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As you consider taking the supply of the electricity your family needs into your own hands, you will need to work out just how much electricity your household uses. This article will help you think about that and work out a rough guide of what your power demand is. Reliable constant supply from the national grid or municipality is becoming rarer and rarer as the infrastructure in South Africa and Southern Africa ages. The reliability of the system is further undermined because the equipment for decades has not been receiving the normal, regular maintenance necessary to keep it running. Good examples of this is the increasing percentage of generation equipment which is constantly not in use (20% in South Africa) and substations fail completely after every blackout, Johannesburg had to spend tens of millions last year to replace these damaged and failed items.

One of the first steps in reducing your dependence on these big old failing centralised systems and replacing them with something you can manage and control, is to know exactly how much electricity your household uses. Once you know that the electrical power you need to live comfortably you will be able to arrive at the size of the battery system you need.

You’ll also want to decide if you just want to provide power during the increasingly frequent blackouts or if you want to provide more of your power needs using batteries and other green power technologies. Once you know how much electricity you need to run everything in your household you can decide if you want to support it all or if you’d prefer to select some items to run and some items to leave off while you’re running on batteries. You might ask yourself, “Do I want to run with a few lights, and just the things I consider vital to your home and family’s wellbeing or would I like to just keep everything running no matter what the electricity suppliers do?

There are five main parts for me when calculating the electricity needs of the devices you want to support with your batteries. Of course, you may well choose an accompanying environmentally friendly energy generation system to keep your batteries charged like Solar or Wind systems.

  1. The big energy guzzlers
  2. The things that need extra power to start up.
  3. Consumer Electronics
  4. Security
  5. The rest
  1. The big energy guzzlers:  
    1. The biggest usage of electricity in most electrified households in South Africa is for heating water. All heating appliances such as stoves, microwave ovens, geysers, kettles, toasters, heaters, tumble dryers and hairdryers are responsible for most of the household’s power usage.
  • Extra power to start up:

Anything that has an electric motor needs extra electricity to start up. A rule of thumb is that, to start up, a device needs double the amount of power it uses to run normally the rest of the time.
b. You need to work out the demand each of these items will place on your batteries when they start if you want to run them while you are powering the house with your battery system.
c. Common examples of these items are fridges, freezers, cold rooms and air conditioners which switch on and off as they work to maintain a constant temperature, as well as pool pumps, borehole pumps, gate and garage openers, washing machines and tumble dryers.

  1. Consumer electronics:
    1. These are the devices we use for entertainment like Tv’s, decoders, set-top boxes and game consoles, for staying connected to the internet like WIFI and Fibre routers, laptops, printers, computers and their screens, and mobile devices like tablets and phone which need charging.
    1. Remember that some of these devices may be sensitive to power fluctuations and need steady voltage or they may be damaged. This is why batteries may well be preferable to a generator if you are looking to reduce your dependence on the grid.
  1. Security:
    1. This covers your alarm systems, security lighting, electric fences, beams, cameras, all of which draw some power to keep your family or business safe.
  1. The rest:
    1. This is a set of items that we often hardly think about. It includes lights, lamps, a vacuum cleaner or iron and anything else you may want to plug in.

You need to choose if you would like to be able to turn on all the lights in the house and those outside during a blackout or if you are prepared to have only a selected set of lights on at any one time.

Please note that the power ratings presented in this article are examples from device we checked, yours may differ. These figures may be used for estimates, but nothing works as well as getting all the info together from your household. are Your home or business power needs may vary depending on the exact ratings of the items you wish to support through battery power.

Here is an example of one way to work out what load you would want to support. In this approach you take the total running power requirements of all the devices and then add additional power to be able to start one device at a time (obviously if we take the rating of the device that is most power hungry when starting we’ll have enough power to be able to start any of the smaller items).

In this example your household demand to run the list of items above would be 1 900W or 1.9kW (Take the item with the highest starting power demand + total running power demand for all other items = total wattage needed). Obviously if you wanted to support all these items and be able to start them all together then your total possible demand would be 2700W or 2.7kW.

To decide on the size of battery system you would need you take the demand you have calculated and work out how many hours you would like to run those items on battery for. That give you an answer of kilowatt hours. So, using the above example we would want to have 1.9kW, add a little for peace of mind to get 2kW, then you decide you want to run those things for 4h from 6pm till 10pm, that will give you an answer of 2kW x 4h = 8kWh