A factory can have enough roof space for a substantial solar array yet still be offered a limited export connection. That does not automatically rule out the project. It means the financial model and electrical design must account for how much electricity can flow back to the distribution network.
This guide explains G100 export limitation, zero-export arrangements and solar curtailment for UK manufacturers. It is written for finance directors, factory owners and facilities managers deciding whether a constrained grid connection still supports a viable investment. For the wider project decision, see our solar panels for factories guide.
1. What is a factory solar export limit?
When a factory’s solar panels generate more electricity than its equipment is using at that moment, the surplus may flow into the local electricity network. The distribution network operator (DNO) assesses whether that export can be accommodated safely. A connection offer may specify a Maximum Export Capacity, which can be lower than the generating equipment’s installed capacity.
An export limit is a limit on net flow at the agreed connection point, not necessarily a limit on the electricity that the factory can generate and consume behind its meter. A factory with strong daytime demand may therefore use substantial solar generation on site even when its permitted export is modest.
Our DNO and G99 grid-connection guide explains the broader approval process. This article concentrates on the export-control decision and its effect on the business case.
2. What is G100, and how does it differ from G99?
Engineering Recommendation G100 sets technical requirements for customer export and import limitation schemes. A compliant scheme measures electrical flow at the relevant connection point and controls generation, storage or loads to keep the agreed limit from being exceeded. It also needs appropriate fail-safe behaviour if a component or communication path fails.
G99 addresses the connection of generating equipment to the distribution network. G100 does not replace G99 approval. A commercial solar installation can require both a G99-compliant generation connection and a G100-compliant limitation scheme, depending on its design and the DNO’s conditions. A low export setting does not automatically make a large generating system eligible for a simpler G98 route.
The Energy Networks Association’s G100 technical recommendation and National Grid Electricity Distribution’s customer limitation guidance provide authoritative starting points. The competent designer should confirm the current requirements for the factory’s network area and connection offer.
3. Zero export is not the same as off-grid solar
A zero-export arrangement aims to prevent net electricity export at the connection point. Solar can still supply machinery, compressors, ventilation and other on-site loads while the grid remains connected. If factory demand falls below the available solar output, the controls may reduce inverter generation so the agreed export condition is maintained.
Zero export does not mean the factory has disconnected from the grid, and it does not make a standard grid-connected array an emergency power supply. During a grid outage, ordinary grid-following PV inverters cease energising the installation as required by their protection arrangements. Backup or islanded operation requires a separately engineered and approved solution with suitable isolation, control and potentially storage.
Before accepting a zero-export offer, ask whether the factory’s weekend, holiday and shutdown loads are sufficient to use the electricity that the proposed array could otherwise generate.
4. How does an export-limiting system work?
A typical scheme uses measurement at or near the factory’s point of connection, a controller and compatible inverter or other equipment controls. The controller monitors net import or export and adjusts the relevant output when the agreed export threshold is approached. The exact architecture, redundancy, protection and test requirements depend on the approved design.
- Measurement: the correct meter or current-transformer arrangement must represent the whole relevant site connection, not merely one solar inverter.
- Coordination: where multiple inverters or batteries are installed, the scheme must account for their combined effect on net flow.
- Fail-safe operation: the design must demonstrate the required response if power, sensing or communications fail.
- Protected settings: agreed limits should not be altered casually; changes may need written DNO approval.
- Commissioning: test results and configuration records should be retained with the factory’s electrical handover documents.
The DNO still considers matters such as voltage, protection, network loading and short-term conditions while the limiter responds. An export cap is not permission to install unlimited generation capacity.
5. What is solar curtailment, and when does it cost money?
Curtailment means reducing available solar generation because the site cannot consume, store or export it within the applicable constraints. Curtailment can occur during low-demand periods, such as weekends, maintenance shutdowns or production changes, even if the array could produce more power in the prevailing sunlight.
Illustrative example — not a site forecast: assume a factory’s solar system could produce 300 kW at a particular moment, while the factory is using 180 kW and its permitted export is 50 kW. Without storage or another flexible load, the scheme may need to limit solar output to about 230 kW. Around 70 kW of potential output is curtailed at that moment. If factory demand increases, less output may need to be curtailed.
That 70 kW is an instantaneous power difference, not 70 kWh of lost annual energy. Annual curtailment must be calculated by modelling many intervals across a representative year, with weather, demand and system assumptions stated. Avoid multiplying a single sunny-hour example by arbitrary operating hours.
6. Model the economics before choosing zero export
A robust investment appraisal should compare at least three cases: the proposed unrestricted connection (including any reinforcement costs or delay), a DNO-agreed capped-export design, and a smaller or differently configured array. For each, model on-site self-consumption, paid export, curtailed energy, capital costs and ongoing maintenance.
Use the factory’s actual half-hourly electricity data, including weekend and seasonal shutdowns, alongside a realistic generation profile. Review whether shifts, production lines, new machinery or electrification projects could materially change demand during the system’s life.
Self-consumed solar generally has a different financial value from exported electricity. Our guides to maximising factory solar self-consumption and surplus solar export explain the distinction. Do not assume that every exported unit will earn the same amount as a unit of purchased electricity avoided.
If curtailment is substantial, consider whether a revised array size, operational load shifting or battery storage would improve the economics. Batteries add their own costs, losses, operational constraints and connection requirements, so they should be evaluated rather than assumed to be the answer.
7. What should the factory request from its installer and DNO?
Before signing a solar contract, ask for the proposed maximum export figure in writing and ensure it matches the electrical design, connection application and financial model. The following questions should form part of the technical and commercial review:
- What is the agreed export capacity, and at which connection point will it be measured?
- Is a G100 limitation scheme required, and who is responsible for designing, supplying and testing it?
- Does the scheme cover every relevant solar inverter and battery system?
- What happens when a sensor, controller or communications link fails?
- How much annual generation is expected to be curtailed, and what assumptions support that estimate?
- What are the alternative reinforcement, export-limit or array-sizing options, including costs and timescales?
- What approval and retesting would be required to change the export limit later?
- Who retains the settings, drawings, test certificates, monitoring access and DNO correspondence?
For example, National Grid Electricity Distribution describes a limitation-scheme application and commissioning process alongside the relevant generation forms. Other DNOs may use different forms or procedures. Your contractor should confirm the route applicable to the actual factory connection.
8. Monitor export and curtailment after commissioning
The original business case should not disappear into a filing cabinet once the solar array is switched on. Agree how the factory will track generation, grid import, export and any curtailed output. If the system records curtailment events or available-but-unused generation, retain those data alongside the original forecast and explain the calculation method.
Compare actual results against the forecast after allowing for weather, production hours, maintenance and changing demand. Unexpected curtailment may indicate a genuine export constraint, an incorrect setting, a sensor fault or a change in factory operations. A competent engineer should investigate rather than bypass the limiter.
Use our solar monitoring and savings-verification guide for ongoing reporting, and our commissioning and handover checklist to confirm that the export-control documentation is complete before acceptance.
Frequently asked questions
Can a UK factory install more solar capacity than it is allowed to export?
Potentially, yes. The DNO may agree a compliant limited-export design with more generation behind the connection than the permitted net export. Approval depends on the electrical design and network assessment; it is not automatic.
Does G100 approval mean G99 is unnecessary?
No. G100 governs the limitation scheme. The generating equipment and connection still need to follow the applicable G98 or G99 requirements.
Is zero-export solar always a poor investment?
No. It may work well where factory demand absorbs most generation. It can be less attractive where weekends, shutdowns or seasonal demand cause significant curtailment. The decision should be based on interval-level modelling.
Can we increase the export limit later?
Possibly, but do not assume the controller setting can simply be changed. The DNO may need to approve a revised connection agreement, design or tests.
Conclusion: treat the export limit as a design input, not an afterthought
A constrained export offer does not automatically make factory solar unviable. The important question is how much solar electricity the factory can use, how much it can export and how much may be curtailed. An approved G100 scheme can be part of the solution, but the financial case must reflect the actual DNO conditions.
For a practical review of your factory’s roof, half-hourly demand, connection options and commercial case, contact Commercial Solar Systems. We can help you frame the questions to put to the appropriate technical specialists before you commit to an installation.
Technical note: this is general UK manufacturing guidance, not a substitute for a site-specific electrical design, DNO connection offer or competent engineering advice. Requirements and forms can vary by network operator and system design.
