Introduction: Why BESS Sizing Matters in Solar Projects

A Battery Energy Storage System (BESS) can help bridge this gap by storing electricity when it is available and releasing it when it is needed. When properly integrated with a solar PV plant, battery storage can support energy shifting, peak demand management, renewable energy firming, grid services and improved utilisation of available solar generation.

The effectiveness of a solar-plus-storage project depends heavily on BESS sizing for solar projects. The battery must be designed around the required power output, energy capacity, discharge duration, operating profile, grid limitations, equipment characteristics, safety requirements and commercial objectives.

An oversized battery may increase project capital expenditure without generating sufficient additional value. An undersized system may fail to meet the required discharge schedule, contracted energy delivery or backup requirement. Similarly, selecting a battery solely on the basis of megawatt-hours without considering power conversion, usable capacity, degradation and grid constraints can lead to an incomplete design.

For project developers, Independent Power Producers (IPPs), utilities, industrial consumers and Engineering, Procurement and Construction (EPC) contractors, a structured BESS feasibility study is therefore essential.

AlgEnergy Engineering Consultancy Services supports renewable energy and infrastructure projects through feasibility studies, techno-economic analysis, Detailed Project Reports (DPRs), engineering design, technical documentation and project execution support.

This guide explains the principal considerations involved in battery capacity sizing, duration analysis, load profile assessment, solar integration, grid studies and BESS CAPEX evaluation.

1. What Is BESS Sizing for Solar Projects?

BESS sizing is the engineering process of determining the power capacity, energy capacity, operating duration and configuration of a battery energy storage system required to meet a project's technical and commercial objectives.

For a solar-plus-BESS project, the sizing exercise considers both the solar generation profile and the intended use of stored electricity.

The principal design parameters are:

• Power capacity (MW): The rate at which the battery can charge or discharge.

• Energy capacity (MWh): The amount of energy the battery can store or deliver, subject to the applicable capacity definition.

• Discharge duration (hours): The time the system can sustain a specified discharge power.

• Usable energy: The energy available within the permitted operating limits.

• Round-trip efficiency: The ratio of energy discharged to energy used for charging over a defined cycle.

• State of charge (SOC): The battery's available charge expressed as a percentage of its reference capacity.

• Depth of discharge (DoD): The fraction of capacity withdrawn during discharge.

• Degradation allowance: The capacity reduction expected over the operating life.

• Availability and auxiliary consumption: The effects of downtime and equipment loads on deliverable energy.

These parameters must be considered together. A battery with sufficient nominal energy capacity may still be unable to meet the required output if its inverter power rating is too low, its operating SOC window is restricted or its temperature-management systems reduce available performance.

1.1 Power Capacity Versus Energy Capacity

Power and energy are different engineering quantities.

Power is measured in kilowatts (kW) or megawatts (MW), while energy is measured in kilowatt-hours (kWh) or megawatt-hours (MWh).

For example, a 20 MW / 80 MWh BESS has a nominal energy-to-power ratio corresponding to four hours at 20 MW, assuming the stated energy is available at the same measurement boundary and the system can sustain the required output.

The simple relationship is:

Discharge duration = Energy capacity ÷ Discharge power

Therefore:

80 MWh ÷ 20 MW = 4 hours.

This is a nominal calculation, not a guarantee of four hours of usable AC output under all conditions. Actual performance depends on usable capacity, conversion losses, auxiliary consumption, operating limits, degradation and the supplier's performance guarantees.

1.2 Why Solar Capacity Alone Cannot Determine Battery Size

A 100 MW solar plant does not automatically require a 100 MW battery. Nor does it necessarily require a 200 MWh, 400 MWh or 800 MWh battery.

The appropriate configuration depends on the application.

A project designed to reduce midday solar curtailment may require a different battery from a project designed to deliver a specified amount of electricity during evening peak demand.

Similarly, a commercial and industrial facility seeking to reduce its maximum demand may need a relatively high-power battery with a shorter discharge duration. A renewable project contracted to deliver power over a longer evening window may require more energy capacity.

The first step is therefore to define the required service and operating schedule before selecting battery capacity.

2. Define the Project Objective Before Sizing the Battery

A reliable BESS sizing methodology begins with the project use case.

2.1 Solar Energy Shifting

Solar energy shifting involves charging the battery during periods of high solar generation and discharging it later.

This arrangement can help move energy from a low-value or constrained period into a period when electricity has greater commercial or operational value.

The analysis should establish:

• Solar energy available for charging.

• Expected charging window.

• Required discharge window.

• Target discharge power.

• Energy delivery requirement.

• Charging and discharging losses.

• Permitted grid imports and exports.

• Expected number of cycles.

The battery should be sized against the energy that can realistically be captured, not simply the total daily solar generation.

2.2 Peak Demand Management

For commercial and industrial consumers, a BESS may reduce peak grid demand by supplying part of the facility's electrical load.

The required battery size depends on the difference between the facility's demand and the desired grid-import limit.

A detailed load profile analysis should identify the magnitude, timing and duration of demand peaks. It should also establish whether the peaks occur when the solar plant is generating or after solar generation has declined.

2.3 Renewable Energy Firming

Renewable energy firming involves using storage and an appropriate control strategy to reduce variations in the delivered power profile.

The design must consider the required output schedule, the speed of generation changes, the accuracy of solar forecasts and the battery's response capability.

Short-duration fluctuations and multi-hour energy shifting are different engineering problems. The battery power rating, energy capacity and control system must reflect the actual requirement.

2.4 Grid Support and Ancillary Services

Depending on the applicable market rules, grid-connected BESS installations may provide services such as frequency response, voltage support, reserve capacity or other grid-support functions.

These services require assessment of the relevant grid-code provisions, interconnection requirements, response times, power quality, control interfaces and operating restrictions.

The project developer should not assume that all services are automatically available or commercially remunerated in every jurisdiction.

2.5 Backup Power and Resilience

For facilities requiring backup power, the battery must be sized around critical load, backup duration, permissible load shedding and the expected availability of charging sources.

A grid-connected battery is not necessarily capable of supplying an isolated facility during an outage. Islanding, protection, grid-forming capability, black-start requirements and electrical architecture must be assessed separately.

3. Core Methodology for Battery Capacity Sizing

The most useful starting point is to define the required discharge power and energy at a clearly specified measurement boundary.

3.1 Calculate the Required Discharge Energy

For a constant load, a preliminary estimate is:

Required energy = Discharge power × Discharge duration

For example, suppose a project must deliver 15 MW for four hours.

Required delivered energy:

15 MW × 4 hours = 60 MWh.

This is the energy delivered to the specified load or grid boundary. It is not necessarily the nominal DC energy capacity required inside the battery.

3.2 Account for Usable Capacity

Battery capacity cannot always be fully discharged. Manufacturers specify operating limits, minimum SOC, maximum SOC and other conditions to maintain safety, performance and warranted life.

A preliminary relationship is:

Required nominal energy = Required delivered energy ÷ Usable fraction

If 60 MWh must be delivered and the assumed usable fraction is 90%:

60 MWh ÷ 0.90 = 66.7 MWh.

This calculation assumes that the delivered-energy requirement and usable-energy definition use compatible measurement boundaries. It does not independently account for inverter losses, auxiliary consumption or end-of-life degradation.

3.3 Account for Discharge Efficiency and Auxiliary Consumption

A more complete preliminary model is:

Required nominal energy = Required delivered AC energy ÷ (Usable fraction × Discharge efficiency)

Suppose the required AC energy is 60 MWh, the usable fraction is 90%, and the assumed discharge efficiency from the relevant battery-energy reference point to the AC delivery boundary is 96%.

Required nominal energy:

60 ÷ (0.90 × 0.96) = approximately 69.4 MWh.

These values are illustrative engineering assumptions, not specifications for a particular battery product.

If auxiliary loads are supplied from the BESS, their consumption must also be included. If the battery is expected to meet the requirement near the end of its service life, the design must additionally account for degradation or include an agreed augmentation strategy.

3.4 Consider End-of-Life Capacity

Battery capacity typically declines with calendar age, cycling, temperature exposure and operating conditions.

If the system must deliver a specified energy quantity at the end of the design life, the initial capacity may need to be larger than the minimum required at commissioning.

A simplified preliminary relationship is:

Initial required energy = Required end-of-life energy ÷ Expected retained capacity fraction

For example, if the required capacity at a future design point is 70 MWh and the assumed retained capacity fraction is 80%:

70 MWh ÷ 0.80 = 87.5 MWh.

This is a simplified illustration. A bankable design should use the supplier's warranted degradation model, expected cycling, environmental conditions, operating profile and the project's augmentation strategy.

3.5 Distinguish AC and DC Capacity

A frequent source of error in energy storage design is comparing capacities that are measured at different electrical boundaries.

Battery cell or rack capacity is generally associated with the DC side. Grid-deliverable power and energy are usually evaluated at a defined AC point of connection.

The conversion between these quantities depends on:

• Battery configuration.

• Power Conversion System (PCS) efficiency.

• Transformer losses.

• Cable losses.

• Auxiliary loads.

• Operating temperature.

• SOC limits.

• Operating power.

• System availability.

Every BESS specification should identify whether the stated MW and MWh figures refer to the battery DC terminals, PCS AC terminals or the point of connection.

4. BESS Duration Analysis: Choosing the Right Storage Duration

BESS duration is the period for which a battery can sustain a specified discharge power under defined operating conditions.

It is commonly expressed in hours.

A four-hour battery is not inherently better than a two-hour or six-hour battery. The right duration depends on the application and the value generated by additional stored energy.

4.1 Short-Duration Storage

Short-duration storage may be suitable for applications such as:

• Rapid power balancing.

• Short peak-demand events.

• Solar output smoothing.

• Selected grid-support services.

• Short-duration ride-through applications.

The required energy capacity may be relatively modest compared with a system designed for several hours of energy shifting.

However, power electronics, control response, thermal management and cycle requirements remain important.

4.2 Medium-Duration Storage

Medium-duration storage can support several-hour energy shifting, demand management and certain renewable energy delivery schedules.

Sizing should consider the full charging and discharging profile, including periods when the battery cannot charge at its maximum rating because solar generation is insufficient.

4.3 Longer-Duration Storage

Longer-duration storage may be relevant where the project must deliver electricity through an extended evening period, meet a longer load requirement or support a specified renewable energy schedule.

Additional duration increases the amount of energy that must be installed, maintained and financed. The commercial case must therefore demonstrate that the additional energy capacity creates sufficient value.

4.4 Use the Actual Operating Profile

A useful BESS duration study should compare alternative configurations rather than assuming one standard duration.

For example, an engineer could evaluate a set of candidate configurations such as:

• 20 MW / 40 MWh.

• 20 MW / 80 MWh.

• 20 MW / 120 MWh.

These correspond to nominal two-, four- and six-hour configurations at the stated power rating, based on the stated energy capacity.

The alternatives should then be tested against the actual charging opportunity, discharge requirement, degradation profile, grid constraints and financial assumptions.

The preferred configuration is the one that meets the required technical performance and provides the strongest justified commercial outcome, not necessarily the one with the greatest installed capacity.

5. Load Profile Analysis for Solar Battery Storage Design

Load profile analysis is particularly important for commercial and industrial solar projects, captive power plants and systems designed to reduce peak grid imports.

A battery sizing calculation based on average demand may fail to capture short-duration peaks, evening loads or seasonal changes.

5.1 Collect High-Resolution Demand Data

Useful inputs include:

• Interval electricity consumption.

• Maximum demand.

• Daily load curves.

• Monthly electricity bills.

• Time-of-use tariff schedules.

• Weekend and weekday profiles.

• Seasonal operating patterns.

• Critical and non-critical loads.

• Existing solar generation.

• Grid outage records, where relevant.

• Planned facility expansion.

Where possible, interval data should be collected at a resolution suitable for the intended application. Fifteen-minute data may be useful for many demand-management studies, while applications involving rapid power fluctuations may require higher-resolution information.

5.2 Identify the Peak Demand Window

The engineer should determine when the facility's highest demand occurs and how long the peak persists.

A single high-demand interval may require a different solution from a moderate demand excess that continues for four or five hours.

For peak shaving, the battery power rating must be sufficient to cover the target reduction, while energy capacity must be sufficient to sustain that reduction over the relevant duration.

5.3 Match Load and Solar Generation

The load profile should be compared with the expected solar generation profile.

Three broad operating patterns are common:

Daytime demand: Solar generation may directly serve much of the facility load, leaving surplus energy available for storage during some periods.

Evening demand: Battery discharge may be needed after solar generation falls.

Continuous demand: The system may need to combine direct solar use, storage and grid supply according to the facility's operating objectives.

A proper study should model the interaction between solar generation, battery charging, battery discharge and grid imports at each time interval.

5.4 Evaluate Multiple Operating Scenarios

The analysis should test different demand conditions and operating assumptions, including:

• High-demand production days.

• Low-demand days.

• Weekends and holidays.

• Seasonal changes.

• Reduced solar generation.

• Battery unavailability.

• Planned maintenance.

• Future load growth.

This approach helps avoid selecting a battery that performs well under an average day but fails during the conditions that matter most commercially.

6. Solar Generation Profile and Charging Opportunity

Solar battery storage sizing must account for how much energy can be charged into the battery and when it is available.

A solar PV plant may generate substantial daily energy, but the amount available for storage depends on direct consumption, export limits, curtailment, inverter constraints and charging controls.

6.1 Solar Resource and Energy Yield

Solar generation estimates should consider:

• Site-specific solar irradiation.

• Seasonal weather patterns.

• PV module performance.

• Inverter performance.

• Temperature effects.

• Shading and soiling.

• Plant availability.

• Electrical losses.

• Degradation.

• Grid export constraints.

An energy-yield assessment can provide the expected hourly or sub-hourly generation profile needed for BESS modelling.

Where suitable data are available, engineers should model representative weather years and evaluate uncertainty rather than relying only on annual average generation.

6.2 Surplus Solar Energy

Surplus solar energy is the portion of generation that is available for charging after accounting for direct consumption and other applicable constraints.

For a grid-connected project, surplus energy may arise because generation exceeds the contracted export limit or because electricity has a greater value at another time.

For a commercial facility, surplus energy may occur when PV output exceeds the instantaneous facility load.

The study should distinguish energy that can actually be captured from theoretical surplus energy that is unavailable because of electrical, operational or contractual constraints.

6.3 Charging Power

The battery's charging power rating must be compatible with the solar generation profile, the PCS rating and the available electrical connection.

A battery with substantial energy capacity may remain underutilised if the charging window is too short or the available charging power is insufficient.

The design should evaluate:

• Maximum charging power.

• Available charging duration.

• Solar generation variability.

• Permitted grid charging.

• Charging efficiency.

• SOC at the beginning of the charging window.

• Restrictions imposed by the grid connection.

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6.4 Solar PV and BESS DC-Coupled or AC-Coupled Architecture

In an AC-coupled system, solar PV and the battery generally use separate power conversion equipment connected through an AC system.

In a DC-coupled system, PV and battery equipment share parts of the DC architecture, typically with a suitable hybrid or shared conversion arrangement.

The preferred arrangement depends on the project design, existing equipment, charging requirements, conversion losses, operating flexibility, controls and commercial assumptions.

AC coupling may provide flexibility for some retrofit applications. DC coupling may be attractive for certain new-build projects where the architecture allows efficient capture of otherwise constrained PV generation. Neither approach is universally superior.

The engineering study should compare the total system rather than choosing an architecture based on a single efficiency claim.

7. Grid Integration Study for Solar Plus BESS

A BESS is not simply a battery container connected to a solar plant. It is an electrical power system that must comply with the relevant interconnection requirements.

Grid integration studies assess whether the proposed system can operate safely and reliably within the intended network.

7.1 Point of Interconnection

The project should establish the point of interconnection, the permitted import and export limits, the voltage level, the available fault level and the applicable network requirements.

The study should also consider whether the BESS can charge from the grid, whether charging is restricted during particular periods and whether export is limited by the solar plant's interconnection agreement.

7.2 Power Flow and Voltage Assessment

Load-flow studies can help assess voltage levels, equipment loading, reactive power requirements and potential network constraints under relevant operating scenarios.

The study should consider charging and discharging conditions, solar generation variability, minimum and maximum grid demand and any relevant contingency conditions.

7.3 Short-Circuit and Protection Coordination

The BESS and associated power electronics can influence fault behaviour and protection requirements.

The protection assessment should evaluate the relevant equipment ratings, fault contributions, relay settings, isolation arrangements and coordination with the existing solar plant and utility network.

7.4 Power Quality and Harmonics

Power conversion equipment may introduce harmonics or other power-quality considerations.

The study should review the applicable limits, equipment performance, filter requirements and measurement arrangements. The requirements should be established from the grid code and interconnection agreement rather than assumed to be identical across countries.

7.5 Reactive Power and Power Factor

The PCS may provide reactive power within specified operating limits, depending on the selected equipment and its operating conditions.

The engineer should assess the required power factor, voltage-control strategy, active-versus-reactive power capability and any impact on the available active power rating.

7.6 Dynamic and Stability Studies

Depending on project size and network requirements, additional studies may include dynamic performance, frequency response, voltage recovery, fault ride-through, control interactions and grid-forming or grid-following behaviour.

Not every project requires every study. The required scope depends on the utility, system operator, project configuration and interconnection conditions.

For background on solar integration and storage, refer to the U.S. Department of Energy's solar integration guide.

8. Battery Technology and System Configuration

Battery technology selection should follow the project requirements, operating environment and commercial evaluation.

8.1 Lithium-Ion Battery Systems

Lithium-ion batteries are widely used in stationary energy storage applications. Different lithium-ion chemistries offer different combinations of energy density, power capability, thermal characteristics, cycle life and cost.

The final selection should consider the supplier's technical documentation, applicable safety requirements, warranties and the project's expected duty cycle,

8.2 Battery Management System

The Battery Management System (BMS) monitors and manages battery operation within defined limits.

Depending on the architecture, it may monitor voltage, temperature, current, SOC and other parameters. It also supports protective functions and communicates operating information to higher-level control systems.

The design should establish the communication interfaces, alarm handling, fault response and responsibilities between the BMS, PCS and Energy Management System (EMS).

8.3 Power Conversion System

The PCS converts electrical energy between the battery DC system and the AC network.

Its design rating should be selected against the required charging and discharging power, operating voltage, reactive power requirements, ambient conditions and relevant grid-code provisions.

8.4 Energy Management System

The EMS coordinates battery operation according to the project strategy.

Depending on the application, the control system may schedule charging, manage discharge, maintain SOC reserves, respond to dispatch instructions, prevent prohibited imports or exports and communicate with the plant SCADA system.

Control logic should be tested against normal operations, fault conditions, communication failures and changes in grid availability.

8.5 Thermal Management and Fire Safety

Battery performance and service life can be influenced by ambient temperature and internal thermal conditions.

The engineering scope should address temperature management, container ventilation where applicable, fire detection and suppression design, emergency isolation, safe access, equipment separation and emergency response procedures.

Applicable standards and regulations should be established for the project jurisdiction, battery chemistry and installation type. Fire protection requirements should be confirmed with qualified specialists and the relevant authorities.

9. BESS CAPEX Analysis and Techno-Economic Feasibility

BESS CAPEX analysis is essential because the lowest initial equipment price does not necessarily produce the lowest lifetime cost.

A battery project should be evaluated across its expected operating life, including charging costs, efficiency, degradation, maintenance, augmentation and replacement requirements.

9.1 Main Capital Cost Components

A BESS project cost estimate may include:

• Battery cells, modules, racks and enclosures.

• Power Conversion System.

• Battery Management System.

• Energy Management System and SCADA integration.

• Transformers and switchgear.

• Protection and metering.

• Cables and electrical balance of plant.

• Civil foundations and site development.

• Thermal management.

• Fire detection and protection.

• Grid interconnection works.

• Engineering, procurement and construction.

• Testing and commissioning.

• Development, permitting and owner costs.

• Contingency and other project-specific allowances.

The exact cost breakdown depends on whether the scope is battery-only, an integrated turnkey system or a complete solar-plus-BESS installation.

9.2 Operating Expenditure

Operating expenditure may include:

• Routine maintenance.

• Auxiliary electricity consumption.

• Monitoring and control systems.

• Service agreements.

• Replacement parts.

• Insurance.

• Land and facility costs.

• Periodic inspections.

• Battery augmentation.

• Decommissioning and recycling provisions.

The estimate should be based on a defined operating model and the contractual allocation of responsibilities.

9.3 Cost per Unit of Power and Energy

Cost comparisons can be expressed using power capacity and energy capacity metrics, provided that the cost scope and measurement basis are consistent.

For example, cost per MW can be useful when comparing systems with similar duration and similar scope. Cost per MWh can help compare energy capacity, but it may not adequately capture the cost of power electronics, grid connection or other fixed components.

For meaningful comparisons, the engineer should record:

• Battery power rating.

• Energy capacity and measurement boundary.

• Discharge duration.

• AC or DC configuration.

• Included balance-of-plant equipment.

• Warranty terms.

• Delivery and installation scope.

• Grid connection costs.

• Commissioning and performance testing.

9.4 Lifetime Cost and Levelised Storage Cost

A lifetime cost analysis should account for capital investment, charging energy, efficiency losses, maintenance, degradation, augmentation, replacement and other relevant costs.

A levelised storage cost metric can help compare alternatives, but the calculation methodology must be stated. Results can differ significantly depending on whether charging electricity, financing, degradation, replacement and residual value are included.

The lowest levelised cost does not automatically represent the best commercial solution if the system fails to meet the required dispatch schedule or operating constraints.

9.5 Revenue and Savings Assessment

Potential commercial value may come from:

• Time-of-use energy shifting.

• Reduced peak demand charges.

• Reduced curtailment.

• Improved use of contracted solar energy.

• Capacity or availability payments.

• Eligible ancillary services.

• Avoided backup generation costs.

• Reduced grid imports during specified periods.

Not all revenue streams are available to every project. The study must confirm the applicable tariff, market access, contractual rules, metering requirements and permitted operating modes.

9.6 Sensitivity Analysis

A bankable techno-economic assessment should test the effect of uncertainty in important assumptions.

Typical sensitivities include:

• Battery installed cost.

• Charging electricity cost.

• Discharge energy value.

• Round-trip efficiency.

• Annual cycling.

• Capacity degradation.

• Augmentation costs.

• Availability.

• Project lifetime.

• Financing assumptions.

• Grid curtailment.

• Solar energy yield.

The results should help the project owner understand which variables have the greatest influence on commercial performance and whether the project remains viable under less favourable conditions.

10. Illustrative BESS Sizing Example for a Solar Project

Consider a hypothetical utility-scale solar project with a requirement to deliver a specified amount of energy after solar generation declines.

Assume the project needs 25 MW of discharge power for four hours.

Step 1: Calculate required delivered energy

25 MW × 4 hours = 100 MWh.

Step 2: Establish preliminary usable capacity

Assume an illustrative usable fraction of 90%.

100 MWh ÷ 0.90 = 111.1 MWh.

Step 3: Account for discharge efficiency

Assume an illustrative discharge efficiency of 96%, measured from the relevant battery-energy reference point to the delivery boundary.

100 ÷ (0.90 × 0.96) = approximately 115.7 MWh.

Step 4: Consider end-of-life requirements

If the project must still meet the same delivery requirement at a specified future point in the battery's life, additional initial capacity or planned augmentation may be required.

The appropriate allowance must be calculated using the manufacturer's warranted degradation profile and the project's expected operating schedule.

Step 5: Check charging feasibility

The engineer must verify whether the solar plant can supply sufficient energy to recharge the battery within the available charging window, after accounting for direct loads, export constraints and charging losses.

Step 6: Verify electrical and grid constraints

The proposed PCS rating, transformers, cables, switchgear, protection, interconnection limits and control systems must be checked against the required operating modes.

This example demonstrates why a nominal 100 MWh energy requirement does not necessarily mean that a 100 MWh battery installation will be sufficient.

All figures are illustrative only and are not a design recommendation or equipment specification.

11. Key Engineering Risks in BESS Sizing

An effective feasibility study should identify and manage risks before equipment procurement.

11.1 Incorrect Load Assumptions

Sizing the battery from average demand rather than interval data can produce a mismatch between the required discharge schedule and installed capacity.

Mitigation: Use verified load profiles and test relevant seasonal and operational scenarios.

11.2 Insufficient Charging Energy

A battery may be too large relative to the available solar surplus or permitted grid charging.

Mitigation: Simulate charging and discharging across representative generation and demand profiles.

11.3 Inadequate End-of-Life Performance

A design based only on initial capacity may fail to meet future energy delivery requirements.

Mitigation: Model degradation, warranty conditions, operating limits and augmentation.

11.4 Grid Interconnection Constraints

Export limits, transformer capacity, voltage conditions or protection requirements may restrict the usable BESS output.

Mitigation: Complete the necessary grid integration studies and coordinate with the utility or system operator.

11.5 Inadequate Safety and Site Planning

Poorly coordinated layouts, access, emergency response provisions or thermal management can create safety and operational risks.

Mitigation: Integrate battery safety, civil, electrical, fire protection and emergency planning during design.

11.6 Unverified Commercial Assumptions

The project may appear financially attractive under assumed energy prices or revenue streams that are not contractually available.

Mitigation: Validate tariffs, market rules, dispatch obligations and contractual arrangements before investment approval.

12. BESS Sizing Checklist for Project Developers and EPC Contractors

Before finalising a solar battery storage design, review the following information.

Project Requirements

• Define the purpose of the BESS.

• Confirm the required power output.

• Confirm the required discharge duration.

• Identify the energy delivery boundary.

• Establish the required availability and performance guarantees.

• Define the design life and end-of-life performance requirement.

Solar and Load Data

• Collect solar generation data or validated yield simulations.

• Collect interval load data, where applicable.

• Establish the available charging window.

• Identify curtailment and export restrictions.

• Assess seasonal and operating variations.

• Evaluate future load growth or generation changes.

Battery and Electrical Design

• Compare candidate battery technologies.

• Establish usable capacity and SOC limits.

• Model charging and discharging efficiency.

• Evaluate degradation and augmentation.

• Select PCS ratings.

• Review transformers, switchgear and protection.

• Establish EMS and SCADA requirements.

• Evaluate thermal management and fire safety.

Grid and Commercial Assessment

• Confirm interconnection requirements.

• Complete applicable grid studies.

• Estimate CAPEX and OPEX.

• Model revenue and energy savings.

• Perform sensitivity analysis.

• Review applicable regulations and permits.

• Confirm warranty and performance guarantees.

• Prepare the feasibility report and implementation plan.

13. How AlgEnergy Supports BESS Feasibility and Engineering

AlgEnergy Engineering Consultancy Services provides multidisciplinary engineering consultancy for energy, renewable energy, power and infrastructure projects.

For solar-plus-storage developments, the scope can be tailored to the project's development stage, technical requirements and procurement strategy.

13.1 Feasibility and Project Planning

The feasibility stage establishes the project objectives, technical configuration, key constraints, alternative options and preliminary investment requirements.

Potential deliverables include:

• Project design basis.

• Technical feasibility assessment.

• Solar generation and storage integration assessment.

• Preliminary capacity and duration analysis.

• Technology comparison.

• Grid connection requirements review.

• CAPEX and OPEX assessment.

• Risk register.

• Implementation strategy.

13.2 Detailed Engineering Support

Depending on the agreed scope, detailed engineering may include coordination of electrical systems, plant layouts, equipment interfaces, cable and equipment requirements, technical specifications and engineering documentation.

The design should maintain consistency between the battery system, PCS, transformers, protection, SCADA and the existing or proposed solar plant.

13.3 DPR and Tender Documentation

A project-specific DPR can consolidate the technical and commercial basis of the development.

Tender documentation may include technical specifications, equipment schedules, performance requirements, testing criteria, interface responsibilities and documentation requirements.

Well-defined specifications help project owners compare bids on a consistent basis rather than relying solely on the lowest quoted equipment price.

13.4 Technical and Vendor Coordination

Vendor coordination may include review of equipment data, technical deviations, interface requirements, performance guarantees, warranty conditions and commissioning documentation.

The scope should clearly identify the responsibilities of the project owner, EPC contractor, battery supplier, PCS supplier and other package vendors.

13.5 Project Management and Execution Support

Where required, engineering support can continue into procurement, construction coordination, progress monitoring, QA/QC and commissioning support.

Explore AlgEnergy's engineering consultancy services to understand its broader feasibility, project planning and engineering capabilities.

14. BESS Opportunities in India and International Markets

Battery storage opportunities vary by country, electricity market, grid requirements, renewable energy policy and project economics.

India

Indian solar-plus-storage developers should assess the applicable Ministry of New and Renewable Energy (MNRE), Ministry of Power, Central Electricity Authority, Central Electricity Regulatory Commission, state regulatory and utility requirements relevant to their projects.

The MNRE maintains an Energy Storage Systems policies and guidelines portal that includes storage-related policy documents and updates.

Developers should verify the latest applicable provisions for their specific project and procurement structure rather than relying on general statements about incentives or regulatory treatment.

United States

Projects in the United States require assessment of the applicable interconnection procedures, utility requirements, market arrangements, safety provisions and permitting conditions.

The U.S. Department of Energy provides useful background on solar and energy storage integration.

Europe

European projects should assess the relevant national electricity market, grid code, connection requirements, fire and building regulations, environmental requirements and battery-related obligations.

Middle East, Africa and Southeast Asia

Projects in these markets may face distinct temperature conditions, dust exposure, grid strength, utility constraints, land requirements and procurement arrangements.

The design should be adapted to the actual site and local requirements. An engineering configuration suitable for one country should not be assumed to be directly transferable to another.

15. Why an Independent BESS Engineering Assessment Is Valuable

Battery storage projects combine electrical engineering, energy modelling, commercial analysis, controls, safety and grid integration.

An independent technical assessment can help project owners:

• Verify whether the proposed battery meets the intended application.

• Compare alternative power and energy configurations.

• Review vendor performance assumptions.

• Identify missing engineering interfaces.

• Assess charging feasibility.

• Evaluate degradation and augmentation.

• Examine project CAPEX and OPEX.

• Identify grid and safety risks.

• Improve the clarity of tender requirements.

• Establish a more reliable basis for investment decisions.

The scope of an independent assessment should be agreed in advance, including the available data, required calculations, design responsibility and expected deliverables.

Frequently Asked Questions About BESS Sizing for Solar Projects

1. What is BESS sizing for solar projects?

BESS sizing is the process of determining the battery power rating, energy capacity, discharge duration and operating configuration needed to meet a solar project's technical and commercial requirements.

2. How do I calculate battery capacity for a solar project?

Start by multiplying the required discharge power by the required duration to determine delivered energy. Then account for usable capacity, conversion losses, auxiliary loads, degradation and the required end-of-life performance.

3. What is the difference between MW and MWh in a BESS?

MW measures power, or the rate of charging or discharging. MWh measures energy capacity or energy delivered over time. Both are needed to define the battery system adequately.

4. How many hours of storage does a solar project need?

There is no universal duration. The requirement depends on the intended service, charging opportunity, load profile, dispatch schedule, grid constraints and commercial value of stored electricity.

5. Can BESS reduce solar energy curtailment?

Yes, where surplus solar energy can be captured and later discharged within the project's operating and interconnection constraints. The amount of curtailment that can be reduced must be established through time-series modelling.

6. What information is required for a BESS feasibility study?

Typical inputs include solar generation profiles, load data where applicable, required power and duration, grid connection details, operating schedules, battery performance data, cost assumptions and applicable technical requirements.

7. What is included in BESS CAPEX?

Depending on the project's scope, CAPEX may include battery equipment, PCS, controls, transformers, switchgear, civil works, cabling, thermal management, fire protection, grid connection, engineering and commissioning.

8. Why should battery degradation be considered?

Battery degradation reduces available capacity over time. If the project must meet a specified discharge requirement throughout its operating life, the design must account for capacity retention and any planned augmentation.

9. What is the role of a BESS engineering consultant?

A BESS engineering consultant can support feasibility studies, capacity and duration analysis, technical specifications, electrical integration, grid studies, CAPEX assessment, tender documentation and engineering coordination, subject to the agreed scope.

10. Does every solar-plus-BESS project require a grid integration study?

The required studies depend on the project configuration, interconnection requirements, network characteristics and applicable regulations. The scope should be confirmed with the utility, system operator and project engineering team.

Conclusion: Make BESS Sizing an Engineering Decision, Not a Guess

Successful solar-plus-storage development requires more than selecting a battery with a particular MWh rating.

The right BESS configuration must match the required power output, energy delivery schedule, usable capacity, charging opportunity, load profile, degradation allowance, grid conditions, safety requirements and commercial objectives.

A systematic BESS feasibility study helps project developers compare alternatives, identify technical risks and establish a more reliable basis for procurement and investment.

For utility-scale renewable projects, commercial and industrial installations, hybrid energy systems and grid-connected storage developments, integrated engineering and techno-economic analysis can support better-informed decisions from early feasibility through detailed design and project execution.

AlgEnergy Engineering Consultancy Services supports project owners, EPC contractors, renewable energy developers and international engineering organisations with feasibility studies, DPR preparation, multidisciplinary engineering, tender documentation and project support.

Planning a solar-plus-BESS project in India or an international market?

Contact AlgEnergy to discuss your project requirements, battery sizing study, grid integration assessment, technical specifications or techno-economic feasibility.

Share your project location, solar capacity, intended battery application, required discharge duration and available technical data so that an appropriate engineering scope can be defined.

Engineering the path from project concept to execution.