Export Metering and Export Limitation Devices

When a home generates its own electricity, there are moments when the panels make more than the house can use. What happens to that surplus is not entirely the householder's decision: the local electricity network has to be able to accept it, and the company that runs that network, the Distribution Network Operator (DNO), may cap how much a home is allowed to send back. That cap is enforced by an export limitation device, a controller that watches the flow of electricity at the point where the home meets the grid and holds export at or below the agreed figure.

This page explains why those caps exist, the engineering standard that governs them, how a limitation scheme is applied for and set, and how it differs from the separate business of export metering, which is about recording and paying for the electricity a home sends out rather than restricting it. The two are often confused, because both involve equipment at the supply point, but they answer different questions.

Why the network operator caps what you can send back

A DNO may limit how much electricity a home exports, usually to protect the grid from overload in areas with high renewable electricity generation⁶. The cables and substations that serve a street were sized for electricity flowing one way, from the network into homes. When many houses on the same feeder start pushing power back out at the same time, on a bright afternoon when few people are home, the network can reach limits it was never designed for. The constraint is local: two homes with identical solar systems can face very different rules depending on the capacity of the cables around them.

The purpose of an Export Limitation Scheme is stated plainly by network operators: these schemes prevent overloading the network, voltage issues, and protect both the network and customer equipment from damage⁷. Voltage is the quieter of the two problems. Electricity leaving a home raises the voltage on the local network slightly, and enough homes exporting at once can push voltage towards statutory limits. Limitation is one of the tools a DNO uses to keep the whole feeder inside those limits.

Where a limit applies, the installer has two broad responses: fit a smaller inverter, the device that converts the electrical current for use and export, or fit an export limiter⁶. The first approach caps the system permanently at the hardware level; the second allows a larger inverter to be installed while a separate controller holds export to the agreed figure. The second is what most people mean by an export limitation device.

Not every home faces a cap. If you plan to export power to the grid and the DNO confirms there is enough spare capacity in the network to accommodate it, no Export Limitation Scheme is needed³. Conversely, if you plan to install generation but do not want to export at all, you will need an Export Limitation Scheme unless your generation capacity is lower than your minimum demand, that is, the smallest amount of electricity your home draws at any time¹. In some cases the requirement can be strict: a government call for evidence on solar carports notes that some DNOs would require export limitation for a period of time, potentially at zero⁸. A zero export condition means the home may generate freely for its own use but must never send power out.

EREC G100: the standard behind every limitation scheme

Engineering Recommendation G100, usually written EREC G100, is the technical standard that governs how export limitation is done. The rule from network operators is unambiguous: all export limitation schemes must be G100 compliant⁷. This applies to the arrangement as a whole, the controller, its sensing, and its behaviour, not just to a labelled box on a wall.

There is one important exception, and it covers many ordinary installations. Where the export capacity limitation of the inverter is set by the manufacturer of the equipment, an EREC G100 Export Limitation Scheme is not required⁷. In other words, if the inverter itself is configured at the factory or at commissioning so that it can never export above a stated figure, the manufacturer's own limitation does the job and no separate scheme is needed. The term used for that figure is Registered Capacity, defined as the export limit set by the manufacturer⁷.

The distinction matters when reading a connection offer. A DNO may accept a manufacturer-set inverter limit as sufficient, or it may require a dedicated scheme with its own controller, depending on the size of the system and the state of the local network. Where a dedicated scheme is required, G100 sets out how it must behave: it must measure the relevant flows, act on them, and fail in a way that does not endanger the network. A householder does not need to know the detail of the standard, but any installer proposing a limitation scheme is expected to name it and confirm compliance.

G100 sits alongside the better known G98 and G99 recommendations, which govern how generating units connect in the first place. The three work as a set: G98 and G99 define the connection and the type of equipment allowed, and G100 defines what happens when the connection comes with an export cap. More on the connection standards follows in the next section.

G99 applications and when limitation enters the picture

The dividing line in the connection process is 3.68kW per phase. Installations up to that figure at a single premises fall under the simpler G98 route; anything larger requires a G99 application and prior approval from the DNO before connection. Bedford Borough Council's renewables guidance puts it directly: "Apply to connect" is for larger installations exceeding 3.68kWp and requires a G99 application⁹. A Sell2Wales notice describes the same boundary, noting that installations over 3.68kWp require prior approval from the DNO¹⁰. The UK solar roadmap uses the same threshold, listing G99 as applying above 3.68kW².

The G98 route has its own ceiling in some contexts. A Northern Ireland consultation document refers to the G98 11.04 kWp limit in connection with buildings other than dwellings¹¹, a reminder that the thresholds are per phase and that the rules for domestic and non-domestic buildings are not identical.

The type of equipment is fixed by the process. Any generating units, including electricity storage, connected through the fast track process must use EREC G99 or G98 Type Tested Inverters; if the unit was installed before 27 April 2019, EREC G59 or G83 Type Tested Inverters are also accepted⁷. Type testing means the inverter has been certified to behave correctly during network faults, and it is a hard requirement, not a preference.

The standards themselves have been revised to keep pace with batteries. A modification decision by the authority that approves these recommendations brought ERECs G98 and G99 into line with the existing G59 fast track process, and introduced a fast track process for storage applications of less than 16 amps per phase¹². That matters to households adding a battery to an existing solar system, because storage counts as a generating unit in its own right for connection purposes and can trigger an application even when the panels did not.

What an export limitation device actually is

In practice, an export limitation device is a controller that sits between the generation system and the grid connection and holds export at or below the figure in the connection agreement. As Energy Saving Trust describes, where export limits apply the installer can fit a smaller inverter or fit an export limiter⁶. The limiter approach keeps the full capability of the inverter for the home's own use while preventing surplus from crossing the boundary.

The most common form of limitation is built into the inverter itself. Where the export capacity limitation of the inverter is set by the manufacturer, a separate EREC G100 Export Limitation Scheme is not required⁷. Many modern solar and battery inverters can be configured with an export cap at commissioning, and for a great many homes this is the whole of the arrangement: the DNO agrees a figure, the installer sets the inverter to it, and the commissioning documents record it.

Where a separate device is used, it is typically a power diverter or controller that senses the flow at the supply point and either throttles the inverter or diverts surplus into a load, most often a water heater or a battery. No specific commercial models are named or compared here; what matters with any proposed device is that the scheme it forms part of is G100 compliant⁷ and that the DNO has accepted it in the connection offer.

One further piece of equipment belongs in this discussion because it is often installed at the same time: the export meter. Under the licence conditions that govern export payments, an eligible installation must have an export MPAN to manage exported electricity volumes to the SEG licensee, and the meter must be capable of taking measurements at half-hourly intervals in relation to the exported electricity volumes for which the generator seeks payment¹³. The MPAN, or Meter Point Administration Number, is the unique identifier for the export meter point, and without it there is no route to export payments. Limitation and metering are separate functions, and the rest of this page keeps them apart.

How the limit is set, agreed and enforced

The limit is not a national figure. It is written into the individual connection agreement between the householder and their DNO, and the process starts with the application. A household planning to install an Export Limitation Scheme includes details of the scheme with its connection application, or the DNO's design team includes the requirement in the connection offer¹.

For domestic customers, the maximum amount of permitted generation will typically be between 5kW and 15kW¹. That range reflects the diversity of local networks rather than any rule about house size: a home on a strong urban feeder may be offered the top of the range, while a home at the end of a long rural cable may be offered less.

Two specific rules govern how the maximum is calculated. The first is that permitted generation may be set at 125% of your import or export agreement, whichever is greatest³. The second is a voltage rule: the limit may be set at the amount of exported power required to cause the voltage at any customer's point of supply to exceed the statutory voltage limit by 1%¹. The second rule is the harder constraint on crowded networks, because it protects every customer on the feeder, not just the exporting household.

Enforcement runs through paperwork as much as through the device. Most suppliers require a DNO Response, the email from the network operator confirming that commissioning documents are logged and the system is compliant with G98 or G99, before a household can apply for an export tariff¹. In other words, the export payment route is gated on the network operator's confirmation that the connection, including any limitation, is in order. Suppliers must also be satisfied that exporters' installations are suitably safe before offering a tariff¹⁴.

Limitation is not metering: two different jobs at the supply point

Export limitation caps what leaves the home. Export metering records what leaves the home and underpins payment for it. The two are frequently conflated because both involve equipment at the same point, but the rules for each are entirely separate.

An export meter is always located at the point where the installation connects into the distribution or transmission network, and it must measure export separately from any other energy source unless pro-rating is available¹⁵. Ofgem's key terms explain the two payment bases. Metered export means "export payments which are made based on export meter readings"⁴, while deemed export means "export payments which are made based on estimated electricity export set by the Department for Energy Security and Net Zero"⁴.

Under the Feed-in Tariffs scheme, deeming has a hard threshold. Installations are only eligible for deemed export payments if they have a capacity of 30 kilowatts or less and do not have an export meter fitted⁴. Ofgem's guidance for generators repeats the condition: generators of installations with a TIC of 30kW or less are eligible to receive deemed export payments where it is not possible or practical to measure export by meter readings¹⁵. Once an export meter is commissioned on an installation of 30kW or less, export can no longer be deemed¹⁶. Above 30kW, an export meter is compulsory: an accredited FIT installation with a total installed capacity of over 30kW must have an export meter to receive export payments¹⁶. A generation meter cannot be used to claim FIT export payments, though its reading can support deemed export where eligible¹⁵.

For households on the Smart Export Guarantee, the successor scheme, metering is the only route. The SEG requires licensed electricity suppliers to offer export tariffs to eligible generators¹⁷, and it is governed by the Smart Export Guarantee Order 2019 and Conditions 57 and 58 of the Standard Conditions of the Electricity Supply Licence¹⁸. Exports under the SEG must be metered on a half-hourly basis and registered for settlement, though not settled on a half-hourly basis¹⁴. The meter must have an associated export MPAN and be capable of measuring export at half-hourly intervals¹⁹. Ofgem's guidance states the requirement plainly: generators qualify "provided they are fitted with an export or smart meter capable of taking measurements at half-hourly intervals"⁵, and a parliamentary research briefing notes that generators must have a smart meter to monitor exports²⁰. Most accredited FIT installations will be eligible for the SEG, provided they have a smart or export meter installed²¹, and Ofgem administers the SEG on suppliers' behalf²².

The value of metered export under FIT is set administratively: for FIT year 17, the value of metered exports for net metered export payments is the average time-weighted system sell price for electricity given in the Balancing and Settlement Code²³. FIT generators with the ability to export must also make an initial choice between the guaranteed export payment and selling exported electricity on the open market²⁴.

What a cap means for a self-sufficient home

An export cap is one of the clearest boundaries on a household's energy independence, and it cuts in both directions. On one hand, a home with a limitation scheme can install a larger generating system than the network would otherwise accept, because the limiter guarantees the network will never see more than the agreed figure. On the other, the home remains dependent on the DNO's agreement for what it may do with its own surplus, and that agreement reflects the state of the local network, not the household's ambitions.

The practical consequence is that surplus electricity that cannot be exported must be used or stored on site. This is where limitation pushes a household towards batteries, diversion to hot water, and the load-shifting habits that home energy management systems support. A capped home has a stronger reason than an uncapped one to consume its own generation, and monitoring, of the kind covered in our guide to solar and battery system monitoring, becomes the tool for seeing how close the cap is being ridden.

One caveat for households sizing a system: common planning tools ignore the issue. Energy Saving Trust's solar panel calculator assumes no export limits, so actual earnings may differ⁶. A home that models its payback on unrestricted export may find the real figures lower if a cap applies.

The wider direction of policy is towards more export, not less. The government has removed the limitation that non-domestic solar equipment can generate up to 1MW of electricity, leaving no limit on capacity of electricity generated²⁵, and the Community and Smaller-scale Electricity Export Guarantee Scheme covers exporting sites generating low carbon electricity with a capacity below 5MW²⁵. But national policy and local network capacity are different things, and for the individual home the binding constraint remains the connection agreement. Independence here means knowing the cap, using the surplus within the home, and understanding that the route to payment for any export still runs through a meter, an export MPAN, and a supplier's tariff.