My Smart Meter Seems Wrong Since Installing Plug-in Solar — What's Happening?

Germany had to replace hundreds of thousands of old meters when balcony solar took off. The UK has its own version of this problem. Here's what to expect.

When Germany's balcony solar market scaled past half a million installations, a meter problem surfaced at scale: old analogue "Ferraris" meters — the spinning disc type — physically ran backwards when plug-in solar fed electricity into the circuit. The disc spins forward when you draw from the grid and backward when you export. With no backstop mechanism on older models, export would literally subtract from your import reading, giving you free electricity.

The German government eventually legislated that DNOs must replace incompatible meters within four months of a Balkonkraftwerk installation. Thousands of meter replacement requests queued up. Delays were common.

The UK has a different but related set of issues heading our way.

The UK Meter Landscape

The UK is in the middle of a smart meter rollout. There are three categories of meter UK plug-in solar owners may have:

SMETS1 (first-generation smart meters) — installed mainly between 2011-2018. These are partially smart but had known issues, particularly around supplier switches and loss of smart functionality. Around 4 million were still in SMETS1 mode as of 2025. Some don't accurately separate import and export.

SMETS2 (second-generation smart meters) — the current standard. These should correctly measure both import and export, making them compatible with Smart Export Guarantee tariffs. If you have a SMETS2 meter and install plug-in solar, you should be fine.

Traditional credit meters — the older analogue or digital non-smart meters. These should not run backwards (modern credit meters have backstop mechanisms that prevent this), but they also can't measure export — so if you ever want to claim SEG payments, you'll need an upgrade.

What to Check

First, identify what meter you have. Your energy bill will usually list the meter type, or you can check the display. SMETS2 meters typically have an in-home display (IHD) and a prominent LCD screen. You can also ask your supplier.

If you have a SMETS2 meter: you're in the best position. Your supplier can see your import and export separately. If you're generating more than you consume, exports will register correctly. You won't be overpaying or underpaying based on meter errors.

If you have a SMETS1 meter in "dumb mode": this is worth flagging to your supplier. Some SMETS1 meters in dumb mode revert to a single import reading and don't correctly handle solar export. Ask your supplier to upgrade you to a SMETS2 meter — they're obliged to do so on request, though there can be waiting times.

If you have a traditional credit meter: in theory, a backstop mechanism prevents backwards running. But if you notice your meter reading dropping on a very sunny day when you're not at home (and therefore not consuming much), report it to your supplier immediately. This would indicate a fault.

The "Meter Is Wrong" Feeling

Even with a correctly functioning SMETS2 meter, many new solar owners feel like something is off. This usually comes from a mismatch between what the monitoring app says (e.g., generated 3.2 kWh today) and what the meter shows (import reading dropped by only 1 kWh).

This isn't a meter error. It reflects the fact that some of your generation was exported — it reduced your import reading by 1 kWh, but the other 2.2 kWh left the meter going the other way (export). You don't get a subtraction for exports on a standard meter without SEG — they count as zero.

An Emporia Vue 3 fitted at your consumer unit shows both import and export in real time and makes the full picture immediately clear.

The In-Home Display Problem

Many SMETS1 and early SMETS2 in-home displays (IHDs) weren't designed to show solar generation. They show grid import in the normal way, but they may confusingly show negative or zero consumption readings during peak generation — which looks like the meter is broken. It isn't. The display just wasn't built for this scenario.

If your IHD is behaving oddly, it's cosmetic: the underlying meter data is usually correct. You can verify by checking your supplier's online portal or app, which often shows a more complete picture than the physical display.

Smart Meters and SEG: The Catch

To receive Smart Export Guarantee payments, your supplier needs to be able to measure your export in half-hourly intervals. This requires a SMETS2 meter in smart mode. If you have a SMETS1 in dumb mode or a traditional meter, you can't access most SEG tariffs.

Given that most plug-in solar self-installs can't access SEG due to the MCS certification requirement anyway (see our SEG guide), this is a secondary concern for most owners. But if you're in one of the situations where SEG is accessible (Octopus Energy's informal arrangement, or future regulatory changes), having the right meter will matter.

What to Do

If you have a SMETS2 meter, no action is needed. If you have a SMETS1 or traditional meter, contact your supplier and request a free upgrade. Wait times vary — some suppliers are quicker than others. Given the UK's plug-in solar launch, smart meter demand is likely to increase, so earlier requests will encounter shorter queues.

After installation, use a Tapo P110 smart plug on the inverter output as an independent generation monitor. This gives you a reliable record of what you've generated that doesn't depend on the meter or any cloud service — useful if you ever need to demonstrate generation for a complaint or warranty claim.

For the broader picture on how plug-in solar interacts with tariffs, see our best energy tariff for solar owners guide.