The Independent and Yahoo will earn a commission from purchases made via links in this article. Pricing and availability are subject to change.
Plug-in solar panels are now legal in Great Britain, but anyone browsing the first systems to go on sale may have spotted what, on the surface, looks like a contradiction with the government's new rules for compliance.
The new rules limit plug-in solar to 800W, yet Argos is already selling UKSOL kits labelled 890W, 1,030W and even 1,260W. So how can they be allowed under the new rules?
The answer is that those larger numbers describe the combined generating capacity of the solar panels, while the legal limit applies to the amount of power the system can feed into your home.
Under the government's new plug-in solar specification, a compliant system can have a maximum apparent AC power output of 800VA – generally presented to consumers as an 800W limit. The plug-in panels have a microinverter built into the system that ensures it can't supply more than this amount to your household circuit.
Read more: First look at plug-in solar panels
Solar panels generate direct current (DC) electricity, which passes through the system's microinverter and is converted into alternating current (AC) electricity, which is used by the appliances in your home.
The plug-in solar panels and the inverter therefore have their own separate power ratings.
Take, for example, the £989 UKSOL Pro Max kit currently listed by Argos. It includes two 630W solar panels, giving it a total nominal panel capacity of 1,260W, but those panels feed into an 800W microinverter. No matter how much electricity the panels are capable of producing, the inverter still limits the AC output supplied to the house.
That means a system can legitimately contain more than 800W of solar panel capacity without exceeding the plug-in solar limit.
Read more: Plug-in vs installed solar panels
Your next question is probably: What's the point, then, of getting panels with more than 800W capacity? It's a good question. It might sound wasteful, but solar panels rarely produce their headline output on a continuous basis.
A panel's wattage is measured under standard laboratory test conditions. But in the real world, output varies according to factors such as the time of day, season, cloud cover, temperature, shading and the direction and angle of the panels.
Using a system that's more than 800W of panel capacity can therefore help an 800W microinverter get closer to its maximum output for more of the day.
Argos, for example, says the oversized 1,260W panel capacity in its UKSOL kit is intended to maximise generation during poorer weather. On a cloudy morning, the panels might collectively produce considerably less than their theoretical maximum, meaning all of that electricity can still pass through the inverter.
When conditions are good enough for the panels to generate more power than the inverter can handle, the inverter simply caps its AC output at its maximum. This is sometimes known as "clipping".
Read more: Are plug-in solar panels worth buying?
The important figure for shoppers is therefore not necessarily the number printed on the solar panels.
Britain's new rules allow a compliant plug-in solar product with a maximum apparent power output of 800VA. The government specification defines a plug-in solar product as a complete system including at least one solar panel, a grid-following microinverter, a manufacturer-supplied lead and UK plug, and a mounting system.
So seeing a 1,030W or 1,260W plug-in solar kit doesn't mean a manufacturer or retailer has found a loophole in the new 800W rules. It simply means the panels have been oversized relative to the inverter. What reaches your household electrical circuit is still capped at 800W.
The structure could alter visual connections between some of Washington’s iconic landmarks
Penalties for travel to blacklisted countries have recently risen, while aid workers and activists say they have also been caught up in the law
The executive action comes as trade negotiations between Washington and Ottawa collapse, prompting 50 percent US tariffs on $20 billion worth of Canadian goods
Donald Trump is reportedly considering selling off land in Yosemite National Park to a developer.
Trump, who was nearly half an hour late to the Texas ceremony, also wound up in the awkward position of presenting the first medal to a Canadian astronaut, Jeremy Hansen, amid a raging tariff war with the US’s northern neighbors
SpaceX has pulled off its biggest salvage operation yet, recovering its most recently launched Starship from the Indian Ocean
Barron Trump ‘doesn’t go out,’ a source familiar with his movements reportedly said
Hugh Grosvenor owns more than 1,500 listed buildings across London and three rural estates
From morning showers to evening bath time, family homes can put heating and hot water systems under pressure
The plan comes shortly after the country music icon’s death and follows an online petition signed by more than 155,000 fans
Official death toll approaches 600, with many of the missing Americans having been on a pilgrimage to a sacred site
Army helicopters ferry survivors from inaccessible areas to a camp at a barracks in Bidur
The bodies of victims swept away in Nepal’s devastating flash floods have washed up over a hundred miles from the disaster zone.
The NI Secretary said both he and the Prime Minister are committed to the Good Friday Agreement.
A senior civil servant at the Cabinet Office shared a social media post wishing Benjamin Netanyahu had died instead of Dolly Parton.
High court quashes latest restriction on Orange Order march, reigniting political row over Garvaghy Road
The boy, 14, pleaded guilty to recording information useful to persons engaged in terrorism, racially or religiously aggravated criminal damage and possessing an offensive weapon
Westminster town hall has written to the Government demanding that TfL carry out a full environmental impact assessment ahead of the scheme going ahead
Danny Kruger said anyone wanting to cast a ballot in British polls would ‘need to do it in person’ unless they are ‘literally unable to get there’.
The charge relates to the attack on ambulances in Golders Green, north London, in the early hours of March 23.

source