Photovoltaic Arrays LINK. Pv module and array

What is Solar Module? Types of Solar Modules

Every day we keep seeing the Solar Energy usage increasing, and the future also has many good things in this industry that we can avail. There are soo many benefits Solar Modules can address from remote power systems for cabins, remote sensing to many more but do you know what a solar module is?

What is Solar Module?

A single photovoltaic Module/Panel is an assembly of connected solar cells that will absorb sunlight as source of energy to develop electricity.

A group of PV modules (also called PV panels) is wired into an extensive array called PV array to gain a required current and voltage.

When you make up your mind to buy a solar power system, you will encounter three types, and as a layman, it becomes challenging to understand the difference between these technologies. So let’s have a brief understanding of these below:

Mono-crystalline Solar Modules

It is a solar modules comprising mono-crystalline solar cells.

When sunlight falls on the mono-crystalline solar modules, the cells absorb the energy and create an electric field through a complicated process. Hence it comprises of voltage and current which is directly used to run DC.

• The panel cells have a pyramid pattern that offers a larger surface area to collect more energy from the sun’s rays.
• It reduces reflection and thereby increase absorption; the cells are coated with silicon nitride.
• These panels have life span up to 25-30 years.
• They are useful in exhibiting more excellent heat resistance.
• The produced electricity is collected through metal conductors printed into cells.

Polycrystalline Solar Modules

PolyCrystalline solar modules are solar modules that consist of several crystals of silicon in a single PV cell.

Polycrystalline PV panels cover 50% of the global production of modules.

Made of multiple photovoltaic cells and each cell contains silicon crystals that function as a semiconductor device. As the photons from the sunlight fall on the PN junction, it imparts energy to the electrons to flow as electric current.

• Polycrystalline silicon is the most consolidated and tested photovoltaic technology.
• The conversion efficiency in diffused light conditions (e.g. on a cloudy day) is better than in monocrystalline modules.
• Poly-crystalline cells are slightly cheaper than monocrystalline ones.
• Poly-crystalline is having 25 years of life span.

Thin-film Solar Modules

If there’s one product that has the opportunity to benefit from the tariffs on crystalline silicon solar modules, it’s the thin-film module.

It is a good option for projects with lesser power requirements but needs for lightweight and portability. Thin-film technologies have produced a maximum efficiency of 20.3%, with the most common material amorphous silicon at 12.5%.

• Thin-film panels have 30% less than crystalline panels due to the module itself and its installation process.
• It is easy to handle.
• flexible compared to conventional solar technology.
• You can get ut quickly in thin wafer sheets.

Solar PV Efficiency

Solar modules are between 15% and 20% efficient, with outliers on either side of the range. High-quality solar modules can exceed 22% efficiency, but the majority of photovoltaic panels available are not above 20% efficiency.

On average, today have efficiency ratings as high as 22.8%, whereas the majority of modules range from 16% to 18% efficiency rating. SolarSmiths solar modules are known for being the most efficient solar module brand available on the market. Our experts always strive hard to be there with you with your plan for the solar module, so connect today and help you with maximum efficiency projects.

Photovoltaic Arrays[LINK]

The Photovoltaics.f90 module includes three different models referred to as “Simple”, “Equivalent One-Diode” and “Sandia” and the choice will determine the mathematical models (and input data) used to determine the energy produced by solar/electric conversion panels. The EnergyPlus photovoltaic array models are called one at a time at the HVAC system timestep along with other electrical generation components such as gas turbines and diesel engines.

All of the photovoltaic models share the same models for predicting incident solar radiation that are also used for the solar thermal calculations and are described in the section Climate, Sky and Solar/Shading Calculations.

Note that some of the terminology used to discussed photovoltaics overlaps with terminology used to discuss Fortran programs. The word module may refer to a PV panel or to a fortran90 programming entity. Model may refer to a manufacturers production model for a specific type of PV module or to a mathematical model used for engineering analysis. Array may refer to a collection of PV modules wired together or to a mathematical variable with multiple elements.

The PV modules are assumed to always run when the total incident solar is greater than 0.3 Watts. If the incident solar is less than 0.3, then the modules produce no power.

PV arrays are managed by an electric load center. The load center is a “load” with respect to generating equipment but is a “supply center” for the rest of the building. PV arrays need to be connected to ElectricLoadCenter:Distribution objects that have a DC buss type.

Simple Model[LINK]

The Generator:PV:Simple object describes about the simplest model for predicting photovoltaic energy production. In this model the user specifies the efficiency with which surfaces convert incident solar radiation to electricity. (In the other models this efficiency is determined as part of the model.) The full geometric model for solar radiation is used, including sky models, shading, and reflections, to determine the incident solar resource. The model accepts arbitrary conversion efficiencies and does not require actual production units be tested to obtain empirical performance coefficients. (The Energy.idd sets the range of conversion efficiencies to be on [0.1], but the user could alter the Energy.idd to extend this range if desired.)

Mathematical Description[LINK]

Nomenclature for Simple Photovoltaic model

PAsurf factiv GT cell invert

Electrical power produced by photovoltaics [W]

Net area of surface [m 2 ]

Fraction of surface area with active solar cells [ ]

Total solar radiation incident on PV array [W/m 2 ]

Module conversion efficiency [ ]

DC to AC conversion efficiency [ ]

The usable electrical power produced by a PV surface are calculated using:

On the right hand side of this equation, only GT is calculated by EnergyPlus and the rest are user inputs. Power levels are assumed constant over the timestep to arrive at energy production.

There are two modes that can be selected by the user that govern how the PV system is coupled to the building surfaces. If the integration mode is selected as ‘DECOUPLED’ then no adjustments are made to account for energy extracted in the form of electricity. If the integration mode is selected as ‘INTEGRATED’ then the energy extracted in the form of electricity is removed from surface heat transfer calculations using a sink term. This sink term is lagged from the previous timestep.

Equivalent One-Diode Model[LINK]

This model predicts the electrical performance of a photovoltaic (PV) array. This model is also known as the “TRNSYS PV” model.

Mathematically speaking, the EnergyPlus PV module employs equations for an empirical equivalent circuit model to predict the current-voltage characteristics of a single module. This circuit consists of a DC current source, diode, and either one or two resistors. The strength of the current source is dependent on solar radiation and the IV characteristics of the diode are temperature-dependent. The results for a single module equivalent circuit are extrapolated to predict the performance of a multi-module array.

The module employs a “four-parameter” equivalent circuit to model crystalline (both mono and poly) PV modules developed at the University of Wisconsin – Madison [2]. The values of these parameters cannot normally be obtained directly from manufacturers’ catalogs. However, the PV module will automatically calculate them from commonly available data. The PV module also includes an optional incidence angle modifier correlation to calculate how the reflectance of the PV module surface varies with the angle of incidence of solar radiation.

The module determines PV current as a function of load voltage. Other OUTPUTS include current and voltage at the maximum power point along the IV curve, open-circuit voltage, short circuit current as well as electrical load met and unmet.

General Nomenclature for the PV model

 c   normal GT GT,beam GT,diff GT,gnd GT,NOCT GT,ref IIL IL,ref Io Io,ref Isc Isc,ref Imp Imp,ref IAMKNPNSNs PPmax QRs Rsh Tc Tc,NOCT Tc,ref UL VVmp Vmp,ref Voc Voc,ref

Slope of PV array [degrees]

Empirical PV curve-fitting parameter

Semiconductor bandgap [eV]

Module conversion efficiency

Temperature coefficient of short-circuit current [A/K]

Temperature coefficient of open-circuit voltage [V/K]

Angle of incidence for solar radiation [degrees]

Module transmittance-absorptance product

Module transmittance-absorptance product at normal incidence

Total radiation incident on PV array

Beam component of incident radiation

Diffuse component of incident radiation

Ground-reflected component of incident radiation

Incident radiation at NOCT conditions

Incident radiation at reference conditions

Current

Module photocurrent

Module photocurrent at reference conditions

Diode reverse saturation current

Diode reverse saturation current at reference conditions

Short-circuit current

Short-circuit current at reference conditions

Current at maximum power point along IV curve

Current at maximum power point along IV curve, reference conditions

Dimensionless incidence angle modifier

Boltzmann constant [J/K]

Number of modules in parallel in array

Number of modules in series in array

Number of individual cells in module

PV output power

PV output power at maximum power point along IV curve

Electron charge constant

Module series resistance []

Module shunt resistance []

Module temperature [K]

Module temperature at NOCT conditions [K]

Module temperature at reference conditions [K]

Array thermal loss coefficient

Voltage

Voltage at maximum power point along IV curve

Voltage at maximum power point along IV curve, reference conditions

Open-circuit voltage

Open-circuit voltage at reference conditions [V]

General Nomenclature for the PV model

PV Section 1: Four-Parameter Model[LINK]

The four-parameter equivalent circuit model was developed largely by Townsend [1989] and is detailed by Duffie and Beckman [1991]. The model was first incorporated into a component for the TRNSYS simulation package by Eckstein [1990]. The EnergyPlus module employs the Eckstein model for crystalline PV modules, using it whenever the short-circuit IV slope is set to zero or a positive value as modified by Ulleberg [2000]. The four parameter model assumes that the slope of the IV curve is zero at the short-circuit condition:

This is a reasonable approximation for crystalline modules. The “four parameters” in the model are IL,ref, Io,ref, , and Rs. These are empirical values that cannot be determined directly through physical measurement. The EnergyPlus model calculates these values from manufactures’ catalog data as discussed in the following section on calculating these parameters

The four-parameter equivalent circuit is shown in the following figure:

Equivalent circuit in the four parameter model

V is the load voltage and I is the current flowing through the load and PV.

Determining Performance under Operating Conditions

The IV characteristics of a PV change with both insolation and temperature. The PV model employs these environmental conditions along with the four module constants IL,ref, Io,ref, , and Rs to generate an IV curve at each timestep.

The current-voltage equation of circuit shown in the previous figure is as follows:

Rs and  are constants. The photocurrent IL depends linearly on incident radiation:

The reference insolation Gref is nearly always defined as 1000 W/m 2. The diode reverse saturation current Io is a temperature dependent quantity:

Equation gives the current implicitly as a function of voltage. Once Io and IL are found from Eqs. 3 and 4, Newton’s method is employed to calculate the PV current. In addition, an iterative search routine finds the current (Imp)~~ and voltage (Vmp) at the point of maximum power along the IV curve.

Calculating IL,ref, Io,ref, , and Rs

The Idf specification for the PV model include several values which must be read from manufacturers’ PV module catalogs. The manufactures’ values are used to determine the equivalent circuit characteristics IL,ref, Io,ref, , and Rs. These characteristics define an equivalent circuit that is employed to find the PV performance at each timestep, as described previously. This section describes the algebra and calculation algorithms used to solve for the four equivalent circuit characteristics.

Three of these values, IL,ref, Io,ref, , may be isolated algebraically. The first step is to substitute the current and voltage into Eq. at the open-circuit, short circuit, and maximum power conditions:

In each case the “-1” term is may be dropped to simplify the algebra. This approximation has little influence on the right side of the equations since because the magnitude of Iois very small, generally on the order of 10.6 A. Some rearrangement then yields the following three expressions which isolate IL,ref, Io,ref, :

At this point an additional equation is needed in order to determine the last unknown parameter. Taking the analytical derivative of voltage with respect to temperature at the reference open-circuit condition derives the fourth equation. This analytical value is matched to the open-circuit temperature coefficient, a catalog specification:

The “TRNSYS PV model” uses an iterative search routine in these four equations to calculate the equivalent circuit characteristics. The first step is to set upper and lower bounds for the series resistance parameter Rs: physical constraints require the Rs~~value to lie between 0 and the value such that  = Ns. The initial guess for Rs is midway between these bounds.  and Io,ref are found from Eq. and Eq while Eq. gives a trivial solution for IL,ref. The model then employs Eq. to compare the analytical and catalog values for voc. When all other variables are held constant, the analytical value for voc increases monotonically with series resistance (Townsend 1989). If the analytical voltage coefficient is less than the catalog value, the lower bound for Rs is reset to the present guess value. Likewise, the upper bound is set to the current value if the calculated voc is too large. After resetting the upper or lower bound for Rs, a new guess value is found by averaging the bounds. This procedure repeats until Rs and  converge. Note that for IL,ref, Io,ref, , and Rs are assumed to be constant and are calculated only on the first call in the simulation. Alternatively, the user may enter a known series resistance by entering a positive value in the IDF. In this case the iterative routine described above is skipped and Eqs. and find IL,ref, Io,ref, and  directly from the given value of Rs.

PV Section 2 : Module Operating Temperature[LINK]

The PV model uses one of five methods for determining cell temperature data. The cell temperature of a PV module is important because the hotter the temperature of the panel, the lower its electrical output. The cell temperature calculation method is chosen by the user in the EnergyPlus IDF file through a parameter choice in the IDD entry called Integration and Cell Temperature Mode.

If the value of this parameter is “Decoupled NOCT Conditions” then the cell temperature of the PV is modeled using the method from the Duffie and Beckman (1991) for estimating cell temperature. This is based upon the standard NOCT (Nominal Operating Cell Temperature) measurements to compute the module temperature Tc at each timestep. The NOCT temperature (Tc,NOCT) is the operating temperature of the module with a wind speed of 1 m/s, no electrical load, and a certain specified insolation and ambient temperature [Beckman and Duffie, 1991]. The values for insolation GT,NOCT~~ and ambient temperature Ta,NOCT are usually 800 W/m 2 and 20º C. c is the convesion efficiency of the module, which varies with ambient conditions.  is a user-defined constant.

If the user specifies the “Decoupled Ulleberg Dynamic” mode for calculating cell temperature, then a method developed by Ulleberg is used:

In other words, the cell temperature is a function of the privious cell temperature and the thermal capacity of the PV module material.

If the user specifies “Integrated Surface Outside Face” for this parameter, then the temperature result from EnergyPlus’s modeling of surfaces is used for the cell temperature. Also the energy exported from the surface as electricity becomes a sink in the internal source modeling for the heat transfer surface.

If the user specifies “Integrated Transpired Collector” for this parameter, then the temperature result for the unglazed transpired collector surfaces is used for the cell temperature. Also the energy exported from the collector surface as electricity is deprecated using source term in the collector’s temperature modeling.

If the user specifies “Integrated Exterior Vented Cavity” for this parameter, then the temperature result for the exterior cavity is used for the cell temperature. Also the energy exported from the baffle surface as electricity is deprecated using source term in the baffle’s temperature modeling.

PV Section 3 : Multi-Array Modules[LINK]

The electrical calculations discussed in the sections above deal only with a single module. The EnergyPlus PV component may be used to simulate arrays with any number of modules. The IDF defines the number of modules in series (NS) and modules in parallel (NP) for the entire array. The total number of modules in the array is the product of NS and NP. When simulating a single module only, both NS and NP are set to 1. The single-module values for all currents and voltages discussed in PV Section 1 are multiplied by NP or NS to find values for the entire array. This approach neglects module mismatch losses.

With the above equations, and the assumption that the panels operate at the maximum power point, it is a direct calculation to determine DC power production. The performance of an array of identical modules is assumed to be linear with the number of modules in series and parallel. The inverter efficiency is applied linearly to derate the energy production. The inverter capacity forms a limit for power production from a PV generator. A ‘load’ is passed the PV array acting as a generator and various trivial calculations compare PV production to this load. If the PV array is associated with a surface that is associated with a zone, then if the zone has any multipliers associated with it, electricity production will be multiplied accordingly.

References[LINK]

Duffie, John A. and William A. Beckman. 1991. Solar Engineering of Thermal Processes. New York: John Wiley Sons, Inc.

Eckstein, Jürgen Helmut. 1990. Detailed Modeling of Photovoltaic Components. M. S. Thesis – Solar Energy Laboratory, University of Wisconsin, Madison: 1990.

Ulleberg, Øystein. HYDROGEMS Component Library for TRNSYS 15 User Manual, Institute for Energy Technology, Kjeller, Norway

Sandia Photovoltaic Performance Model[LINK]

The third model available in EnergyPlus for predicting the electricity generated by photovoltaics is referred to as the Sandia model. This model is based on work done at Sandia National Lab, Albuquerque, NM by David King – with the help of many others. The model consists of a series of empirical relationships with coefficients that are derived from actual testing. Once the coefficients for a particular module are available, it is straightforward matter to use the model equations to calculate five select points on the current-voltage curve.

The implementation in EnergyPlus is also based on work done by Greg Barker (2003) for the National Renewable Energy Lab who implemented the Sandia model in FORTRAN77 as a custom type (Type101) for the TRNSYS computer program.

There are several climate and solar orientation inputs to the model that are managed elsewhere in EnergyPlus including: incident beam solar, incident diffuse solar, incidence angle of beam solar, solar zenith Angle, outdoor drybulb, wind speed, and elevation.

Mathematical Description[LINK]

This section presents the mathematical description of the Sandia model from a draft report by King et, al. (2003). The core of the model predicts the performance of a single PV module. The following nomenclature and equations summarize the Sandia model.

Nomenclature for Sandia PV model

Isc Imp Ix Ixx Voc Vmp Pmp fdNs Np kqTc δ(Tc)Ee Eb Ediff C0. C1 C2. C3 C4. C5 C6. C7 nAMaAOIf1(AMa)f2(AOI)a0, a1, a2, a3, a4 b0, b1, b2, b3, b4,b5,b6 To Isco Impo Vmpo Voco Ixo Ixxo αIsc αImp βVoc(Ee)βVoco mβVoco βVmp(Ee)βVmpo mβVmpo Tm Ta EWSabTc Eo ΔT

Short-circuit current (A)

Current at the maximum-power point (A)

Current at module V = 0.5 Voc, defines 4th point on I-V curve

Current at module V = 0.5 (Voc Vmp), defines a 5th point on the I-V curve

Open-circuit voltage (V)

Voltage at maximum-power point (V)

Power at maximum-power point (W)

Fraction of diffuse irradiance used by module

Number of cells in series in a module’s cell-string

Number of cell-strings in parallel in module

Boltzmann’s constant, 1.38066E-23 (J/k)

Elementary charge, 1.60218E-19 (coulomb)

Cell temperature inside module (°C)

‘Thermal voltage’ per cell at temperature Tc, approximately 1 volt for a typical 26-cell crystalline silicon module

‘Effective’ solar irradiance

Beam solar irradiance

Diffuse solar irradiance

Empirical coefficients relating Imp to Ee. C0 C1= 1 (both dimensionless)

Empirical coefficients relating Vmp to Ee(C2 dimensionless, C3 is 1/V)

Empirical coefficients relating Ix to Ee, C4 C5 = 1 (both dimensionless)

Empirical coefficients relating Ixx to Ee,C6 C7 = 1 (both dimensionless)

Empirically determined ‘diode factor’ for individual cells

Absolute Air Mas

Solar angle-of-incidence (degrees) from normal

Empirical polynomial function used to relate short-circuit current to the solar spectrum via air mass

Empirical polynomial function used to relate short-circuit current to the solar angle-of-incidence

Empirical coefficients for f1(AMa) polynomial

Empirical coefficients for f1(AOI) polynomial

Reference cell temperature for rating, typically fixed at 25°C

Short circuit current at reference conditions

Max power point current at reference conditions

Voltage at max power at reference conditions

Open circuit voltage at reference conditions

Current at V = 0.5 Voc and at reference conditions

Current at V = 0.5 (Vmp Voc) and at reference conditions

Normalized temperature coefficient for Isc (1/°C)

Normalized temperature coefficient for Imp (1/°C)

Temperature coefficient for module open-circuit-voltage as function of Ee

Temperature coefficient for module open-circuit-voltage at reference conditions

Coefficient for irradiance dependence of open-circuit-voltage-temperature coefficient, often zero (V/°C)

Temperature coefficient for module maximum-power-voltage as a function of Ee

Temperature coefficient for module maximum-power-voltage at reference conditions

Cofficient for irradiance dependence of maximum-power-voltage-temperature coefficient, often zero (V/°C)

PV module temperature at back suface (°C)

Ambient outdoor drybulb temperature (°C)

Solar irradiance incident on module surface (W/m 2 )

Wind speed at standard 10-m height (m/s)

Empirical coefficient relating module temperature at low wind and high solar irradiance

Empirical coefficient relating module temperature decrease with increasing wind speed

Temperature of solar cell inside module (°C)

Reference solar irradiance (1000 W/m 2 )

Temperature difference between Tc and Tmat Eo(°C),

Nomenclature for Sandia PV model

PV Array Voltage and Size: What You Need to Know

Jan 5th 2022

If you’re hoping to design your own PV array to harness clean, renewable energy, there’s a good chance you’re feeling a little lost. PV arrays are one of the best ways to get off-grid or provide your home with power in case of emergency. The trouble is actually designing your system. Suddenly, you need to know things like “array voltage” and “PV voltage” just to figure out how many panels you should install.

While learning the ins and outs of PV array voltage can be tricky at first, the results are worth the effort. You’ll be one step closer to energy independence and enjoy a little security during future blackouts. Or, you can outfit an RV with solar panels and take some green energy on the go.

What is PV?

Generally, Photovoltaics (PV) refers to photovoltaic generation systems, which use solar cells to convert irradiance into electricity. For example, a solar panel can be called PV panels.

What is a solar array?

Generally, a solar array is a collection of multiple PV(photovoltaic) panels that produce electricity power, solar array is usually made use of massive solar panel groups, nonetheless, it can be utilized to define nearly any type of group of solar panels for any scenario, today we will talk about everything about PV(photovoltaic) array voltage and size that you need to know, you can also learn how to wire solar panels in series vs parallel here.

What Is Array Voltage?

When building a PV array, you need a few important numbers. These numbers are your inverter’s maximum input voltage and your PV array voltage. Your PV array voltage is the total voltage of all of your modules when connected in a series. The more modules connected in series, the higher your array voltage.

This is important because the more modules you have, the more power you can generate. The more power you have, the more you can store or use to stay off-grid. However, your power generation is limited by your inverter’s maximum input voltage. If you don’t know your PV array voltage and you oversize your PV array, you risk overloading your inverter.

If you overload your inverter, there’s a chance that problems will occur, and your electrical system will suffer damage as a result. Even worse, damage caused by an overloaded inverter could potentially lead to an electrical fire. No matter what, a damaged PV array is no good, so it’s wise to start with an array that’s sized appropriately.

How you connect your modules affects your PV array voltage. Modules can be connected in series, in parallel, or in a combination.

When connected in series, adding the voltage of each module will get you your total array voltage. However, when connected in parallel, the voltage is simply the voltage of a single module.

Keep in mind that modules connected in parallel will still affect the total amperage of the array. Typically, it’s recommended to connect modules in series to maximize output.

The arrangement of your modules will depend on how much output you want, how much space you have, and where you install your modules. With a properly assembled PV array maximizing PV array voltage, you can lessen your dependence on the grid, create a battery backup system, or get off the grid entirely.

When building your array, it is very important to keep your modules uniform. Once you choose a module, stick with the manufacturer of that module. Don’t mix manufacturers, even when power and voltages are the same. While it can be tempting, especially if it seems like it will save you some money, you will most likely lose precious efficiency.

A system that isn’t as efficient as possible is a waste, so get the most value by sticking with one manufacturer.

What Is PV Voltage?

PV voltage, or photovoltaic voltage, is the energy produced by a single PV cell. Each PV cell creates open-circuit voltage, typically referred to as VOC. At standard testing conditions, a PV cell will produce around 0.5 or 0.6 volts, no matter how big or small the cell actually is.

Keep in mind that PV voltage is different from solar thermal energy. While it can be easy to confuse or conflate the two terms, they refer to energy generated through different processes.

Solar thermal energy is generated with solar thermal panels, which rely on sunlight to heat fluid media like oil, water, or air. Instead, PV arrays rely on the photovoltaic effect to generate power. The photovoltaic effect describes a process of voltage generation where a charge carrying material is exposed to light, causing the excitation of electrons.

Voltage at open circuit can be found with a multimeter or a voltmeter when the module isn’t under load. You can find this number on the module’s datasheet, also. Keep this number handy for later in case you need to calculate the size of the PV array you’re hoping to build.

Just like regular AC power, you can use PV voltage to power whatever you like. With a battery bank and a grid-tied system, you can create a very effective energy backup system for blackouts or emergencies. All you need to do is switch over to your battery banks while you’re off the grid.

With some RV solar panels, you could easily enjoy a powered camping trip. With a large enough battery bank, you could potentially go off-grid for good.

How Do You Calculate PV Voltage?

Calculating PV voltage is very important when determining the size of your PV system. The reason this is so important is because voltage has an inverse relationship with ambient temperature.

When it gets colder in your area, your string of panels will produce more voltage. When it’s hot outside, the voltage produced by your panels will go down. If you mistakenly put together a system that exceeds the maximum input voltage of your inverter, you can potentially damage your electrical and cause a fire.

This is why we start by finding the Module Voc_max, the max module voltage, when correcting for the lowest expected ambient temperature at the install site. To find the Module Voc_max, you’ll need to plug in a few details into the following formula:

Module Voc_max = Voc x [1 (Tmin. T_STC) x (Tk_Voc/100)]

Let’s start with VOC. VOC is the rated open current voltage for your modules, which can be found on their datasheet. The lowest expected ambient temperature is Tmin. A little bit of research on your area’s climate should reveal that. Next is T_STC. That’s the temperature at standard test conditions, which is always 25°C.

Lastly, Tk_Voc is the temperature coefficient of the module’s open-circuit voltage. This is usually found as a %/°C on the module’s datasheet, and it is always expressed as a negative number.

Once you have your max module voltage, all you need is the max voltage input for your inverter. Typically, you can find this on the inverter’s datasheet. From here, divide your inverter’s max input voltage by your Module Voc_max, and you will end up with the maximum string size for your array. The resulting number will let you know how big your array string size can be.

How Do You Calculate Solar Array Voltage?

Finding your solar array voltage depends entirely on your system design. You can either connect your modules in series or parallel, with series being the most common style. If you connect your modules in series, add up the voltage of each module. It’s as simple as that. In this case, your solar array voltage is always the total voltage of all of your panels.

Connecting your modules in parallel is just as simple but entirely different. When connected in parallel, you need to add up the amps of each panel, as amperage is the only thing that changes. In this case, solar array voltage is always the voltage of an individual panel, regardless of how many you have connected.

Calculating your solar array voltage is critical if you’re designing your system yourself. This is because having too many panels in a series can exceed your inverter’s maximum input voltage and that is usually a bad idea.

With the inverter being one of the most critical parts of your PV system, you can’t afford to damage it. Without it, you won’t be able to convert the energy produced by your PV array into a usable AC (alternating current).

Become Energy Independent Today

Once you have the numbers down, you can safely move on to designing your own PV system. Now, all you’ll need to do is decide whether you want it ground-mounted or roof-mounted. After that, it’s just a matter of connecting it with your existing electrical.

If any of this makes you feel unsure about your installation capabilities, don’t worry. Most electricians will be able to help you with a PV array installation. However, if you want to learn more or expand the capabilities of your PV system, we’re here for you.

Explore all of our educational videos, resources, and articles about topics like net metering to find out what a solar array can really do for you. Get off the grid entirely with a tiny home solar system. Add battery banks to your system to store power to use less grid power, or stay powered during blackouts. You can even use a portable solar generator to power devices while hiking or traveling.

See our other related articles to learn more：

Understanding PV System Losses, Part 1: Nameplate, Mismatch, and LID Losses

There are many factors that impact the energy production of a solar installation. These range from the characteristics of the modules themselves, to the way the system is designed and installed (tilt, orientation, stringing configuration, etc.). Environmental factors like shade, soiling, and snow also play a role.

An accurate estimate of how much energy your PV system design will produce is essential to ensuring the system meets your customer’s needs. But without a strong understanding of the factors that can reduce system output, arriving at an accurate estimate can be challenging — even with the help of software applications that simulate system performance.

About this series

In this series, we’ll provide an overview of various causes of energy production loss in solar PV systems. Each article will explain specific types of system losses, drawing from Aurora’s Performance Simulation Settings, and discuss why they affect system performance.

For Aurora users, this series will provide tips for improving the accuracy of your performance simulations by sharing research-backed recommendations for what values to input in your Simulation Settings for different loss types. While Aurora provides default values for these fields that fit most use cases, this series will also highlight cases in which you might want to use different values depending on the specifics of your design. (For a quick summary of system losses, and how to configure your account settings in Aurora, see the Aurora Help Center. )

This guide for picking better loss values will help you give your customers the most accurate estimate of how much their system will produce and how much they can save by going solar.

What are PV system losses?

System losses refer to effects that simulation engines do not explicitly model; these linear loss factors are applied as percentage reductions to the estimated system production calculated by the simulation engine. (For the purposes of this article, we assume the simulations are run using the Aurora Simulation Engine; however, PVWatts will also use these settings if selected.)

Common DC losses: nameplate, mismatch, and light-induced degradation

In today’s article we’ll cover three common types of DC losses: nameplate, mismatch, and light-induced degradation.

What is DC loss?

By DC losses we mean factors that reduce the amount of direct current (DC) energy that is produced by the solar panels before that energy is converted into alternating current (AC) by the inverter for use in the home and on the electric grid.

These are all applied as fixed-percentage DC-side losses to the system, meaning that the output of the PV modules will be reduced by these percentage values.

Aurora allows admins to customize the default system losses for their organization. This makes it possible to ensure your default system losses accurately reflect the characteristics of your designs.

Module nameplate rating loss

0% for modern modules Lower Tolerance Pmax,STC / Pmax,STC for conservative production estimate

Module nameplate rating loss accounts for the difference in the stated power of the module from a datasheet compared with how it actually performs at Standard Test Conditions (1000 W/m 2 and 25 o C). Most modern modules will have datasheets that accurately reflect module operation at STC, so the default value for this loss is 0%.

Some older modules, particularly when some manufacturers did not “bin” modules into 5W or 10W increments, may need a small loss in this field. (Binning refers to grouping modules based on their power rating because the manufacturing process results in slight variations between modules).

Additionally, if a module has an error range on the wattage rating, such as “250W /- 2.5W,” you can enter a 1% loss (2.5/250) to ensure that your simulation provides a conservative estimate of power production.

Today, most solar modules perform consistent with their nameplate rating under standard test conditions; however, historically there were sometimes slight discrepancies between what a module’s datasheet indicated and actual performance.

Mismatch Loss

Suggested Values: 2% for most modules and systems with long strings 1% for modules that have tight wattage tolerances 0% is automatically used on modules with DC optimizers or microinverters

Mismatch loss refers to losses caused by slight differences in the electrical characteristics of the installed modules, applied as fixed percentage reduction of the system’s DC power output.

These losses will be higher for systems that have a wider error range on rated power. Industry research has shown mismatch values range from 0.01% up to 3%, depending on the setup of the system and the length of strings. Aurora uses a default value of 2% based on past industry consensus.

It should be noted that in some PV modeling tools, mismatch loss includes differences in string lengths, Cloud shading, and edge effects, in addition to the module electrical characteristics.

How Aurora handles mismatch situations

Aurora’s simulation engine calculates string length differences from the PV module layout so that the user is not required to estimate a loss from unequal string lengths.

Aurora also sets the mismatch between modules to 0% if DC optimizers or microinverters are used. This is because these module-level power electronics perform maximum power point tracking for each module to which they are connected.

Some installers will use a combination of modules with and without a module-level maximum power point tracker. For example, modules on a shaded portion of the house may have an optimizer while unshaded ones do not; in this case, the modules with MPPTs will be evaluated with 0% mismatch losses while other modules will use the provided loss percentage.

Mismatch losses refer to losses resulting from slight differences in the electrical characteristics of different solar modules.

Light-induced degradation

Suggested Values: 1.5% for most crystalline solar modules 0.5% for most multi-crystalline solar modules 0% for n-type modules, including SunPower – check with the manufacturer for more info

Light-induced degradation (LID) is a less-well-known phenomenon that impacts a large segment of the crystalline-silicon cell market. In short, it is degradation that occurs in a solar cell over the first few days after installation as a result of exposure to sunlight. This can lead to losses of 0.5% – 1.5%.

Importantly, LID impacts some module types but not others. To understand the causes of LID, and why certain types of modules are affected, one must first understand two factors that differentiate solar cells: their crystal structure (monocrystalline or multicrystalline) and their electrical properties (P-type or N-type).

Solar cell crystal structure

Crystal structure refers to differences in the structure of a solar cell resulting from how it is produced:

• Monocrystalline – solar cells that are grown using a process (the Czochralski process) that produces a uniform crystal structure that is sliced to make solar cells. These tend to have better electrical properties. They also tend to have somewhat higher oxygen concentrations, which is important for LID.
• Multicrystalline – solar cells that are produced by some form of vapor deposition, which grows silicon onto a substrate. These will have many crystalline sections, which show up as different reflective edges in a solar cell. These are less efficient at producing electricity compared to an equivalently-sized monocrystalline cell, but are cheaper and faster to produce. They also have less oxygen present in the material.

Silicon wafer electrical properties

Electrical properties refer to properties of silicon wafers (which make up a solar cell) that are needed to create a voltage difference in the cell when exposed to sunlight:

• P-type: a p-type silicon wafer contains a controlled quantity of impurities, referred to as doping elements, that accept electrons more readily and let a PV module create a voltage difference to produce power under sunlight. Most p-type cells use boron as the doping element, while some others use gallium. Boron plays an important role in LID.
• N-type: these silicon wafers contain impurities that have the opposite effect; they release, rather than accept, electrons. N-type silicon wafers do not exhibit LID.

LID is typically caused by the formation of boron-oxygen compounds in the silicon wafers that make up the solar cell. This means that monocrystalline solar cells that are p-type with boron will exhibit the most LID, and p-type multicrystalline cells will also exhibit LID, but to a lesser extent due to a smaller oxygen concentration. The LID process is usually not accounted for in lab testing of modules, so it won’t be included in the PV module datasheet. Aurora uses a default 1.5% loss.

Some manufacturers use n-type silicon—including SunPower in nearly all of their modules, and LG in some of their newer ones—which is not subject to LID because no boron is present in the material. In this case, the LID loss should be set to 0% instead of the default.

Ironically, some solar panels experience degradation when first exposed to sunlight, which can reduce system losses. This is referred to as light-induced degradation.

Why PV system losses matter in solar sales

By understanding these system losses—nameplate, mismatch, and light-induced degradation—and the recommended percentage loss to apply for each in different scenarios, you can ensure that your estimates of system performance are accurate. Your customers will be happy when their installed system produces the energy they were promised!

In subsequent installments of this series, we will explore other types of system losses, such as Tilt/Orientation, Wiring, DC-AC Conversion, and others.

About Our PV System Losses Series

This article is part of Aurora’s PV System Losses Series. Each article explains specific types of system losses, drawing from Aurora’s Performance Simulation Settings, and discusses why they affect system performance.

To get all this information in one handy package, download The Ultimate Guide to PV System Losses.