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PPA Mechanics · Structures
Behind-the-Meter PPA: Solar Inside Your Private Wire
A behind-the-meter PPA puts solar generation on the customer side of your supply meter, inside your own private wire, so the kilowatt-hours never touch the public grid — and never pick up network charges. That is why it carries the lowest tariff band of any PPA structure in the UK: 8 to 14 p/kWh in year one.
What is a behind-the-meter PPA?
A behind-the-meter PPA is an on-site PPA where solar sits on your side of the supply meter, on a private wire, so generation is self-consumed without ever exporting to the grid. Because the electrons never use the distribution network, the tariff avoids network use-of-system charges — delivering the lowest band of any PPA structure at 8-14 p/kWh in year one. It only works where you have high, coincident daytime load.
Key takeaways
- Behind-the-meter means the solar connects on your side of the supply meter, inside your private wire, so every kWh is self-consumed and never exported to the public grid.
- It is the lowest tariff band in the market — 8-14 p/kWh year one — because self-consumed power escapes the network use-of-system charges (BSUoS, TNUoS, DUoS) baked into a grid-routed price.
- The economics live or die on daytime load coincidence: you need a flat, high base load that overlaps the midday generation peak, which is why cold storage, data centres and continuous-process plants are the natural fit.
- A G99 / DNO connection is still required even though you never export — the grid relationship governs your import top-up and any export-limitation device.
- Office and retail sites with evening peaks are usually the wrong fit — they should look at an in-front-of-meter PPA instead.
Where the meter sits — and why that single boundary sets the price
Every commercial site has a supply (or 'fiscal') meter: the point where your electricity supplier measures what you import from the grid and bills you for it. The whole behind-the-meter idea turns on which side of that meter the solar array connects to.
In a behind-the-meter PPA the array, inverters and cabling all sit downstream of the supply meter, wired into your own distribution boards through a private wire you (or the generator) control. A solar kWh produced at noon flows straight into your machinery without ever passing the fiscal meter in the export direction. The grid simply never sees it. Contrast that with an in-front-of-meter PPA, where generation is metered as export, travels onto the distribution network, and comes back to you as import — picking up a full stack of network charges on the round trip.
That boundary is the entire reason behind-the-meter is the cheapest structure on the board. A grid-routed kilowatt-hour carries Transmission and Distribution Use of System charges (TNUoS, DUoS), Balancing Services Use of System (BSUoS), and the policy and supplier overheads bundled into a delivered tariff. Self-consumed power behind the meter avoids all of it. The result is a year-one PPA tariff of 8-14 p/kWh against the 13-22 p/kWh you would typically see on an in-front-of-meter structure — and against the 28-32 p/kWh most commercial off-takers pay for grid import. The pricing logic behind every band is set out on our PPA tariffs page.
How the private wire actually works on site
A private wire is exactly what it sounds like: electrical infrastructure you own that distributes power within your boundary without using the public network. In a behind-the-meter PPA the generator funds and installs the array, but the connection design is what unlocks the tariff.
- The PV array connects into your internal LV or HV switchgear, not into a new grid connection point. On a large industrial site this often means tying into an 11kV ring main rather than a 400V board.
- A check meter (separate from the fiscal meter) measures generation behind the boundary. This is the figure you are invoiced against under the PPA — you pay the tariff for every kWh the array delivers into your wire.
- An export-limitation or zero-export device is almost always fitted, because the commercial case assumes no export. If a sunny Sunday produces more than the site can absorb, the inverters curtail rather than spill onto the grid.
- Your existing supply continues in parallel as the import top-up. Solar shaves the daytime block off your grid demand; you still draw from the grid at night and on dull days.
The corollary of curtailment is the one weakness of behind-the-meter: any solar your site cannot consume in the moment is simply thrown away, earning nothing. There is no Smart Export Guarantee income to cushion a mismatch. That is why load coincidence, not roof size, governs whether the structure stacks up.
Why daytime load coincidence is the make-or-break number
Behind-the-meter is unforgiving about when you use power. Solar generates on a bell curve peaking around midday; your savings come only from the kWh you consume at the instant they are produced. The metric that matters is your self-consumption ratio — the share of generation the site swallows in real time.
A continuous-process plant running three shifts has a flat load line that sits well above the solar curve all day, so it self-consumes close to 100% of a correctly-sized array. That is the ideal. A site whose demand collapses at 5pm and stays low all weekend will self-consume a far smaller fraction, stranding generation and wrecking the payback the low tariff promised.
| Site demand profile | Daytime / weekend coincidence | Behind-the-meter verdict |
|---|---|---|
| Cold storage, 24/7 refrigeration | Flat base load, day and night | Excellent — near-total self-consumption |
| Continuous-process manufacturing (glass, steel, cement, food) | High, shift-pattern, weekday-heavy | Excellent |
| Data centre | Constant 24/7 IT and cooling load | Strong, but array is small vs total demand |
| Single-shift factory | Strong 8am-6pm, weak weekends | Good if array sized to weekday load |
| Office / retail | Evening or weekend peaks | Poor — choose in-front-of-meter instead |
The practical rule: size the array to the summer weekend minimum of your load, not the annual peak. An array that never out-generates the site's lowest realistic demand throws nothing away and earns its 8-14 p/kWh on every unit.
The sectors built for behind-the-meter
The structure suits a narrow but high-value band of industrial off-takers — the ones with relentless daytime electrical demand and the physical scale to justify a private-wire connection.
- Cold storage and refrigerated logistics. Compressors run around the clock and the load barely dips at weekends. A cold store is close to the platonic ideal of a self-consuming site, which is why it appears under good-fit on almost every PPA structure.
- Data centres. IT and cooling load is constant and large. The constraint is the reverse of most sites: even a rooftop-maximising array covers only a slice of total demand, so behind-the-meter solar is a margin-trimming layer rather than the headline supply — but every kWh self-consumes.
- Continuous-process manufacturing. Glass, steel, cement, ceramics and high-throughput food processing run furnaces, kilns, chillers and drying lines on a flat, weekday-heavy profile that maps tightly onto the PV curve.
- Industrial bakeries and food processors. 24/7 oven and chilling loads give high self-consumption — the kind of profile we flag as behind-the-meter-ideal across the manufacturing niches.
If your operation looks like one of these, the deeper sector economics — typical system sizes, tariff bands and savings ranges — are set out on our solar PPAs for factories page, which carries the manufacturing demand-match detail this structure depends on.
G99 and the DNO connection you still need
A common misconception is that because behind-the-meter power never exports, the Distribution Network Operator (DNO) is out of the picture. It is not. The grid relationship still governs the design, and the connection application is a real cost and timeline item.
- G99 still applies. Any generation above 50kW connecting to a site that is itself grid-connected requires a G99 application to the DNO, even where the intent is zero export. The DNO is assessing what happens if the export-limitation device fails, not just normal operation.
- Export-limitation schemes can ease the connection. A DNO-accepted limitation device or relevant relay can let a large array connect to a constrained part of the network on the basis that it will never spill — but it must be specified, witnessed and signed off.
- Your import capacity is unchanged. You still hold an agreed supply capacity (kVA) for grid import; solar reduces how often you draw on it but does not remove the connection or its standing charges.
- Timelines feed the build programme. DNO assessment can take weeks to months on larger HV connections, and it sits on the critical path alongside the EPC build. Factor it into the heads-of-terms date, not as an afterthought.
The upshot: behind-the-meter removes network charges from your tariff, but not the network relationship. Budget for the G99 process and a competent connections engineer in the diligence phase.
Behind-the-meter vs in-front-of-meter — the contrast that decides it
These two structures are the fork in the road for any single-site off-taker, and they are chosen by the shape of your load curve, not by preference. Behind-the-meter wins on price; in-front-of-meter wins on flexibility when your demand and the sun do not line up.
| Feature | Behind-the-meter PPA | In-front-of-meter PPA |
|---|---|---|
| Where solar connects | Inside your private wire, customer side of meter | Exports to grid, returns via supply meter |
| Year-one tariff band | 8-14 p/kWh (lowest) | 13-22 p/kWh |
| Network charges | Avoided entirely | BSUoS / TNUoS / DUoS apply |
| Surplus generation | Curtailed — earns nothing | Exported, can earn under SEG / export tariff |
| Best for | High, flat daytime industrial load | Roof-rich sites with weak daytime self-use |
| Typical term | 15-25 years | 10-20 years |
In one sentence: if your machinery is humming all day and most of the weekend, take the behind-the-meter tariff and accept the curtailment risk; if your roof is large but your daytime demand is patchy, the in-front-of-meter route lets you monetise the surplus instead of throwing it away. The full structure family — on-site, sleeved, virtual and corporate included — is mapped on the PPA structures hub.
What to check before signing a behind-the-meter PPA
Because the low tariff is conditional on self-consumption, the diligence here is different from a standard on-site deal. Before you sign, pressure-test these points with the provider.
- Half-hourly load data. Insist the array is sized against twelve months of your actual HH consumption, not an annual average. The summer-weekend minimum is the number that protects you from stranded generation.
- Curtailment treatment. Confirm you are invoiced on metered generation delivered into your wire, not theoretical output, so curtailed energy you never used is not billed to you.
- G99 / connection responsibility. Pin down who carries the DNO application cost and the risk of a connection offer coming back constrained or expensive.
- Assignment on sale of business. A private-wire PPA is a 15-25 year fixture on your site. Make sure the change-of-control and assignment-on-sale clauses are workable, because a future buyer of your business inherits the contract.
- Site tenure. As with any on-site structure, your occupancy must comfortably outlast the term — a private wire is not something you take with you.
Get those right and behind-the-meter is the cheapest power your site will buy for a generation. Get the load coincidence wrong and the headline tariff is a mirage. If you want a sense check on whether your demand profile fits, send us the basics and we will tell you straight.
FAQs
Frequently asked questions
Is a behind-the-meter PPA cheaper than a normal on-site PPA?
Usually yes. Both put solar on your site, but behind-the-meter keeps every kWh inside your private wire so it never picks up network use-of-system charges. That pushes the tariff to the lowest band of 8-14 p/kWh year one, against 9-18 p/kWh for a standard on-site PPA that may export surplus to the grid.
Do I still need a DNO connection if the power never exports?
Yes. Any generation above 50kW on a grid-connected site needs a G99 application to your Distribution Network Operator, even with a zero-export design. The DNO assesses what happens if your export-limitation device fails, and your import top-up still runs through an agreed supply capacity. The network charges disappear from your tariff, but the network relationship does not.
What is a private wire in a behind-the-meter PPA?
A private wire is electrical infrastructure within your site boundary that distributes power without using the public network. The solar array ties into your own switchgear, a check meter records generation behind the supply meter, and an export-limitation device prevents spill to the grid. Power flows straight into your machinery, so it is self-consumed rather than imported.
Which sectors are best suited to a behind-the-meter PPA?
Sites with high, flat daytime electrical demand: cold storage and refrigerated logistics, continuous-process manufacturing (glass, steel, cement, food), data centres, and industrial bakeries. They self-consume close to all the generation in real time, which is what makes the low tariff pay. Office and retail sites with evening peaks are a poor fit and should consider in-front-of-meter instead.
What happens to surplus solar I cannot use behind the meter?
It is curtailed — the inverters throttle back and that energy earns nothing. Unlike an in-front-of-meter or export structure, there is no Smart Export Guarantee income to catch the overflow. This is why the array should be sized to your summer-weekend minimum load, so it never out-generates what the site can absorb.
How long does a behind-the-meter PPA run?
Typically 15-25 years, the same horizon as a standard on-site PPA, with a fixed or RPI-linked escalator. The long term reflects the private-wire infrastructure the generator funds. Your site tenure must comfortably outlast the contract, and the change-of-control clauses matter because a buyer of your business would inherit the agreement.
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