A senior electrical safety expert has called on the government to impose a mandatory wiring inspection for any home planning to install plug-in solar.
The call comes less than a month before the launch of the scheme at the end of August, and with several retailers already selling uncertified equipment online.
Electrical safety organisations are alarmed that the government will allow most houses to install more than one plug-in solar system when it has not yet tested how multiple units would behave in an emergency.
“If the home has two or more plug-in systems we have no idea how quickly they would shut down in an electrical emergency because it hasn’t been tested”, says Mark Coles, Head of Technical Regulations for the Institution of Engineering and Technology (IET), which sets wiring safety standards for the UK. “We are concerned that the government has approved a major departure from international practice without safety testing it first.”
The idea is copied from Germany, where over a million homes now have small-scale ‘balcony’ solar systems that plug directly into a wall socket, which retailers like Lidl have been selling for as little as 400 euros.
The government hopes it will spread the benefits of cheap renewable energy to renters and flat-dwellers – who don’t have control over their own roof or the funds to install a full-scale system.
But there are significant differences between the two countries’ plug-in solar schemes and their respective domestic electricity safety standards.
Announcing its plans in March, the government framed them as a response to the cost-of-living crisis and estimates annual savings could range from £70 to £110 per year – roughly twice the average value of the abolition of VAT on electricity bills that prime minister Andy Burnham announced on his first full day in office.
But the policy has raised safety concerns around the state of the wiring in Britain’s older housing stock, the adequacy of protective devices in household consumer units and the potential for misuse. In June, five electrical safety organisations issued a joint statement warning of “increased risk of fire and danger to life”.
After a two-week consultation the Department of Energy Security and Net Zero (DESNZ) published revised plans in mid-July, a week ahead of schedule and just days before Ed Miliband’s departure as energy secretary. Statutory instruments were immediately laid before parliament and the plug-in solar scheme will go live on 27 August.
In response to the consultation, the government strengthened the product specification for plug-in solar systems but many of the new safety measures rely on manufacturers providing more written guidance and consumers following it. In a statement, the IET criticised the measures for depending on “consumers making technically complex decisions correctly every time”.
The British scheme differs significantly from the German model in that Germany allows only one plug-in solar system per home, whereas Britain will allow one per electrical circuit.
“Most houses have separate circuits for sockets upstairs and downstairs, so they could install two systems, and others maybe three” says Piers Courtney, who writes for the website Plug-in Solar, Explained. “But in principle some larger homes could install many more”.
DESNZ justified the decision as a “proportionate balance between consumer flexibility and safety”.
Another difference is that the minimum protection provided by German domestic consumer units has been higher than those in Britain since the 1980s. The wiring in 70% of British homes has not been checked in the last ten years according to an IET survey.
DESNZ insists the scheme is safe and supported by a safety study it commissioned from Arceio, a consultancy, and Eurofins E&E UK, an electrical testing firm. The study lab-tested six plug-in solar systems on a range of typical British wiring set-ups and concluded that “safe operation is achievable within representative domestic installations” without changes to wiring or protective devices – although the authors acknowledged the study could not “capture the full variability of real-world domestic installations”.
The testing did not include the safety performance of plug-in solar when more than one system is installed in a home, however. This matters, says the IET, because it could affect the speed at which the solar systems stop generating in the event of an electrical emergency.
If someone cuts through the power cable of an electric lawnmower, for example, or accidentally touches the pins of a lighting socket, they would normally be protected by a residual current device (RCD) in the consumer unit, which should cut off the power in less than a tenth of a second. If the home had a plug-in solar system, at this point it would still be generating, so power could still reach the light socket or severed cable for a short period after the RCD has tripped. The solar system’s microinverter, which converts the power from DC to AC current, should then reduce voltage to safe levels (34 volts) in another tenth of a second, according to the government’s product specification. But experts fear that with multiple systems, complete shut-down of generation could take longer and increase the risk of injury or even electrocution.
The IET wants the government to test the behaviour of multiple systems connected to the same home and further strengthen the product specification if necessary. In an interview with writefirstdraft, Mr Coles called on the government to introduce a mandatory wiring inspection for any home planning to install plug-in solar.
“It may be possible to make these products safe through the product specification alone but we don’t have the evidence”, says Coles. “The government should impose mandatory wiring inspections until it can prove plug-in solar is safe in all reasonable circumstances.”
Mandatory safety testing could increase the overall cost of plug-in solar by 50% to 100%. A standard Electrical Installation Condition Report (EICR) carried out by a qualified electrician typically costs around £200 and any remedial work – such as upgrading RCDs to the equivalent of German standards – would come on top.
The government’s safety study had already identified multiple device circuit behaviour as a priority for future work but concluded this need not delay the launch of the scheme. The energy department has also said it would limit systems to one per home until the procedure for reporting microgeneration assets to the local grid operator has been updated.
Nevertheless, the IET continues to advise consumers thinking of installing plug-in solar to have their wiring checked by a professional. “There’s just too much risk at the moment”, says Coles.
A DESNZ spokesperson said “Plug in solar panels have been rigorously tested on UK house wiring. There is no evidence that installing plug-in solar devices on separate circuits within the same property would impact safety protections.
“Already widely used throughout Europe, these easy-to-install panels could save many households significant amounts of money while supporting our drive for clean, homegrown power”.