What you need to know
What is an inverter?
This is a key component of any alternative power system. It’s an electronic device that changes direct current (such as energy stored in a battery) into alternating current (power for your home). We recommend a hybrid inverter, which can be gridtied to augment supply and seamlessly work as an off-grid solution during load-shedding. This can connect to the grid, battery backup and solar panels. To extract the maximum power from the solar panels, be sure to get one that has maximum power point tracking.
What size should the system be?
This should be a long-term investment. The inverter must be able to carry the sum of all the loads drawing power at any instant, and the battery must be able to supply the energy required. To reduce the cost, you need to decide what is essential. Lights? Your washing machine? The stove and kettle? Then you need to make sure they are as energy efficient as possible. For example, old incandescent lights use 10 times more energy than LED lights do.
Why do I need batteries for my system?
It is theoretically possible for an inverter to generate electricity for household use directly from solar panels. But the supply from panels is intermittent and often not powerful enough to reliably supply power. To overcome this problem, energy is stored in the batteries. Battery capacity is specified as kilowatt-hours (kWh) or ampere-hours (Ah). A battery with a capacity of 5kWh can theoretically supply 5kW for an hour. But if a lithium battery is discharged beyond 20% of its capacity, it loses capacity and ages faster. As a prac
solutions, here are the four basic categories of systems.
Portable backup: This, the simplest and cheapest option, consists of a battery that can be used to power smaller home appliances such as lights, Wi-Fi and laptops.
The size of the battery is expressed in kilowatt hours (kWh) and refers to the “amount” of energy that can be stored and used.
The size of a portable battery unit averages 0.75kWh and costs about R11,000R13,000. The unit isn’t connected into a property’s main distribution board, and is charged via Eskom electricity.
Appliances are plugged directly into the unit so there’s a limit to how many you can use at the same time.
Installed backup system: If you want an uninterrupted power supply for most of your larger appliances (televisions, microwaves and kettles, for example), an installed backup system consists of a battery plus an inverter. This connects directly into your home’s distribution board, and solar can be added later.
Prices vary depending on the size of the battery, but they range roughly from
R35,000 (for 2.5kWh) to R175,000 (for 10kWh).
Solar with backup: This is the full Monty, including solar panels. The price of this set-up (battery, inverter and panels) varies significantly depending on the brand you choose and how you configure it. But the average starter solar package will cost about R75,000-R135,000 and typically consists of a 5kWh battery and 12 panels. The most comprehensive system, including a 15kWh battery and 36 panels, will set you back R290,000-R345,000 on average.
Going fully off-grid: For many, this is an unjustifiable expense. It entails putting in place a small-scale embedded generation system, which can cost up to R700,000 by some estimates.
But this leaves you significantly exposed, and the smart money says a grid-tied system is best.
In all these options, batteries typically need to be replaced within eight to 10 years.
Steven Barker, Standard Bank’s head of product for consumer and high net worth, says the average customer spends R170,000 on a backup system, which should cover the cost of a medium-sized battery, an inverter system of 7.5kWh, and 12-18 solar panels.
That would be sufficient to keep most appliances running during load-shedding, except heavy power guzzlers such as electric ovens, pool pumps and geysers.
Barker says the number of panels you need depends on various factors, including cloud and tree cover, as well as roof angles. “They all play a role in the kilowatt per hour output,’’ he says. Even though it’s expensive, Barker says solar is the only option that reduces your reliance on the national grid. “Solar will bring down your monthly municipal electricity bills, unlike batteries and inverters,” he says.
Another important upshot is that most people who invest in solar inevitably reduce consumption, which Barker believes is central to fixing the country’s energy crisis.
For many people, it will come down to the financing. If you can add the cost of such a system to your home loan through an access bond or re-advance, this is a cheaper solution.
The personal loan option often repayable over 72 months matches your liability with the lifetime of the backup system. As Barker puts it: “It wouldn’t make financial sense to pay something off over 20 years that has a lifespan of only eight to 10 years.”
However, the monthly repayments on a