Connectors of a plug-in solar device with a solar roof in the background / photoschmidt
2024-01-01 VDE dialog

Plug-in solar devices: With standards and seals

Small photovoltaic sets for the home are seeing a boom in Germany. However, the lack of clear standards makes it hard to tell quality products and dubious devices apart. Certification under the new product standard for plug-in solar equipment is set to change that.

By Eva Augsten

Generating solar power at home is easy. A plug-in solar set can be had for just a few hundred euros from a supermarket or DIY store. Some systems take less than an hour to set up: find a sunny spot, position the module on its assembly system, clip some connections together and plug it in – done! With energy prices high and a VAT exemption in place for photovoltaic products, mini PV systems have recently been flying off the shelves faster than ever. The exact figures are hard to get a handle on, however. The latest data from the market master data register at Germany’s Federal Network Agency indicates that the country has almost 400,000 PV systems with up to four modules, the majority of which are likely to be plug-in solar devices. But although registration is a legal requirement (with fines for non-compliance), many owners of plug-in solar equipment continue to generate their power in “guerrilla” mode. Christian Ofenheusle from EmpowerSource, which has been following the technology’s development for years, estimates that there were actually around 1.5 million devices connected to the grid in Germany in summer 2023 – a figure he bases on conversations with leading providers.

First standard for feeding into final circuits

Given the sheer number of the devices, plug-in solar generators can now be considered commonplace. That said, the familiarity of such products is no guarantee that they are safe. Using DIY methods, technical amateurs can use plug-in solar power systems to feed power into final circuits that were not designed for this purpose and lack corresponding protection. The DIN VDE V 0100-551-1 (VDE V 0100-551-1) installation standard for low-voltage installations was therefore revised in 2016 to cover the safety aspects of feeding power into household sockets. The plug connections were a crucial point. The low-voltage standard requires them to protect users so that they do not sustain an electric shock from the contact pins. Along with a fixed connection, the standard requires a special energy socket for this purpose. The mains and system protection in the inverter, which prevents the feed-in of electricity if there is no frequency signal from the grid, does not in itself provide sufficient protection from electrocution.

A second update from 2016 also enabled amateur electricians to register plug-in systems rated at up to 600 watts with their grid operator. For mini PV systems, the revision of the standard marked a milestone. It was the first time there had been any such standards governing grid feed-in. However, since the norm has no legal force and there are few ways (particularly in single-family homes) to prevent people from plugging their devices into standard sockets, many solar plug-in operators have ignored this part of the rules.

The quest to establish a practical seal

It’s a situation that's obviously less than ideal, and one VDE has been attempting to address – including in a position paper in early 2023 that called for simplifications to various standards. These would include a safe solution for enabling connections to standard sockets. So far, what plug-in solar power systems look like and whether they come with instructions and safety advice has been largely left up to the manufacturers.

Two workers install a solar panel on the roof of a house

A recent study by Agora Energiewende puts the technical PV potential of roofs in Germany at a respectable 409 GW.

| / photoschmidt

Customers have often put assembly systems, inverters and modules together themselves to their best ability – not realizing that this has put them on thin ice regarding issues of liability. Serious plug-in solar providers, solar energy organizations and standardization specialists from VDE have therefore long agreed that a product standard is needed alongside the low-voltage standard. Getting such a standard on the table, however, has been a long process.

The consortium members of the SteckerSolar project, which is being funded by the German Federal Ministry for Economic Affairs and Climate Action, discussed the details of the future product standard from August 2020 to July 2023. The participants included the DKE, the German Solar Energy Society (DGS) and the plug-in solar providers Indielux and Solarinvert. The publication of the standard with binding statements on the 600 or 800 VA power limit and the much-discussed plug issue was expected at the beginning of January.

Update: Path to the product standard

2024-01-01 VDE dialog

The product standard for plug-in solar devices has been discussed for a long time, the draft standard was expected in December 2023 after the objection consultation. The objection procedure is now entering a new round.

Read more

Another key aspect of the product standard will cover how the devices are physically secured, which is currently left to the user for the most part. Providers will now have to include installation instructions and prove that their assembly method is structurally suitable.

They will be able to request certification from a recognized testing institute such as VDE to show that their plug-in solar device meets the new standard. Thanks to the certificate, consumers will be able to recognize right away whether a device is safe. “People who use a standardized device and follow the instructions will be able to prove to an insurance company that they have not been negligent,” says Arnd Roth, pointing out an advantage for consumers in the event of any damage caused by their solar installations. Roth is a technical manager at VDE Renewables, where his responsibilities include testing plug-in solar power systems.

The importance of a suitable location

VDE has already been offering certification for plug-in solar devices since September based – for now – on the draft standard from October 2022. As soon as the final version is available, certification under the new rules will begin. Plug-in solar is being advertised with sometimes impressively short payback periods. The comparison platform Verivox, for example, cites four to six years under “ideal conditions.” This assumes that a 600-watt system can produce an annual yield of 570 kWh. On top of a sunny carport in southern Germany, for example, that figure is certainly achievable. Buy a low-cost solar set and consume most of the power yourself, and your installation will quickly pay for itself.

Solar panels installed on a residential balcony, tilted slightly upwards

Plug-in solar devices mounted in a near-vertical position on balconies with partial shade often deliver less power than hoped.

| / robert poorten

Apartment dwellers, however, can’t necessarily mount their solar devices in the ideal position. HTW Berlin has therefore developed a plug-in solar calculator that enables would-be users to estimate a plausible yield in advance. The results are dampening some of the euphoria. According to the calculator, mounting a 600-watt device vertically on a west-facing balcony with partial shade would yield around 309 kWh. But depending on the lifespan of the equipment, its cost and the price of electricity, this could still make financial sense.

Quality products with ecological benefits

While the financial payback can take some time depending on the installation location, there are good signs that the environmental payoff will be quicker. According to recent figures from the Fraunhofer Institute for Solar Energy Systems (ISE), a PV system built from monocrystalline solar modules will take around 1.3 years in Germany to produce the amount of energy used to manufacture it. Even when assuming that balcony-mounted PV modules produce only around half the potential yield, the energy payback period is only around three years. Today's standard photovoltaic modules have warranties covering 25 years. Microinverter producers such as Enphase promise an equally long lifespan for their devices.

Roth has his doubts, however, that the service life of conventional PV systems will be replicated by plug-in solar, especially in light of the price war. “In the lab, we saw inverters where electronic components were only designed for an ambient temperature of 25 degrees (Celsius). These devices are being installed permanently on balconies and exposed to high temperatures. In a few years, they probably won’t work anymore,” he says. As of right now, a quality seal that considers all these factors doesn’t exist.

A “nine-euro ticket” for the energy transition

In mathematical terms, the benefits of plug-in solar for the energy transition appear limited. The German government's plans project a total installed PV output of 215 GW by 2030. Even if a quarter of Germany’s 40 million private households were to connect an 800-watt solar device, the output would add up to no more than 8 GW – better than nothing, but less than the heavy publicity around the devices might imply. In terms of its potential to generate enthusiasm, however, the plug-in technology could have an effect similar to the nine-euro ticket for public transport, which Germany experimented with in 2022. It’s easy to understand, accessible and has a direct impact at the individual level. From 2024, new legislation (not yet passed at the time of writing) is set to further simplify the use of plug-in solar devices. Among other provisions, it will grant homeowners’ associations and apartment buildings the same sort of privileges for plug-in solar as for electric vehicle chargers.

One set of laws, known as Solar Package I, will also help residents in apartment buildings jointly generate and share solar power from their roofs. Installing solar panels here promises much better yields than on balconies. A recent study by Agora puts the technical PV potential of roofs in Germany at a respectable 409 GW. Even with minimal bureaucratic hurdles, this will still need planning and agreement among residents. Ofenheusle from EmpowerSource therefore sees the easy accessibility of mini PV systems as their main benefit: “Many people decide to start with a low-cost plug-in solar device. Once they are more confident about generating their own power, they then soon invest in a large photovoltaic system”

Eva Augsten is a freelance journalist in Hamburg, Germany, who specializes in renewable energy.

VDE dialog - the technology magazine