Solar power with Eskom grid backup vs going off-grid — surprising price difference

There is a monumental difference in the price you would pay for a solar power system capable of providing around 95% of your electricity usage compared to one that can achieve 100%.

AWPower’s managing director and head of operations, Christiaan Hattingh, recently told MyBroadband that, for most households, he would strongly advise against an entirely off-grid solar energy system without Eskom as a backup.

Hattingh explained that going off-grid means oversizing a home’s solar power system to ensure it can meet the household’s electricity demands during cloudy periods.

When it is overcast and raining, generation from photovoltaic (PV) solar panels can drop as low as 10%.

Even with relatively big batteries, if such generation levels continue for multiple days, you will soon run out of power.

An off-grid system would need to be three or four times larger than a grid-tied system that uses Eskom as a backup when the sun doesn’t shine for extended periods.

Alternatively, you could use a generator to fill batteries, but this would also come at a high cost due to fuel prices.

Having access to Eskom’s grid provides additional redundancy should your batteries run empty or your PV generation not be sufficient to supply demand.

In addition, an Eskom connection can provide peak power of up to 13kW in average households, meaning you can easily run multiple power-hungry appliances such as stoves, kettles, geysers, washing machines, and pumps without the power tripping.

Cost-effective inverters typically only go up to 8kW of output capacity.

Hattingh provided specifications and pricing for various grid-tied systems that would require 5% or less Eskom power annually.

His estimates showed a system capable of producing 95% of the 600kWh monthly usage of a small household would start at around R138,000.

The price increases to R197,000 for households with 900kWh monthly usage and about R242,000 for 1,200kWh of consumption.

PV solar panels can produce copious amounts of electricity, but this can go to waste without sufficient battery storage, which can be expensive. Their performance is also highly susceptible to weather conditions.

Illustrating the point, Rubicon chief product officer Nick Roche provided pricing estimates for completely off-grid systems designed for similar household consumption levels — 600 kWh, 900kWh, and 1,200kWh.

Roche’s numbers confirmed Hattingh’s statements that a true Eskom-free system would cost much more.

Aside from panels, inverters, and batteries with much larger capacities, he also recommended a fuel-based generator priced from around R15,000.

“In general, more storage is better and more generation is better to cater for inclement weather and unexpected high-demand periods,” Roche said.

The result — even a moderately small-sized household with 600kWh of monthly usage would have to cough up about R437,000 for a 100% off-grid system.

That jumps to roughly R618,000 for 900kWh of usage and R836,000 for 1,200kWh.

Roche told MyBroadband that despite the cost implication of off-grid sometimes being misunderstood, Rubicon saw significant interest from various sectors looking for precisely such systems.

“It seems that this interest is driven by steeply rising energy costs, higher levels of load-shedding and general grid stability concerns,” Roche stated.

The table below compares the specifications and prices of high-capacity grid-tied and off-grid backup power systems from AWPower and Rubicon. It should be noted these prices are estimates.

Grid-tried vs off-grid costs
Component Grid-tied Off-grid
600kWh monthly (20kWh per day)
PV panel capacity 4.14kWp JA Solar or Canadian Solar 8kWp JA Solar or Canadian Solar
Inverter 5kW DEYE Hybrid Inverter 8kW Apex Oasis bidirectional inverter
Battery capacity 5.12kWh Revov R100
7.4kWh SolarMD Advanced
40kWh Freedom Won or WECO
Generator No Yes
Eskom annual power usage 5% 0%
Price R138,481 — R152,124 R437,000
900kWh monthly (30kWh per day)
PV panel capacity 6.44kWp JA Solar or Canadian Solar 8kWp JA Solar or Canadian Solar
Inverter 5kW DEYE Hybrid Inverter 10kW Apex Oasis bidirectional inverter
Battery capacity 10.24kWh Revov R100 (2 x 5.12kWh)
14kWh SolarMD Advanced
80KWh Freedom Won or WECO
Generator No Yes
Eskom annual power usage 2% 0%
Price R196,977 — R207,439  R618,000
1,200kWh monthly (40kWh per day)
PV panel capacity 8.28kWp JA Solar or Canadian Solar 11kWp JA Solar or Canadian Solar
Inverter 8kW DEYE Hybrid Inverter 10kW Apex Oasis bidirectional inverter
Battery capacity 14kWh SolarMD Advanced
or
15.36kWh Revov R100
80kW Freedom Won or WECO
Generator No Yes
Eskom annual power usage 5% 0%
Price R241,713 — R257,529 R836,000

Now read: Charging solar power users higher prices in South Africa — Eskom’s plans

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Solar power with Eskom grid backup vs going off-grid — surprising price difference