Sales of photovoltaic systems with electricity storage (guide) or solar storage, as the batteries are also called, have been increasing significantly for years. While only around 42 percent of newly installed solar power systems were combined with battery storage in 2019, this proportion rose to almost 75 percent last year. In 2022 alone, more than 197,000 power storage units were newly installed or retrofitted together with a PV system across Germany – in 2019 there were only 42,000. A total of 269,000 solar systems were put into operation last year, which corresponds to an average annual growth of 46 percent since 2019. The addition last year totaled 7.2 gigawatts.
So the energy transition is in full swing. And the more heat pumps and electric cars are in use, the more worthwhile is a photovoltaic system including battery storage and wall box (guide). Over 1 million e-vehicles are now registered in Germany. In 2019 it was less than 100,000. Sales of electric cars are also likely to increase in the future, as many consumers are looking for alternatives to vehicles with internal combustion engines in order to become less dependent on rising prices for fossil fuels. And what could be more obvious than producing the energy for it yourself. Especially in times when the components for the production of self-generated electricity such as solar panels, inverters and battery storage are significantly cheaper than in 2022. After all, the legislator has suspended sales tax for these components since the beginning of the year.
In addition to a higher self-consumption rate and the resulting lower energy costs, many want a power storage device that also offers an emergency power function. This is also shown by a survey by Eon among 10,000 homeowners. 77 percent of those surveyed who want to invest in a photovoltaic system would like to combine it with an electricity storage device that also offers an emergency power solution. The reasons for this could be the sharp increase in the registration of e-cars and the increasing spread of heat pumps, which operators of solar systems would like to continue operating in the event of a power failure.
The geopolitical developments of the last few years with rising energy prices are also increasing the desire of many for more self-sufficiency in energy supply. At TechStage, too, we are registering a strong increase in the number of hits for corresponding reports: the most read articles in recent months include articles about solar power stations and electricity storage for photovoltaic systems.
PV system with emergency power function
It therefore makes sense for owners of photovoltaic systems to use the PV power themselves and benefit from it in the event of a power failure. However, most photovoltaic systems are not designed for an emergency power supply. They are usually connected to a functioning power grid. If this fails, the domestic solar system is automatically disconnected from the grid and the conversion of solar energy into electricity is stopped. This is for security reasons to protect anyone attempting to restore power to the public grid.
In order for a PV system to be able to supply domestic consumers with electricity in the event of a power failure, suitable inverters must be used in combination with a power storage unit and an emergency power function.
The inverters Primo GEN24 Plus (single-phase) and Symo GEN24 Plus (three-phase), which in connection with power storage units from BYD landed in the top places in the test of the HTW Berlin in the last power storage inspection (guide), offer such a “basic emergency power supply”. . This is a socket that is supplied with power in the event of a power failure, which Fronius calls a PV-Point and supplies single-phase loads of up to 3 kW. However, this can only be used to supply electricity to individual devices. In combination with a compatible power storage unit from BYD, the Fronius inverters can even continue to charge it with power from the photovoltaic system. Without simultaneous charging of the power storage, the supply of emergency power ends when the capacity of the battery is exhausted.
However, such an emergency power function is likely to be too uncomfortable for most users, since not all consumers in the house benefit from it.
PV system with backup power
If you want to supply all electrical devices in the house with electricity in the event of a power failure, you have to implement circuits in addition to inverters and power storage units that disconnect the entire house network from the public power grid in the event of a power failure. Appropriate inverters are required if three-phase consumers are also to be supplied. In addition, the components must be “black start capable”. Originally, the term was used for the ability of a power plant unit to start up independently of the power grid from the shutdown state.
As a rule, however, continuous operation of the so-called island operation is not recommended, since the inverters used are often not designed for this operating mode on a permanent basis. For example, Fronius limits stand-alone operation to 15 percent of usage time. That would be almost 55 days per year. Since an interruption to the supply of electricity in Germany averages only 10 minutes per year, you can live well with this limit in this country.
On top of that, the changeover to island operation can take some time. With the Fronius inverter, it takes around 90 seconds for the system to disconnect from the grid after a power failure and switch to self-sufficiency (see video).
Other inverters such as models from Victron, SMA or Sungrow switch over much faster with 20 ms or less. Since Victron, SMA and Sungrow inverters already contain circuits for disconnecting from the public power grid, interested parties do not have to invest in a switch box that costs more than 1000 euros.
In addition to the Multiplus II 48/3000 from Victron Energy, the more powerful models 48/5000, 48/8000 and 48/10000 are now also certified in Germany.
However, the selection of a power storage unit and a suitable inverter should not be reduced to the emergency power function alone. The maximum charging and discharging power also plays a role. In addition, the energy efficiency of the overall solution is certainly of greater importance for the profitability of a PV system. The University of Applied Sciences in Berlin (HTW) carries out corresponding tests every year.
This also applies to solutions from RCT-Power, which recently won the efficiency test of the HTW for electricity storage with 10 kWh. With the RCT Power Switch Box, the German manufacturer also offers a solution that enables backup power to continue operating the photovoltaic system together with the battery storage in the event of a power failure. The box disconnects the photovoltaic system from the public power grid within 10 seconds and switches to self-sufficiency, while the power storage unit continues to be charged. It is compatible with the RCT power storage units with 4, 6, 8 and 10 kW, with the first two variants only offering single-phase backup power operation with up to 6 kW of power. The larger models, on the other hand, offer three-phase backup power with up to 10 kW.
The power storage devices S10 Mini, S10 E, S10 X, S10 X Compact and S10 Pro from E3DC, which the manufacturer calls home power plants, are also prepared for a power failure. Except for the S10 Mini, which only offers an emergency power socket, the other solutions support three-phase backup power operation, for which the power storage devices are disconnected from the public power grid at all poles. All that is required for the three-phase backup power is a motor switch, which is subject to a surcharge and is installed in the factory when ordered or can be retrofitted later. Expensive conversions – even with subsequent installation are not necessary. In practice, the backup power function of E3DC has proven itself with one of our readers.
Subsidies for PV systems and electricity storage
Commissioning and purchasing PV systems has been significantly easier and cheaper since the beginning of the year. The basis is the amendment to the Renewable Energy Sources Act (EEG), which came into force in 2022. Most of the regulations, as well as the waiver of sales tax when purchasing solar modules, inverters and power storage systems, have been in effect since January 1st, 2023. The federal government has significantly increased the feed-in tariff. For systems with self-sufficiency up to 10 kWp, the federal government pays 8.2 cents per kilowatt hour for 20 years and 7.1 cents for systems between 10 and under 40 kWp. From an output of 40 kWp it is only 5.8 cents.
Despite this increase, the market price for a kilowatt hour of electricity is many times higher, so that the personal contribution to consumption should be particularly high. A storage battery helps with this project. It stores the energy generated by the PV modules during the day and passes it on to consumers at night, so that in the best-case scenario no expensive electricity has to be drawn from the grid. Numerous online tools from the HTW Berlin University of Applied Sciences reveal more about this.
Conclusion
Since a power outage in Germany only lasts 10 minutes on average per year, a self-sufficient power supply using a PV system and suitable battery storage does not necessarily appear to be an indispensable feature. But the first impression could be deceiving. The stability of the power grid depends on many factors. Insurance companies have been registering an increase in natural disasters for years, some of which caused significantly longer power outages in the affected areas. And two years ago, according to Ingenieur.de, Europe narrowly avoided a blackout.
The current geopolitical situation with the threat of gas supply failures could also cause a power shortage in Germany with its many gas-fired power plants, which could make it necessary to temporarily switch off certain consumers. After all, the share of natural gas in electricity generation in 2022 will be almost 11 percent. The Federal Network Agency has already implemented the legal framework for switching off certain consumers in the event of a power shortage.
Photovoltaic systems, in combination with power storage, can supply all consumers in the home’s power grid with backup power in the event of a power failure. For this purpose, however, suitable inverters and matching power storage devices must be used. This is associated with additional work, which causes costs of between 500 and 2000 euros. The manufacturers support the installation of such solutions with free circuit diagrams and component lists, so that owners of PV systems can contact electricians with them. The video by YouTuber Eigenwatt shows how such a system works in practice.
With the emergency power function of many power storage devices, there is a more cost-effective variant that can only supply a few devices. Here you should check whether the solution in emergency power mode also loads the memory. Otherwise the lights will go out quickly.
NOTE: Also read the follow-up article on the subject: