Germany has seen a massive surge in the installation of plug-in solar systems. The number of small systems registered increased more than seven-fold in the first quarter of 2023 compared to the same period last year, according to official figures.

"The market is gigantic," plug-in solar advocate Christian Ofenheusle told DW. He runs the Berlin-based company EmpowerSource which promotes these relatively cheap mini systems. By 2030, he predicts there could be "12 million plug-in solar systems in Germany."

Small solar systems are also becoming increasingly popular in China. In the megacity of Hangzhou, they're a common sight on large apartment buildings, according to Hans-Josef Fell, president of the Energy Watch Group, a renewables think-tank in Berlin, and former Green Party lawmaker. 

In Italy, meanwhile, the largest electricity supplier, Enel, is also promoting this form of plug-and-play home energy generation.

There is "a great deal of interest" in the technology in other European countries such as Poland, France, the Netherlands, the UK, Austria, Switzerland and Hungary, said Ofenheusle. Each of the states has also tried to cut the red tape around installing such units. 

Germany too plans to simplify the installation of the devices, with advocates saying they could complement the energy transition if enough people install them. 

But how do plug-in solar modules work? 

Residents can produce solar electricity themselves with one to three photovoltaic modules hung on balconies or walls, or installed on a terrace, roof or in the garden. Most importantly the devices don't require installation by a tradesperson. 

The direct current from the solar module is conducted to a small box where it is converted into grid-standard alternating current (AC) by an inverter. The unit can then be simply plugged into a standard wall outlet. 

How much electricity does balcony solar generate? 

Solar modules produce the most electricity in direct sunlight, which is why they are especially productive in sunny regions and in spring and summer.

In sun-drenched parts of Africa, the Middle East, Australia, China, Latin America and the US, a 400-watt module can generate up to 800 kilowatt hours (kWh) of electricity per year. It's about half that in less sunny Germany and Central Europe.

But module placement is also key. It is optimal to align the modules facing south and at the best power-yielding angle.

A 400-watt module installed on a south-facing facade or balcony in Germany perpendicular to the sun's rays, generates an average of around 260 kWh of electricity per year. A module facing east or west can still generate around 190 kWh annually.

Is a balcony module sufficient for a home's electricity needs?

A plug-in solar module will only cover part of energy demand in industrialized countries where per capita electricity consumption is relatively high. A four-person household in Germany consumes on average about 4000 kWh annually, with a single person using around 1500 kWh.

Still, electricity generated can help reduce power bills, say advocates.

In spring and summer, a south-facing 400-watt module with an optimal inclination angle can generate up to 320 watts on average, half as much when it is slightly cloudy and only about 50 watts when it is very cloudy.

In autumn and winter, mini systems generate 160 watts when the sun shines and only 20 watts when it is very cloudy.

So even in the dark of winter, there is enough power for an internet router, for example, which consumes around 10 watts. And a balcony module can almost always supply enough power for a small 80-watt refrigerator and a laptop of 40 to 100 watts.

But a plug-in module isn't enough to run a powerful PC with two monitors of around 900 watts, a 2000-watt washing machine or even a kettle, which uses between 600 and 2000 watts. 

What do plug-in solar systems cost?

Plug-in solar systems with one to three panels cost anywhere between €400 and €1200 ($449 to $1,348) in German online stores. 

With electricity prices currently around 30 to 50 cents per kWh, the panels will pay for themselves in six to nine years, said Thomas Seltmann of the Berlin-based German Solar Industry Association, which represents the interests of some 1000 solar businesses. 

Thereafter, electricity the module generates is free — and will be for at least another ten years. Solar panels today last on average more than 25 years, while inverters work for up to 15 years. 

How safe are plug-in solar modules? 

"Basically, plug-in solar units are very safe. No damage has been reported so far," said Seltmann.

However, he recommends buying such systems from specialized dealers or online retailers who ensure all the components are matching and provide installation instructions and advice. The VDE, a German technical and scientific institution that tests and certifies electrical equipment, components and systems, makes similar recommendations, for purchasing the devices. 

Such modules are also becoming increasingly available, with 25 of 27 European Union member states approving the systems — only Belgium and Hungary don't yet allow balcony solar. Germany is also considering increasing the maximum limit of the systems from 600 to 800 watts.  

When installing the modules, residents should ensure they are well secured and anchored to balconies or walls so they can withstand wind and harsh weather conditions. 

A DIY energy solution 

Experts in the solar industry agree that plug-in solar units will only be able to cover a small part of future electricity demand.

But the balcony modules also allow users to "have fun" generating their own solar power, while promoting climate friendly energy solutions, said Leo Ganz from Bonn-based international market research company, EUPD.

"These balcony solar installations are super important to mobilize people for the energy transition," he said.

This article was originally published in German.