Selecting a Backup Power System

Selecting a UPS, Hybrid-Inverter or a Generator backup power solution

Backup power systems are typically sold by wattage or KVA, i.e how much they put out determines not only how many lights and appliances you can run at once, but also how well.

  • kVA. A volt-ampere (VA) is the voltage times the current feeding an electrical load. A kilovolt-ampere (kVA) is 1000 volt-amperes. Electrical power is measured in watts (W): The voltage times the current measured each instant.

UPS's and Hybrid inverters will provide an efficiency rating, this percentage will determine the amount of power loss when converting DC power to AC power. The higher the efficiency rating, the better quality of product with less loss of power.

  • Power efficiency is defined as the ratio of the output power divided by the input power: η = 100% ⋅ Pout / Pin. η is the efficiency in percent (%). Pin is the input power consumption in watts (W). Pout is the output power or actual work in watts (W).


In order to determine the size or KW/KVA rating of the required backup power solution for your needs, the following information will be required:

List what matters to you. Some common essentials are the refrigerator (about 800 watts), geyser (3000W-6500W), electric stove (1800W-5000W), sump pump (750 to 2,500 watts), portable heaters (3,500 watts), window air conditioner (1,500 watts), lights (Led up to 60W to and Halogen lamps around 600 watts), and computers (60 to 450 watts). Reliability matters, too. 

Map the outlets and switches in your house to know which circuit on the distribution panel powers what (only for UPS's and Inverters) if you only require essential items or essentially a dedicated circuit that will be utilized


UPS/Inverter or Solar load requirements

       Phases and Voltage
       Single Phase (230V) - Normally for domestic use
       Three phase (400V) - Mainly for industrial use


Generator load requirements

       Phases and Voltage
       Single Phase (230V) - Normally for domestic use
       Three phase (400V) - Mainly for industrial use
       Three phase (525V) - Mining industry
       Three phase (11kV) - Special applications

Generator panel requirements

      Must the panel allow for selecting between ESKOM and generator or  is the generator the only power source?
      If selection is required, must the selection be done automatically or manually?
      The selection will also determine if the generator will start automatically or manual.

Generator Canopy

The main functions of a canopy is attenuation and weather protection. With normal canopy designs, sound levels will typically be between 75dB and 85dB at 10 meters, depending on the size of the engine. Please specify for super silent canopy requirements.                 

Special requirements

    •  Water/coolant heater. The purpose is to prevent cold starts in cold regions.
    •  Dummy loads. It is essential that a diesel engine operates under at least 60% of its rated output capacity at 80% of its running
        time. It is harmful for diesel engines to operate under low load conditions for long periods of time.
    •  Fire switch
    •  Fuel filler pump. Manual or electrical
    •  Audible and visual alarms
    •  SMS systems. These are very powerful systems for status updates and long distance control. The possibilities are endless.

Generator synchronization systems

The basic characteristics of a synchronization system are:

    •  Any number of machines up to sixteen can be synchronised to a single load.
    •  The PLC will determine the load requirement over a short period of time and automatically determine the number of machines
        required for the demand. The PLC will select the machine with the highest amount of hours and switch it off.
    •  When the demand increases, the PLC will automatically start and synchronize the required amount of machines to increase the

Advantages of a generator synchronized system

    •  In cases of supply demand higher than 700kVA, there is a significant cost saving on the purchase price and fuel usage.
    •  Due to the nature of the system, engines will rarely run under low load conditions. This will increase the life expectancy of the
    •  Multiple machine systems have the advantage of having spare capacity when one machine is down.