Six Ways to Read PVSyst Battery Results | For Projects with Battery Storage

In projects that combine solar power generation with batteries, you need to read PVSyst results differently than for standard standalone solar projects. For standalone solar, you can grasp the overall picture mainly by tracking irradiance, array output, inverter output, the power delivered to the grid connection point, PR, and various losses.

However, in projects with batteries, the power generated does not necessarily flow directly to the grid. Some power may first be charged into the battery and later discharged, and charging/discharging efficiency losses, SOC upper and lower limits, operational controls, output limits, load following, peak shaving, and surplus charging all influence the results.

Therefore, when reading the Battery results in PVSyst, you should not just look at whether the amount of generation is high or low, but sequentially check "where the generated power went", "at what times the battery was charged", "to what extent it discharged", "whether the battery reduced the power that was curtailed", and, conversely, "whether net exported power has decreased due to battery losses".

Especially for commercial solar, self-consumption solar, FIP projects, projects with grid constraints, and projects aiming for demand-side peak shaving, battery evaluation directly impacts profitability and the appropriateness of the design. If you cannot correctly read PVSyst’s Battery results, it becomes difficult to determine whether the battery capacity is excessive or insufficient, whether the charge/discharge control aligns with actual operation, and whether the generation assessment is conservative or optimistic.

In this article, for projects with batteries, we organize the basics of reading PVSyst's Battery results into six perspectives. Rather than detailed instructions on operating the settings screens, we focus on where to look and how to interpret which numbers when reviewing reports in practice.

Table of Contents

• Interpret battery results as power flows, not as generated energy

• Infer battery losses from the difference between charged and discharged energy

• Assess the adequacy of capacity and operational control from SOC trends

• Evaluate the surplus power reduction and output curtailment achieved by the battery

• Assess the impact on grid export volumes and self-consumption

• Do not judge battery results in isolation; verify them with loss diagrams and time-series data

Battery results should be interpreted as power flow, not as generated energy.

The first point to be aware of in the Battery results of PVSyst is that, in projects with batteries, the "generated energy" and the "energy ultimately available for use" do not match. The electricity generated by the solar panels flows to the load, the grid, or the battery while incurring losses on the DC and AC sides. When a battery is present, part of that energy is used for charging and is discharged at later times. At this stage, simply looking at the annual generated energy alone cannot determine the overall performance of the project.

For example, even if solar generation is sufficient during the daytime, if demand is low at that time and reverse power flow to the grid is restricted, surplus electricity is either wasted or charged into batteries. If it can be stored in batteries, it can be discharged in the evening, at night, or during periods of high demand. In this case, because it allows use of power that would have been wasted with solar alone, the introduction of batteries is considered effective.

On the other hand, the electricity charged into a storage battery suffers losses during charging, storage, discharging, and conversion. Routing generated electricity through a storage battery once reduces the amount of energy compared with using it directly.

Therefore, in projects with storage batteries, it is necessary to distinguish between “whether adding the storage battery has increased the effectively usable electricity” and “whether passing through the storage battery has increased losses.”

When reviewing PVSyst results, first check whether the power produced by the solar array was supplied directly to the load, used to charge the battery, sent to the grid, or lost due to curtailment. If you compare only the final annual energy production without looking at this, you can easily misunderstand the role of the battery.

It is particularly important to note that the metrics to be evaluated change depending on the purpose of installing a storage battery. If the objective is to raise the self-consumption rate, the amount of energy supplied to the load and the reduction in purchased electricity are more important than the amount of electricity sold to the grid. If the objective is to avoid output curtailment, how much surplus power the battery absorbed is important. If the objective is peak shaving, not only the annual energy amount but also the effect on reducing the maximum demand and the appropriateness of the discharge timing are important.

Therefore, when interpreting Battery results, it is important to first clarify "what this battery has been installed for." If you look at the results while the purpose is unclear, you may judge a high amount of charging as a good result or a low amount of discharging as a bad result. In reality, however, what constitutes an appropriate result depends on the project's constraints and control policy.

PVSyst's Battery results are not a performance sheet for the battery itself. They are the results of the energy flow when solar generation, load, grid, battery, and control conditions are combined. Therefore, when first interpreting them, it is most important to follow where the power goes rather than the amount of generation.

Estimating battery losses from the difference between charge and discharge amounts

What to look at next in the Battery results is the difference between the amount of energy charged into the battery and the amount discharged from it. A battery is a system that stores electrical energy for later use, but the energy you charge into it does not all come back out as usable power. Charging efficiency, discharging efficiency, conversion losses in the PCS and converters, standby losses, self-discharge, and so on mean that the amount of energy that can be discharged is less than the charged amount.

For example, if 1,000 MWh is charged into the battery annually and 900 MWh is discharged, a simple view shows that 100 MWh is lost as battery-related losses. In reality, the breakdown of those losses depends on the equipment configuration and the definitions in PVSyst, but by first looking at the difference between the charged and discharged amounts, you can grasp the scale of energy loss incurred by routing energy through the battery.

If this difference is large, you need to check the battery’s efficiency settings, conversion pathways, charge/discharge control, and the conditions for standby losses. If the battery capacity is too large and it remains on standby for long periods, the amount of unused capacity increases, which can be detrimental to efficiency. Also, if the control strategy results in too many charge/discharge cycles, losses from round‑trip efficiency will accumulate.

On the other hand, the fact that there is a difference between the amount charged and the amount discharged is not itself abnormal. Because storage batteries always involve losses, it is natural for the discharged amount to be less than the charged amount. What matters is whether those losses are reasonable given the intended equipment specifications and operational purposes. In projects based on lithium-ion batteries, if the efficiency appears extremely low, you should check the configured number of conversion stages and how AC and DC connections are handled.

Also, in PVSyst, the battery connection location and system configuration change which losses appear under which items. Whether it is connected to the PV’s DC side or to the AC side, and whether the load or the grid is prioritized, alters how the results should be interpreted. Therefore, rather than judging based only on the amounts charged and discharged, you also need to check what power conversions are occurring before and after the battery.

A common oversight in practice is assuming that installing a battery will increase the amount of electricity exported and self-consumption, and thereby underestimating battery losses. It is true that batteries can make surplus power available for later use. However, in projects where the surplus is originally small or daytime demand is sufficiently large, routing power through a battery can actually reduce the net usable energy.

Therefore, in the Battery results, we always check the magnitude of the energy that passed through the battery together with the amount of energy lost as a result. A high amount of charging indicates the battery is being heavily used, but it may also imply that greater losses are occurring. A high amount of discharging indicates effective utilization is progressing, but it is necessary to separately verify whether that discharging is actually taking place during high-value time periods.

When interpreting battery results, grasping the relationships between charge amount, discharge amount, losses, and round-trip efficiency makes it easier to determine whether the battery is contributing net positive to the energy balance or is simply circulating power and increasing losses.

Assessing the Validity of Capacity and Operational Control from SOC Trends

In projects with battery storage, the SOC trend is extremely important. SOC stands for State of Charge and indicates the battery’s charge state. Put simply, it is an indicator of how charged the battery is. In PVSyst’s Battery results, by checking the time variation of SOC you can determine whether the battery capacity is appropriate, whether charge/discharge control is operating as expected, and whether the battery is being sufficiently utilized.

If the SOC rises during the daytime and falls from evening into the night, it can be assumed that excess solar generation is being charged and then discharged in later periods. Such behavior is natural for self-consumption projects and projects designed to meet evening demand. On the other hand, if the SOC remains consistently near full charge, it may indicate that the energy stored in the battery is not being adequately discharged. This can indicate oversized capacity, constraints in discharge control, insufficient load, or limitations on discharge destinations.

Conversely, if the SOC is consistently stuck near the lower limit, the battery capacity may be insufficient, charging opportunities may be few, solar surplus may be low, or the discharge demand may be too high. In this case, the battery may be operated in a state that is almost empty at all times and may not be able to discharge sufficiently during the required time periods.

When interpreting SOC, it is important to look not only at the annual average but also at daily, monthly, and hourly behavior. If you only look at the annual charge/discharge amounts, the battery may appear to be well utilized, but in reality it may be fully charged only in certain seasons and hardly used in others. Because solar power generation has large seasonal variations, battery usage also changes significantly from month to month.

For example, in summer generation is high and, because there is a large daytime surplus, the battery tends to become fully charged, whereas in winter generation is low and there may be little surplus available for charging in the first place. Conversely, at facilities with high winter demand the battery may be discharged frequently even with low generation, and the SOC may remain low. If you judge based only on annual values without considering such seasonal differences, you may misjudge the appropriateness of the battery capacity.

Also, setting the SOC upper and lower limits is important. In actual storage batteries, for reasons of lifespan protection and safety, it is common practice not to discharge them completely to 0% or charge them fully to 100%. The usable battery capacity changes depending on how you set the SOC lower and upper limits in PVSyst. Even if the nominal capacity is 1,000 kWh, if the operable SOC range is 10% to 90%, the actually usable range is equivalent to 800 kWh.

Therefore, when reading the Battery results, rather than simply looking at the battery capacity figure, check how much is being used as usable capacity. If SOC frequently reaches its upper or lower limits, the battery capacity or control strategy may not be appropriate for the project conditions. If it frequently reaches the upper limit, there may be surplus power that cannot be charged and is being wasted. If it frequently reaches the lower limit, the battery capacity may be insufficient for the demand.

The SOC trend does not directly evaluate the health of the storage battery itself, but it is very useful for understanding operational conditions in simulations. In battery-storage projects, checking not only the annual discharge volume but also the rhythm in which SOC moves makes it easier to judge the consistency between design and operation.

Interpreting surplus electricity and output curtailment reduced by storage batteries

One of the main purposes of installing battery storage is to reduce surplus power and output curtailment. In solar power generation, a surplus occurs when generation exceeds demand or the grid’s capacity to accept it. If this surplus cannot be sold or output is limited due to grid constraints, potential generation goes unused and is lost. With battery storage, some of that surplus can be absorbed and later discharged for effective use.

In PVSyst's Battery results, it is important to check how much surplus power the battery charged and how much it reduced output curtailment and unused energy. Comparing the cases with and without a battery makes the benefit of installing one easier to understand. If power that would have been discarded without a battery is charged when a battery is present and later discharged, you can conclude that the battery is having an effect.

However, there is a point to be careful about here as well. The surplus power charged into a battery does not necessarily all generate effective value. If the timing of discharge after charging does not match demand, it will not lead to an improvement in the self-consumption rate. When assuming operation under FIP or market-linked schemes, whether you can discharge during high-price periods is important. Simply charging surplus power may not be sufficient from an economic standpoint.

Also, if the battery capacity is too small, it cannot absorb all surplus power, and a large amount of output curtailment will remain. In this case, in the Battery results the SOC quickly reaches its upper limit, and subsequent surplus is effectively discarded. Conversely, if the battery capacity is too large, there is room to absorb surplus, but it is difficult to reach full charge over the course of the year, and the equipment utilization rate may be low.

In practice, it is important not to look only at the results after adding battery storage, but to compare them with a baseline case without a battery. You should check how much surplus or curtailment there was without the battery, how much of that was reduced with the battery, and how much battery loss occurred relative to that reduction. Without this comparison, the effect of the battery can easily be overestimated.

For example, even if a battery can absorb 200 MWh of surplus annually, if only 170 MWh can be extracted at discharge, about 30 MWh is lost as battery-related losses. That 170 MWh is valuable if used during high-value periods, but if it is discharged only during low-value periods, the return on investment may be limited.

When reading PVSyst's Battery results, it is important to look not only at the amount of surplus reduction but also at the net effect after curtailment avoidance. A battery is a device that absorbs surplus, but it is also a device that generates losses. By determining which is larger, it becomes easier to evaluate the viability of introducing a battery.

Understanding the Impact on Grid Feed-In and Self-Consumption

In projects with battery storage, the way you read grid export and self-consumption changes. In solar-only projects, you look at how much of the generated electricity is self-consumed, how much is sold to the grid, and how much is lost as surplus. When a battery is added, daytime surplus can be shifted to nighttime or peak periods, so the time distribution of self-consumption and exported energy changes.

In self-consumption projects, whether a battery increases the self-consumption rate is important. If you can charge solar power that cannot be used up during the day and discharge it in the morning, evening, or at night, you can reduce electricity purchases from the grid. In this case, in the Battery results you should check the amount of energy supplied from the battery to the load. It’s not just the amount of discharge that matters, but whether that discharge is actually being used by the load.

On the other hand, for power-selling projects and FIP projects, changes in grid feed-in volumes and the timing are important. By using batteries to suppress daytime peak feed-in and discharge during other time periods, projects may aim to address grid constraints and optimize revenue. In this case, looking only at annual grid feed-in volumes is not sufficient. It is necessary to check which time periods the energy is being fed into the grid and how it is being controlled relative to the output limit.

When a battery storage system is introduced, the amount of electricity sent directly from solar to the grid may decrease, while the amount sent later via the battery may increase. In such cases, even if the annual amount of electricity sent to the grid does not change much, the time-of-day transmission patterns can change significantly. In projects where the value of electricity varies by time of day, this time-shifting effect is important.

Also, for projects that include a battery, care is needed in how PR is interpreted. PR is a representative indicator showing the performance of a solar power generation system, but when a battery is included, the interpretation changes depending on which point’s energy is used as the numerator. The PR used to assess the performance of the solar array or inverter and an evaluation that includes the final amount of energy supplied after passing through the battery do not mean the same thing.

For example, even if introducing a storage battery increases the final usable energy, because storage battery losses have increased it may appear lower on certain PR metrics. Conversely, even if the PR on the solar side is good, if storage battery control is poor the results may not be sufficient in terms of self-consumption or revenue from electricity sales.

Therefore, in the Battery results, you need to read them separately for the performance as a solar power generation facility, the performance as energy management including the storage battery, and the performance in terms of the project's financials. Even if the losses on the solar side are reasonable, if the battery's operation is not appropriate, the overall project evaluation will decline. Conversely, even if there are some battery losses, if it can substantially avoid output curtailment or reduce purchases during periods of high electricity prices, it may be judged that there is a beneficial effect from the installation.

When looking at the amount of power exported to the grid and self-consumption, it's important to check not only annual totals but also monthly, daily, and hourly results. Because a battery storage system shifts energy in time, its true effect is hard to see from annual totals alone.

Do not judge Battery results alone; verify with the loss diagram and time-based data

Finally, it is important not to judge the Battery results in isolation. PVSyst's battery-related figures are useful for understanding the battery's charge/discharge behavior and losses, but looking at them alone cannot determine the overall validity of a project. You must always review them together with the loss diagram, main results, monthly results, time-based data, and system settings.

In particular, loss diagrams are useful for broadly understanding the flow of energy from solar generation to final output. They allow you to check how much is lost at each stage and what proportion of the total is attributable to battery-related losses. Even if battery losses are large, it may be judged acceptable if they result in a substantial increase in the effective utilization of surplus power. Conversely, if battery losses are conspicuous while surplus reduction and improvements in self-consumption are small, a review of the design or control strategy is necessary.

Time-of-day data is also very important. A battery's role changes depending on the time of day. Whether it charges during the daytime and discharges in the evening, discharges at night, discharges only during peak demand, or charges and discharges to match grid constraints, the value can differ even with the same annual discharged energy. By looking at time-of-day data, you can confirm whether the battery is operating in the intended time periods.

Also, by looking at monthly results, you can understand operational status by season. Solar power generation has large seasonal variations, and battery usage patterns also change with the seasons. In spring and autumn, generation is high and demand is low, so surpluses may occur. In summer, even if generation is high, air-conditioning demand is high and self-consumption may increase. In winter, generation is low, so batteries may not be able to charge sufficiently. If you judge only by annual values without considering these seasonal characteristics, you may overlook operational challenges.

When checking battery results, it is also essential to verify consistency with the input conditions. Confirm that battery capacity, maximum charging output, maximum discharging output, SOC upper limit, SOC lower limit, charge/discharge efficiency, connection configuration, control strategy, load profile, and grid constraints match the actual design conditions. If the results appear unnatural, the cause is often in the input conditions rather than the results.

For example, if the battery storage capacity is large but the discharged amount is small, it could be that the load is small, discharge control is strict, the SOC lower limit is high, the allowable discharge time is limited, or discharging to the grid is not permitted. Conversely, if the number of charge–discharge cycles is too high, the control may be operating too finely and may not be realistic for actual operation.

Also, for projects that include batteries, it is important that the PVSyst results match the actual operational control. In real systems, the BMS, PCS, EMS, customer equipment, and grid-side constraints operate in coordination. It is necessary to verify whether the control assumed in PVSyst can actually be implemented in the EMS, whether it is permitted by contract, and whether it conflicts with protection settings.

Thus, the Battery results are not simply the output of the storage battery, but simulation results that combine solar power generation, battery storage, loads, the grid, and control. To correctly interpret the results, it is important to trace and check the flow of energy, charging/discharging losses, SOC, surplus reduction, the impacts on self-consumption and the amount of energy exported to the grid, and the time‑by‑time behavior.

Practical workflow for reading PVSyst Battery results

When checking PVSyst Battery results in practice, first confirm the project's objective. The metrics you should examine change depending on whether you want to increase the self-consumption rate, reduce output curtailment, perform peak shaving, or shift the feed-in (selling) times. If you review the Battery results without understanding the objective, the evaluation criteria will be ambiguous.

Next, we will examine the flow of electricity generated by solar power. We will look at the power supplied directly to loads, the power sent to the grid, the power charged into the battery, and the power lost as surplus. This will reveal the role the battery plays in the overall project.

Next, compare the amount of energy charged into the battery with the amount discharged. By looking at how much is discharged relative to the amount charged, you can grasp the scale of battery-related losses. Because losses inevitably occur when energy passes through the battery, confirm whether those losses are reasonable relative to the benefits of installation.

Furthermore, examine the SOC trend. If the SOC is stuck at the upper limit, it suggests not a capacity shortage but rather insufficient discharge or a lack of ways to use the energy after surplus absorption. If the SOC is stuck at the lower limit, a capacity shortage or a lack of charging opportunities is suspected. If the SOC fluctuates appropriately, the battery may be functioning as a charge-discharge cycle.

On that basis, we compare with the case without a battery. We compare how much surplus power decreased by adding the battery, how much self-consumption increased, how the amount of power sent to the grid changed, and how much losses increased. This comparison allows us to determine whether the battery is actually delivering benefits.

Finally, verify the validity of the control with time-series data. Even if annual values look fine, examining time-series data can reveal discharging at unintended times. Time-series behavior is particularly important for demand-following, responding to output limits, FIP compliance, and peak shaving.

For projects that include battery storage, explanatory materials describing the PVSyst results also become important

For projects with battery storage, preparing materials to explain PVSyst results to internal teams and clients is also important. Because the energy flows become more complex than in solar-only projects, simply handing over the report can make it difficult to convey the intended meaning. In particular, the relationships among charged energy, discharged energy, losses, SOC, surplus reduction, and self-consumption rate are areas that are easily misunderstood unless organized with diagrams and time series.

For example, you may hear comments like "even though a battery storage was installed, the total electricity transmitted hasn't increased much." However, if the goal is peak shaving or improving the self-consumption rate, it is not appropriate to judge effectiveness solely by the total electricity transmitted. There are also remarks that "the amount discharged is small compared to the amount charged," but this can be natural when considering round-trip efficiency and standby losses.

In such explanations, rather than simply showing PVSyst's Battery results as-is, it is clearer to separate and organize PV generation, direct use, battery charging, battery discharging, losses, surplus, grid exports, and reductions in purchased electricity. Furthermore, showing the SOC profile and charge/discharge graphs for a representative day makes it easier to intuitively understand how the battery is operating.

From the perspective of site verification and design reviews, it is also important to ensure that the simulation results match the actual equipment layout, PCS capacity, battery capacity, cubicles, point of supply, load equipment, and grid interconnection conditions. Even if the PVSyst results are correct, if the on-site connection configuration, control panel design, and measurement point design do not align, the expected results may not be achieved during operation.

A system that leverages high-precision GNSS usable on an iPhone, like LRTK, to record on-site equipment locations, racking layouts, cubicle positions, wiring routes, and inspection targets is also useful for site management of solar power plants and projects with battery storage. By recording actual on-site information with high precision—not just the simulation results from PVSyst—and being able to cross-check it against drawings and inspection records, it becomes easier to identify discrepancies between design values and site conditions. In projects with battery storage, the positional relationships among PCS, battery containers, power receiving equipment, and measurement points also become important, so accurately preserving site information is effective for future maintenance and retrofits.

Summary

When reading PVSyst's Battery results, you must not look only at annual energy production or PR as you would for a solar-only project. For projects with a battery, you need to check, in order, whether the generated electricity is used directly, charged into the battery, discharged later, or lost as system losses.

The first thing to look at is the flow of power. Check where the power generated by solar went: to the load, the grid, the battery, or as surplus. Next, look at the difference between the amount charged and discharged to grasp the magnitude of battery-related losses. Furthermore, examine the SOC trend to determine whether the battery capacity and operational controls are appropriate.

On that basis, we check how much surplus power and output curtailment have been reduced by the battery, and how self-consumption and grid export volumes have changed. Finally, it is important to cross-check with loss diagrams and time-series data to identify operational issues that cannot be seen from annual totals alone.

A battery energy storage system is not equipment for increasing power generation, but equipment for adjusting how electricity is used and the times at which it is used. Therefore, PVSyst's Battery results should be read not only in terms of increases or decreases in generation, but from the perspective of when it charged, when it discharged, and which electricity was effectively utilized.

In evaluating projects with batteries, it is important to link and assess the simulation figures, control strategies, site conditions, and business objectives. Once you can correctly read the Battery results in PVSyst, you will be able to explain more concretely the appropriateness of battery capacity, the suitability of control conditions, the degree of utilization of surplus power, and the impact on profitability.