5kW Battey/8kW Inverter Advice Needed


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May 13, 2023
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I am looking to install a solar system for my house but in a phased approach to limit initial costs. Phase 1 would be to ensure constant power supply (i.e. eliminate loadshedding). Phase 2 would be to reduce monthly electricity costs (currently approx R3000pm).

My average power usage (tracked over last 8 years) is 37.5kWh per day, 33% of which is due to my geyser alone (a single 200l, 4kW Kwikot geyser).
I have CBI timers installed on my geyser and pool pump. I also have a gas stove.

  • Phase 1: install 8kW Sunsync Inverter with a single 5kW (1C) battery (i.e. essentially operating as a UPS) to ensure constant power supply through loadshedding. Loadshedding in Port Elizabeth is currently no longer than 2 hours at a time which i dont expect will change in the next 6 month when i expect to be able to proceed with phase 2. As part of phase 1 loads will be split into essential and non-essential with essential circuit operating lights and plugs only! Geyser and pool pump will of course operate off non-essential circuit.
  • Phase 2: begin adding solar panels and additional batteries (in 5kW increments). The timing of phase 2 would depend on available finances as well as when i could source my prefered black on black panels (aesthetically nicer) which are proving difficult to source. The number of panels and batteries installed is subject to a cost comparison calc based on the note below.
Note: As the NMBM municipailty allows for feeding of power back into the grid a completely off grid system (many panels with many batteries) is not necessarily required.
My understanding of the principle (disregarding baterry storage) is as follows:
In general residential solar systems generate power during off peak periods (sunlight hours) with any surplus power pushed back into the grid at a "low" tarrif. Approx 70% (not sure if this is accurate) of daily power is then drawn during peak and night time periods (peak periods = high tarrif) resulting in a cost differential that is charged by the municipality (ToU tarrif). Should this cost differential over the lifespan of a battery be lower than the cost of a battery itself (required to store excess power), then it makes sense to rather use the grid as a battery (rather than store self generated power in expensive batteries).

  • I have heard it is not good practice to install a battery with a lower capacity than the inverter size (in this case 5kW battery with 8kW inverter). Although i realise a 5kW (1C) battery will mean the inverter is unable to operate as max capacity, considering this phase is only for 2hr loadshedding periods to feed essential loads, is this anticipated to be a problem?
  • Once installed should the 5kW battery ultimately end up regulalry tripping during load shedding (should essential loads exceed +-5kW), i could install a second 5kW battery.
  • I am considering using the iGen3 5kW battery which is locally manufactured and therefore locally supported. I understand it is a LiFePO battery, 1C and is compatible with Sunsynk inverters. It appears also to be reasonably priced. Any thoughts and or alternatives?
Any thoughts on the above solar setup would be highly appreciated.