What was the challenge?
Temple was appointed to undertake a plant noise assessment in support of a full planning application for a new solar farm, a grid connection, an on-site substation and connection into existing overhead lines.
The proposed development is for rows of Solar PV arrays to generate approximately 27MW, set by the capacity of its export connection to the grid, for a duration of up to 40 years. The solar arrays will be supported by inverters to convert the direct current (DC) electricity output from the solar panels into usable alternating current (AC) power for the electricity distribution network. Inverters and transformers will be located in centralised Medium Voltage Stations (MVS) across the site. A larger transformer will also be installed at the substation to step up the low voltage electricity produced at the site to a higher voltage for efficient transportation to the grid connection point.
The 57.7 hectare proposed development site is located in a rural area and is currently being used for agricultural purposes. Five noise sensitive receptors were identified at distances between 110 m and 300 m from the site boundary in different directions, which required to be assessed.
In an area where background noise levels were expected to be low, noise from the electrical plant (inverters and transformers) has the potential to be noticeable at receptors further away and could lead to disturbances; therefore, a noise assessment was required.
The proposed plant will be operational between 04:30 and 22:00 during the days of the year with peak daylight hours (summer) and with reduced operating hours on shorter days. Therefore, the assessment was required for both day and night-time periods.
What was our solution?
The proposed survey methodology was presented to and approved by the Durham County Council Environmental Health Department. Our team was then able to mobilise to the site quickly once the design was frozen and conduct the unattended noise survey. Two locations were surveyed within the site boundary to capture background noise levels representative of the nearest noise sensitive receptors. As the solar arrays which cover the majority of the site are not noise generating, the design information was reviewed to determine which areas would be used for the noise generating plant. This enabled Temple to determine appropriate monitoring locations and a number of measurements.
What was the conclusion?
A 3D noise model was constructed of the proposed development and surrounding area, accounting for the ground contours due to the complex landscape topography. Plant noise levels provided by suppliers indicated the sound pressure levels from each MVS and the substation transformer would be 82 and 74 dBA 1 metre away, respectively. The full octave band noise spectrums were input into the model along with the plant locations and predicted at the identified receptors. Character corrections for the plant noise were also considered, including undertaking the BS 4142 objective method for assessing the audibility of tones using one third octave band data. This resulted in a +6 dB correction for dwellings that were dominated by the substation transformer due to a prominent tone in the 250 Hz one third octave band.
Based on the measured survey data, noise limits in line with DCC requirements were derived at 1m from the façades of the sensitive receptors. The predicted noise levels were within the DCC noise limits, and the overall impact was considered to be low when assessed using BS 4142 methodologies. The large site, centralisation of noise generating plant in the MVS’s (as opposed to being distributed across the entire site) and distance between plant and the receptors were all contributing factors in achieving the noise limits and a low impact. The assessment was concluded with a written report to be submitted as part of the planning application, confirming the proposals would comply with the local criteria.
