Which backup generator for the detached house?

A prolonged power outage can quickly paralyze a detached house: heating, cooling, light, and communication cease to function. A backup generator ensures that your home remains supplied even in the event of a grid failure. But which generator is the right one? Careful planning is key.

Introduction: Basic Requirements

Before choosing a backup generator, you should determine which devices must continue to operate in an emergency. This prevents over-dimensioning and saves costs. Typical household consumers have the following power requirements:

• Heating and Hot Water:
  – Gas heating: approx. 300 W
  – Oil heating including hot water: approx. 600–3000 W
  – Heat pump (air/water, geothermal or water source heat pump): approx. 5000–10,000 W

• Water Heater: Electric boiler approx. 600–1000 W

• Cooling Appliances: Refrigerator and freezer each approx. 300 W

• Kitchen:
  – Hot plate (standard): approx. 800 W
  – Electric hot plate: approx. 2200 W
  – Microwave: 600–1500 W depending on size

• Communication and Security: Telephone, router, TV, radio, alarm system: total under 100 W

• Lighting: LED lights approx. 15–100 W per lamp

• Water pump or domestic water system: Power requirement depends on the model

Not all devices need to be supplied in an emergency. Electric stoves and dryers have high power requirements and can usually be replaced for the duration of the outage (e.g., with a gas stove or grill). A list of priorities helps to determine the appropriate power class of the generator.

Technical Details for Selection

Power Reserve and Starting Current
Inductive loads such as pumps and motors require significantly more current at start-up than during operation. Therefore, plan a reserve of around 20–30% for the generator output. This protects against voltage drops if several loads start up simultaneously.

Single-phase or three-phase?
Most household appliances run on 230 V (single-phase). Three-phase generators distribute their power across three phases; if these are unevenly loaded, the voltage can fluctuate. If no three-phase appliances are present, a single-phase generator is often the better choice. For heat pumps or large pumps, a three-phase unit is necessary; then it should be sufficiently dimensioned to cope with unbalanced loads.

Fuel Choice and Runtime
Diesel generators are considered robust and are designed for longer runtimes. Gasoline generators are more suitable for shorter uses and are often cheaper. For gas appliances, fuel storage is uncomplicated, but they are less common. Remember to store fuels in safe, shatterproof containers and only keep legally permissible quantities.

Correct Connection to the House Grid

A common myth is that a backup generator can simply be fed into the house grid via any power outlet. This is dangerous and prohibited: Connecting via a power outlet can lead to damage to the house installation and carries the risk of electric shock. Furthermore, there is a risk of uncontrolled backfeeding into the public grid, which endangers both grid operators and other households.

To avoid this, the generator must always be connected via a professionally installed grid transfer switch (transfer system) or ATS. This ensures that the house system is completely disconnected from the public grid during emergency power operation. The installation of such a transfer system may only be carried out by a qualified electrician. In addition, RCDs (residual current devices) and proper grounding of the generator are mandatory. Without these safety mechanisms, life-threatening situations and, in the worst case, the destruction of your generator due to uncontrolled voltages and frequencies are imminent.

Safety and Operating Instructions

A backup generator must never simply be fed into the house grid via a normal power outlet. According to the guidelines of grid operators, the installation must be designed to ensure a safe and all-pole disconnection between the public grid and the emergency power supply. The most important points:

• Grid Disconnect Switch: A transfer switch completely disconnects the house grid from the public grid before the generator is switched on. Parallel operation is only permitted for short periods for synchronization and is generally not required for simple house systems.

• Prevent Backfeeding: No energy from the generator may flow back into the public grid, as this can lead to dangerous voltages and damage to the installation. An automatic circuit ensures that the grid is only reconnected when the public supply returns stably.

• RCD and Grounding: A residual current device (RCD) must be present to prevent dangerous contact currents. The generator must be properly grounded; for models with insulation monitoring, grounding is not required if this function is provided.

• Professional Electrical Installation: Planning, connection, and maintenance should be carried out by a qualified electrician. This ensures that the correct cable type is used, the transfer device functions correctly, and all regulations are complied with.

• Regular Tests: Regularly run the generator for test runs; this ensures that it starts immediately in an emergency. Also observe maintenance intervals for oil and filter changes.

• Location: Always place the generator in a well-ventilated area so that exhaust gases are safely discharged and there is no risk of carbon monoxide poisoning. It must never be operated in enclosed spaces.

Conclusion

A suitable backup generator provides security and autonomy in a detached house. Crucial are a careful needs analysis, correct dimensioning, and a secure connection via a grid transfer switch. Observing technical details such as starting currents, phase load, and fuel storage ensures trouble-free operation. When selecting and installing, it is worthwhile to consult experienced specialists – we will gladly help you find the optimal generator for your home.