In the event of a power failure, PV systems can use a power storage unit to provide emergency power or backup power. But by no means all solutions are suitable for this.
The positive trend in the expansion of PV systems with electricity storage is likely to continue in the future. According to an Eon survey of 10,000 homeowners, 72 percent of those surveyed who want to invest in a PV system want to combine it with an electricity storage system. Another twelve percent are planning a later purchase. An emergency power solution is important for 77 percent. In addition, the strong increase in the registration of e-cars should also promote sales of PV systems with electricity storage. Over 600,000 electric vehicles are now registered in Germany. In 2019 it was less than 100,000. One reason for the increasing popularity of electric vehicles is that many are looking for alternatives to vehicles with internal combustion engines in order to become less dependent on rising prices for fossil fuels.
PV system with emergency power function
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 a corresponding emergency power function.
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 consumers 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 grid in the event of a power failure. If three-phase loads are also to be supplied, a corresponding inverter is required. 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 isolated operation is not recommended, since the inverters used are 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 a year, you can live with this limit in this country.
Other inverters such as Sungrow models switch over much faster at 20 ms. The latter are also used by electricity providers such as Eon in combination with BYD storage. However, the Eon solution only provides backup power for a maximum of three circuits. Since the Sungrow inverter already contains circuits for disconnecting from the public power grid, interested parties do not have to invest in a switch box from Enwitec, which costs more than 1000 euros – the only one on the market.
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 should also be considered. 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.
The power storage devices S10 Mini, S10 E, S10 X 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 outlet, 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.
Since an interruption to the supply of electricity in Germany only lasts 10 minutes on average over the year, an emergency power supply or backup power supply 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 last year, according to Ingenieur.de, Europe narrowly avoided a blackout.
With the emergency power function of many power storage devices, there is a 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.