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In order to assist you in understanding the ‘tricks of the trade’,selecting the correct solution to your specific  Back-Up power problems, you need to know your options, this page is meant as a guideline only.

OPTION 1: Generator

A generator petrol or diesel, is for most of the application and requirements still the lowest cost initial investment.

a 5-6 kVA generator today will cost +- R8000, for the amount of power it delivers (6kW) and the ease to add nearly unlimited energy source at anytime (petrol), makes this a very attractive solution.

A 5-6 kVA generator is also big enough to run most of the emergency convenient required items for both houses and small to medium sized business during a load shedding.

A Generator do have the inconvenience of noise, refilling the fuel and starting it up when required.

The starting up of a generator can also be triggered by a short time UPS , for instance in hospitals and clinics a short time UPS will be used to supply power for a short period to start up a generator.

There is no fixed rule to guide one here, but I would suggest that a system that requires about 20kW continuous and/or use approximately 100kW.h per day or more,  an other alternative than a Generator becomes costly unpractical and space wise unpractical.

For instance companies or factories which run heating machines or 3 phase machinery or a office building block /Shopping mall use so much power that using an Inverter/UPS systems as a power back-up is not realistic. It is do-able, but not financially viable.

For such big systems, it could be the best to connect the critical management items, such as computers, a few lights and a servers onto a UPS uninterrupted Power Supply system and connect the main power requirements onto a generator system.

Please read the page first - There after you can click on link to assist you with calculation of your system


OPTION 2 - SHORT TIME  UPS (Uninterrupted Power Supply)

A short time UPS, is a typical UPS bought from computer shops or various suppliers. The UPS is designed for 10-30Min power backup to computers or servers doing power failures. They are not designed for LOAD shedding periods as we experience them.

You get various kinds of UPS, Online,Off line, Short term, Extended time etc. For this purpose we divide it into 2 groups only, it is either Extended time UPS or a Short time UPS. This does not mean it is a small UPS by any means.

T1 Series normal UPSA Hospital might have a 100kVA 3 Phase UPS, banks, will have 100-300kVA UPS units, these are usually by design still a short time UPS, as it is designed, to give a backup of 15 minutes - maybe to 30 minutes, this is only to allow an external other power source such an a generator to be started up and take the load over.

It is off course possible, that a 10kVA short time UPS used in an application where only 1kVA is used, will give 10x longer backup time, ie 300 minutes or 5 hours.

The limitations with using these UPS units for power backup during load shedding is 2 fold

People often do the mistake to buy a UPS, even thou they advertised as “solutions to load shedding” and add additional external batteries . This will not work, initially is does work, but within a few months those batteries do not hold charge and they damaged. Make sure, when you buy an UPS that is it a ups with External battery connection facilities and it has the ability to recharge the external batteries. Look at the specs

Specification Document of a Long time UPS

The table 1 above is a typical part of the spec sheet of a short term UPS, note is specify time of backup at full load, varied between 14 minutes and 20 minutes only


The most important aspect of backing-up power is to limit yourself to the minimum power consumption as, in so doing, you will also limit your costs! Most people are happy with some lighting, a TV and the ability to operate a computer. If you can keep it down to this, then you will make it a relatively cheap exercise. If you run energy-efficient lights, or LED lights, then your consumption will be much lower and you will thus use less battery power and get longer back-up periods as a result.

T3 Extended Time double double conversion UPSHow much  battery power you would need, would depend upon the number of appliances and the length of the power cut.  With Load shedding of up to 4-5 hours,  you would have no concerns with your geyser,  freezer, or fridge . A fridge, like a geyser, will retain temperature for 4-5 hours, depending upon ambient temperature.

If Load shedding last longer (6 hours plus) then you will have to start considering  running your fridge off the reserve backup power, and this significantly increases the costs.


A UPS is a DC AC Power inverter, with a build in battery charger and an automatic transfer switch all combined, thus all dc ac power inverters and are not UPS systems and suitable for use as power back-up systems.

A discreet build up UPS for power backup -at home (DIY -Low cost)

A discreet DIY UPS power backup system can be build up, thus using 3 components

This simple system works well for occasional load shedding's, you will typically charge the batteries up during periods of healthy power, When a load shed occur you can then plug your appliances into the inverter . This works well, it has a bit of inconvenience  it is the simplest and cheapest form of having power for power back-up periods. If you have a load which is small such as a TV it is also possible to have a battery charger with a higher power rating than the TV, in which case the load can be connected permanently

An Extend time UPS and DC AC Power inverter with charger

Peak Inverter-charger  back-up inverterAn Extended time UPS and a Inverter-charger unit with build in transfer switch are basically the same kind of system. They differ mainly by esthetic design a UPS, will typically have a computer box type layout, with external battery connection points at the back and a Inverter-charger, would look more robust

Another difference is, the UPS will unusually not allow for Peak power overloads, it will be limited tot the power it is deigned for, where a Inverter-charger unit will allow for short term up to 100% overload abilities. This is to allow for pumps /motors and fridges to be start up.

In order to choose the correct size of unit, you need to know and understand the following requirements.

The best way is to check your own appliances and see what you think you can live with (or without!) over a period of say 4 hours.  Once you have established the appliances and the wattage that they draw, you can use our template to gauge the cost of your specific application. You peak total power possibly used at one moment determines the physical inverter/UPS inverter size

Batteries is the main energy source, as a rule of thumb 1x 100A.h 12V battery store approximately 700W.h of useable energy. Thus if you have a TV of 100W which need to run for 5 hours..that would be 5 hours x 100W= 500 W.h

From the same, if you have a TV and lights adding up to 300W, which you will need to run for 5 hours, this is 300W x 5 hours= 1500W.h , you will thus need 2 x 100A.h batteries etc.  This will be discussed in detail on another page

The backup UPS/inverter unit, is then sized according to you maximum peak load I.e if you load is 800W, you need a 1kW backup inverter unit, if you have 3kW load, you need an Backup Inverter unit, which has a rating higher than that ie, 3kW or 5kW

Please refer to our site on power inverters for choices


In countries other than South-Africa or probably few Africa countries the option as a Solar Power Backup system, probably does not have place. Here however we have different challenges ,

In some of these situations we thus require an additional source of energy- something to fill up our resources, in a generator it is Petrol, but on a UPS/power inverter application we do not have an alternative, the only alternative is Sun energy by means of photovoltaic solar panel solution.

Nb: I need to highlight here that purely for occasional load shedding periods of up to 4- hours, Solar panels solutions is NOT required

We will discuss solar power backup solutions in more detail on another page “solar power backup solutions”

What is the difference between a Solar power backup solution and a normal power backup solution ?

This page is only a guideline introduction to various power backup power solutions, more detail about each is discussed within the relevant pages as per the site hierarchy. Please feel free to send us an email or give us a call, we will gladly assist

Copyright : Dr Gawie van der Merwe - PlanMyPower (PTY) Ltd