Side-stepping load-shedding by going green

With current global and local attention focused on health and economic turbulence, load-shedding has fallen several rungs down the concern list for South Africans confined to their homes during the nationwide lockdown. Energy experts have, however, warned that the respite is temporary; as large-scale commercial operations resume, South Africa's national electricity grid will again be under pressure. When this pressure increases, so will the likelihood of load-shedding.

In Harfield Village, a leafy suburb in Cape Town, AWPower was commissioned during the course of 2019 to design and install a solar PV system to achieve the homeowner's goal of avoiding downtime during prolonged load-shedding, while saving on electricity costs over the long term.

The homeowner's requirements were to:

* Provide fail-over electricity supply to the entire three-bedroom house for up to eight hours, powering the geyser, all internal and external lights (already previously converted to all LED), two fridges, ceiling fans, Internet router, multiple laptops and audio-visual equipment.

* Enable the washing machine, tumble dryer, dishwasher, plus electric oven and hob to be used (albeit not all at the same time) during daytime, while still allowing the battery to be replenished by a rooftop-mounted PV array.

The AWPower engineering team designed a system with the following specifications:

• Single-phase off-grid system utilising grid as a backup – (also known as a passive standby UPS utilised as off-grid hybrid SSEG);
• MLT Oasis 848 Inverter (6kVA/6kW continuous rating, 8kVA/8kW half-hour);
• MLT Nomad 4kW MPPT (oversized with 12*400W = 4.8kWp PV panels);
• If grid is available and the inverter overloads, it will bypass the batteries and be able to provide power to a 60A load (max load size of roughly 13kW, which is a typical residential house max load); and
• The geyser element was downgraded from 3kW to 2kW to reduce peak load and prevent overloading of the inverter while other appliances are in use.

The system was installed in June 2019. During the first month of operation, fine-tuning was performed to achieve the following:

• During heavy usage periods – such as early evening cooking – power is drawn from the grid instead of unnecessarily depleting the battery.
• Primary geyser heating takes place when ample solar power is available. Heat is then topped up for short timed periods to supply just enough hot water for evening and early morning showers.

During the winter and spring months, it was found that municipal electricity usage on average dropped to roughly 30% of previous levels. During summer, the system can deliver all the house's consumption needs for weeks at a time, with grid top-up only required on overcast or rainy days. Monitoring of the solar input, usage and battery patterns revealed that during many summer days, the battery would be fully charged before 11am each day. This substantial excess solar capacity enabled installation of an inverter-based air-conditioning unit in the house's home office, running effectively cost-free on days when it is needed.

According to the happy homeowner:

"Our initial goal was to side-step load-shedding, with long-term energy savings factoring in the likely continued increase in Eskom rates as a secondary objective. The system has met and exceeded expectations on both these fronts. We have not had any load-shedding downtime at all since it was installed, and the excess power during hot summer days has now enabled us to add zero-cost air-conditioning, which is fantastic! The AWPower team were very thorough in their initial design and specification, installation was done extremely neatly and professionally, and the real-time remote monitoring tools they have provided enables us to keep an eye on usage and battery levels from anywhere. Our house is now both unaffected by the worries of load-shedding and practically off the grid for a large portion of the year!"