Solar Panel Calculator

How the Solar Calculator Works

A residential solar PV system converts sunlight into electricity. South Africa has some of the best solar irradiance in the world - most regions receive 4.5–6 peak sun hours per day (compared to 2–3 hours in Germany, the world leader in solar installations per capita). This means South African solar installations are exceptionally productive for their cost.

The required system size (in kilowatts-peak, or kWp) is calculated as:

The calculator uses a panel efficiency factor of 80% to account for losses from temperature, shading, inverter conversion, and wiring. Panel efficiency degrades approximately 0.5% per year over time.

The ROI projection compounds Eskom tariff escalation at 10% per year (the approximate long-term average increase) and deducts 0.5% annual panel degradation from the savings. The break-even point typically falls between 5 and 8 years for a well-sized South African residential installation, depending on local tariff rates and system cost.

Note that this calculator sizes the solar generation component only. If you need battery backup for load-shedding, use the Inverter and Battery Calculator to size the storage component separately.

How to Use This Calculator

1. 1

   Enter your current monthly Eskom bill

   Enter the rand amount of your average monthly electricity bill. The calculator derives your daily kWh usage from this figure using the tariff rate you set. Check your last 3 bills and use an average — South African household bills typically range from R500 to R5 000+ per month depending on size and appliances.

2. 2

   Set your peak sun hours

   Peak sun hours measure solar irradiance intensity, not hours of daylight. Cape Town and the Western Cape receive approximately 5.5–6 peak sun hours/day; Johannesburg and the interior 5–5.5; Durban and the coast 4.5–5. Check a solar irradiance map for your specific location or use the default 5 hours as a conservative estimate.

3. 3

   Review the recommended system size

   The calculator shows the kWp needed and an estimated number of standard 400W panels. A typical 4–5 kWp system (10–13 panels) covers a medium-sized South African home. Larger homes or those with swimming pools or geysers may need 6–10 kWp.

4. 4

   Review the cost and ROI

   Installation cost is estimated at approximately R16 000/kWp for a grid-tied system in South Africa (2025 market rate). Battery storage adds significant cost (see Inverter and Battery Calculator). The 10-year savings projection accounts for Eskom tariff escalation - every rand saved compounds in value as electricity prices rise.

5. 5

   Get multiple installation quotes

   Use this calculator for planning purposes only. Always get at least three quotes from SAPVIA-registered solar installers. Prices vary by system design, panel and inverter brand, and installation complexity. Ensure the quote includes all labour, mounting, cable, breakers, and a CIDB-registered electrician for the Certificate of Compliance.

Frequently Asked Questions

How much does a solar installation cost in South Africa?

A typical residential grid-tied solar installation (panels + inverter, no battery) costs R80 000–R200 000 for a 4–8 kWp system depending on panel brand, inverter quality, and installation complexity. Adding a lithium battery for load-shedding backup adds R40 000–R100 000 for a 5–10 kWh battery. Premium systems with multiple batteries can cost R300 000+. Prices have fallen significantly since 2021 due to increased competition and lower panel import costs.

Can I sell excess solar electricity back to the grid in South Africa?

Feed-in tariffs (selling excess electricity to Eskom or your municipality) are available in some areas but not universal. Cape Town's municipality, Ethekwini, and several other metros have operational Small-Scale Embedded Generation (SSEG) programmes that allow net metering or feed-in credits. Eskom direct customers can apply under the SSEG framework. Check with your municipality - the availability and tariff rate for exported electricity varies significantly by area.

Does South Africa offer tax incentives for solar installations?

Yes. The South African government introduced a solar panel tax rebate for individuals in the 2023/24 tax year: 25% of the cost of new and unused solar panels can be claimed as a tax credit, up to a maximum credit of R15 000, for residential installations between 1 March 2023 and 29 February 2024. For businesses, Section 12B of the Income Tax Act allows accelerated depreciation on renewable energy assets - a 100% deduction in year one for systems under 1 MW. Check the SARS website for the latest incentive status.

What is a grid-tied vs off-grid solar system?

A grid-tied system connects to the municipal or Eskom grid and exports excess power when your panels produce more than you use. When the grid goes down (load-shedding), a grid-tied system without battery also goes down - a safety requirement to protect Eskom workers on the lines. An off-grid system is completely independent with large battery storage. A hybrid system (grid-tied with battery) gives load-shedding protection while maintaining grid connectivity - the most popular option for South African residential buyers.

How long do solar panels last in South Africa?

Quality solar panels have a 25–30 year lifespan and come with a linear performance guarantee (typically 80% of rated output after 25 years). Panel degradation is approximately 0.5% per year. Inverters typically last 10–15 years and may need replacement once during the panel lifetime. Lithium battery warranties are usually 10 years or a certain number of charge cycles. When calculating ROI, factor in one inverter replacement after year 12–15.

What happens to my solar system during load-shedding?

A grid-tied system without battery storage automatically shuts down during load-shedding for safety reasons. A hybrid or off-grid system with battery storage continues to power your home from the battery while the grid is down, automatically switching to battery mode when the grid fails. For load-shedding protection, you need at least an inverter and battery - the solar panels alone are not sufficient. Use the Inverter and Battery Calculator to size the backup system for your needs.