Designing homes to conserve energy and use it efficiently, from sources that cause least environmental harm.

Back-up power generation

Back-up power, typically in the form of a generator, is included in most systems to top-up battery storage or meet electricity requirements during periods of low generation, maintenance, or very high energy demand.

On this page:

  • Generators
  • UPS (uninterruptable power supply) systems


Generators are often used as back-up power supply. They are commonly installed with photovoltaic and wind systems, but not necessarily with micro-hydro systems. Back-up generators give out heat and exhaust gases, may be noisy and need maintenance. Most run on non-renewable petrol or diesel, although many of these can also run on bioethanol or biodiesel blends – ask the generator supplier for advice.

When installing a generator, considerations include:

  • fuel type (and whether it can run on a biofuel blend)
  • whether to have manual or automatic operation
  • sound-proofing of the enclosure to mitigate operating noise
  • providing protection from the weather
  • separation provision from the batteries and inverters
  • an effective exhaust and silencer system
  • good access for maintenance.

A 3–5 kW (or 6–10 kW for higher demand situations) inverter-type petrol generator will suit a household back-up power requirement. As the frequency is generated by the inverter, only load varies the RPM, so it is quieter, relatively fuel-efficient and gives good quality power to run electronic items. It should be wired through a plug-in connection into a three-position main switch on the MEN switchboard.

It is usually more efficient to use a generator to charge a battery bank when it is low, rather than powering the household directly, because the generator can be run at close to its optimum load.

UPS (uninterruptable power supply) systems

UPS units vary in size from a plug-in multi-box that can power a computer for 10–30 minutes to large units that will power an office for a day. UPS systems are typically used to protect sensitive electronic equipment.

There are two main types available:

  • An online UPS generally offers the best protection as it powers the appliances continuously using grid power to charge the batteries and the inverter that supply power to the appliances. If critical power is required, this is the most appropriate option.
  • An interactive UPS has the battery and inverter on standby. As soon as the power fails or goes outside the normal parameters, the inverter will start supplying power to the appliances. Some inverters will switch to battery power within 20 milliseconds and will act as a standby UPS for all the circuits connected to them.


Updated: 20 April 2021