Harmonic Studies for BESS, Solar and Wind Farms: A Complete Guide to Power Quality and Grid Compliance
The 100 MW solar-plus-storage project has completed its load-flow and short-circuit studies, and construction is proceeding according to schedule. The network operator then requests a harmonic assessment; the initial submission fails because the model has assumed a stable, idle grid; the filters are redesigned, energisation is delayed, and the revenue plan is affected.
It is occurring more and more frequently. Harmonic studies for BESS, solar and wind farms are no longer just a late-stage formality; they determine whether a plant can connect on time. The following guide outlines the factors that cause harmonic distortion, which standards are in force, and how to avoid the errors that lead to studies being rejected.
Why Harmonics Matter in Modern Renewable Energy Systems
Inverters produce a sinusoidal output by switching their power electronics tens of thousands of times each second; the outcome is that a perfect sine wave is never achieved, with small harmonic currents flowing into the network and thus increasing the voltage distortion at the point of connection.
If left uncontrolled, distortion causes transformers and cables to overheat, places stress on capacitor banks, triggers protective devices, and results in inaccurate metering. Regarding renewable energy systems, the greater risk is generally the interaction rather than the harmonic emissions themselves. Resonances can be created by the capacitance of the cables, the inductance of the transformers, and the filters, thereby causing a small harmonic current to be amplified into a serious voltage issue[6].
Where Harmonics Come From
Solar PV and BESS inverters
In both technologies, it is the PWM inverters that are the main source of emissions; in the case of the BESS, the output varies with the power being charged or discharged, the state of charge and the control mode, so the emission profile is not a single fixed spectrum.
Wind turbines
Wind power energy plants employ either doubly fed or full-converter machines; full-converter turbines are analogous to large inverters, while doubly fed machines generate harmonics through the rotor-side converter. As emissions are a function of wind speed and loading, the type-test data given in IEC 61400–21-1 shall be evaluated over the full range of operation.
The hidden contributors
Long MV collector cables, HV export cables, STATCOMs, shunt reactors, and neighbouring plants all shape the network response. A study that models only the inverter misses most of this [6].
Standards and Grid Requirements by Region
Region | Key reference | What it focuses on |
UK | ENA EREC G5/5, referenced by the Grid Code[3] | Three-stage assessment, planning levels to the 100th harmonic (5 kHz), headroom allocation[2] |
Europe | BS EN 50160, IEC 61000-3-6, IEC 61400-21-1 | Supply voltage quality, emission allocation, wind turbine test data |
India | CEA Connectivity Regulations (Amendment) 2019, IEEE 519[7] | Harmonic current limits at the PCC, measurement before commissioning[8] |
Middle East | Utility grid code and connection agreement | Often IEC or IEEE based; confirm early with the utility |
In Britain, the G5/5 rules came into effect in June 2020[1]. In Stage 3, limits for a new connection are determined by dividing the available distortion headroom between the planned levels. Stage 2 is applied when the voltage is below 33 kV, and the connection fails. Stage 1 [2]; it also makes use of measured background harmonics instead of the assumed values [4].
IEEE 519-2022 adds a useful clarification. Where the site has inverter-based generation above 10% of average load, it directs engineers to IEEE 1547 or IEEE 2800 for current limits.
What a Proper Harmonic Study Involves
Collect emission data. Obtain harmonic spectra or frequency-domain models from the inverter and turbine OEM, ideally for several operating points.
Get the network impedance. Request the frequency-dependent impedance locus from the operator. A single fault level is not enough [1].
Measure the background. Capture at least a week of Class A data per IEC 61000-4-30 at the point of connection.
Build the model. Include transformers, collector cables, reactive compensation and any filters.
Run frequency scans and sensitivity cases. Test outage conditions, different dispatch levels and, for BESS, both charging and discharging.
Compare against limits and design mitigation if any order exceeds its allocation.
Verify after commissioning with power quality measurements.
Common Reasons Studies Get Rejected
Using one worst-case fault level instead of the full impedance locus
Modelling BESS in only one operating mode
Treating inverters as ideal current sources. CIGRE Working Group C4.65 is reviewing Norton and Thévenin harmonic models of inverter-based resources because simple models can miss interaction and instability effects [6]
Ignoring the capacitance of long cable circuits
Overlooking later project phases or nearby plants that share the same headroom
Starting the study after the equipment is procured
A Practical Example: Hybrid Solar and BESS Site
Suppose a hybrid installation includes solar inverters and a battery system using a single medium-voltage collector and a single export transformer. Each of the inverters undergoes its own type testing. Nevertheless, a frequency scan reveals the presence of a parallel resonance close to the 17th harmonic, this resonance occurring only when the batteries are being charged and the cable network is under light load.
Neither the solar OEM nor the BESS OEM would have caught this alone. It surfaces only when the whole plant, the cable network and the grid impedance are modelled together. The fix in a case like this is often small, such as a detuning reactor or a control adjustment, but it is far cheaper before procurement than after energisation.
Mitigation Options
If a problem is identified by a study, engineers generally have four levers:
Detuned passive filters for targeted orders, designed with the resonance in mind
Active filters or STATCOM-based compensation for broader spectrum control
Inverter control and switching-frequency tuning, often the cheapest fix if agreed with the OEM early
Layout changes, such as cable lengths, transformer configuration or splitting the plant into sections
The optimal outcome is generally achieved by combining a slight design change with getting in involved at an early stage by the OEM.
Emerging Trends to Plan For
Grid operators are now placing greater emphasis on harmonic instability and on the interaction between converters, as well as on steady-state limits[6].Interest in supraharmonics (2 to 150 kHz) is increasing too, and grid-forming BESS is changing how power plants respond across the frequency range[11]. Engineers collaborating with green energy companies in the UK and Europe should expect the scope of assessments to keep expanding.
Conclusion
Early and thoroughly planned harmonic studies when it comes to integrating renewable energy into the grid will safeguard your connection date, your budget and the grid. Begin with reliable data from the original equipment manufacturer, take into account the actual network impedance and measured background levels, and design the necessary mitigation measures before the equipment is ordered.
If you are planning a BESS, solar, or wind connection, VSS Power can help. As a solar and wind energy design and engineering company, our power systems engineers carry out harmonic assessments, filter design and grid compliance studies. Contact VSS Power at vsspower.com to discuss your project.
Takeaways
Harmonic compliance is a connection requirement, so start the study before equipment is procured.
Resonance between cables, transformers, and filters is often a bigger risk than the inverter’s own emissions.
UK projects must satisfy ENA EREC G5/5, while India applies IEEE 519 limits through the CEA regulations.
BESS needs to study in both charging and discharging modes, because its emissions change with operating point.
Frequency-dependent grid impedance and measured background levels are essential inputs. A single fault level is not enough.
FAQs
1. What is a harmonic study for a solar, wind or BESS plant?
It is a frequency-domain analysis that predicts the harmonic voltage distortion a plant will cause at the grid connection point and checks it against the operator’s limits.
2. Which standard applies to harmonic compliance in the UK?
The recommendation of G5/5 of ENA Engineering, as referred to in the Grid Code, establishes planning levels extending up to the 100th harmonic and involves a three-stage assessment.
3. Does IEEE 519 apply to inverter-based renewable plants?
The IEEE 519-2022 standard refers to either IEEE 1547 or IEEE 2800 when the amount of generation is 10% or more of the average site load. The harmonic current injection regulations issued by India's CEA still base their reference on IEEE 519.
4. Why do BESS projects need special harmonic analysis?
Battery inverters can charge or discharge, and the electrical noise they produce—and how it interacts with resonances—depends on their output level and control settings.
5. How can harmonic problems be fixed after a failed study?
The solutions available are detuned or active filters, inverter control tuning, and modifications to the cable or transformer arrangement. Early participation by the original equipment manufacturer generally results in the lowest costs.
References
TNEI Group, The new ENA EREC G5/5: What has changed and how will it impact harmonic compliance assessments? https://www.tneigroup.com/news_event/the-new-ena-erec-g5-5-what-has-changed-and-how-will-it-impact-harmonic-compliance-assessments/
Drives & Controls, Engineering Recommendation G5/5 overview. https://www.drivesncontrols.com/news/fullstory.php/aid/6499/.html
NESO, Grid Code modification to use EREC G5/5 (GC0129). https://neso.energy/document/152661/download
Electricity North West, Design Policy Update webinar, G5/5 implementation (2020). https://www.enwl.co.uk/globalassets/get-connected/ice/ice-event-presentations/ice-event-slides-archive/2020/policy-design-update-webinar-4-september-2020--slides.pdf
Power Quality Blog, IEEE Standard 519-2022 update and changes from prior version. https://powerquality.blog/2022/10/27/ieee-standard-519-2022-update-and-changes-from-prior-version-2014/
CIGRE, WG C4.65: Specification, validation and application of harmonic models of inverter based resources. https://www.cigre.org/userfiles/files/News/2021/TOR-WG%20C4_65_Specification%2C%20validation%20and%20application%20of%20harmonic%20models%20of%20inverter%20based%20resources.pdf
Central Electricity Authority (India), Draft amendment to connectivity regulations, power quality standards. https://cea.nic.in/old/reports/others/enc/legal/amendments.pdf
UL India, CEA Technical Standards for Connectivity to Grid (Amendment) Regulation 2019. https://india.ul.com/download-resources/central-electricity-authority/
IEEE PES, Harmonics Modeling and Simulation of Large Wind and Solar Power Plants (panel, 2023). https://resourcecenter.ieee-pes.org/conferences/general-meeting/pes_cvs_gm23_0720_tdpl09
Power Monitors, Distributed Generation Power Quality Standards. https://powermonitors.com/whitepapers/distributed-generation-power-quality-standards/
IEEE Region 3, Harmonic Challenges for Distribution Grid Design. https://r3.ieee.org/wnc/wp-content/uploads/sites/84/Harmonic-Challenges-for-Distribution-Grid-Design.pdf
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