12 Abbreviations to Learn First When Reading PVSyst

When you open a PVSyst report, what people usually stumble over first is not the formulas themselves but the meanings of the abbreviations that line the screen and result tables. Terms like GlobHor, GlobInc, EArray, E_Grid, PR, Yf, Yr, Lc, and Ls can be hard to interpret when you’re not yet familiar with solar power system design or energy-yield simulation — it can be difficult to tell which ones represent irradiance, which represent generation, and which represent losses.

However, when reading PVSyst you don't need to memorize every item at once. The abbreviations you should learn first are limited. In particular, if you're only checking whether the energy production is reasonable, whether the PR is not too low, where losses are occurring, and how the results differ compared with other companies' reports, simply mastering the 12 key abbreviations will greatly change how the results are perceived.

PVSyst is a specialized simulation software for predicting the annual energy production of photovoltaic power plants. The report organizes meteorological data, solar irradiance, incidence on tilted surfaces, the output of the photovoltaic array, the energy after passing through the inverter, the amount transmitted to the grid, and various losses. In other words, understanding the abbreviations is not mere memorization of terms but a task closer to understanding the energy flow of a photovoltaic power plant.

This article explains the 12 abbreviations you should learn first when reading PVSyst, ordered by how likely they are to cause confusion in practical work. For beginners, it organizes which screens or results each abbreviation is important on, what to check, and what kinds of misreadings are likely to occur.

Table of Contents

• Remember PVSyst abbreviations by the flow of generated energy

• GlobHor represents the global (all-sky) irradiance on the horizontal plane

• DiffHor represents the sky diffuse irradiance on the horizontal plane

• T_Amb represents the ambient air temperature

• GlobInc represents the irradiance incident on the tilted plane

• GlobEff represents the irradiance that can be effectively used

• EArray represents the output of the PV array

• EOutInv represents the inverter output

• E_Grid represents the energy delivered to the grid

• PR represents the performance ratio of the entire system

• Yr represents the theoretical time based on the reference irradiance

• Ya represents the equivalent time of the array output

• Yf represents the final equivalent generation time obtained

• Lc and Ls are abbreviations used to distinguish where losses occur

• Common mistakes beginners make when reading the abbreviations

• How to turn PVSyst abbreviations into practical, usable knowledge

• Summary

Learn PVSyst abbreviations by following the flow of energy production

PVSyst's abbreviations can become very confusing if you try to memorize them individually. Rather than learning one by one what GlobHor is, what GlobInc is, and what EArray is, it is far more practical for everyday work to understand them along the flow of energy in a solar power plant.

The basic flow is that, first, meteorological data such as irradiance on the horizontal plane and ambient air temperature are available, and these are converted to the irradiance incident on the tilted surface of the solar panels. After that, following reflection, shading, soiling, IAM, temperature effects, mismatch, and wiring losses, it becomes the DC power of the photovoltaic array. It then passes through the inverter to become AC power, and, if necessary, after subtracting losses in transformers, power-receiving equipment, and up to the grid interconnection point, the result is presented as the final transmitted energy.

If you keep this flow in mind, abbreviations can be broadly divided into three groups. The first group consists of abbreviations representing solar radiation and weather, the second group consists of abbreviations representing power generation and electrical energy, and the third group consists of abbreviations representing performance and losses.

When reading a PVSyst report, rather than diving straight into the details of Detailed Losses or the Loss Diagram, it is important to first look at the relationships between irradiance, array output, power exported to the grid, and PR. If you understand the abbreviations in the flow, it becomes easier to distinguish whether low generation is caused by the meteorological data, tilt conditions, array-side losses, or losses after the inverter.

GlobHor represents the global horizontal irradiance.

GlobHor is an abbreviation of Global Horizontal Irradiation and represents the total solar irradiation on a horizontal surface. In PVSyst, it is a very important value that forms the basis of the meteorological data. It is easiest to understand as the sum of the direct solar radiation from the sun and the diffuse sky radiation received by a horizontal ground surface.

PVSyst's annual energy production is first and foremost greatly influenced by the quality of this GlobHor. Depending on which meteorological data is used—Meteonorm, satellite data, on-site observation data, SolarGIS, etc.—the GlobHor values change, and the subsequent energy production changes as well. Therefore, if you feel that PVSyst's results are too high or too low, you should first check whether the GlobHor is reasonable.

GlobHor is not the actual irradiance received by solar panels. In many solar power plants, panels are not horizontal but are tilted southward or oriented east–west. Therefore, GlobHor should be regarded only as baseline meteorological data, and the irradiance reflecting the design conditions is checked with GlobInc, which follows.

A common mistake beginners make is to simply assume that because GlobHor is high, power generation will necessarily be high. In reality, factors such as tilt angle, azimuth, shading, snow, reflection, temperature, PCS capacity, and wiring conditions also come into play, so you cannot judge the expected power output by GlobHor alone. However, as an entry point to check whether the meteorological data assumptions are correct, GlobHor is one of the abbreviations you should look at first.

DiffHor represents the diffuse sky irradiance on a horizontal surface

DiffHor is an abbreviation of Diffuse Horizontal Irradiation and represents the diffuse sky irradiation on a horizontal surface. It is not the direct solar radiation arriving straight from the sun, but the component of solar radiation that has been scattered in the atmosphere and arrives from the entire sky.

In solar power simulations, the ratio of direct to diffuse irradiance is important. Even with the same annual irradiation, regions with more direct irradiance and regions with more diffuse irradiance differ in the irradiance incident on tilted surfaces, shading effects, and how reflections are treated. In particular, in cloudy regions, snow-prone areas, mountainous areas, and coastal zones, the handling of DiffHor can affect the results.

In PVSyst, the direct and diffuse components are used when converting irradiance on the horizontal plane to irradiance on a tilted plane. Therefore, DiffHor is not a parameter that alone determines energy production, but it is important for understanding why GlobInc and GlobEff have the values they do.

For example, even with the same GlobHor, if the proportion of diffuse irradiance is large, the difference in power generation when changing the tilt angle can be smaller than in regions where direct irradiance is dominant. Also, the effect of shading is handled differently for direct and diffuse irradiance. At the stage of reading PVSyst’s Loss Diagram in depth, whether you are aware of the existence of DiffHor can make a difference in your understanding of irradiance conversion.

T_Amb represents the outside air temperature

T_Amb is an abbreviation for Ambient Temperature and denotes the outside air temperature. In PVSyst, it is treated as the temperature condition included in meteorological data and is important when considering temperature-related losses of photovoltaic modules.

Solar panels generally experience reduced output as temperatures rise. Therefore, even in regions with high solar irradiance, temperature-related losses can be significant when ambient temperatures are high and module temperatures tend to increase. Conversely, in cold regions, although solar irradiance may be limited, temperature losses are smaller and module efficiency can be higher during winter.

An important point when reading PVSyst is that T_Amb is not the module temperature itself. Module temperature is calculated from the ambient air temperature plus solar irradiance, wind speed, racking conditions, mounting configuration, ventilation, thermal loss coefficient, and other factors. For roof-mounted, ground-mounted, agrivoltaic, snowy-region, corrugated-metal-roof, or low-rack installations, the way module temperature rises differs even when ambient air temperature is the same.

When temperature losses are large in a PVSyst report, you need to check not only T_Amb but also the Thermal Loss Factor, Uc, Uv, and the ventilation conditions on the rear side of the mounting rack. Beginners tend to simply assume that high ambient temperature causes large temperature losses, but in practice the assessment includes the module installation conditions.

GlobInc represents the amount of solar radiation incident on an inclined surface.

GlobInc stands for Global Incident in Collector Plane and denotes the global irradiance incident on the surface of a solar panel. It is a very important abbreviation when reading PVSyst. It is easiest to understand if you think of GlobHor, the irradiance on the horizontal plane, after it has been converted to the designed tilt and azimuth angles.

In a solar power plant, the radiation that actually contributes to power generation is not the solar irradiance falling on a horizontal plane, but the irradiance incident on the panel surface. Therefore, when checking the assumptions for power output, GlobInc is more directly important than GlobHor.

GlobInc varies with tilt angle, azimuth, latitude, season, the ratio of direct to diffuse irradiance, reflected components, and other factors. For example, even at the same site, GlobInc differs between a south-facing design with a 20° tilt and an east-west-facing design with a 10° tilt. In PVSyst case comparisons, by first looking at differences in GlobInc you can understand how layout and orientation conditions affect the amount of solar irradiation captured.

One important point to note is that a high GlobInc does not necessarily mean the final power output will be high. Even if irradiance on the tilted surface is high, E_Grid will not increase if nearby shading, electrical losses, temperature-related losses, PCS clipping, or output curtailment are significant. Therefore, GlobInc should be regarded as an input metric for energy production and must be interpreted separately from the final result.

GlobEff represents the amount of solar radiation that can be effectively used

GlobEff is an abbreviation of Effective Global Irradiance and denotes the effective solar irradiance. It is the value treated as the irradiance that is effectively available to the photovoltaic array after subtracting the effects of shading, IAM, soiling, and other influences from GlobInc.

In PVSyst's Loss Diagram, the losses from GlobInc to GlobEff—such as near shading, far shading, losses from reflection and angle of incidence, and losses from soiling—are organized. By looking at this difference, you can confirm how much of the irradiance that reaches the panel surface remains available for power generation.

GlobEff is important for beginners because it makes it easier to grasp irradiance-side losses. When power generation is low, you need to determine whether the cause lies in electrical losses or whether, in the first place, the effective irradiance has decreased. If GlobInc is sufficient but GlobEff has dropped significantly, focus on checking for shading, soiling, angle-of-incidence losses, and similar issues.

For example, mountain shadows, shadows from surrounding structures, row-to-row shading, settings for snow and soiling, and reflection losses at low solar altitude all affect GlobEff. When explaining PVSyst results to clients or stakeholders, you will be more persuasive if, instead of simply saying that energy production is low, you can explain what is being deducted at the effective irradiance stage.

EArray represents the output of the solar cell array

EArray stands for Array Energy and represents the DC energy output from a photovoltaic array. In PVSyst, it is treated as the array output after the incident solar radiation enters the modules and is affected by module characteristics, temperature losses, low‑irradiance behavior, mismatch, DC wiring losses, and other factors.

EArray is important for evaluating the DC-side performance of a power plant. While GlobEff represents the effective amount of solar irradiance, EArray is the value after converting that into electrical energy. In other words, it indicates how much DC power the modules produced from the irradiance conditions.

As a way to read PVSyst, by looking at the difference between EArray and E_Grid you can separate losses up to the DC side from losses on and after the AC side. If EArray is lower than expected, check module capacity, temperature losses, module quality losses, LID, mismatch, DC wiring losses, shading effects, etc. Conversely, if EArray is sufficient but E_Grid is low, check inverter losses, clipping, transformer losses, AC wiring losses, and losses up to the point of interconnection.

What beginners should be aware of is that EArray is not the final amount of electricity sold to the grid. EArray is the energy on the DC side, so it differs from the energy actually sent to the grid. When checking generation figures for bank submissions or business plans, you need to look at E_Grid or the amount injected into the Grid, not EArray.

EOutInv represents the inverter output.

EOutInv is an abbreviation for Energy Output of Inverter, and represents the AC electrical energy output from the inverter. It is the value after the DC power generated by the photovoltaic array passes through the inverter and is converted to AC.

In PVSyst, inverter efficiency, the inverter’s input voltage range, the MPPT range, output limitation due to rated capacity, and clipping losses all influence the energy from EArray to EOutInv. In particular, in designs where the PCS capacity is small relative to the DC capacity, the inverter may reach its upper limit under high irradiance, causing output limitation.

By looking at EOutInv, you can see how much losses or limitations are occurring at the inverter despite sufficient generation on the DC side. It is important when evaluating Pnom ratio, DC/AC ratio, PCS capacity, power factor settings, and oversizing design.

In practice, the difference between EOutInv and E_Grid is also important. EOutInv is the energy at the inverter output point, from which additional losses for AC wiring, transformers, receiving (service) equipment, and the grid connection point may be subtracted. Therefore, when comparing PVSyst results, you must be clear about which point’s energy you are comparing.

E_Grid represents the amount of electric energy sent to the grid

E_Grid is an abbreviation of "Energy injected into grid" and represents the amount of electrical energy injected into the grid. In PVSyst reports, it is often considered the most important metric for final energy production.

In business planning, electricity sales revenue, P50 and P90 evaluations, documents submitted to banks, and performance evaluations of EPC and O&M, what ultimately matters is how much energy is injected into the grid. Therefore, when looking at PVSyst results, it is basic to confirm E_Grid as the final result.

E_Grid is the result reflecting various factors such as solar irradiance, module output, temperature losses, wiring losses, inverter losses, transformer losses, and auxiliary losses. Therefore, even if E_Grid is low, its cause is not necessarily a single factor. First, trace the flow of GlobInc, GlobEff, EArray, EOutInv, and E_Grid, and check at which stage the value is dropping significantly.

As a point of caution, depending on the report or contract the comparison target may differ — not E_Grid but inverter output, the point of receipt (receiving point), the transmission/sending end, export meter readings, etc. Even when comparing PVSyst results with each other, if they differ in which energy quantity is being looked at you cannot correctly explain the difference in outcomes. E_Grid is important, but in practice the key is to always read it together with the evaluation point.

PR represents the performance ratio of the entire system

PR stands for Performance Ratio and indicates the overall performance ratio of a solar power generation system. It is one of the most commonly used abbreviations when reading PVSyst results.

PR is an indicator that shows how efficiently the actual energy produced is obtained relative to the received solar irradiation and the system's installed capacity. It is used to assess the system's conversion efficiency and the magnitude of losses, rather than the sheer amount of solar irradiation.

If PR is high, it means that losses from solar irradiance to grid delivery are relatively small. If PR is low, there may be large losses occurring somewhere, such as temperature losses, shading, soiling, wiring losses, inverter losses, transformer losses, auxiliary equipment losses, or output curtailment.

However, PR is not an all-purpose indicator. PR is useful for evaluating the performance of a power plant, but it does not represent the annual energy generation itself. In regions with low solar irradiance, PR can appear high if losses are small, whereas in regions with high solar irradiance, PR can be lower if temperature-related losses are large.

Also, PR varies depending on which point’s energy is used. Whether it is based on inverter output, the grid interconnection point, whether auxiliary losses are included, or whether output curtailment is included changes the meaning of the number. When comparing PVSyst’s PR with other companies’ reports, you must always confirm the definitions and the scope of the evaluation.

Yr represents the theoretical time based on the reference solar irradiance

Yr stands for Reference Yield and represents the theoretical solar irradiation time based on the reference irradiance. The unit is often expressed in hours, and it can be understood as the received solar irradiation divided by the standard solar irradiance.

In simple terms, Yr is an indicator that expresses how much solar resource a power plant has received, converted into hours. For example, if the annual insolation on the tilted surface is large, Yr will also be large. This is an indicator of the solar resource conditions rather than the plant’s performance.

When reading PVSyst, understanding the relationship between Yr, Ya, and Yf makes the meaning of PR and losses clearer. Yr is the input of solar irradiance, Ya is the array-side output, and Yf is the final output. In other words, the drop from Yr to Ya can be regarded mainly as array-side losses, and the drop from Ya to Yf mainly as system-side losses.

Beginners should be careful not to confuse Yr with electricity generation. Yr is not an energy quantity but an index that converts solar irradiance into time. If you want to look at the final electricity generation that accounts for the power plant’s installed capacity and losses, check Yf and E_Grid.

Ya represents the equivalent time of the array output

Ya stands for Array Yield and is an indicator that expresses the output of a photovoltaic array as the equivalent time per unit of installed capacity. It can be understood as the value obtained by dividing EArray by the nominal capacity of the photovoltaic array.

By looking at Ya, you can compare how much DC power a photovoltaic array produced per unit of capacity. Even when plant sizes differ, Ya makes it easier to compare array-side performance.

The portion that drops from Yr to Ya mainly comprises the losses that occur between solar irradiance and DC output. Specifically, these involve shading, IAM, soiling, low-irradiance losses, temperature losses, module quality losses, mismatch, DC wiring losses, etc.

When PR is low in the PVSyst results, it becomes easier to isolate the cause by checking whether Ya is already low or whether Ya is reasonable and Yf is low. If Ya is low, check the array-side design and the irradiation-side conditions. If Ya is sufficient but Yf is low, check for losses or restrictions downstream of the inverter.

Yf represents the equivalent power generation time ultimately obtained

Yf stands for Final Yield and is an indicator that expresses the final amount of energy obtained as equivalent hours per unit of installed capacity. Generally, it can be understood as E_Grid divided by the installed capacity.

Yf is a convenient metric for comparing a power plant’s final power generation output on a per-capacity basis. For example, when comparing multiple plants or design options with different installed capacities, simple annual generation figures are affected by differences in scale. By looking at Yf, you can compare how much was generated per 1 kW or per 1 kWp.

Viewed in relation to PR, PR can be considered as Yf divided by Yr. In other words, PR indicates how much generation was ultimately obtained from the incident solar resource. Even if Yf is low, PR is not necessarily low if Yr is also low. Conversely, even if the solar irradiation is high, large losses can mean that Yf rises while PR remains low.

In practice, Yf is often used for assessing a power plant's profitability and for comparing projects. However, depending on the PVSyst report, you need to check whether the capacity basis is DC capacity or AC capacity and which point's energy is being used. If you don't align definitions with the party you're comparing against, apparent differences can look larger than they actually are.

Lc and Ls are abbreviations used to distinguish the locations of losses.

Lc represents Array Capture Loss and indicates the losses from incident solar radiation to the output of the photovoltaic array. Ls represents System Loss and indicates the system-side losses from the array output to the final power delivered to the grid.

These two are very useful for understanding PVSyst's loss structure. When the power output is low, you can distinguish whether the losses are on the array side or on the system side downstream of the inverter.

If Lc is large, check for shading, soiling, IAM, temperature losses, module quality, mismatch, DC wiring losses, and so on. In other words, this suggests that significant losses are occurring in the stages before and after the solar panels generate power.

If Ls is large, check inverter losses, clipping due to PCS capacity, AC wiring losses, transformer losses, auxiliary equipment losses, and so on. In other words, this indicates that losses are occurring in the stage after DC power has already been generated, when it is converted to AC and sent to the grid.

For beginners, it’s important not to view losses as one large number. When reading PVSyst’s Loss Diagram, use the concepts of Lc and Ls and organize them in the order of the irradiance side, the array side, the inverter side, and the grid side to make it easier to explain the causes.

Common mistakes beginners make when reading abbreviations

The most common misconception about abbreviations in PVSyst is treating similar items as having the same meaning. GlobHor and GlobInc, GlobInc and GlobEff, EArray and E_Grid, and PR and generated energy each have different meanings.

GlobHor is the solar irradiance on the horizontal plane, and GlobInc is the solar irradiance incident on the panel surface. GlobEff is the effective irradiance that accounts for shading, reflections, and similar effects. Confusing these three makes it unclear whether differences in power output stem from the meteorological data or from the layout and shading.

Confusion between EArray and E_Grid often occurs in practice. EArray is the DC-side array output, while E_Grid is the amount of energy ultimately delivered to the grid. When looking at business plans and the amount of electricity sold, E_Grid is important, but when verifying module and DC-side design, EArray is important.

Care must also be taken with PR. A high PR does not necessarily mean a power plant is good, and a low PR does not necessarily mean it is bad. PR is a metric that indicates the magnitude of losses, and is distinct from the amount of solar irradiance or the electricity sold. Generation output, PR, irradiance, and installed capacity should be evaluated together.

Also, when comparing reports from other companies, even if the definitions of abbreviations are the same, the evaluation scope and underlying assumptions may differ. Whether auxiliary equipment losses are included, whether transformer losses are included, whether output curtailment is included, and how snow or soiling are handled can change the values of E_Grid and PR. Instead of comparing only the abbreviations, it is important to confirm which location, which conditions, and which range of losses the abbreviation covers.

How to Turn PVSyst Abbreviations into Practical Knowledge for Use in the Field

The purpose of learning PVSyst abbreviations is not to memorize the terms. It is to be able to explain why the amount of energy produced took the values it did. For that reason, it is important to develop the habit of reading the abbreviations along the flow of energy.

Initially, it is recommended to start with GlobHor and then follow GlobInc, GlobEff, EArray, EOutInv, and E_Grid in that order. Viewing them in this sequence lets you grasp the flow from meteorological data to irradiance on the panel surface, the irradiance available for power generation, the DC output, the AC output, and the final amount delivered to the grid.

Next, we check PR, Yr, Ya, Yf, Lc, and Ls. These are metrics for looking at a plant’s performance and losses per unit of capacity or per unit of solar irradiation. They help compare performance differences that are difficult to discern from absolute values alone.

In practice, it is important not only to rely on PVSyst results but also to cross-check them against site conditions. For example, verify that shading settings are correct; that the tilt and azimuth of the mounting structure match the site; that the PCS capacity and power factor settings are consistent with the actual equipment specifications; that wiring lengths and cable sizes are reasonable; and that the treatment of snow and soiling is appropriate for the local conditions.

Also, when conducting on-site verification of a solar power plant, it is important to reconcile drawings, survey data, post-construction as-built information, and the assumptions used in PVSyst. For on-site position checks and drawing verification, using a system such as LRTK that leverages an iPhone and GNSS makes it easier to confirm on site the racking positions, boundaries, site grading, equipment layout, and so on. The closer the assumptions in PVSyst are to the actual site conditions, the higher the explanatory accuracy of the simulation results.

Especially in analyses of differences in power generation, relying solely on the desk-based PVSyst report sometimes does not reveal the cause. This is because site conditions — surrounding terrain, shadows from structures, between-panel-row shading, locations prone to snow accumulation, installation errors, wiring routes, and so on — can have an impact. By understanding the meanings of abbreviations and cross-checking with field data, interpreting PVSyst transforms from mere report checking into a skill usable for design reviews and improvement proposals.

Summary

The abbreviations you should learn first when reading PVSyst are easier to understand if organized according to the flow of solar irradiance, energy production, performance, and losses. GlobHor denotes the solar irradiance on the horizontal plane, DiffHor denotes the diffuse irradiance on the horizontal plane, T_Amb is the ambient air temperature, GlobInc is the irradiance incident on the panel surface, and GlobEff represents the effective irradiance. These abbreviations are used to interpret the meteorological and irradiance conditions that serve as the inputs to energy production.

Next, by focusing on EArray, EOutInv, and E_Grid, you can understand the differences between DC output, inverter output, and energy sent to the grid. EArray is the amount of energy on the DC side of the solar array, EOutInv is the AC energy after passing through the inverter, and E_Grid is the energy ultimately delivered to the grid. E_Grid is important for business planning and power sales, but for root-cause analysis you should always check EArray and EOutInv as well.

Furthermore, understanding PR, Yr, Ya, Yf, Lc, and Ls will allow you to read PVSyst's results as performance indicators. PR is the performance ratio of the overall system. Yr is the equivalent hours of the solar resource, Ya is the equivalent hours of the array output, and Yf is the equivalent hours of the final energy production. Lc represents array-side losses, and Ls represents system-side losses.

It is important to view PVSyst abbreviations not as isolated items to memorize one by one, but as the flow of energy from GlobHor to E_Grid. When generation is low, check in order whether it is due to low irradiance, reduced effective irradiance, large losses on the array side, or losses occurring downstream of the inverter.

If you first understand these 12 abbreviations, your confusion when reading PVSyst's Result Sheet, Loss Diagram, Detailed Losses, and Monthly Results will be greatly reduced. This will enable you not only to read the numbers but also to explain at which stage energy is being lost, making it easier to use for design reviews, comparisons with other companies' reports, checking documents for bank submissions, and post-construction energy production variance analysis.