South Africans looking to go 100% off-grid with no backup power from Eskom should be aware that it could come at an unjustifiably high price.
The recent re-emergence of Stage 4 load-shedding has many people riled up and some threatening (again) to finally kick the power utility to the curb.
Although some households have installed backup power products to stave off load-shedding, these setups are often grid-tied, which means they still have access to Eskom power when their own systems are insufficient.
While many have grown tired of the utility’s dismal record in keeping the lights on, the truth is that severing ties with the utility is not simple — or cheap.
This was highlighted by AWPower managing director and head of operations Christiaan Hattingh in an interview with MyBroadband.
Hattingh said that while many might be frustrated with Eskom during load-shedding, the reality was that grid supply offered enormous convenience and cost benefits to households when load-shedding was not in effect.
To understand why, he said it would be prudent to revisit how home solar systems work.
Most systems consist of three primary components — photovoltaic (PV) panels, batteries, and inverters.
PV panels generate electrical energy from the sun’s light, which is transported to an inverter that can convert the energy into a form that is useable for general household applications.
Excess energy is diverted to backup battery storage for when the panels themselves cannot generate enough electricity to meet a household’s demands.
One of the big problems with these systems is that they have limited output capacity, which is determined by the inverter.
Capable, cost-effective inverters can typically output about 5kW or 8kW, unlike a single-phase household connection that can output around 13kW of grid power on demand.
With pool and water pumps, stoves, ovens, and air conditioners that have high peak power demand, backup systems can often trip unless you take meticulous care in limiting your usage at any given time.
Hattingh said that going fully-off grid would require a radical mind shift where the household becomes very conscious of how and when they use certain appliances.
“If you go the off-grid route, you need to be fully committed to knowing your system and knowing what it can do,” Hattingh stated.
An essential starting point would be monitoring systems that allow you to get a clearer picture of your usage habits.
Furthermore, while South Africa gets copious amounts of sunshine to generate electricity, it can also experience prolonged periods of overcast weather.
That can bring down the power generating potential of a solar PV system to around 10-20% of its maximum capacity, significantly reducing how much electricity is pushed into the home’s electricity network or battery storage.
For 100% off-grid capability, Hattingh said it was necessary to oversize your system to compensate for the fluctuation in solar availability.
“Whatever you think you need — you need more than double, triple, quadruple,” Hattingh said.
If you wish to carry on using power without adapting your usage habits, large households can expect to cough up roughly half a million rand for an oversized off-grid system.
Rubicon chief product officer Nick Roche agreed, saying that households using 1,200kWh on average per month are looking at R727,000 excluding VAT to go completely off-grid.
That price also excludes an optional R25,000 generator, which comes highly recommended.
However, a system that can meet around 95% of your electricity need will cost substantially less.
Eskom’s connection service fees within suburban areas are also generally not expensive enough to justify a complete cut-off. Most customers pay around R115 per month to have access to the grid.
In cases where keeping Eskom as a backup is not an option or where connection fees might be exorbitant, Hattingh advised pairing the system with a generator.
Households can use the generator to charge up the batteries on days when the sunlight does not provide enough energy to supply their home or charge their batteries to a sufficient level.
Hattingh also warned that having your grid connection disconnected by the distributor would make your house difficult to sell.
The table below provides a breakdown of three possible grid-tied systems from AWPower that Hattingh recommended for households that use an average of 600kWh, 900kWh, or 1,200kWh of electricity per month.
|Semi-off-grid backup power options|
|Average monthly usage||600 kWh||900 kWh||1,200 kWh|
|Inverter||1 x 5kW DEYE Hybrid Inverter||1 x 5kW DEYE Hybrid Inverter||1 x 8kW DEYE Hybrid Inverter|
|Excluded from cost estimate||Additional load-splitting if necessary||Additional load-splitting if necessary||Additional load-splitting if necessary|
|PV panel array size||4.14kWp (9 x 460W panels)||6.44kWp (14 x 460W panels)||8.28kWp (18 x 460W panels)|
|Est. electricity savings p/m||R1,368*||R2,401*||R3,283*|
|Payback period||6.7 – 7.2 years||5.7 – 5.9 years||5.2 – 5.5 years|
|Total system cost (incl. VAT)||R138,481 – R152 124||R196,977 – R207,439||R241,713 – R257,529|
|Estimated % of energy requirements from grid and own generation||Own generation — 95%
Eskom grid — 5%
|Own generation — 98%
Eskom grid — 2%
|Own generation — 95%
Eskom grid — 5%
|* Based on standard City of Cape Town home user tariff of R2.40/kWh for first 600kWh and R3.31/kWh above 600kWh. Annual tariffs increase of 9.06% is assumed for payback period calculation.|