Considerations

Type of consumer unit

Your consumer unit (fuse box) matters more than most people realise. There are, broadly, three generations you will find in UK homes:

• Old rewireable fuse boardFuse wire in a ceramic holder, no RCD protection at all - the type most likely to prompt "get an electrician to check first" advice before fitting any new electrical load, plug-in solar included
• Older MCB board, no RCD or a single whole-board RCDModern circuit breakers, but if there is only one RCD covering the whole board, a fault anywhere trips everything - inconvenient, and a sign the board predates 18th Edition wiring regulations
• Modern dual-RCD or RCBO boardEach circuit (or small group of circuits) has its own RCBO - a combined residual-current + overcurrent device - so a fault on one socket circuit will not take out your lighting or your fridge circuit too. This is what an 18th Edition-compliant installation looks like today.

The Interim Product Specification requires kit instructions to tell you to check that your installation has modern residual current protection (an RCBO), and to test it periodically by pressing its test button while the kit is generating. If your board is the first or second type above, or you do not know which type you have, get a qualified electrician to check it before you fit a kit. The instructions must also explain how to identify which sockets share a circuit, and when to get professional advice.

Extension leads

The Interim Product Specification is explicit: a plug-in solar kit connects directly into a wall socket via its own manufacturer-supplied plug. Extension leads, multi-way adaptors, travel adaptors, RCD adaptors and plug convertors are all prohibited for this connection - not a recommendation, a rule, and the plug itself must carry the warning. An extension lead adds extra plug/socket junctions (extra points that can loosen, overheat or arc), and most are not rated or tested for a semi-permanent outdoor-to-indoor run.

If you need to use extension leads elsewhere in the room for other appliances, make sure any lead is fully unwound (a coiled lead under load can overheat), rated for at least 13A, and not itself daisy-chained into another extension lead.

Air conditioning and other high loads at the same time

Running a portable air conditioner, a tumble dryer, an immersion heater or an electric heater on the same ring as your plug-in solar socket does not create a new electrical hazard by itself - your ring/socket circuit's own protection (its RCBO and the ring's 32A rating) is what is protecting against overload from those appliances, exactly as it would without any solar kit plugged in at all. What it does do is make the solar kit practically irrelevant at that moment: an 800W kit's output is small next to a 2-3kW air conditioner or heater, so on the accounting side you will be importing almost all of what that appliance needs regardless of whether the sun's out.

The one genuine interaction worth knowing: never treat "there is spare capacity on the ring" as a reason to add a second plug-in solar kit - a second kit is not permitted anywhere in your home (see the warning above).

Ring final circuits, and the risk of sharing one

Most UK homes wire their socket outlets as a "ring final circuit" - a single cable that loops out from the consumer unit, around the room(s), and back again, with both ends landing on the same 32A MCB/RCBO. This ring topology is exactly what lets a 2.5mm² cable safely serve a whole floor's worth of sockets: the assumption behind the 32A rating is that normal domestic use is spread out, not that every socket draws hard at once.

Plugging in a single ~800W solar kit on a ring does not change that assumption meaningfully - it is a small injection, well within the ring's normal headroom. The situations actually worth avoiding (a second kit is not allowed at all - see the warning above) are: a solar kit sharing a ring with something that is already close to the ring's limit on its own (a space heater plus a kettle plus a tumble dryer, for instance); or an older property where the ring has had unauthorised extra sockets ("spurs") added over the years without checking the total load - which is a pre-existing risk plug-in solar does not cause, but is worth having checked regardless if you are not sure of your home's wiring history.

Worked example: plug-in solar and a portable air conditioner

A common real-world combination: a plug-in solar kit in the living room, and a portable air conditioner plugged in nearby during a heatwave. Whether that combination is fine comes down to one question - are the two sockets on the same ring final circuit, and what else is on it at the same time?

Simplified illustration of a ring final circuit: one cable leaves the consumer unit, loops past a series of sockets, and returns to the same 32A MCB/RCBO - it is not a set of independent branches. The solar kit and the air conditioner shown here share one ring; a socket in a different part of the house, or one wired as a "spur", might not.

• The solar kit itselfMust connect directly into its own wall socket using the manufacturer's plug. Never put it on an extension lead, multi-way adaptor or travel adaptor - see Extension leads above.
• A portable air conditioner on the same ringElectrically fine on its own terms - the ring's 32A protection covers it exactly as it would without any solar kit present - but it will draw far more than the kit ever feeds in, so do not expect the kit to meaningfully offset its running cost. Do not run it alongside a kettle, tumble dryer and heater all on the same ring at once, solar kit or not.

How to check which sockets are on the same ring

1. Check your consumer unit's labelling first. Many boards label circuits by room or area ("Downstairs sockets", "Kitchen ring") - a useful starting point, but not a guarantee it is accurate or up to date.
2. Switch off one MCB/RCBO at a time. With a lamp or similar plugged in and switched on at each socket you want to test, turn off one breaker and see which sockets lose power - everything that goes off together is on that circuit.
3. Use a plug-in socket tester or circuit finder. An inexpensive tester plugs into a socket while a receiver unit at the consumer unit beeps or lights up on the matching circuit - quicker than the switch-off method when there are a lot of sockets to check.
4. Do not assume by room or wall. Rings often loop between rooms (a landing socket can share a ring with a bedroom, or a kitchen with a hallway), and older properties may have unrecorded "spurs" added over the years - physical proximity is not a reliable guide.
5. When in doubt, ask an electrician. A qualified, registered electrician can test and map your circuits properly and tell you with certainty what shares a ring with what.

What happens in a power cut

A common misconception: your plug-in solar panel will not keep any of your home running during a power cut, even on a sunny day. Every compliant kit has mandatory "anti-islanding" protection - the inverter constantly checks for the presence of grid mains, and its loss-of-mains protection (required under G98) shuts it off if the supply disappears. The specification also requires it to disconnect within 100 milliseconds of losing the mains, with the plug pins below 34V within 100ms. This is a deliberate, non-optional safety feature: it exists so that a network engineer working on what they believe is a dead line during a fault or planned outage is not put at risk by your panel quietly "islanding" and re-energising it.

If you want genuine backup power during an outage, that is a different product category entirely - an off-grid/battery system with a proper transfer switch, professionally installed and certified for that purpose - not something a plug-in solar kit provides, and plug-in batteries are not permitted (see Battery power).

Why bigger panels can still help, even though the inverter is capped at 800W

The inverter's 800VA/800W ceiling is fixed no matter how many watts of panel you connect (up to the 2,000W maximum). So why does the Interim Product Specification allow panels rated well above 800W at all? Because irradiance is rarely at its peak - most of the day, a panel is producing well under its nameplate rating, and a bigger array means the inverter reaches its 800W ceiling earlier in the morning, later in the evening, and more often on hazy or overcast days, rather than only for a couple of hours around solar noon on a clear day.

The specification's limits on the panel side: no more than 2,000W of panels, up to four panels with no more than two in series, no more than 120V DC (open circuit) at the inverter, and no Y-connectors. Above 960W of panels, manufacturers must advise you to consider a professional assessment of your existing wiring before fitting.

The trade-off: on a genuinely clear day, extra capacity above 800W is "clipped" (the inverter cannot pass it through), so it is wasted at the very peak - but that lost peak is smaller than the gain made on the shoulders of the day and on duller days. As a worked example using this site's own model (see the Energy calculator): in London in April, an 800W array produces roughly 3.0 kWh on an average day, while a 2,000W array - about two and a half times the panel capacity - produces roughly 4.6 kWh, not 7.5 kWh, precisely because of clipping, but it is still a genuine ~50% uplift for a modest extra outlay on panels alone (no change to the inverter or registration, though above 960W the specification advises a professional check of your wiring first). Try changing the panel-capacity slider on the calculator to see this for your own location and month.

Best panel placement, including behind windows

Where you physically point the panel is, after location and season, the next biggest factor in what it generates. The figures below are relative to an ideal south-facing, optimally-tilted panel (the calculator's location dataset already assumes this "best case" baseline, so these are extra multipliers on top of it):

The two "behind glass" figures are this site's estimates, not lab measurements. They combine the orientation figure with an assumed glass loss of roughly 30-35%, from the middle of the range glass manufacturers' own data gives. Measured square-on (to the EN 410 standard), clear 4mm single glazing lets through about 89% of the sun's energy (Saint-Gobain PLANICLEAR) - roughly an 11% loss. A modern low-E ("low-emissivity") double-glazed unit lets through 73% of visible light but only 48% of total solar energy (Saint-Gobain PLANITHERM NEO, 4-16-4mm argon-filled), because its coating reflects much of the near-infrared, part of which silicon solar cells use. Since a solar cell uses visible and some near-infrared light, the real loss behind glass like that falls between those two figures - roughly 27-52%. If your windows have been replaced to meet current Building Regulations energy standards (a maximum U-value of 1.4 W/m²K in England, under Approved Document L), they are likely to be low-E, so expect the worse end of the range. Sun hitting glass at a steep angle (low winter sun on a vertical window) loses more than these square-on figures. Indoor/behind-glass placement also is not really what a registered 800W plug-in kit is designed for - it is included here for completeness (e.g. for a small portable panel trickle-charging a device on a windowsill), not as a recommended way to run a full kit. See the Energy calculator, which includes both window options alongside the four outdoor orientations.

Other things worth knowing

• Wind and weather loadingA panel is a sizeable sail in strong wind - use a bracket rated for the location's exposure, not just for the panel's weight
• Cleaning and maintenanceDust, pollen, bird droppings and fallen leaves measurably reduce output - a periodic wipe-down with water restores most of it, but do not create a fall risk reaching an awkward spot to do it
• Tell your home insurerEspecially for anything mounted externally - some policies want to know about permanently fixed external equipment
• A faint hum is normalMicroinverters can produce a very quiet high-frequency hum - rarely noticeable, but worth knowing it is not a fault
• Moving house or ending a tenancyA plug-in kit is designed to be portable - you can generally take it with you; notify your network operator of the removal so their records stay accurate (see Registration)

Sources

Rules last checked: 29 October 2026, against the Interim Product Specification v2 (16 July 2026), SI 2026/848 and Ofgem's G98 decision of 11 August 2026. The specification has not been updated or replaced since July 2026.

• Plug-in Solar Device Interim Product Specification, version 2 (DESNZ, 16 July 2026) - the current version, referenced by name in the law.
• legislation.gov.uk: SI 2026/848 - amends the Plugs and Sockets etc. (Safety) Regulations 1994 and the Electricity Safety, Quality and Continuity Regulations 2002; in force 27 August 2026.
• Ofgem: decision to approve DCRP/MP/26/02 (11 August 2026) - the G98 amendment for plug-in solar: one device per household and notification to your network operator.
• GOV.UK: Plug-in solar - regulatory amendment and interim product specification (DESNZ, July 2026) - connection method, anti-islanding, panel/inverter limits.
• Electrical Safety First - consumer unit types, ring final circuits, extension lead safety.
• Saint-Gobain Glass: PLANICLEAR data sheet (14 March 2024) - clear float glass light and solar energy transmittance, to EN 410.
• Saint-Gobain Glass: PLANITHERM NEO data sheet (January 2026) - low-E double glazing light and solar energy transmittance.
• Guardian Glass: performance value terms - definitions of light transmittance (380-780nm) and solar energy transmittance (300-2500nm).
• GOV.UK: Approved Document L, Volume 1 - limiting U-value for replacement windows in existing homes.

This page is informational, not electrical-safety advice for your specific home. If your consumer unit is old, your circuits are unidentified, or your ring's history is uncertain, get a qualified, registered electrician's opinion before fitting one yourself.