What to do in the event of a power outage?

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Updated – November 1, 2023

In the event of a power outage, PV systems, fuel cells and micro CHPs are of no use because what they all have in common is that they require grid synchronization to operate, which is not the case during a power outage.

The only alternative is to use a power generator to supply larger loads or an island PV system with a hybrid inverter.

Emergency generator

Power generators are available in different versions in terms of fuel, such as petrol/gas or diesel. Diesel generators are usually for larger loads (greater than 10 kW), while gasoline or hybrid generators (petrol or gas operation) cover ranges up to 10 kW.

The dimensioning results from twice the standard required load. Assuming that oil heaters, refrigerators/freezers, medically required equipment, chargers, lamps, etc. require a maximum of 1,200 W in total, then a generator with 2,500 W (2.5 kW) is the right choice.

It should be noted that all generators are not filled with oil when delivered (usually 10W30 / 10W40). You should definitely stock up on a liter of 4-stroke oil. Of course, this also applies to the corresponding operating materials, such as petrol, gas or diesel.

Depending on the duration of the power outage, sufficient operating materials should be kept in stock according to the consumption information. As an example: a 2 - 3 kW generator requires approx. 1 liter of petrol / hour at 50% load. This means that more than 24 liters are quickly consumed per day!

The installation location of a running generator should be chosen so that exhaust gases can be blown out freely, i.e. outdoors, if necessary protected from the weather. Exhaust gas routing in the wind direction away from the house.

The generator should only be switched off AFTER the consumer connections have been disconnected in order to avoid damage to the generator.

PV system with hybrid inverter

Hybrid inverters differ from conventional inverters in the ability to store excess electricity not in the supply network, but in batteries, for example. One speaks here of so-called island systems.

Various manufacturers offer such systems, both inexpensive and seemingly expensive at first glance.

If the purpose of such a system is to provide emergency power supply, then the system should be able to be used reliably at all times - not just in an emergency - and should therefore function continuously.

From my own decades of experience, I can consistently mention Kostal inverters positively. The structure, installation, operation, administration, service and warranty periods of up to 5 years speak for this.

The series Kostal Piko MP plus is suitable for smaller PV systems with outputs of up to 7.5 kWp. They already include MPPT controllers and corresponding shading and battery management with the corresponding accessories.

The purchase price, which initially seems higher, is quickly put into perspective when you look at the data for the various devices from various manufacturers.

I like to compare frequently offered “sets” that include PV modules, brackets, inverters and batteries with the previously popular compact hi-fi systems: every hi-fi manufacturer had its focus. DUAL was strong in turntables. Tuners, cassette decks, amplifiers, some other manufacturers may have been favoured. So if you wanted to be well equipped at all levels, you bought individual components. Same here. Without (comparison) hard work, there is no realistic price!

The mounting of the PV modules should also be given careful attention. It should be set up to be storm and suction proof. In regions with increasing distance from the equator, it makes sense to align them more with the sun's appropriate winter tilt. A device that allows two angles of inclination, which can be locked for summer and winter, is ideal. Especially when the sky is overcast and/or the sun is at a low position, every degree of inclination change is relevant.

A detailed description of inverters, their differences and technical details can be found here.

A concrete planning aid using an exemplary installation is described here.

Connect consumers

Sufficient cable lengths must be available to connect consumers.

Cable drums with 3x 2.5 mm² serve to distribute the electricity generated in the building. Smaller cable cross-sections should be avoided in order to prevent overloading/heating of the cable and to minimize cable losses.

Cable cross-sections and line losses for AC applications can be calculated here. The fields highlighted in yellow can be edited. Please ensure that the spelling is correct: enter 2.5 instead of 2.5!

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The cable supply of a cable drum must always be fully rolled out under load. A wound cable drum that is operated under load becomes a heater and can potentially pose a fire hazard!

Cascading multiple sockets should be avoided. Instead, several cable drums must be connected via the generator's sockets (usually two). Consumers are supplied via the built-in sockets in the cable drums.

For all connected consumers, the rated power of the generator and the cabling must not be exceeded.

Responding fuses must not be bridged or replaced with stronger ones than approved. They serve to protect against overload and possible fire development.
A trip always indicates an error/overload. The culprit must be identified by unplugging one consumer after the other.
The defective consumer may only be reconnected after the error has been rectified.

If you have a mobile home, you should also include it in the power supply so that you can access this resource in an emergency. It goes without saying that resources should be filled to the maximum here too.