Balcony power plants help reduce or even meet the basic need for electricity during the day. At least 800 watts and more output is possible in good weather if the solar system is placed wisely. However, the yield is significantly lower when the sky is cloudy. To counteract this, you can use more solar panels at the same time. But there are two problems here. Since a maximum of 800 watts can be supplied, this solution wastes power once the weather is good. In addition, any electricity generated that is not consumed immediately goes back into the general electricity grid without compensation.
In addition to batteries developed specifically for this purpose such as the Xendure SolarFlow (test report) or the Anker Solix SolarBank E1600 (test report), there are now also solutions from EcoFlow, Oukitel, SunBooster and Maintech that rely on a mobile power station as a storage system. We show which power stations are generally suitable as storage for BKW and how this approach compares to classic storage systems.
basic requirement
There are different approaches here. The new and very convenient version are power stations with integrated feed function. These are simply placed in the apartment and connected to the socket using a Schuko cable.
During the day, when the balcony power plant is supplying too much power, you charge the power station to have access to power at night. However, converting direct current to alternating current and back causes significant conversion losses. It is therefore better to replace the existing inverter and connect the solar modules directly to the power station. However, since mobile storage devices are not waterproof, the device must be installed indoors. An additional window feedthrough is then required for the solar cables to connect the panels.
With the old approach, the mobile solar generator had to be connected directly to additional solar panels and eventually work in parallel with the actual plug-in solar system. For this to be worthwhile, the power station must be able to tolerate a sufficiently high input power and have sufficient capacity. Only larger models with a capacity of around 2 kilowatt hours (kWh) are suitable here. Even better are power stations whose batteries can be extended with additional batteries. The next important requirement for storage without a special feed-in function is a sufficiently strong DC output for connection to the inverter. The reason for this is the better efficiency compared to using a 230 volt output. If you use the alternating current output, you first have to convert it back to direct current and therefore lose additional energy. The problem here: Most power stations supply a maximum of 12 volts at 10 amperes – in reality, the inverter here can supply a maximum of 120 watts. The actual feed-in will be even slightly less. In practice, this is much less and therefore unprofitable. Therefore, only power stations with strong direct current outputs are suitable – and these are rare.
The third requirement for the DIY approach is a suitable inverter to deliver the power to the household network. However, the classic microinverters of the balcony power plant require an input voltage higher than 12 volts and therefore only very low power stations are suitable for this. Although some models such as the Oukitel P5000 (test report) or the BP2300 (test report) also provide 24 volts, these are exceptions. As a rule, an additional inverter is required. We use models with an approximately 12-volt input voltage and an adjustable feed-in power of up to a maximum of 500 watts 116 euros. The small inverter is connected to the home network via a WLAN socket with current measurement (guide) and starts feeding in a time-controlled manner after sunset. With the currently used BlueTi AC200 Max (test report), up to 360 watts of power is possible. The Oukitel BP2000 (test report), which is officially advertised as a BKW storage device, has an output limited to 240 watts.
How are power stations and BKW batteries different?
In the past, the power station as a BKW storage system for a home photovoltaic system was a bricolage solution with serious limitations. It starts with the more complex integration of the memory. While special BKW storage systems are easily connected to existing inverters, the self-build solution requires you to install a second mini solar system and use both systems alternately. The actual BKW will supply power during the day, the power station at night. This is not very convenient and any excess power from the BKW will continue to be dissipated rather than being exhausted into the batteries. Another problem is the low and inflexible feed power, which is a maximum of 360 watts even for powerful devices. Ultimately, with this solution you can only set a fixed feed-in value. This is continued until the batteries in the power station are empty. We criticized this in the test of the BKW Oukitel BP2000 storage device (test report).
Made by human hands: photos from week 26
An exception are the classic power stations from ecoFlow, which are also perfect as BKW storage thanks to the ecoFlow PowerStream inverter (test report). The manufacturer’s own inverter with app control replaces the classic microinverter of the balcony power plant and thus enables a powerful connection to the power station. In this solution, the solar panels are traditionally connected to the inverter. To make the memory really worth it, you can connect additional modules directly to the power station since the last firmware update. In addition to convenient handling, the system also offers another advantage – dynamic feed-in is already possible via the WLAN socket from ecoFlow and Shelly. The battery then supplies only the power needed at that moment to the household network, instead of only releasing static electricity. This increases your own consumption and reduces energy costs.
Installing a balcony power plant storage system is even easier with devices that have a feed-in function on board. No additional inverter is required here. The power stations from Sunbooster (test report), Revolt (test report), Lanpower (test report), Obo Mentec (test report) and Teetven (test report) released in the last few months are currently able to control the output of electricity according to a schedule. Unfortunately, the options to smartly adapt to your needs using the WiFi socket or the three-phase Shelly Pro 3EM power meter (guide) are not yet available. However, the solar storage manufacturers have already announced the corresponding function updates to us.
However, all mobile power generators still have an advantage over pure storage options such as the Zendure Solarflow (test report) or the Anker Solix Solar Bank E1600 (test report) – in the event of a power outage, you can use the power station as emergency power storage. Once disconnected from the home network, consumers can be powered even during power outages or away from the electricity network. But here too there are now exciting approaches, such as the new version of the PV storage system from Anker, the Solix Battery, which is available with an integrated socket for emergencies.
Which power stations are suitable as BKW storage?
Below we show mobile power storage units with more than 120 watts of power via a direct current connection. Some models provide sufficient power, but are only suitable for a limited range of applications due to their low capacity.
We have not included here the special power stations with integrated feed function and the devices from Ecoflow. These can be found in the next section.
How much do specialized BKW power stations cost?
conclusion
The idea of ​​balcony power station storage as a power station is tempting, but it’s not all about the benefits. If you don’t use the EcoFlow system or one of the few models with an integrated feed function, you’ll have to live with serious limitations, as we found out when testing the Oukitel BP2000 (test report).
