At the end of 2021, almost 200,000 balcony power plants were already operating in Germany; the real boom probably only came last year in the wake of the energy cost crisis. No wonder, because there is little to no bureaucracy, you don’t need an electrician (ideally) and you can save money immediately – with a manageable investment. When the balcony power plant pays off depends heavily on the framework conditions. Above all, of course, the performance and orientation of the PV panels is important. But the fact of whether you use the self-generated electricity at the time of its generation also has a major influence.
Balcony power plants are currently allowed to feed in a maximum of 600 watts in Germany; an increase to 800 watts is to come. The peak is around noon. If you consume less than you generate, you give away the energy to your grid operator; a feed-in tariff is rare for the balcony power plant. Ideally, you should use a lot of electricity at lunchtime and preferably leave the washing machine and dishwasher as well as the stove and oven running so that you don’t give anything away. But this behavior is in contrast to the typical daily routine of working people, who only come home in the evening; but then also have to wash and want to eat.
In this context, it would be useful if the energy generated at midday could be stored in order to be used in the evening. Zendure Solarflow promises exactly that – as a retrofit solution, compatible with any balcony power plant. Suitable balcony power plants in the test.
Construction
Solarflow mainly consists of two components: the smart PV hub and the battery, product code AB1000. The battery has a capacity of almost 1 kWh, the manufacturer states 960 Wh. Up to four such battery packs can be connected to the PV Hub. The structure of the components seems well thought out. The batteries look like small car batteries. They are installed in a high-quality, stable and waterproof aluminum housing. The connector is on the top, and the manufacturer has integrated a suitable counterpart at the bottom of the case. Up to four AB1000 can be easily stacked and the electrical connection between the batteries works without cables.
The core is the Smart PV Hub. The device looks like a slightly oversized microinverter from a typical balcony power plant. It is installed between the solar panels and the inverter. The energy flows from the panels into the hub. How much of it ends up in the battery and how much is fed in is a matter of setting. The hub is not connected to the power grid; Accordingly, it can only be reached via the app when either the sun is shining or the Zendure battery is not yet empty.
App
Speaking of the app: installation and setup are simple and exemplary. The manufacturer has integrated both WLAN and Bluetooth for reasons of convenience. The iOS app immediately found the Smart PV Hub in the test. There is not much to set, the only important thing is the maximum power of the microinverter – if you choose a value that is too high, you risk damage. In our case, a simple Hoymiles with 600 watts is used.
In the next step, you set how much energy the balcony power plant should feed into the home network in 100-watt increments. It makes sense to choose a value that just doesn’t cover the base load. With the author of these lines, the electricity meter stops at 300 watts of feed-in, as long as no large electricity consumers are running. So we chose 200 watts for the test so as not to give anything away – especially since what you don’t feed ends up in the battery. Of course, you should also make sure that the battery still has capacity to absorb the excess energy.
With the help of various graphs, you can conveniently view the performance of the balcony power plant including the battery in detail. The electricity flow animation on the app’s start page is so interesting that you keep checking how much electricity you’re currently generating and what’s happening with it. The fact that the app had a few difficulties with the translation here and if you want to see monthly statistics you have to select “Moon” – for free. Everything that is important works reliably and is understandable.
Praxis
At 380 watts, the solar panels of the connected balcony power plant are slightly weaker than the current standard. The position isn’t quite optimal either: one panel gets a little shade in the afternoon and the angle is steeper than it should be in summer. The balcony power plant with this setup generated between 2 and 2.5 kWh on sunny days.
If there were no spoilsports in the form of clouds, the balcony power plant saved the electricity bill by 200 watts between 11:30 a.m. and 11:30 p.m. – well after sunset. However, the battery was only really full on a few, very sunny days; in average weather its charge rarely went above 40.50 percent. With a battery, mind you.
The first thing to do is to improve the entry page. The best possible alignment of the panels is mandatory so that the battery can be worthwhile. Optimally aligned balcony power plants achieve almost double that of our test installation. Here we report on suitable brackets and mounting options. If this is not possible, you can at least help with additional panels, as long as you do not exceed 60 volts per input. However, you should also calculate with a sharp pencil whether the whole purchase is worthwhile: After all, the additional panels also cost a surcharge.
The invoice
Is a balcony power plant with storage worthwhile? The calculation is not entirely trivial. First you have to find out how much electricity you don’t have to pay because of the balcony power plant – because only the electricity you use yourself is “free”, not the electricity generated. You should write down your electricity meter reading several times throughout the day and determine how much energy you usually use in the morning, at noon, in the afternoon, in the evening and at night. Depending on the orientation of the PV modules, generation peaks around midday or in the early afternoon.
Anyone who always consumes more than the currently maximum permitted 600 watts does not need storage – because it would not be full if Solarflow fed the generated energy directly into the grid. Most working people need less energy during the day than in the evening. Everything that exceeds the quiescent current consumption ends up in the battery – and can then be released when the sun is no longer shining.
At a price of 36 cents per kWh and the currently discounted price of 1176 euros for Solarflow, you would first have to store almost 3200 kWh in the battery and then give it up again to make it worth buying the storage module. With a battery capacity of 1 kWh, this means 3200 full charging and discharging cycles, i.e. almost 10 years with optimal solar radiation. It is therefore difficult to operate the battery in our test setup in an economically viable manner; With a better “harvest” of solar energy and possibly a higher capacity, things look different. With two battery packs, the package currently costs 1680 euros; here you would need 2350 full charging and discharging cycles – whereby the battery, which is twice as large, of course also has to be fully charged first.
Zendure Solarflow is currently available directly from Zendure for 1176 euros or from Priwatt with a code Techstage105 available for 1071 euros.
Conclusion
Zendure Solarflow is an excellent product. The installation is easy and can also be carried out by beginners. The processing is at a high level, the app is exemplary except for minor translation errors.
Certainly the best thing about Solarflow is that it is good at visualizing energy production, storage and delivery. Because those who understand when they use how much electricity and when, how and on what scale they can generate it have taken the biggest step on their way to sustainability.
In many cases, however, storage for the balcony power plant does not make economic sense – it is simply too expensive for that, and the amounts of energy stored and released are simply not large enough. The content that fits into one of the expensive batteries is only worth 36 cents on the electricity meter – or a few more or less, depending on the tariff.
In short: the fun and learning effect is enormous. Anyone who is not only concerned with economic efficiency when it comes to renewable energies should definitely take a look at the storage facility. If you have to calculate with a sharp pencil, you are currently wrong in most cases.