The 3.68 kW export limit: G98, G99 and what you can do about it
Most UK homes can send up to 3.68 kW back to the grid without asking anyone. Above that, the network operator has a say, and its answer shapes how a battery should be run every sunny day.
Where 3.68 kW comes from
A standard UK home has a single-phase supply at a nominal 230 volts. The rules for small generators are written in amps per phase, and the threshold for the simplest process is 16 A. Multiply the two and you get 3,680 W, or 3.68 kW. That is the whole origin of the number. It is not a limit on what your home can use or how big your panels can be. It is the generating capacity that can be connected to one phase under the lightest-touch rules.
The rules are applied by your distribution network operator, or DNO, which owns the cables and substations in your area. It is not your supplier, and switching supplier never changes which DNO you have.
G98 and G99
G98: notify after installing
G98 covers generators up to 16 A per phase. The installer fits the system, commissions it, and then tells the DNO it is there, within a set number of days. There is no waiting and no approval. Most small solar installations in Britain were connected this way, and a 3.6 kW solar inverter is a common size because it sits just under the line.
G99: approval before installing
Anything larger goes through G99. The installer applies to the DNO before the work starts, the DNO looks at the local network, and it replies with one of three things: a straight approval, an approval with an export limit, or a request for reinforcement work that you would have to pay for. How long this takes varies by DNO and by how busy the local network is. Weeks is normal.
Adding a battery can tip you over
This is the part that catches people out. The DNO counts the inverter capacity of everything that can push power onto the grid, and a battery has an inverter too. A Powerwall 2 can deliver 5 kW continuously; a Powerwall 3 can deliver 11.5 kW. Add either to an existing 3.6 kW solar inverter and the total is well above 16 A. So a home connected under G98 for its panels usually needs a G99 application when the battery goes in, even though the panels have not changed. The installer handles this as part of the job, and the DNO's reply often comes with an export limit attached.
What an export limit is and how it is enforced
An export limit is the DNO saying: connect what you like, but never push more than a set amount onto the network. Very often that amount is 3.68 kW, because the local cables were sized on that assumption. The limit is about what crosses into the street, not what your equipment can make.
The installer enforces it with an export limitation scheme. A current sensor sits where your home meets the grid, and either the solar inverter or the battery system's gateway reads it continuously. When export approaches the limit, the equipment throttles generation to hold it there. On a Powerwall system this job normally falls to the Tesla gateway, which already measures the grid connection and controls the battery. The scheme has to fail safe: if the sensor is lost, the system stops generating rather than risk exceeding the limit.
The setting lives in the installer's configuration, not in the Tesla app. It is part of the connection agreement with the DNO, and not something to change yourself.
What clipping looks like on a sunny day
Picture a June day with a 6 kWp array. Around noon the panels could make 5 kW. The house is using 0.5 kW and the battery filled up at eleven. The surplus is 4.5 kW, but only 3.68 kW may leave the house, so the inverter is told to make less. About 0.8 kW is never produced.
In the Tesla app this shows as a solar curve with a flat top. Instead of the usual hump peaking at midday, generation rises, hits a ceiling, runs along it for a few hours, and then falls away. The energy that would have filled in the hump is lost, and over a summer of bright days on a large array that adds up.
The house's own use helps. Export is generation minus consumption, so running the dishwasher or charging a car at noon lowers what has to be exported and lifts the ceiling on generation.
Why the limit changes battery strategy
Without a limit, the plan on a peak-export tariff is simple: fill the battery from solar, then sell into the evening peak. With a limit there are two things to think about.
- The export pipe is full at midday. On a bright day the panels alone reach the limit, so the battery cannot add anything to exports then. Any solar above the limit either goes into the battery or is clipped.
- The pipe is empty in the evening. Once the sun drops, the full 3.68 kW is available for the battery to sell.
So on a sunny day the battery should often start the morning emptier, with room to soak up the surplus that would otherwise be clipped, and then sell into the evening when export capacity is free again. On a Flux-style tariff that evening window is also when export pays most. The limit still caps the total: at 3.68 kW, a three-hour peak moves at most about 11 kWh, roughly one Powerwall. UK export tariffs explained covers the tariff side.
Beyond 3.68 kW
Three-phase homes
A three-phase supply has three conductors, and the 16 A figure applies to each. In principle that allows about 11 kW under G98, but only if the generation is spread evenly across the phases. A single-phase Powerwall on one phase of a three-phase supply is judged on that phase alone, and DNOs also have rules about how unbalanced the phases may be. Three-phase supplies are the exception in UK housing. If you have one, ask the installer to explain what was applied for and why.
Applying for a higher limit
You can ask. A G99 application, usually made by the installer on your behalf, asks the DNO to allow a higher export. The DNO looks at the local transformer, the cable sizes and how many other generators are already on the street. A quiet rural feeder may say yes; a suburban street with solar on every roof may not. If the answer needs reinforcement, the cost falls to you and is often more than the extra export would ever earn.
It is worth pursuing with a large array, a large battery and a tariff that pays well for evening export. It is rarely worth it for a small array on a flat export rate. If the limit changes, the installer reconfigures the export limitation scheme.
How to tell what your limit is
- The installation paperwork. The commissioning documents say whether the system was connected under G98 or G99, and a G99 connection comes with a letter from the DNO stating any export limit.
- The equipment's settings. The limit is set in the inverter or gateway by the installer. The Tesla app does not show it, but the installer can read it.
- The DNO's records. Contact your DNO with your address and meter details. It keeps a register of what is connected and on what terms.
- The data. A solar curve with a flat top at the same level on every bright day is the sign, and the level of that top is the limit.
If the paperwork and the data disagree, ask the installer.
In SunHarvest
The export cap is one of the site facts SunHarvest carries alongside the battery's capacity and reserve. The AI planner's context pack includes it, with a pre-computed figure for how much of today's forecast solar will sit above the cap, so a plan can leave that much room in the battery before a bright day rather than charging to full overnight. Rules can do the same by hand, using the solar tomorrow signal to set the reserve lower before sunny days. The tariff comparison replays your history with the same cap applied, so surplus that could not have been exported is never counted as income.
General information, not financial or electrical advice. Tariff terms, prices, warranties and connection rules change and differ by supplier, region and installation; check the current documents for yours. SunHarvest is not affiliated with Tesla or Octopus Energy.