G99 Grid Connection for Rural Barns Explained

The one thing that decides how fast your barn solar gets switched on

Most barn owners assume the long pole in a solar project is the roof — stripping asbestos, fixing panels, getting the scaffold up. It usually isn’t. On a rural site, the part that most often holds everything up is the grid connection, and the rules that govern it sit under a engineering standard called G99.

Get G99 right early and your barn array can be generating within weeks of the panels going up. Get it wrong — or leave it until last — and you can be sat with a finished system you’re not allowed to switch on, waiting months for a Distribution Network Operator (DNO) to come back to you. This guide explains what G99 actually is, why rural networks are the slow part, and the design routes that get a working barn connected faster.

What G99 is, in plain terms

G99 is the connection standard for any generator — solar, battery, wind, CHP — that connects to the grid above a small threshold. The simpler standard, G98, covers tiny systems that can connect on a notify-and-connect basis. Above that, you move into G99, which means the DNO has to approve your connection before you energise it, not just be told about it afterwards.

The practical trigger most barn owners need to remember is this: you need a G99 application for anything above 3.68 kW per phase. A 3.68 kW limit per phase is roughly 16 amps — a deliberately small figure. In real terms, almost every genuine barn PV system clears it. A 30 kW poultry-shed array, a 100 kW grain-store roof, even a modest 10 kW system on a three-phase supply — all of them are G99 territory. The only barn installs that typically stay under G99 are very small single-phase domestic systems, and even there it’s borderline.

So for the working-barn owner the honest position is: assume your project needs a G99 application, and plan the timeline around it.

Why rural networks are the slow part

Here’s the bit that catches farmers out. The G99 process itself is a paperwork-and-engineering exercise — your installer submits the application, the DNO assesses it. What makes it slow in the countryside isn’t the form; it’s what’s at the end of the wire.

Rural distribution networks were built to deliver power to scattered farms and villages, not to receive a flood of it back from hundreds of solar roofs. The lines are often long, the local transformers modest, and the headroom to absorb exported electricity limited. When you apply to export a meaningful amount of power into a constrained rural network, the DNO has to check whether the local network can take it without voltages drifting out of limits. That assessment — sometimes a full connection study, sometimes reinforcement of a transformer or a length of line — is where the months go.

Which DNO you’re dealing with depends purely on geography; the network in your area is a regional monopoly, so you don’t get to shop around. The constraint is the same story across all of them: a network that was never designed for large-scale rural export, now fielding a wave of applications from exactly the kind of big, south-facing barn roofs this site exists to serve.

None of this means a dead end. It means the connection has to be designed around, not just applied for — and that’s where the next part matters.

The routes that connect a barn faster

If the grid won’t quickly let you export a large amount of power, the answer is usually to stop trying to export a large amount of power. For a working barn, that’s far less of a sacrifice than it sounds, because a barn with real on-site load uses most of its own generation anyway. Three approaches do the heavy lifting:

1. Design for self-consumption. The simplest route is to size the system to the load the barn actually uses in daylight, rather than to the full roof. A barn with a steady daytime demand — poultry ventilation, dairy cooling, a grain-drying fan, workshop machinery — soaks up most of what the panels make on site, so very little needs to leave the property. A self-consumption-led design is smaller, cheaper, and asks far less of the network, so it clears the G99 assessment more easily. It’s often the fastest-paying option too, because every unit you use on site offsets a unit you’d otherwise buy at the full grid price.

2. Add an export limiter. An export limiter is a control device that physically caps how much power your system pushes onto the grid — say, to zero, or to a low agreed figure. From the DNO’s point of view, a system that’s guaranteed never to export beyond a set limit is a much smaller ask, because it can’t overload the local network. A no-export (G100) design — where the system is set to export nothing at all and serves the barn’s own load only — can side-step the slow capacity assessment almost entirely, turning a connection that might have taken many months into one that takes a few weeks. You generate, you self-consume, and nothing spills onto the constrained rural line.

3. Put a battery behind it. A battery lets a barn store its midday solar surplus and use it later — into an evening load, an overnight ventilation cycle, or the next morning — instead of trying to push it onto the grid the instant it’s made. That flattens the export profile the DNO cares about and, paired with an export limiter, lets you capture far more of your own generation without asking the network for export headroom you can’t get. For a barn whose load doesn’t line up neatly with the sun, storage is often what makes a constrained-grid site work at all.

These routes aren’t mutually exclusive — a typical constrained-grid barn ends up with a self-consumption-led array, an export limiter set to a low or zero figure, and sometimes a battery to mop up the surplus. The point is that the grid stops being the thing that shrinks or delays your scheme.

What good timing looks like

The single biggest lever you control is when the G99 application goes in. The mistake is to treat it as the last job, after the roof and the kit are sorted. The right move is to submit the G99 application at the same time as the structural survey, right at the start — so the DNO’s clock starts running while everything else is still in motion. By the time the scaffold comes down, the connection agreement is often already in hand.

For a worked illustration: a typical 100 kW shed array on a three-phase rural supply is firmly G99, and a straight grid-export application could sit with the DNO for several months. The same barn, designed as a self-consumption system with an export limiter, asks the network for little or nothing and can frequently be connected far sooner — while still cutting the bill on nearly all of the same generation, because the load was there to use it. That’s the trade the design conversation is really about.

If you’d like to know which route your barn falls into — whether your supply, your load, and your local network point to a straightforward export connection or an export-limited design — we can look at your meter data and your DNO position and tell you honestly before you commit to anything. The same thinking applies whether you’re connecting a working shed to the grid or going the other way entirely with off-grid solar for barns, and it sits at the heart of how we approach solar panels for agricultural buildings of every size.

Start with a no-obligation look at your barn and your grid position — get a quote and we’ll map the fastest realistic route to switching your roof on.