power Point, MPP. In practice we can seldom reach this point, because at higher solar irradition even the cell temperature increases, and consequently decreasing the output power. Series and paralell parasitic resistances have influence on I-V curve slope. As a measure for solar cell quality fill-factor, FF is used. It can be calculated with the following equation:
IMPP. MPP current (A), VMPP. MPP voltage (V) Isc. short circuit current (A), Voc. open circuit voltage (V)
In the case of ideal solar cell fill-factor is a function of open circuit parameters and can be calculated as follows:
Where voc is normalised Voc voltage (V) calculated with equation below:
k. Boltzmann constant = 1,38·10.23 J/K, T. temperature (K) q. charge of electron = 1,6·10.19 As, n. diode ideality factor (-) Voc. open circuit voltage (V)
For detailed numerical simulations more accurate models, like two diode model, should be used. For additional explanations and further solar cell models description please see literature below.
Solar Cell Characteristics
Samples of solar cell I-V and power characteristics are presented on pictures below. Typical point on solar cell characteristics are open circuit (when no load is connected), short circuit and maximum power point. Presented characteristics were calculated for solar cell with following data: Voc = 0,595 mV, Isc = 4,6 A, IMPP = 4,25 A, VMPP = 0,51 V, and PMPP temperature coefficient γ =.0,005 %/K. Calculation algorithm presented in the book Photovoltaik Engineering (Wagner, see sources) was used.
FIGURE 3: Solar cell I-V characteristics for different irradiation values
FIGURE 4: Solar cell power characteristics for different irradiation values
FIGURE 5: Solar cell I-V characteristics temperature dependency
FIGURE 6: Solar cell power characteristics temperature dependency
| [1] | Sometimes term photocurrent IPh is also used. |
| [2] | Sometimes term dark current Io is also used. |
| [3] | For paralell resistanse term shunt resistor Rsh is also used. |
Simulation Tools
Open Photovoltaics Analysis Platform. Open Photovoltaics Analysis Platform (OPVAP) is a group of software used in the field of solar cells, which include analyzing experimental data, calculating optimum architecture based on your materials, and even some research assistant tools such as PicureProcess.
Organic Photovoltaic Device Model. Organic Photovoltaic Device Model (OPVDM) is a free 1D drift diffusion model specifically designed to simulate bulk-heterojuncton organic solar cells, such as those based on the P3HT:PCBM material system. The model contains both an electrical and an optical solver, enabling both current/voltage characteristics to be simulated as well as the optical modal profile within the device. The model and it’s easy to use graphical interface is available for both Linux and Windows.
Other Technologies. Links
NanoFlex Power. flexible organic solar cells.
sphelar power. spherical solar cells technology.
Solar Panel Maximum Voltage Calculator
Just so you know, this page contains affiliate links. If you make a purchase after clicking on one, at no extra cost to you I may earn a small commission.
Use our calculator to easily find the maximum open circuit voltage of your solar array.
Note: Based on your inputs, this charge controller has a suitable maximum PV voltage for your solar array. However, it may not be the right option for your setup based on other factors such as current rating and battery bank voltage, so check that it meets all your other requirements before going with this option.
Calculator Assumptions
- All the solar panels you input into the calculator are wired together in a single series string. If you have multiple series strings wired in parallel, I recommend using the calculator to find the max voltage for each series string. Then use the lowest max voltage as your array’s max open circuit voltage. This is because, when wiring different series strings in parallel, the voltage of the resulting array is equal to the voltage of the lowest-rated series string.
- If you don’t enter a temperature coefficient of Voc for a panel, the calculator assumes that all the panels with those specs are monocrystalline and/or polycrystalline silicon solar panels, the predominant types of solar panels on the market today.
How to Use This Calculator
Find the technical specifications label on the back of your solar panel. For example, this is the label on the back of my Renogy 100W 12V Solar Panel.
Note: If your panel doesn’t have a label, you can usually find its technical specs in its product manual or online on its product page.
Enter the open circuit voltage (Voc). My panel’s was 22.3V.
Enter how many of this solar panel you’re wiring in series. For this example, let’s say that I have 4 of these Renogy 100W 12V Solar Panels. They’re identical panels and I’m wiring them all 4 of them in series. In this case, I’d enter 4 in the Quantity field.
Optional: Enter the panel’s temperature coefficient of Voc and select the correct unit (%/°C or mV/°C). My panel’s was.0.28%/°C. You can leave this field blank, in which case the calculator uses the appropriate voltage correction factor based on your lowest expected temperature.
If you’re wiring different solar panels together in series, click Add a Panel and repeat the above steps to add that panel’s specs and quantity. At any point you can click Remove a Panel to remove the last panel.
Enter the lowest temperature you expect your solar array to experience in daylight and select the correct unit (°F or °C). Often, people will use the lowest recorded temperature at their location. For example, I live in Atlanta and did a quick Google search to find out that the lowest recorded temperature here was.9°F (-22.8°C).
Note: If your solar panels are mounted on a vehicle, consider the various locations you plan on visiting in your vehicle when entering your lowest expected temperature.
Click Calculate Max Voltage to get your results. For the example I gave of the 4 Renogy panels, I got a maximum solar array voltage of 101.1V. When designing my solar system, I need to pick a charge controller whose max PV voltage rating is greater than this number.
Ways to Calculate Maximum Solar Panel Voltage
Here are a couple more ways to find your max solar panel voltage besides using our calculator. Use one of these methods if you’d like to understand the math underlying the calculations.
Note: If you’d also like to calculate the power output of your solar array, check out our solar panel series and parallel calculator.
Use Correction Factors
The National Electrical Code (NEC) provides a table of voltage correction factors for solar panels based on ambient temperature. The correction factors make it easy to calculate your maximum solar system voltage yourself.
| 1.02 | 76 to 68 | 24 to 20 |
| 1.04 | 67 to 59 | 19 to 15 |
| 1.06 | 58 to 50 | 14 to 10 |
| 1.08 | 49 to 41 | 9 to 5 |
| 1.10 | 40 to 32 | 4 to 0 |
| 1.12 | 31 to 23 | -1 to.5 |
| 1.14 | 22 to 14 | -6 to.10 |
| 1.16 | 13 to 5 | -11 to.15 |
| 1.18 | 4 to.4 | -16 to.20 |
| 1.20 | -5 to.13 | -21 to.25 |
| 1.21 | -14 to.22 | -26 to.30 |
| 1.23 | -23 to.31 | -31 to.35 |
| 1.25 | -32 to.40 | -36 to.40 |
Note: The above table has been adapted from Table 690.7(A) from the 2023 edition of the NEC. It applies to monocrystalline and polycrystalline silicon panels, the predominant types of solar panels on the market today.
For this method, you’ll need the table along with the following numbers:
- Open circuit voltage (Voc) of each solar panel
- Number of each type of solar panel
- Lowest expected temperature
Instructions
Find the appropriate correction factor from the above table using your lowest expected temperature.
Calculate the max open circuit voltage of each solar panel by multiplying its open circuit voltage by your correction factor.
If your panels are identical:
Max solar panel Voc = Solar panel Voc × Correction factor
If your panels are different:
Max solar panel Voc #1 = Solar panel Voc #1 × Correction factor Max solar panel Voc #2 = Solar panel Voc #2 × Correction factor Max solar panel Voc #3 = Solar panel Voc #3 × Correction factor. etc
Sum the max open circuit voltages of all your solar panels wired in series.
If your panels are identical:
Max solar array Voc = Max solar panel Voc × Number of panels
If your panels are different:
Max solar array Voc = Max solar panel Voc #1 Max solar panel Voc #2 Max solar panel Voc #3
Pretty easy! For once, the NEC makes life a little easier.
Example #1: Identical Solar Panels
Let’s say these are the specs for 2 identical solar panels you’re wiring in series:
- Solar panel Voc: 19.83V
- Number of solar panels wired in series: 2
- Lowest expected temperature:.10°F (-23°C)
Here’s how you’d find your max solar array voltage:
Find the appropriate correction factor using the above table. In this example, based on my lowest expected temperature of.10°F (-23°C), my correction factor is 1.2.
Multiply solar panel Voc by your correction factor.
Max solar panel Voc = 19.83V × 1.2 = 23.796
Multiply the max solar panel Voc by the number of panels wired in series.
Max solar array Voc = 23.796V × 2 = 47.592V ≈ 47.6V
In this example, the max open circuit voltage of your solar array is 47.6V.
Example #2: Different Solar Panels
Let’s say instead that your 2 solar panels are different. They have the following open circuit voltages:
- Solar panel Voc #1: 22.6V
- Solar panel Voc #2: 21.4V
- Number of panels wired in series: 2
- Lowest expected temperature:.25°F (-32°C)
Here’s how you’d find your max solar array voltage:
Find the appropriate correction factor using the above table. In this example, based on my lowest expected temperature of.25°F (-32°C), my correction factor is 1.23.
Multiply each panel’s Voc by your correction factor.
Max solar panel Voc #1 = 22.6V × 1.23 = 27.798V Max solar panel Voc #2 = 21.4V × 1.23 = 26.322V
Sum the panels’ max open circuit voltages together.
Max solar array Voc = 27.798V 26.322V = 54.12V ≈ 54.1V
In this example, the max open circuit voltage of your solar array is 54.1V.
Use Temperature Coefficient of Voc
For this method, you’ll need the following numbers:
- Voc of each solar panel
- Temperature coefficient of Voc of each solar panel
- Number of solar panels wired in series
- Lowest expected temperature (°C)
Note: I’ll just cover how to use this method if your temperature coefficient’s unit is %/°C, which, in my experience, is much more common than mV/°C.
Instructions
Calculate the maximum temperature differential by subtracting 25°C from your lowest expected temperature. We use 25°C because that is the industry-standard temperature at which solar panels are rated. If using Fahrenheit, I recommend converting your lowest expected temperature to Celsius. It makes the calculations easier.
Max temp differential = Lowest expected temperature. 25°C
Calculate the maximum voltage increase percentage for each solar panel by multiplying the maximum temperature differential by the panel’s temperature coefficient of Voc. Once again, this is assuming your solar panel’s temp coefficient is given in %/°C.
If your panels are identical:
Max voltage increase percentage = Max temp differential × Temp coefficient of Voc
If your panels are different:
Max voltage increase percentage #1 = Max temp differential × Temp coefficient of Voc #1 Max voltage increase percentage #2 = Max temp differential × Temp coefficient of Voc #2 Max voltage increase percentage #3 = Max temp differential × Temp coefficient of Voc #3. etc
Calculate the maximum voltage increase of each panel by multiplying its maximum voltage increase percentage by its open circuit voltage.
If your panels are identical:
Max voltage increase = Solar panel Voc × Max voltage increase percentage
If your panels are different:
Max voltage increase #1 = Solar panel Voc #1 × Max voltage increase percentage #1 Max voltage increase #2 = Solar panel Voc #2 × Max voltage increase percentage #2 Max voltage increase #3 = Solar panel Voc #3 × Max voltage increase percentage #3. etc
Calculate the maximum open circuit voltage of each panel by summing its open circuit voltage and maximum voltage increase.
If your panels are all identical:
Max solar panel Voc = Solar panel Voc Max voltage increase
If your panels are different:
Max solar panel Voc #1 = Solar panel Voc #1 Max voltage increase #1 Max solar panel Voc #2 = Solar panel Voc #2 Max voltage increase #2 Max solar panel Voc #3 = Solar panel Voc #3 Max voltage increase #3. etc
Sum the max open circuit voltages of all your solar panels wired in series.
If your panels are all identical:
Max solar array Voc = Max solar panel Voc × Number of panels in series
If your panels are different:
Max solar array Voc = Max solar panel Voc #1 Max solar panel Voc #2 Max solar panel Voc #3
Example #1: Identical Solar Panels
Let’s run through an example using the following numbers:
- Solar panel Voc: 20.2V for all panels
- Number of solar panels wired in series: 3
- Lowest expected temperature:.15°C (5°F)
- Temperature coefficient of Voc:.0.3%/°C for all panels
Subtract 25°C from your lowest expected temperature.
Max temp differential =.15°C. 25°C =.40°C
Multiply the maximum temperature differential by the temperature coefficient of Voc.
Max voltage increase percentage =.0.3%/°C ×.40°C = 12%
Multiply the solar panel open circuit voltage by the maximum voltage increase percentage.
Max voltage increase = 20.2V × 12% = 2.424V
Add the maximum voltage increase to the solar panel open circuit voltage.
Max solar panel Voc = 20.2V 2.424V = 22.624V
Multiply the maximum solar panel open circuit voltage by the number of panels wired in series.
Max solar array Voc = 22.624V × 3 = 67.872V ≈ 67.9V
In this example, the maximum open circuit voltage of your solar array is 67.9V.
Example #2: Different Solar Panels
Let’s say you have 2 different panels with the following specs:
- Solar panel Voc #1: 19.7V
- Solar panel Voc #2: 22.1V
- Number of panels wired in series: 2
- Lowest expected temperature:.20°C (-4°F)
- Temperature coefficient of Voc #1:.0.28%/°C
- Temperature coefficient of Voc #2:.0.3%/°C
Here’s how you’d find your max Voc in this scenario:
Subtract 25°C from your lowest expected temperature.
Max temp differential =.20°C. 25°C =.45°C
Multiply the maximum temperature differential by each panels’ temperature coefficient of Voc.
Max voltage increase percentage #1 =.0.28%/°C ×.45°C = 12.6% Max voltage increase percentage #2 =.0.3%/°C ×.45°C = 13.5%
Multiply each panel’s Voc by its maximum voltage increase percentage.
Max voltage increase #1 = 19.7V × 12.6% = 2.4822V Max voltage increase #2 = 22.1V × 13.5% = 2.9835V
Add each panel’s maximum voltage increase to its Voc.
Max solar panel Voc #1 = 19.7V 2.4822V = 22.1822V Max solar panel Voc #2 = 22.1V 2.9835V = 25.0835V
Sum the max open circuit voltages of all the solar panels wired in series.
Max solar array Voc = 22.1822V 25.0835V = 47.2657V ≈ 47.3V
In this example, the max voltage of your solar array is 47.3V.
How to Size a Charge Controller Using Max Solar Panel Voltage
Now that you know your maximum solar array voltage, it’s time to pick a solar charge controller.
When shopping for a charge controller, look for its maximum PV voltage (sometimes called maximum PV open circuit voltage or maximum input voltage).
Make sure your charge controller’s maximum PV voltage is higher than the maximum open circuit voltage of your solar array.
For example, let’s say you calculate your max solar array voltage to be 105V. Then a charge controller with a max PV voltage of 100V is too low. You’ll need to instead get one with a max PV voltage of, say, 150V.
Common Mistakes When Calculating Max Solar Panel Voltage
Based on my experience.- and lots of reader emails and Комментарии и мнения владельцев.- here are the most common mistakes I see people make when trying to find their solar system’s max open circuit voltage:
- Forgetting to correct for temperature. Solar panel voltage increases as temperature drops. Often, beginners aren’t aware of this fact. (I definitely wasn’t when I first started.) As a result, they just calculate the Voc of their solar array and use that number to size their solar charge controller. That puts them at risk of frying their charge controller on cold days.
- Using maximum power voltage (Vmp or Vmpp) instead of open circuit voltage (Voc). Many panels also list a maximum power voltage (aka optimum operating voltage), denoted Vmp or Vmpp. Some people mistakenly think they should use Vmp rather than Voc in their max voltage calculations. Always use Voc.
- Using rules of thumb without understanding their limits. A couple times, I’ve seen people online give a rule of thumb for calculating max Voc.- such as add 5V to each panel’s Voc or add 20% to the array’s Voc. These can be helpful, but readers often fail to understand that these quick and dirty methods are best suited for certain temperature ranges.
Lastly, it’s important to point out that the max solar array voltage you calculate is based on your lowest expected temperature. If your array ever gets colder than that in daylight, there’s a chance it could exceed this number.