What matters most
Solar-farm Wenner testing supports grounding analysis for utility-scale photovoltaic facilities, collector systems, inverter or transformer areas, and the interconnection substation. A useful program divides the site into representative zones and selects stations and spacings around geology, grading, drainage, array blocks, electrical layout, and access.
Key takeaways
- Large acreage requires a coverage strategy, not one sitewide value.
- Track inverter blocks, substations, collector routes, and cut/fill zones.
- Coordinate with the grounding designer and applicable solar guidance.
- Document season, irrigation or agriculture, and future grading.
A solar plant is a distributed grounding problem
PV rows, equipment pads, buried collector circuits, inverter stations, fences, operations buildings, and the interconnection substation extend across a large footprint. Soil may change laterally and with depth across that area.
IEEE 2778 addresses grounding for personnel protection at utility-scale solar plants and expands on substation-grounding concepts for the distributed facility. The interconnection substation may have separate requirements.
Build station coverage around meaningful site zones
Use geologic mapping, borings, grading, washes, drainage, agricultural history, planned array blocks, and access roads to divide the site. Select stations that test differences rather than evenly spacing points without a reason.
Where the site is uniform and repeat curves agree, fewer models may be appropriate. Where values or ground conditions diverge, preserve separate zones for the grounding engineer.
Field logistics are part of the scope
Large sites may require off-road travel, gates, landowner coordination, environmental restrictions, crop timing, heat plans, and utility clearance. Long spacings can cross fences, roads, or existing conductors.
Provide GIS or CAD locations, requested spacings, access routes, known utilities, construction status, and the party responsible for locating and clearing electrode points.
Calicore mobilizes nationwide for appropriately sized solar and storage survey programs. The proposal should define acreage, station count, spacing sequence, access, terrain, and reporting needs.
This page provides general educational information, not a grounding-system design, cathodic-protection design, installed-system acceptance test, or parcel-wide resistivity conclusion. A Wenner result is apparent soil electrical resistivity for the documented array, spacing, location, orientation, and field condition. The responsible grounding or corrosion engineer must evaluate the complete dataset, earth model, asset geometry, governing documents, and uncertainty.
Frequently asked
Questions about this topic
Can one station represent a solar farm?+
Only when site conditions and the grounding engineer support that conclusion. Large or variable facilities commonly need multiple stations or zones.
Does IEEE 2778 replace IEEE 81?+
No. They serve different roles. IEEE 2778 provides solar grounding guidance; IEEE 81 addresses measurement methods including earth resistivity.
Should the interconnection substation be tested separately?+
Often yes. Its location, grid geometry, grading, and design criteria may differ from the broader PV field.
Primary references and further reading
- IEEE Standards Association — IEEE 2778-2020 Official guide for personnel-protection grounding at utility-scale photovoltaic plants.
- IEEE Standards Association — IEEE 81-2025 Current IEEE guide for measuring earth resistivity, grounding-system impedance, and earth-surface potentials.
- ASTM International — ASTM G57-20 Official record for the Wenner four-electrode field and four-electrode soil-box method.
- Soil Tests Laboratory — Wenner Four-Pin Testing Calicore Engineering’s testing division and field-service information.