6 Year Off-grid Case study – AWPower’s sustainability project house

In March 2016, AWPower engineers designed and installed an off-grid solar PV system in its sustainability project house in Glencairn, Simon’s Town.

The plan was to follow a modular approach by expanding the system to a full off-grid solar PV system that would use the grid as a backup during typical Cape Town winter rainy days.

Main considerations when the system was designed:

  • The solar PV system should be able to support the full load of a 4-bedroom house of approximately 400 square meters, a granny flat, 4 bathrooms with two geysers.
  • The geyser elements were reduced from standard 3 kW to 2kW to reduce peak load.
  • Provision was made to deploy a fully integrated rainwater harvesting system consisting of 16.5kL of water collection and storage tanks, feeding harvested rainwater through a Variable Speed Pump (VSP) through carbon and UV filters to the household.
  • Charge station for a BMW i3 Electric Vehicle with a charging capacity from 1.5 to 5kW was installed.

South Africa is the perfect location for an off-grid solution. Says Henri Hattingh, owner of this off-grid house:

“A great feeling about living in this house is when I get into the hot shower, knowing that the water was harvested from rainwater, and heated by the sun through solar PV. When driving my BMW i3 Electric Vehicle (EV) on my daily 55km round trip to the office in Kenilworth, having charged the batteries from solar-generated power at zero cost… knowing that using my Pajero on the same trip would have cost me approximately R160 for the diesel. By using the EV, I was also emitting no harmful gasses into the environment.”

“I have not mentioned loadshedding, because we are not aware of it. Last week, whilst driving home at about 18:30, I noticed traffic lights without power. When walking into our house my wife was busy heating a dish in the electric oven for about 40 minutes, totally unaware of the loadshedding outside our house. I also work from my home office a lot and it is wonderful to not have any power interruptions – everything works beautifully.”

“In terms of reliability, our solar PV system never stopped producing power for the house during the past six years, except for the day that the battery capacity was expanded.”

Timelines for modular expansion

March 2016 – Install 6kW off-grid inverter, 5kWh lead-acid batteries, 3kWP solar PV.

From April 2016 – Approximate monthly cost of electricity from the grid (costs incurred mostly during winter months) reduced from R1,700 to about R300 pm.

August 2019 – Expansion to 6kWp solar PV and 10kWh lead-acid batteries, reduced cost of electricity from the grid to less than R40 per month. Total cost of the system to date: approximately R250,000.

Total saving in cost of electricity from the grid in excess of R160,000, however at the current rate of Eskom increases, the savings are growing exponentially.

Estimated annual savings of fuel costs by driving an EV (and solar charging it) to the office and back (per year) = R40,000

Future upgrades – Upgrade batteries to 10kWh Lithium in June 2022. If the load on the house increases, the battery capacity can be expanded by increments of 5kWh and solar PV expanded to 9kW.

To view the solar installation, see it here:

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