Building the best solar power system for your needs — what to consider

Eskom’s system outlook for 2024 paints a bleak picture, and more households may be ready to pull the trigger on building a solar power system.

However, it isn’t as simple as going to a retailer and taking components you think will work off the shelves. There is some groundwork to be done before you can decide on the best solar system for your needs.

Major components of solar backup systems include photovoltaic panels, an inverter to switch between grid, solar, and battery power, and batteries to store energy.

While choosing components is important, renewable energy project manager at the South African National Energy Development Institute Karen Surridge recently told MyBroadband that selecting a reputable installer is essential.

“The starting point is a reputable installer with a solid reputation and good references,” she said.

One of the best ways to do this is to find installers in your area who are registered with the South African Photovoltaic Industry Association. They are listed on the PV GreenCard website.

“You can also Google your potential installers and ask friends or social-media community groups for references. Word of mouth can be a powerful recommendation,” added Surridge.

While the installer should provide an itemised invoice once they have assessed your property and your energy requirements, many will likely want to confirm that the proposed system will meet their needs.

Below are the most important aspects to consider regarding the major components of a solar system.

Inverter choice

An inverter’s job is to convert direct current (DC) electricity, which is generated through sunlight or stored in batteries, into alternating current (AC) for household appliances and devices to use.

Considering your peak power draw before deciding on an inverter is important, as this determines the inverter capacity you will need.

Single-phase grid connections provide households up to 13kW, letting customers run appliances that consume a lot of power, such as kettles and stoves.

However, cost-effective inverters are typically rated for 3kW, 5kW, and 8kW. It is possible to convert some energy-heavy appliances like stoves and geysers to gas to avoid overloading the inverter.

Sunsynk inverter

The alternative is to opt for a larger inverter or install multiple, which carries a hefty cost.

There are three types of solar power systems that homeowners can install, which will determine the type of inverter required. These system types are as follows:

  • Off-grid — these are designed to run without power from the grid, but they can also be connected to it. Essentially, it won’t switch to pulling power from the grid unless your solar generation and batteries don’t have enough capacity.
  • Grid-tied — these solar systems are designed with solar and grid power running in parallel, with power from solar generation being consumed first.
  • Hybrid — 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.

Solar panels

In addition to influencing the size of the inverter required, your peak power draw also affects the size and number of solar panels you need. It is also essential to consider your average power usage.

You can determine your average electricity usage by checking your electricity bill for the past few months. One unit of electricity translates to one kilowatt-hour (kWh).

Solar installer SolarAdvice offers a helpful tool on its website that lets customers enter their average monthly electricity bill to be recommended a solar power kit, including the number of solar panels and wattage of each.

For example, when entering an average monthly bill of R2,000, it will recommend a system with eleven 455W solar panels, providing up to 5,005W or 5kW of peak output.

However, this hasn’t taken peak power usage into account, and households that exceed 5kW of usage at any one time will start to pull power from the grid.

Longi solar panel

SolarAdvice recommends doing the following before deciding on a brand and model of solar panel for your system:

  • Compare the product to products from other brands.
  • Compare its warranty to other brands.
  • Does it have a good rating online?
  • Does the brand offer technical support?
  • Is there an aftersales service available should the equipment be or become faulty?
  • Are replacement parts available in South Africa?

Battery requirements

Batteries are essential components of solar power systems as they allow users to continue to avoid using grid power, even during periods when solar panels aren’t generating any power.

These periods include nighttime and poor weather where sunlight is limited.

Therefore, once you have determined your average power usage over the past few months, it is crucial to determine how much electricity you use overnight versus during the day.

The average South African household uses roughly 60% of its electricity in the evenings. Assuming an average usage of 1,500kWh a month, the household will use approximately 30kWh each evening.

Choosing a battery backup system that can meet these needs is essential if you don’t want to draw power from the grid at night.

Battery manufacturers often provide amp-hours (Ah) and voltage (V) specifications, which can confuse customers looking to meet a kWh requirement.

However, you can convert Ah and V to kWh using the following calculation.

Amp-hour (Ah) x voltage (V) = wattage (W)

Example battery: 100Ah | 25V

100Ah × 25V = 2,500Wh or 2.5kWh

This will calculate the total capacity of a battery. However, depth-of-discharge (DoD) significantly influences the useable battery capacity.

Freedom Won LiFePO4 battery.

Solar installers recommend lithium-ion batteries as they can discharge further than lead-acid or gel batteries without degrading their capacity.

Lead-acid batteries tend to degrade when they are discharged below 50%. This means customers will have to double up on battery capacity if they opt for lead-acid units.

However, lithium-ion batteries can discharge completely with minimal impact on their capacity, but it is recommended not to let them drop below 20%.

While lithium-ion batteries cost substantially more than lead-acid and gel alternatives, they are cheaper in the long run as they offer far more charging 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.

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Building the best solar power system for your needs — what to consider