Review and validation of photovoltaic solar simulation tools/software based on case study

Accordingly, this work is significant for the wider grid-connected PV systems application and provides useful information to customers and companies to invest in and develop the PV market in Serbia and in regions with similar climates. Besides, by analyzing the actual solar irradiation and PV power output data, and comparing with simulation data, this work could help researchers and developers to increase the PV systems modeling accuracy.

The total available technical solar potential in Serbia is 0.24 Mtoe/year. The technically usable energy potential for the solar energy conversion into thermal energy (for hot water preparation and other purposes) is estimated at 0.194 Mtoe/year, assuming the use of solar thermal collectors at 50% of available facilities in the country. Besides, research in the thermal conversion of solar radiation occurs at several facilities in Serbia and is more common than research in the field of PV conversion. Based on the currently available capacities of the electric power system of the Republic of Serbia for providing tertiary reserves, it was adopted that the maximum technically usable capacity of PV power plants is 450 MW, i.e., their technically usable potential is 540 GWh/year (0.046 Mtoe/year). Almost all existing PV capacities in Serbia were built within the feed-in tariff system (FIT), which entered into force in 2009. The first quota under the FIT policy was set at 5 MW and later increased to 10 MW. The 10 MW quota is divided into 2 MW for small roof PV systems (below 30 kW), 2 MW for larger roof PV systems (up to 500 kW), and 6 MW for ground PV systems. Serbia’s current total installed PV capacity is 8.82 MW within the FIT scheme (107 PV projects in total) of which 5.34 MW are ground installations, and 3.476 MW are roof installations. Thus, the 10 MW quota has not yet been fully reached. Based on the abovementioned data, Serbia has made progress in the RES energy sector, but the solar potential in Serbia is still underutilized [ 5 , 6 ].

Lately, the EU Energy Community intensively spreads the market across Europe, especially to the southeast, relying on legally binding agreements, and Serbia has been dedicated to implementing acts and laws related to the energy sector. In this regard, Serbia has to align with the EU energy models and regulations [ 5 ]. In recent years, the Serbian Government has advanced in that aspect by adopting several legislations to improve RES energy production’s feasibility.

This work aims to evaluate 14 PV simulation tools, give insight into the experimental analysis of PV system operation in Niš, and compare the experimental data and estimated data obtained from different PV simulation tools. Considering that the large share of PV system energy output estimation is derived from the solar radiation data, special attention is focused on solar databases which include data of solar irradiation on a PV panel surface (Plane of Array [POA] irradiation) used by the software described in this study. The presented results can also be used for making investment decisions in Serbia’s RES sector. This work gives a comparison of the PV systems’ simulated and real PV electricity produced in actual meteorological conditions. The results can also be applied in the PV studies and projects to predict electricity production, starting with real energy generation and solar datasets.

Photovoltaic (PV) technology was earlier used mainly in space programs or remote locations and was marginalized. Recently it has been gaining ground, becoming a basic technology for the production and distribution of electrical energy in urban areas with the potential to become, in terms of costs, equally competitive with the costs of energy generated and distributed by the conventional technologies. Lately, the industry of PV conversion of solar irradiation shows constant annual economic growth, and total installed PV capacities worldwide have surpassed more than 1,000 MW and more than a million households are using electrical energy generated utilizing the PV systems [ 1 , 2 ]. PV systems modeling influences many aspects of PV application and it is a key step for determination, financing, and PV project implementation. A larger number of software packages were created for predictions of the PV systems’ operations to maximize renewable energy source (RES) use. PV tools require many input data such as geographical location (geographical coordinates), local meteorological conditions, solar irradiation, and the planned systems’ technical characteristics. Each PV software uses different types of input data and calculation methods. Some of them are created explicitly for energy analysis, while some include financial and greenhouse gas (GHG) analyses [ 1 , 2 , 3 , 4 ].

2 A review of PV software

In this section, the basic description of PV tools such as Solarius PV, solar advisor model (SAM), PVsyst 6.8.6, PVWatts, photovoltaic geographical information system 5 (PVGIS 5), hybrid optimization model for electric renewables (HOMER) Grid, SolarGIS, PV*SOL premium, RETScreen Expert, BlueSol 4, HelioScope, PolySun, Solar Pro 4.6, and PV F-Chart is given.

PVGIS
is a free online tool that aims to research and predict solar resources and PV system performance in most countries worldwide. PVGIS provides monthly and annual electricity generation estimates for any fixed or tracking PV systems with crystalline silicon (c-Si), CdTe, or CIS solar modules. The first versions of PVGIS have included ground measurements of solar radiation but the latest versions contain only satellite obtained estimations. Meteorological databases from satellite measurements, PVGIS- climate monitoring satellite application facility (CMSAF), PVGIS-ERA5, PVGIS-surface solar radiation dataset-heliosat (SARAH), and PVGIS-COSMO, were implemented in PVGIS. Solar radiation data for Europe, Asia, and Africa come from PVGIS-CMSAF and PVGIS-SARAH datasets, for US, the data come from the national renewable energy laboratory (NREL)- national solar radiation database (NSRDB), and for the high latitude locations, the data come from reanalysis products (PVGIS-COSMO and PVGIS-ERA5). The latest version, PVGIS 5, was used in this work and PVGIS-SARAH dataset was used in PVGIS 5 simulation. Based on the satellite measurements, SARAH provides solar datasets of the global and direct solar irradiation and the effective cloud albedo. The data are obtained from geostationary satellites – METEOSAT. This data covers the measured period from 2005 to 2016. PVGIS 5 also provides the solar radiation data on optimally inclined surfaces using the model described in this article. More information on the development, modeling, and application of PVGIS can be found in refs. [5,7–14]. Unfortunately, PVGIS does not provide GHG and techno-financial analyses.

SolarGIS
is an online simulation tool that predicts PV systems’ performance and increases PV systems’ assessment certainty. SolarGIS consists of four applications (iMaps, climData, pvPlanner, and pvSpot). iMaps and climData provide all solar and meteorological datasets for Europe, Africa, Asia, and Brazil. This application estimates different meteorological and solar data parameters and periods: typical meteorological year, monthly, daily, hourly, and 15- or 30-min values. pvPlanner allows designing various PV system types and configurations with c-Si, CdTe, and CIS modules. The high-performance algorithms, implemented in a pvPlanner, provide the calculation of long-term monthly horizontal solar irradiation (global and diffuse), POA radiation, reflected radiation and temperature, modules’ surface reflectance losses, losses due to temperature, and irradiance, shading by terrain, electricity generation, and performance ratio. PV system performance evaluation and monitoring are provided by pvSpot. SolarGIS methodology includes three different models: “Temperature,” “Solar irradiation,” and “PV power” models. The solar radiation model uses geostationary satellites data and meteorological models data. The air temperature model is based on global meteorological models. The module temperature is estimated based on ambient temperature, effective POA, thermal coefficient, and solar module efficiency. In this research, the solar data for Serbia is provided by the Global Solar Atlas 2.0, which SolarGIS has prepared. These data are estimated from Meteosat Prime and IODC satellite measurements from 1994 (2000) to the present. Air temperature is calculated from atmospheric models (European center for medium-range weather forecasts and national centers for environmental prediction) and POA calculations are based on Perez model. PV system performance model unites statistically aggregate solar and meteorological data, one-diode equivalent circuit model with a five-parameter model (De Soto, 2006) for PV array performance calculations, and Sandia Inverter Model for direct current (DC) to alternating current (AC) losses calculations. SolarGIS does not support GHG and financial analyses and advanced shading analysis [7,15,16,17,18].

PVWatts
, based on the PVForm algorithms, is an online simulation tool for the modeling and operation predictions of all types of grid-connected (roof- and/or ground-mounted) PV systems. Based on basic PV design parameters, PVWatts assesses PV system electricity production on a monthly level applying an hour-by-hour simulation over 1-year and an electricity’s monetary value based on a yearly average retail electricity rate. PVWatts is applied for the PV system performance assessment that uses crystalline silicon or thin-film PV modules. PVWatts uses hourly typical meteorological year (TMY) database from the NSRDB. For locations outside of the NSRDB area, PVWatts uses the weather data available from the nearest NREL International weather station. For other sites outside of the US, the NREL International data sources are solar and wind energy resource assessment (SWERA), ASHRAE IWEC Verse 1.1, and Canadian Weather. For the determination of the POA beam, sky diffuse, and ground-reflected radiation, PVWatts used the Perez algorithm [3,4,7,13,19,20,21,22,23].

RETScreen
is a software for different RES systems energy evaluation, financial investment assessments, and environmental impact analysis but cannot model hybrid systems. RETScreen contains a separate “PV Model” that allows simulating the PV systems operations worldwide. This tool integrates many databases, such as a meteorological database, project database, cost database, RES components’ database, etc. RETScreen Expert, used in this work, allows analysis that includes a total project life-cycle and comparing the various types of RES energy performance with a calculated and/or measured monthly energy utilization. RETScreen assesses the performance of different PV technologies that include c-Si and thin-film (CdTe, CiS, and a-Si). On the other hand, RETScreen does not consider the shading and the temperature effects for PV performance analysis and does not include the influence of dust on the solar panels. RETScreen uses the solar and other weather datasets from ground-monitoring stations or from NASA’s satellite meteorological resources. If the specific ground station does not provide data for a given location, RETScreen automatically downloads data from NASA’s satellite databases. In this research, solar data are provided from the NASA-SEE database, while other weather data are taken from ground monitoring stations. A ground-based database contains meteorological measurements data collected from over 50 different sources from 1982 to 2006 for over 6,700 sites worldwide. NASA’s Satellite Climate Database contains data collected for 30 years starting from 1983 based on satellite measurements. For POA radiation calculations, RETScreen uses simply isotropic clear sky model [3,4,7,13,21,22,24,25,26,27,28,29].

BlueSol
is a software intended for professional PV design, starting from the preliminary producibility estimations to the entire project documentation implementations. This tool supports the technical and financial designing, analyzing, and optimizing every type of PV system (fixed or tracking). BlueSol allows modeling the PV system’s behavior in all its components. Solar radiation data are acquired directly from NASA-SSE or PVGIS database. Abilities of BlueSol are direct PV system dimensioning, insertion, and verification of electrical components and cables; integrated CAD system for arranging system components (solar modules, strings, cables, batteries, and inverters); 3D visualization of a layout with shading estimations of the near objects and assessments of solar radiation on PV module surfaces. BlueSol is specifically suitable for calculating and analyzing PV systems’ elements, emphasizing the electrical components’ characteristics. BlueSol has an extensive library of solar modules and inverters [30,31].

PVsyst
is a software intended for any type of PV systems analysis and design. This software allows inputs such as orientation of PV array with the ability of mounting or tracking, PV system components, PV array characteristics, inverter model, battery-pack, etc., to simulate several dozens of variables. Based on real PV components’ prices, investment conditions, and additional costs, PVsyst provides detailed financial assessments. Based on the PV array parameters, location, and solar modules orientation, PVsyst can calculate the inter-row shading effects. A different soiling factor can also be entered for each month. This software can concurrently model PV systems that consist of more than one size or type of inverter and PV arrays with two different tilt and azimuth angles connected to a single inverter. Using the one-diode PV model, PVsyst calculates performances of c-Si, thin-film, and heterojunction intrinsic thin layer (HIT) solar modules and provides detailed system losses estimations. Based on an interpolation method from the METEONORM DLL or a “closest point” method from the NASA-SSE database, PVsyst provides solar and weather data worldwide. PVsyst has the section that constructs a set of hourly meteo data. In this research, PVsyst used monthly measured data (global and diffuse radiation, wind velocity, and temperature) from Meteonorm 7.2, creating hourly synthesized dataset. Monthly solar irradiation datasets are measurement averages over 1991–2009. The diffuse radiation calculations in PVsyst 6.8.6. are based on the Perez model (1987,1988) [3,4,7,18,21,22,32,33,34,35,36,37,38,39].

HelioScope
is a software specifically created for PV system design and analyses. This software has some elements of PVsyst, but design functionality is accomplished by AutoCAD. HelioScope performs energy analysis, including losses due to weather conditions. Besides, HelioScope includes shading and temperature effects, system component efficiencies, wiring, module mismatches, soiling impacts, and aging to carry out PV system performance evaluations with increased accuracy. This tool includes advanced calculations to model every component within the PV array. As simulation results, HelioScope provides hourly values of energy production, weather data, PR, and other PV system parameters. Weather data is integrated as Meteonorm TMY file. In this research, HelioScope used TMY, 10 km Grid, and Meteonorm data. Based on weather data from the Meteonorm, along with the module orientation angle and solar angle calculation, HelioScope calculates the DNI on a module. The PSA algorithm, developed by Blanco and Muriel, is used for the solar angle calculation, Sandia Model is used as a temperature model, and the Perez model is used as the default transposition model. It should be noted that the POA radiation calculation in HelioScope is at the module level. Unfortunately, HelioScope does not provide GHG and financial analyses [4,7,20,21,33,35,40–42].

PV*SOL premium
is a software specifically made for the detailed shading analysis of all types of ground-integrated, tracking, roof-integrated, or roof-mounted PV systems with 2D or 3D visualization. This software also provides PV systems’ performance and financial analysis assessments. The software’s main feature is to consider the shading effects from the nearby objects for each solar module and optimize its coverage. PV*SOL has an extensive library of solar modules and inverters (over 7,500 solar modules and 1,500 inverters). Besides, PV*SOL can assess the implementation of various PV technologies that include monocrystalline Si, thin-film (CiS, a-Si, and CdTe), μc-Si, (HIT), and Ribbon. PV*SOL uses a meteorological dataset obtained by the interpolation method from Meteonorm 7.1 or forms a dataset by “closest point” method using NASA database. POA radiation calculations are based on the anisotropic (Hay and Davies) sky model as a default model, and diffuse radiation calculations are based on the Hofmann and Seckmeyer as a default model. However, users can select other POA calculation models such as Liu and Jordan, Klucher, Perez and Reindl. For the quantity of the reflected radiation determination, an incident angle modifier is used. In this research, PV*SOL premium used Meteonorm 7.1 to provide monthly climatic data. Meteonorm 7.1 provides meteorological data with the averaging period of 1991–2010. For POA radiation calculations, PV*SOL premium used the Hay and Davies anisotropic sky model, and for diffuse radiation calculations, PV*SOL used the Hofmann and Seckmeyer model. Based on the amount of POA radiation and solar module I-U characteristics at standard test conditions (STC), PV*SOL calculates PV array performance while a linear or dynamic temperature model can be selected by the users [3,4,7,18,20,33,43–46].

Solarius PV
is a software intended for the technical, economic, and GHG emission analyses of PV systems of any size and type and any boundary condition (near and far obstacles). Solar data are downloaded from Meteonorm or PVGIS databases depending on the selected location. PV system design is achieved by BIM modeling interface. Solarius PV has extensive libraries of all PV system components, time-slots and energy consumption profiles, electricity tariffs, zonal sales, guaranteed minimum prices, etc. It provides hourly energy production for the full year, detailed profitability assessment, and the entire PV system’s amortization period. Solarius PV also supports 3D modeling and provides operational diagnostics to point out any errors at every step of the PV design. Solarius PV also considers the shading effects projected onto the solar modules by nearby objects and graphically represents shadow interferences. In this research, monthly average daily solar irradiation on a horizontal surface is obtained by Meteonorm 7.1, integrated into Solarius PV. Unfortunately, Solarius PV does not provide any detail on POA radiation calculations [3,7,20,33,45,47–49].

Solar Pro
is an advanced PV software with integrated 3D-CAD. Solar Pro can be used to design flat-roof, roof-integrated, ground-mounted, and tracking PV systems. The main functions are shade, I–V curve, power, and financial analysis. An advanced 3D shading analysis is achieved by taking into account solar module I–V curves. The total I–V curve calculations are based on each solar module’s electrical characteristics, incoming radiation and temperature data, shading, and other loss factors. Solar Pro estimates hourly DC power output and PV system power output, including temperature effects, shading, electrical losses, and soiling. Temperature effects depend on ambient temperature, incoming radiation, and wind speed. Solar Pro calculates total solar radiation using geographic coordinates of the site and meteorological data from the databases: 1,600 Points (1,600 Points, Japan Weather Association, 2001), TMY3 (NREL), MONSOLA-11, METPV-11, Meteonorm Meteo Monthly (Meteotest), NSRDB Hourly (NREL), and SolarGIS TMY Hourly (SolarGIS, GeoModel Solar). In this research, monthly averages of daily solar irradiation are obtained from the 1,600 Points meteorological database and the POA radiation is calculated using the Hay transposition model [Japan Solar Energy Society, New Solar Energy Utilization Handbook, 2010] [3,4,7,20,33,45,50–52].

PV F-Chart
is software for designing all types of PV systems, battery storage systems, solar systems with concentrators, and tracking PV systems. Besides, this program can perform detailed financial analysis for isolated-, central-, and off-grid systems. PV energy output is performed as a function of solar radiation. PV F-chart does not support shading analysis and does not consider meteorological data and other loss factors for PV energy output calculations. POA radiation calculations are based on an isotropic (Liu and Jordan) sky model, while weather data are integrated as TMY2 file. In this research, for weather and solar data, PV F-Chart used TMY2 data and an isotropic (Liu and Jordan) sky model for POA radiation calculation. Based on solar module efficiency and temperature, PV array area, and incident angle, PV F-chart calculates the PV array performance [3,4,7,33,45,51,53–56].

PolySun
is a software for designing, performance analyzing, and optimizing all types of solar (PV and thermal) and geothermal systems, cogeneration units, heat pumps, and combined systems and allows several different types of systems (heat pump, solar thermal, and PV systems) mutually to be combined. PolySun also provides performance, shading, and economic analyses of the designed systems and has an extensive library of various system components with all specific parameters necessary to simulate systems operation. This tool can assess the application of various PV technologies (c-Si, thin-film, μc-Si, HIT, and Ribbon). The dynamic simulation algorithm allows calculating all the relevant output parameters of the desired system. Weather and solar data are acquired from Meteonorm database. PolySun allows several options for weather data downloading: from location (according to Meteonorm 7.2 and Meteonorm 6), “Profile,” “External monthly values,” and “Webservice.” In this research, for the location ‘Niš’ chosen specifically from the map, PolySun used the weather data from Meteonorm “Webservice”. These data are dynamic and modified according to the Meteonorm website. For POA radiation calculations, PolySun uses Perez model. PV system energy output is calculated based on irradiance, module temperature, and loss factors (soiling and degradation, module mismatch, inverter load, and module derating factors) using H.G. Beyer model [3,4,7,20,33,45,57–60].

SAM
is a software for different RES systems energy evaluation and financial assessments but cannot model hybrid systems. This software performs Parametric Analysis, Sensitivity Analysis, Statistical Analysis, and Probability of Exceedance Analysis. SAM has extensive libraries of RES systems’ components along with all their coefficients and specifications data such as type of solar modules and inverters, collectors and parabolic receivers, wind turbines, etc. SAM provides detailed performance and financial analysis of all types of utility-interactive PV systems. SAM can assess the application of various PV technologies that include c-Si, thin-film, HIT, concentration photovoltaics (CPV), and multi-junction CPV. PV array performance calculations are based on the following models: empirical (Sandia), semi-empirical (five-parameter performance), Simple-efficiency, and PVWatts; while for the inverter performance calculations are based on Sandia inverter performance model and Single-point efficiency model. TRNSYS code is implemented in the PV array performance models. For solar resources and weather conditions in the USA, SAM uses data from the NREL Solar Prospector. For other locations, this tool can load data from the following files: TMY2, EnergyPlus weather, PVGIS, METEONORM, and TMY3. POA radiation calculations in SAM are based on isotropic and/or anisotropic sky models such as Liu and Jordan, Hay and Davies, Reindl and Perez models. Considering that ‘Niš’ is not covered by the NSRDB and Solar Resource Library, included in SAM, in this research, the solar data were imported from PVGIS-SARAH and Perez model is used as default transposition model for POA radiation calculations [2–4,7,20,22,33,42,45,48,51,61–66].

HOMER
is a simulation tool for micro-grid and hybrid RES systems design. Besides technical and financial analysis, HOMER also provides system optimization, sensitivity analysis, and GHG analysis. HOMER imports solar data from NREL and NASA databases or users can import data manually. POA radiation calculations are based on the HDKR model. In this research, Homer used NASA database for monthly averages of global horizontal radiation from 1983 to 2005. The correlation of Erbs (1982) is used to calculate diffuse fraction, and the HDKR model is used for POA radiation calculations. PV power output is estimated based on incident solar radiation and PV cell temperature, but shading effects are not included in these calculations. Two versions of HOMER are available: HOMER Grid and HOMER Pro. HOMER Pro was designed for modeling distributed generation, and it focuses on the multi-generator islands or microgrids. HOMER Grid, used in this work, was designed for modeling behind-the-meter distributed energy systems [2–4,7,20,21,24,27,33,45,51,67–72].

As each PV tool contains internal submodels to estimate PV systems performance, the comparative overview of the main submodels integrated into described PV tools is given in Table 1.

Table 1

The comparative overview of the main submodels integrated into described PV tools

PV tool
Solar databases (period)
POA radiation model
PV module model
System type
Analysis type

PVGIS 5
PVGIS–SARAH (2005–2016)
Muneer
Variant of King’s model
• Any type of on-grid PV (flat-roof, roof-integrated, ground-mounted PV, tracking PVs) and off-grid PV
− Energy analyses

PVWatts
SWERA
Perez
PVForm equations
• Any type of on-grid PV
− Energy analyses

SolarGIS
Meteosat (1994-)
Perez
Single-diode model
• Any type of on-grid PV (flat-roof, roof-integrated, ground-mounted PV, and tracking PVs)
− Energy analyses

RETScreen
NASA-SEE (1983–2005)
Simple isotropic model described in in ref. [2]
Model based on work by Evans
• RES
− Energy analyses

• No hybrid systems
− Financial analyses

− GHG analyses

BlueSol 4
NASA-SEE (1983–2005)
Simple isotropic model described in in ref. [2]
N/A
• Any type of on-grid PV (flat-roof, roof-integrated, ground-mounted PV, and tracking PVs)
− Energy analyses

• Off-grid PV
− Financial analyses

− optimization

PVsyst 6.8.6
Meteonorm 7.2 (1991–2009)
Perez
Shockley’s single-diode model
• Any type of on-grid PV (flat-roof, roof-integrated, ground-mounted PV, tracking PVs),
− Energy analyses

− Financial analyses

• Off grid PV

HelioScope
TMY Meteonorm
Perez
Shockley’s single-diode model
• All type of on-grid PV
− Energy analyses

• Single-axis tracking PV

PV*SOL premium
Meteonorm 7.1 (1991–2010)
Hay and Davies anisotropic model
Enhanced single-diode model
• On-grid PV
− Energy analyses

• Off-grid PV
− Financial analyses

• Tracking PVs

Solarius PV
Meteonorm 7.1 (1991–2010)
N/A
N/A
• Any type of on-grid PV
− Energy analyses

− Financial analyses

− GHG analyses

Solar Pro 4.6
1,600 points
Hay transposition model
Single-diode model
• Any type of on-grid PV (flat-roof, roof-integrated, ground-mounted PV, and tracking PVs)
− Energy analyses

− Financial analyses

PV F-Chart
TMY2
Liu and Jordan
Model based on work by Evans
• All types of PV systems
− Energy analyses

• Battery storage systems
− Financial analyses

• Solar systems with concentrators
− GHG analyses

• Tracking PVs

PolySun
Meteonorm web
Perez
H.G. Bayer model
• All types of solar (PV and thermal) and geothermal systems
− Energy analyses

−Optimization

• Cogeneration units

• Heat pumps

• Combined systems

SAM
PVGIS-SARAH
Perez
Single-diode model
• RES
− Energy analyses

• No hybrid systems
− Financial analyses

Homer Grid
NASA-SEE (1983–2005)
HDKR
Equations described in ref. [2]
• Micro-grid
− Energy analyses

• RES
− Optimization

• Hybrid systems
− Sensitivity analysis

− Financial analyses

− GHG analyses