Farm solar export cable routing and rural feeders

For farm solar installations with substantial grid export (above 50 kW typically), the export cable routing through the local rural electricity network matters. Understanding the network topology helps anticipate installation complexity, cost, and timing.

How farm export cables connect

The standard topology:

1. PV panels on the roof generate DC electricity
2. DC cabling runs through the building to the inverter location
3. Inverter converts to AC (typically 415V three-phase)
4. AC output runs through the building’s main switchboard
5. Cable runs from main switchboard to the DNO grid connection point (typically the meter cabinet or transformer pole)
6. From the grid connection point, electricity flows into the local rural feeder
7. The local feeder is the distribution-level cable connecting to the nearest primary substation

For systems below the existing supply capacity, the connection is straightforward — extra electricity flows back through the existing connection.

For systems above the existing supply capacity, the DNO may require: substation upgrade; new feeder cable run from a higher-capacity point; transformer replacement; main switchboard upgrade.

Rural feeder capacity in the UK

UK rural feeders are typically 11 kV distribution lines. Capacity varies significantly:

• Modern feeders with adequate substation capacity: standard 100-500 kW export OK
• Older feeders or those serving rural communities: typically 50-300 kW practical export limit
• Capacity-constrained feeders (West Wales, Highlands, South Devon, parts of Cornwall): may have 0-50 kW practical export

The DNO study identifies the specific feeder capacity at your farm location. For farms on capacity-constrained feeders, design options include: smaller PV system; no-export design (sized for 100% self-consumption); battery storage to absorb peak generation; wait for DNO reinforcement (sometimes 12-24+ months).

Contestable vs non-contestable works

DNO connection works fall into two categories:

Non-contestable works. The DNO performs these directly. Typical scope: main feeder cable extension to your connection point; substation upgrades; primary network changes. Charged at the DNO’s standard rates. Typical for export connection: £5,000-£25,000 for sub-250 kW systems.

Contestable works. The customer can use any qualified ICP (Independent Connection Provider) instead of the DNO. Typical scope: cable run from the meter cabinet to your building’s main switchboard; meter installation; isolation equipment installation. ICPs typically 20-40% cheaper than the DNO equivalent.

For larger projects (above 250 kW), the cost savings from using a competent ICP can be substantial. We routinely use ICPs (e.g., Murphy Group, Last Mile Connections, IC Plus) on commercial-scale farm projects.

Substation upgrade scenarios

For very large farm installations (above 500 kW typical, or smaller on capacity-constrained feeders), the DNO may require substation reinforcement. Typical scope:

• Transformer upgrade or replacement at the local substation
• Switchgear upgrade at primary substation level
• Cable replacement on heavily-loaded feeder sections

Cost: typically £100,000-£500,000+ for substation reinforcement. Cost-prohibitive for most farm projects.

When substation upgrade is needed: explore alternatives including reduced system capacity, no-export design, or battery storage to mitigate the export requirement.

Cable routing through farm buildings

Within the farm, cable routing involves: from the inverter location to the main switchboard (typically the existing electrical room or building entry point); from the main switchboard to the DNO connection point (typically existing meter cabinet outside).

For multi-building farm installs, cable routes between buildings: typically underground in PVC ducts or armoured cable; sometimes overhead on poles for shorter runs.

We design the cable routing as part of the detailed electrical design stage. Routes are documented in the as-built drawings provided at handover.

Phase balance considerations

For three-phase installations, balancing the load across the three phases matters: avoid overloading one phase; preserve clean grid quality; comply with G99 requirements.

Modern three-phase inverters automatically balance their output across the three phases. For combined PV + battery + EV charging installations, balancing across the phases requires more careful design — we coordinate this during the detailed design stage.

What you experience as a farm operator

The overall connection process from your perspective:

1. We submit G99 application (week 2-4)
2. DNO completes technical study (week 14-18)
3. DNO provides connection offer with works specification (week 18-22)
4. You sign acceptance and pay any contestable charges (week 22-24)
5. DNO completes non-contestable works (varies, typically 8-26 weeks)
6. ICP or DNO completes contestable works (1-4 weeks)
7. Final commissioning and energisation (week 30-50 typically)

This runs in parallel with physical PV installation. Most farm projects complete commissioning approximately 30-50 weeks after contract signature — DNO works being the typical longest item.