Behind-the-meter vs in-front-of-meter

How the boundary meter separates on-site energy from grid flows, and what that changes for billing, export, connection and control.

Behind-the-meter equipment is connected on the customer’s side of the meter that records exchange with the public network. In-front-of-meter equipment is connected on the network side or as a network-facing asset in its own right. “Front-of-meter” and “in-front-of-meter” are used for the same broad idea.

For a home, rooftop solar, a battery, heat pump and EV charger are normally behind the import/export boundary meter. A solar farm or grid battery with its own network connection and market metering is normally front-of-meter.

This is an energy-flow and commercial boundary. It is not a complete legal ownership diagram: the DNO service head, supplier metering equipment, customer installation and any private network can have different ownership interfaces around the same location.

What the boundary meter sees

The meter records net flow between the property and the grid:

when on-site generation exceeds on-site demand, the surplus is export
when demand exceeds generation and battery discharge, the shortfall is import
generation consumed at the same time on site does not cross the boundary meter
battery charging from the grid is import
battery discharge beyond on-site demand is export

The meter cannot identify which device caused the flow. It does not know whether an imported unit charged a car, battery or immersion heater, and it does not know whether an exported unit came directly from solar or from storage.

An inverter portal can estimate generation and device flows, but its data is not the same as the regulated boundary-meter record. Compare measurement positions and intervals before treating a difference as a fault.

Self-consumption

Self-consumption is generation used on site before it crosses the export boundary. It reduces the electricity that would otherwise be imported. A battery can move that use from the generation period to a later period, subject to conversion losses, standing losses and its operating reserve.

The value of self-consumption is the import cost avoided at that time. The value of export is the export payment earned at that time. There is no permanent rule that self-consumption is always more valuable.

For each period, compare:

the import price avoided
the export price forgone
battery round-trip losses and degradation where storage is involved
whether charging later at a lower import rate is possible
any tariff or warranty restriction on grid charging and export

On a simple tariff the avoided import price may exceed the export rate. With cheap off-peak import and a premium or time-varying export tariff, exporting solar and charging the battery later can sometimes be worth more. Use the actual paired tariffs and schedule, not an assumed national price hierarchy.

Import, export and generation meters

A suitable smart electricity meter can maintain separate import and export records. A SEG (Smart Export Guarantee) contract also needs an export MPAN and a meter capable of measuring export in half-hourly periods.

That meter does not have to be a particular marketing generation simply because the site is behind the meter. Ofgem says the relevant test is whether the meter can provide the required export measurement and is acceptable to the SEG licensee.

A dedicated PV generation meter measures total output from the generating system. It is distinct from the export register:

generation = on-site use + export, adjusted where storage, auxiliary consumption and measurement positions change the boundary.

Older Feed-in Tariff installations may retain a generation meter because generation payments depend on it. The Feed-in Tariff closed to new applications in 2019, but existing accredited installations can continue under their scheme terms. SEG pays for eligible measured export under a separate contract.

Connection rules still apply behind the meter

Equipment being behind the retail meter does not hide it from the network connection rules. A grid-connected solar inverter or battery can affect voltage, protection and export even when most of its energy is used on site.

The applicable route depends on the complete generating arrangement:

G98 covers qualifying Type Tested micro-generators within its per-phase limits and conditions
G99 applies where the installation falls outside G98
G100 covers customer export-limitation schemes where the DNO accepts a controlled export below the installation’s possible output

The G98 threshold of 16 A per phase is about the qualifying generating units and their Registered Capacity, not a universal export allowance. Existing generation and storage must be included when the rules require aggregation. A configured zero-export or low-export setting does not by itself turn a larger generating installation into G98 equipment.

Apply to the actual DNO or IDNO and retain its acknowledgement or connection offer. Export-tariff acceptance does not replace network acceptance, and network acceptance does not create an export payment contract.

CT clamps and control boundaries

Many home systems use a current transformer clamp or meter at the grid connection point. It gives the inverter or controller a near-real-time direction and magnitude of net flow so it can:

charge a battery from surplus generation
discharge to reduce import
enforce an agreed export limit
manage an EV charger or other flexible load

Placement, direction and phase mapping are critical. A clamp around the wrong conductor, installed backwards or positioned so that it misses another board can make the controller increase the very flow it is meant to reduce.

For three-phase sites, establish whether the system measures and controls each phase or only a net total, and whether the DNO limit is per phase or at the connection as a whole. Commission the system under import and export conditions and record the test.

A proprietary CT reading is a control input, not the settlement meter. If it fails, the installation must move to a safe state that respects the connection terms.

Backup does not change the normal boundary

A behind-the-meter battery can provide backup only if the installation has a compliant changeover and earthing arrangement. During island operation, the protected circuits must be separated from the public network.

Calling equipment “behind the meter” does not imply that it can run during a power cut. Most ordinary grid-connected inverters shut down when the grid fails unless a designed backup function is installed.

Private networks and shared sites

The terminology becomes more contextual on an estate, apartment block or commercial site. Equipment can sit behind the site’s main boundary meter but in front of individual tenant submeters. It may therefore be behind the meter for the public-network connection and in front of the meter from a tenant’s commercial perspective.

Define the meter being discussed. Record:

the public-network connection and MPAN
every settlement and revenue meter
landlord or private-network submeters
the electrical connection point for each generator, battery and load
which party buys import and receives export revenue

Without that diagram, “BTM” is too vague to allocate cost or responsibility.

Front-of-meter assets

A front-of-meter generator or storage asset normally has its own network connection, metering, connection agreement and market route. Its primary commercial purpose is to sell energy or system services rather than reduce one end user’s metered import.

Size alone does not decide the label. A large commercial battery can be behind a site’s boundary meter, while a smaller standalone asset can be front-of-meter. The decisive questions are where it connects, what meter records the exchange and which party is settled for the flow.

Home design boundaries

For a home system, the important boundaries and control points are:

the import/export boundary meter
the connection point for each inverter, battery, charger and protected-load board
the meter or CT controlling each function
aggregate Registered Capacity
agreed import and export limits
the tariff treatment of import and export in each period
operation after failure of a controller, CT, internet or cloud service
records for generation, import, export and battery behaviour

The BTM label on its own does not define any of these arrangements.