EMI Site Survey & Risk Assessment for a Solar Farm Near a Military Airbase

This case study describes an EMI site survey and quantitative risk assessment conducted for a proposed photovoltaic (PV) solar farm located within a few kilometres of a military airbase. Due to concerns about potential electromagnetic interference with critical aviation communication and navigation systems, a comprehensive on-site evaluation was required. Using calibrated antennas, spectrum analysers, and far-field propagation models, the investigation measured emissions from existing PV installations and extrapolated field strengths to assess risk at key distances, ultimately supporting regulatory approval by demonstrating compliance with applicable EMC thresholds.

Client Context

A developer planned the construction of a new photovoltaic (PV) solar farm within a few kilometres of a sensitive military airport. Due to the proximity, the local council mandated a thorough electromagnetic interference (EMI) study to assess the potential impact on critical aviation systems. Approval for the project was conditional upon demonstrating that the EMI risk would remain within acceptable thresholds.

Scope of Work

Conduct an on-site EMI survey at an existing solar farm operated by the client, using identical layout and inverter technology to the proposed site.

Perform a quantitative EMI risk assessment, particularly with regard to sensitive military aircraft systems.

Deliver a full report within 4 working days:

• 2 days of site measurements

• 2 days of technical analysis and documentation

Technical Approach

Military aviation systems operate across a broad frequency spectrum, including:

0.15–1.99 MHz (ADF)

2–30 MHz (HF communications)

30–88 MHz (VHF-FM)

108–152 MHz (VHF-AM, including navigation and communication)

225–400 MHz (UHF-AM)

960–1215 MHz (TACAN)

Other frequency bands

Our assessment focused on 100 kHz to 6 GHz, covering all relevant civil and military bands. At distances of 2–3 km, EMI (100kHz - 6GHz) transitions into the far-field zone, allowing accurate extrapolation of measured field strengths to predict exposure at greater distances.

To accomplish this:

• A preliminary paper-based assessment was conducted by reviewing all technical documentation provided by the client. This included:

  • Verifying that all equipment met relevant EMC standards and that the test reports and results raised no compliance concerns.

  • Assessing whether good engineering practices had been implemented, particularly regarding fixed installation requirements.

• We performed radiated emission measurements at 10 m, 30 m, and 100 m, then applied far-field propagation models to estimate the field levels at 1 km and 3 km.

• Calibrated antennas and spectrum analyzers were used, ensuring traceability to EMC standards.

• Multiple test points were selected through pre-survey desktop analysis, focusing on worst-case exposure zones.

Reviewing EMC test reports as part of the EMI risk assessment process for the project 

Challenges Addressed

Ambient electromagnetic noise in the field—including emissions from AM/FM/DAB broadcasts, and two-way radios—posed significant challenges to measurement accuracy. Since the PV farm was operational, it was not economically viable to perform a full shutdown in order to conduct a baseline ambient EMI scan—typically a preferred method where the site is measured in an "off" state to establish background noise, and then re-measured "on" to isolate emissions. Instead, a different strategy was required.

Another major challenge in site surveys is the presence of broadcast transmitter signals, such as AM, FM, DAB, and two-way radios, which are prevalent in the ambient spectrum. These signals must be correctly identified and distinguished from emissions generated by the PV equipment. While this often depends on engineering experience and spectral pattern recognition, the use of specialised receivers capable of decoding broadcast signals can provide more convincing evidence of signal origin and help avoid misinterpretation.

A biconical antenna was used to measure EMI in the 30–300 MHz range, positioned 30 metres from the main inverter cluster

Antenna measurement points positioned at a 30-metre distance from the inverter cluste

Findings

The inverters in use demonstrated good EMC performance, with emissions well below concerning thresholds.

Measured field strength at 10 m and 30 m was low enough that, after extrapolation, no credible EMI risk was projected at the distance of the military airport.

Outcome

The detailed EMI study allowed the client to proceed confidently with the planning approval process, supported by a technically sound and independently validated report. The council accepted the findings, with our analysis forming the basis for demonstrating regulatory compliance and low EMI risk to military infrastructure.