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(with or without solar panels)

NB! The examples, prices, installation, household appliance energy consumption and battery life cycles used in this example are based on averages for 2022-2023. The actual usage or costs can increase or decrease significantly depending on a varied field of factors including but not limited to Energy Demand, Quality, Manufacturers, House Hold Appliance Energy Usage Ratings & Installation Difficulty Factors. All figures are rounded to the closest decimal point for simplicity.

An inverter or UPS (Uninterrupted Power Supply) consists of an inverter and batteries that are used during power failures or load shedding
. They automatically detect power failures and transfer the load to the batteries in milliseconds. Thus ensuring no delays or interruptions while transferring between grid and battery power. The info below will help with selecting the correct battery and inverter combination to ensure sufficient power and longevity.



The parameters used below are sufficient for current load shedding schedules stages 4 to 6.


INVERTERS - There are basically two types of inverters used for Solar systems. TRANFORMER based and HIGH FREQUENCY (HF) / COMPONENT based inverters. (within these there are MODIFIED SINE WAVE & PURE SINE WAVE - We won't cover MODIFIED SINE WAVE as it is not recommended to use these at all. USE ONLY PURE SINE WAVE inverters!!!)



These are normally Chinese inverters that use semi-conductors to convert DC (Battery / Solar) power to AC (Grid / Home) power. The advantage being that the inverter is cheap to manufacture and lighter which makes shipping cheaper. They do have a huge disadvantage though. INDUCTIVE loads cannot be connected to it. INDUCTIVE loads are anything with a coil, winding, element or heater. Electrical motors use huge amounts of electricity to start eg. A 1KW water pressure pump can easily consume up to 5x (or more) it's rated power just to start., this means that the 1KW pressure pump requires 5KW just to start. An HF inverter can only supply it's maximum rated output. ie. a 5KW inverter can supply a maximum of 5KW (please note it will not be able to sustain a 5KW load for long periods). If you are planning to go "Off-Grid" or trying to completely disconnect form ESKOM do not install a HF inverter.



These inverters make use of large transformers. There are two advantages to this. They can supply 2 or 3 times their rated power for short amounts of time. This is used to start motors or inductive loads (called inrush current). The transformer also serves as an isolation between your DC (Batteries / Solar Panels) and the grid. These inverters are more expensive due to the high cost of the transformer and the weight tends to increase shipping costs. If you are looking at an Off-Grid solution then a transformer based inverter is a must.


BATTERIES - (We'll only discus Lithium)

"Rule of Thumb" your battery bank must be at least twice the size of your inverter's maximum power output rating (5KW inverter / 10KW battery - 8KW inverter / 16KW Battery). Most lithium batteries supply power at a C0.5 rate. This means it can only supply (discharge at) half of it's total power rating at any given time. eg. a 5KW battery can supply a maximum load of 2.5KW, a 10KW battery bank can run a 5KW load and a 20KW battery bank can run a 10KW load. Using "small" batteries with larger inverters will damage the inverter and the batteries. It will also cause batteries to fail much quicker than normal. (in other words, those popular 8KW / 5KW inverters with the 5KW battery "specials" on Facebook. Most of these batteries will not last 3 years)



Calculate (Inverter) - Maximum amount of appliances that could be turned on at any one time.

Check the appliance's labels for power consumption in Watts (per hour). Add all these together eg. TV (250W), PC (350W), Security Lights (200W), House Hold Lights (400W), Fridge (250W), Freezer (250W), Microwave (2000W) - This will be your inverter minimum size. 250W+350W+200W+400W+250W+250W+2000W = 3700W Inverter (minimum). In solar we use a "magic" number for almost all calculations, this no. is 1.2. we then calculate 3700W x 1.2 = 4440W or 4.4KW the closest available inverter would be 5KW. Then choose the inverter type.

(Most Chinese HF inverters have solar charge controllers built in for solar panels. This does limit the amount of batteries and solar panels that can be installed. Most TRANSFORMER based inverters do not have solar charge controller built in. A charge controller will have to be installed if solar panels are added at a later stage. Except for costs this is not a bad thing as the amount of batteries and solar panels that can be installed is limitless).



Calculate (Batteries) - How long the appliances should be powered for in hours. Lets use 4 hours.

Again Check the appliance's labels for power consumption in Watts (per hour). Add all these together eg TV (250W), PC (350W), Security Lights (200W), House Hold Lights (400W), Fridge (250W), Freezer (250W). We are going to leave the Microwave out of this equation as it will only run for short periods of time. 250W+350W+200W+400W+250W+250W = 1700W/H This how much power your batteries need to supply per hour. 1700W x 4 = 6800W/H. Keeping in mind the maximum discharge rate of most lithium batteries is 90% a battery bank of minimum 7555W / 7.55KW will be required. Using our "magic" number 7555W x 1.2 = 9066W or 9.06KW in other words we will need a 10KW battery bank. Look at the data sheet of the batteries some have 3000 cycle life and some have 6000 cycle life. Keep in mind load shedding at 4 hours twice per day means that your batteries will be cycled twice per day. This means 3000 cycles will be 1500 days. This is the batteries' life expectancy. Degradation at 25% is another factor, but we won't get into that now.



Your roof or ground space (if you choose a ground mounted system) is the main deciding factor. Very important! Remember, most Chinese HF inverters have built in solar charge controllers so you will be limited by the maximum charge rate of the solar charge controller (This cannot be increased or replaced). Most TRANSFORMER based units (Victron / Microcare) the charge controllers are installed separate, there is no limit to the amount of solar charge controllers, batteries or solar panels that can be installed.
To achieve optimum life expectancy and performance of our battery bank ideally we should charge the battery bank between C0.25 and C0.5 Using the values for Inverter and Battery sizes above we know that we need to charge a 10KW battery bank at C0.25 / 2.5KW or up to C0.5 / 5KW. Any of the below amount of panels will work 100% with this installation. Simply put, charging times will differ.

6x 465W Panels = 2.79KW (Requires a 60 MPPT Charge Controller)

9X 465W Panels = 4.18KW (Requires a 80A MPPT Charge Controller)

12x 465W Panels = 5.58KW (Requires a 100A MPPT Charge Controller)


COSTS - HOW MUCH CAN ONE EXPECT TO PAY? (NB! 2022/2023 Prices - This is not a quotation)


10KW Lithium batteries = R50,000 to R80,000

100A MPPT Charge Controller = R9,000 to R13,000

6x 465 Panels = R18,000 to R25,000


A system (Victron or Microcare TRANSFORMER inverter) , fully installed to PV GREEN CARD specification with 6x solar panels should cost around R160,000.00 to R220,000.00 (site dependent).


NB! Currently the PV GREEN CARD specifications are at a much higher standard than the required C.O.C Certificate