Alternative supplies to use during loadshedding or power outages

Various backup systems exist in the market to assist customers with an alternative power supply during load shedding to sustain power to their essential electrical equipment. Fuel Generators, un-interruptible power supplies (UPS) and hybrid grid tied photovoltaic systems (PV) are the main systems of choice, however each system has its own features and capabilities. A long backup inverter-charger system, basically a UPS with a larger battery storage capacity, is well suited for longer periods of power interruptions, in particular for the residential and small business sector. Unlike fuel generators that cause noise, air pollution and need refilling and maintenance, these systems could be installed indoors in confined spaces, as long as they meet the correct ventilation requirements. Figure 1: Battery Backup Power System (Source:

Omnitech.co.za)

Fully automated UPS/Inverter System Installation methods The system is fully automated which reduces human interference, thus reducing the Systems can be a stand-alone system risk of electrical contact or manual change-over of and cables. The or can be wired into the main permanently connected system is connected to the mains and constantly charges the . Smaller stand-alone batteries through the charger. During a power failure, the sinewave inverter systems could be a mobile unit that automatically converts the DC battery power to AC power to run the permanently includes a battery cabinet on wheels connected essential equipment. The automatic change-over occurs within 15 with the inverter-charger on top for the milliseconds, which is fast enough to supply backup power without affecting standard Do-It-Yourself (DIY) market and equipment. A standard UPS system has an even quicker automatic change-over connected with ease to a standard wall speed but the battery backup capability of approximately 5 -10 minutes, which is ideal socket. This can power a TV or for sensitive equipment such as servers and medical equipment. personal computer, however the hard- wired option done by a registered As soon as the main supply is restored, the automatic change-over reverts back to its electrical contractor has the ability to normal power supply to the equipment and recharges the batteries. supply more equipment from a single correctly sized system. It is best practice to install the hard-wired system in an unoccupied room of the house such as the garage or basement, and store the battery sets in a specifically designed battery cabinet with adequate ventilation vents and which is lockable. Away from explosive or flammable material. Various battery system configurations exist - from wall mounted to staggered shelf systems to reduce space Figure 2: Stand-alone DIY Figure 3: Hard-wired system (Source: Victron) system (Source: Ellies) System sizing The sizing of the system depends on the load and backup duration required. Inverters are available in various power ratings, starting at a couple of 100 to thousands of Watts. An installed equipment load, start-up requirement and backup duration need to be determined and the inverter needs to be sized accordingly.

Standard equipment such as TVs, decoders, sound systems, lights, a kettle, security systems, garage and gate motors can be connected to an inverter-charger of 5kW or lower. However large systems, 5kW and above, are needed for equipment that uses large amounts of power such as your geyser, stove, washing machine, dishwasher, tumble dryer and air conditioning systems – and you need to add up the power ratings in watts for all of these to determine the total equipment load in Watts. Electrical equipment is rated at a continuous load rating, however some equipment that has electrical motors have a start-up peak rating of 3 to 10 times the continuous . For this reason inverters are rated in continuous power and peak power, of which the latter can only be supplied for a short period, usually when the equipment starts up. Both of these ratings need to be considered during the sizing process and it is advisable to oversize the continuous load rating by a minimum of 20%.

Equipment with a resistive load (electrical element) such as a kettle does not have a start-up load, therefore a 2 200 inverter will be able to supply the kettle. In case of an inductive load (electrical motor) the start-up load could be 3 to 10 times more than the continuous load. A typical inverter of 2 000 Watts continuous power and 5 000 Watts peak power is needed to supply an electrical motor with a continuous output of 1 600 Watts and 4 800 Watts start-up power (3 times more than continuous load). This type of equipment increases the size and the costs of your back-up system and home and business owners needs to decide if it’s worth the extra cost.

The battery size is determined by the backup duration needed to supply the installed equipment load and peak power requirements. A worst-case scenario calculation of maximum equipment load over the total backup period and allowable battery depth of discharge will give a good indication of sizing. If some of the load is removed or is intermittent, the backup period will increase accordingly. The recharge period depends on the depth of discharge (DOD) during a power failure, the charger size and rate of charging. If the system is sized correctly, it will be able to supply backup for a second backup period during the day if adequate recharging time is available, typically 4-6 hours.

Maintenance Battery selection The minimum maintenance is required for The battery type and size depends on the equipment load these systems and depends on the quality and duration as well as the required input to the and type of batteries chosen. By operating the battery according to manufacturer inverter-charger. Smaller inverter-chargers typically require charge and discharge requirements and a 12V input, medium sized inverter-chargers at 24V and following the Institute of Electrical and the larger inverter-chargers at 48V. If a typical 12V battery Electronics Engineers (IEEE) is selected, 1 battery is needed for the 12V inverter recommendations for battery testing, it selection, 2 batteries in series for the 24V inverter selection should be possible to maximize the life of and 4 batteries in series for the 48V inverter selection. the battery system. Deep cycle batteries are preferred for a backup application due to their ability to deliver electricity for a long time, even multiple days, because they are designed for constant discharge and charge cycles with a depth of discharge (DOD) of between 60-80%. For the smaller systems the Lead Acid deep cycle batteries are suitable – this includes technologies such as Absorbent Glass Mat (AGM) and Gel. These battery types are more affordable although the life expectancy is between 3 to 5 years. These are suited for a backup system that don’t go through continuous charge and discharge cycles, this could lead to a longer than specified life span. Larger systems require a more sophisticated battery System specifics system that is typically used for systems When designing a system, especially larger non-DIY to allow for usage cycles. Designers of these systems systems, the designer will need the following information: predominately use Lithium type batteries which ensure • Load required in Watts greater DOD, resulting in more useable capacity, more (both peak and continuous power) charge cycles and a life span closer to 10 years. Battery • Type of equipment used suppliers will specify a disposal methodology for end of life • Duration of backup units, since some of the batteries are recycled to salvage • Frequency of occurrence the precious metals. The backup system could be modular, • Installation type: stand-alone or hard-wired however the battery supplier will specify if new batteries could be installed in series with the older ones. If allowed, a Various product types exist and designing these larger time limitation will be set and typically range between 1 to 2 systems becomes complicated. Therefore it is advisable to years. make use of a competent designer

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