Choosing the right solar power system – a guide for homes and businesses

Load-shedding in 2023 has exceeded previous years, prompting the South African government to encourage the adoption of solar power systems to alleviate strain on the grid. However, selecting the appropriate backup power system can be a daunting task, requiring careful consideration of various factors. In this article, we delve into the key components of a solar power system, discuss the decision between remaining connected to the Eskom grid or going off-grid, and highlights important considerations when choosing inverters, solar panels, and batteries. Read on to make an informed decision for your solar power setup.

How to build the best solar power system for your needs

By Myles Illidge

Eskom load-shedding in 2023 has already surpassed previous years, and to help reduce demand on the grid, government is incentivising solar power installations for households and businesses.

However, choosing the right backup power system for your needs can be challenging, and several aspects must be considered before deciding on one.

The primary components of a solar power system include photovoltaic panels, an inverter to switch between grid, solar, and battery power, and batteries to store electricity.

Deciding whether you want to remain tied to the Eskom grid or install a fully off-grid solar power system is essential.

According to AWPower managing director and head of operations Christiaan Hattingh, going completely off-grid requires an oversized system to compensate for the fluctuation in solar availability.

This pushes up the cost of your installation significantly, with Hattingh estimating that a household using 1,200kWh of electricity each month would likely have to fork out around R700,000 to be entirely self-sufficient.

“Whatever you think you need — you need more than double, triple, quadruple,” said Hattingh.

However, a solar power system with a slight reliance on the grid will be substantially cheaper.

Below are the most important aspects to consider when deciding on a solar power system.

Read more: Do-it-yourself solar could cost 2-3 times more than grid-tied systems

Selecting an inverter

The choice of inverter is arguably the most important decision you will make regarding your solar power setup.

Batteries and solar panels tend to be more flexible regarding upgrades down the line, while inverters can run into big compatibility problems that might require replacing them altogether when upgrading.

From a technical standpoint, batteries and solar panels are far less complex than inverters.

Inverters’ primary job is converting direct current (DC) electricity, generated through sunlight or stored in batteries, into alternating current (AC), which electrical appliances and devices can use.

There are three types of solar power systems — listed below — that determine the type of inverter you need.

  • Grid-tied â€” Solar and grid power run parallel, with solar consumed first. Most affordable inverters supporting this cannot feed electricity back into the grid, while some also require a live grid connection to function.
  • Off-grid â€” Designed for running without grid power but can also be connected to the grid. As long as solar or batteries have enough capacity, they will provide power. The inverter will switch over to grid power if capacity becomes insufficient. Electricity cannot be fed back into the grid.
  • Hybrid â€” Can be either grid-tied or off-grid, but always uses an inverter that can use a mix of solar and grid electricity, as required.

It is also important to determine your peak power draw, which will determine the inverter capacity needed.

Single-phase Eskom connections provide up to 13kW to households, which lets customers run power-hungry appliances, including electric stoves, kettles, and geysers.

Cost-effective inverters are typically rated for 3kW, 5kW, and 8kW, which could mean you need to convert such appliances to gas to ensure you don’t overload the inverter.

The alternative is to get a bigger inverter or to use more than one to meet your needs, but this comes at a higher cost.

Some of the best inverter brands available in South Africa include Deye, GeeWiz Axpert, Growatt, Huawei, Livoltek, Luxpower, Mecer Axpert, RCT Axpert, Sunsynk, Tesla (with an integrated battery), and Victron Energy.

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Solar panels

Your peak and average power usage figures can help determine the required size and number of solar panels.

Solar Advice provides a helpful tool on its website that lets customers enter their average monthly electricity bill to recommend a solar power kit — including the wattage and number of panels required.

However, the tool doesn’t take peak power draw into account.

For example, it recommends that a household with a monthly electricity bill of around R1,800 installs ten 455W solar panels, providing a maximum power output of 4,550W or 4.55kW.

If you exceed this maximum figure, you will start to draw power from the grid to meet your needs.

When choosing your brand of solar panel, Solar Advice suggests you do the following before deciding on one:

  • Does this product have a good rating online?
  • Compare product parameters with other brands.
  • Compare warranties with other brands.
  • Is there an aftersales service available should the equipment be or become faulty?
  • Are the products compatible with each other?
  • Does the brand offer technical support?
  • Are the replacement parts readily available in South Africa?

Some of the best solar panel brands available to South African customers include Canadian Solar, JA Solar, Trina, Longi, and Seraphim.

Read more: Power through loadshedding with these top generator brands

Determining battery requirements

Solar power is only available during the day and only performs well under sunny conditions.

Eskom load-shedding also interrupts grid power to homes and businesses for several hours every day.

This makes batteries an essential component to get you through cloudy weather, and keep your home powered overnight and through scheduled power cuts.

The average South African household uses around 900kWh of electricity per month, and you can determine your average energy usage by checking your electricity bill for the past few months, as one unit of electricity translates to one kilowatt-hour (kWh).

With the average household using around 60% of its electricity during the evenings, one that uses 900kWh a month will need at least 18kWh worth of battery storage.

However, it can be challenging to determine the storage capacity of batteries in kWh as manufacturers often provide these figures in amp-hours (Ah) and voltage (V). You can convert these figures to kWh using the following calculation:

Example battery capacity: 100Ah; Voltage: 25V

100Ah Ă— 25V = 2,500Wh or 2.5kWh

It is also important to consider the battery’s depth of discharge (DoD) and lifespan (number of charge-discharge cycles), which influences your choice of battery type.

Lithium-ion batteries have a far greater DoD than lead-acid or gel alternatives without degrading their capacity.

For reference, lead-acid battery capacity tends to degrade when discharged below 50%, meaning you must install double the battery capacity to meet your requirements.

On the other hand, lithium-ion units can be discharged entirely with minimal impact on capacity. However, it is recommended that you don’t let them drop below 20%.

Another factor to consider when choosing between different battery types is their number of discharge cycles.

According to GeeWiz, lithium-ion batteries are good for over 2,000 cycles, while lead-acid batteries generally only last 150–200 cycles, meaning you will need to replace lead-acid units more often.

Some of the best lithium-ion battery brands available to South African customers include Dyness, PylonTech, BYD, Livoltek, Shoto, HinaESS, Huawei, Hubble, Freedom Won, and Tesla.

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