At the moment South Africa is battling to cope with the existing problem of blackouts which is affecting our businesses and personal lifestyle. Subsequently there is a lot of “hype” around backup power (alternative power).
A lot of people might be thinking that they should be planning on being independent from Eskom power, or at least semi-dependent on Eskom power. But this can get extremely expensive and complex for the average business or home owner to manage.
We are all affected by the load shedding and from the information we have this will continue for the next 5 years or so. It is important to understand that blackouts only last on average 2 - 4 hours at a time. With this in mind people need to decide as to which services are critical in order to run their business or house during the blackouts/load shedding . Geysers on average will retain heat in excess of 5 hours. Fridges and freezers if not opened excessively will keep food cold and frozen for more than 5 hours. So it is not nessacary, at this moment in time, to worry too much about supplying power to such items. However, things like lighting, computers, etc might be extremely important to you and therefore in desperate need of power when there in none.
Not Recommended!
Air conditioners, stoves, kettles, microwaves, hairdryers, photocopiers, dishwashers, washing machines, tumble dryers, vacuum cleaners etc should be excluded from your list of essential devices that need to be run as these items use up a lot of energy. If these items are critical requirements that need to be run then this will effect your requirements and setup costs substantially.
Items such as lighting (not incl. heavy duty outdoor lights), computers, PABX (phones), Point of Sale, TV's, satellite and home theatre systems will fit into the more critical requirements on what a business or household needs to operate during the blackouts.
How Much Power Do I Need?
Base on this then, you might be asking, How much power do I need. Well power usage is measured in wattage. So what you need to do is add up all the wattage of the items that you want to supply power to to find out your total power consumption needed. Then you need to decide for how long you want those items to remain powered on. As UPS's/Inverters essentially rely on storred power, such as batteries, the ammount of stored power allong with the consumption will result in the total up time. Along with understanding what Apparent power, Active Power and Initial demand. You can then decide what size system best suites your needs.
Power Factor
The power factor of an AC electric power system is defined as the ratio of the real power to the apparent power, and is a number between 0 and 1 (frequently expressed as a percentage, e.g. 0.5 pf = 50% pf). Real power is the capacity of the circuit for performing work in a particular time. Apparent power is the product of the current and voltage of the circuit. Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power can be greater than the real power. Low-power-factor loads increase losses in a power distribution system and result in increased energy costs.
Apparent Power.
Apparent power is a measure of alternating current (AC) power that is computed by multiplying the root-mean-square (rms) current by the root-mean-square voltage. In a direct current (DC) circuit, or in an AC circuit whose impedance is a pure resistance, the voltage and current are in phase.
Active/Real Power.
Power is defined as the rate of flow of energy past a given point. In alternating current circuits, energy storage elements such as inductance and capacitance may result in periodic reversals of the direction of energy flow. The portion of power flow that, averaged over a complete cycle of the AC waveform, results in net transfer of energy in one direction is known as real power. On the other hand, the portion of power flow due to stored energy, which returns to the source in each cycle, is known as reactive power.
Unit of Measure
The unit for all forms of power is the watt (symbol: W), but this unit is generally reserved for the real power component. Apparent power is conventionally expressed in volt-amperes (VA) since it is the simple product of rms voltage and rms current.
Battery Life.
The battery capacity that battery manufacturers print on a battery is the product of 20 hours multiplied by the maximum constant current that a new battery can supply for 20 hours at 20 C°, down to a predetermined terminal voltage per cell. A battery rated at 100 A·h will deliver 5 A over a 20 hour period at room temperature. However, if it is instead discharged at 50 A, it will run out of charge before the theoretically-expected 2 hours. For this reason, a battery capacity rating is always related to an expected discharge duration—the standard duration is 20 hours.
Based on this information you should identify what is critical to you to run during these unfortunate blackouts.
Use our UPS/Inverter power calculator to determine the size of UPS/Inverted you need.
Source: Wikipedia; Keepiton