What exactly is emergency power? Is it right for me?

April 2019

What exactly is emergency power? Is it right for me?

Many people think that with a battery in the basement, they’ll automatically have electricity available if there’s a power outage. In this article, we tell you why this isn’t always the case, what your technological options are, and when – if ever – this solution might make sense.

The answer is simple: extremely unlikely. For example, the VDE (German Association for Electrical, Electronic & Information Technologies) estimates that in 2016, ultimate consumers were 99.998 percent supplied with electricity. Applied to all electricity customers, this comes to 11.9 minutes per year without power – so little that you probably wouldn’t even notice if you were asleep or away from home.


Despite the factual evidence, however, more and more people want the subjective security of their own power supply in the basement. That’s understandable, because the human brain ranks extreme events like blackouts extremely high – even if, statistically speaking, they almost never occur. So what are the options? 


VDE, Disruption and availability statistics 2016

Emergency power generally refers to a guaranteed, uninterruptible power supply. Emergency power systems kick in within milliseconds of a power failure and ensure a power supply. These systems are most often deployed by critical infrastructures like hospitals.


Backup power, on the other hand, is when a power supply is guaranteed but isn’t time-critical, meaning that it doesn’t have to start up within milliseconds. It requires that the domestic mains supply first be physically disconnected from the power grid and then the existing battery power made available to single-phase consumers: for example, via a 230-V outlet. It can also be made to supply power to the entire domestic mains supply by installing an all-pole disconnection in the meter cabinet.


Because backup power systems are less technologically complicated and therefore less expensive to install than emergency power systems, they should be the first choice for private homes. But be careful: Emergency and backup power are often confused, and backup power systems are incorrectly designated as emergency power-compatible.

Island systems are systems in which the battery can also draw power from the photovoltaic system during backup-power mode. They are generally DC-coupled systems that have the battery installed between the PV system and the inverter. As long as the sun is shining, they can help to slightly prolong the bridging time.

Although blackouts are extremely unlikely, they occur most often in winter. And because the sun shines so little during that season, batteries aren’t fully charged and simultaneous charging via an island system is ineffective. This means that the power supply can be maintained only for a very short period of time, especially if consumption is high.


You can counteract this situation by having a much larger solar plant and a higher battery capacity. However, you’re physically limited by your available roof space. Some manufacturers also offer the option of blocking off specific battery capacities for backup power. This lets you increase the amount of backup power, but it also robs the system of battery capacity that could be used for optimizing the consumption of self-generated electricity. This means that the system is much less efficient. Alternatively, you can restrict your usage to only a few selected devices, such as your refrigerator and laptop. But then you need to ask yourself whether there’s any real added value for you that justifies the investment costs.

The stability of power grids in Germany is, as the VDE has expressed it, “extraordinarily high,” meaning that there’s no rational basis for owning an emergency or backup power supply. Still, more and more manufacturers are aggressively and successfully promoting these systems, because they can earn a lot of money by playing on people’s fear of blackouts.


If you’re determined to look at this kind of solution, be very sure to check your available roof space and your willingness to have a larger storage system. Ask yourself what consumers you want to continue to operate in a blackout and how much time you want to bridge. And above all, have your electrician show you a cost-benefit analysis – because the easiest way to sell a system is to tap into the customer’s fears.

Released by Philipp Sonnauer