Solar Savings Calculator

A solar PV system isn’t a one-time purchase you compare against today’s electricity bill. It’s a 20-year hedge against an Eskom tariff that has climbed faster than inflation for over a decade. The break-even calculation is dominated by one assumption: how fast electricity gets more expensive.

Eskom tariffs rose 12.74% on 1 April 2025 and another double-digit increase landed in April 2026. Compounded over the lifetime of the panels, even a modest system that “only” covers half your load can pay for itself in 5-7 years and run on free electricity for the next 13.

The single biggest variable in your install quote is the inverter. A grid-tied-only inverter is cheaper but turns off during load-shedding (it can’t safely export to a dead grid). A hybrid inverter is R10,000–R30,000 more but keeps essential circuits running off battery during outages — which is most of the practical benefit of going solar in South Africa.

Forget panel brands and inverter spec sheets. Two assumptions move your break-even year by years in either direction:

• Annual tariff escalation. Conservative is 8%; the long-run Eskom average is closer to 12%. At 8% your break-even is 8 years; at 14% it’s 5. The same panels, the same bill — different decade-end outcome.
• Solar coverage percent. What fraction of your monthly kWh does the system actually replace? A grid-tied 5kW system on a north-facing roof in Gauteng typically covers 70-85% of a R3,500 monthly bill. Add load-shifting (running geyser/pool pump during the day) and you push past 90%.

The calculator lets you adjust both. Try 8% tariff with 70% coverage as a conservative case, then 12% with 85% as the realistic case. The gap is what you’re actually deciding between.

The simple break-even number (3.3 years) is misleading because it ignores that your bill grows. The compounded version is more honest, but counter-intuitively most installers quote the simple version because it sounds better. Always ask which one you’re seeing.

Solar is one of the few major purchases where how you pay materially changes the economics. Three common routes:

• Cash. Best returns. The R110k upfront returns ~R1.5m over 20 years — better than most equities net of inflation. Only works if you have the capital sitting in a low-yield account.
• Bond extension / personal loan. Adding R110k to your bond at 11% over 20 years costs R1,135/month. If your solar saving is R2,800/month, you net R1,665/month from day one — no break-even calculation needed because cashflow is positive immediately. The catch: discipline. Most people don’t actually ring-fence the saving against the new bond payment.
• Rent-to-own / PPA (Power Purchase Agreement). Zero deposit, the installer owns the system, you pay a fixed monthly fee that’s usually 10-20% below your current bill. Inflation-locked at signing. The trade is that you don’t own the system and there’s a 15-20 year lock-in. Best for people who want the load-shedding hedge without capital risk.

Two tax provisions are worth knowing about, but only one is currently active:

• Section 25C residential rebate (expired). The 2023/2024 once-off 25% rebate (capped at R15,000) for individuals on solar PV panel costs ended on 29 February 2024. It does not apply to current installations.
• Section 12B accelerated allowance (active, business only). If you run any business — sole prop, company, or trust — the system qualifies for 100% deduction in year 1 against business taxable income, provided it’s used in production of income. A R110k system at the 27% corporate rate saves ~R29,700 in tax in the year of purchase. Talk to your accountant about whether you can legitimately apportion business use of a home-office system.

• Assuming you can sell back to the grid. Most municipalities still don’t pay for excess generation, or pay 30-50c/kWh against the R3.50+ retail rate. Size your system to your own consumption, not for export.
• Neglecting load-shifting. Run your geyser, pool pump, and dishwasher during solar hours and you push coverage from 70% to 85%+ at zero additional capital cost. That’s a R6,000-R8,000/year free upgrade.
• Cheap inverters age badly. A R20k inverter that needs replacement at year 8 nukes your 20-year return. Stick with established brands (Sunsynk, Victron, Goodwe, Deye) and confirm the warranty is honoured locally.
• Battery depth-of-discharge math. A “10kWh battery” usually means 8-9kWh usable (lithium DoD limits). The retail brochure number and the night-time-power number are not the same.

Enter your system cost, current monthly electricity bill, expected solar coverage, annual Eskom tariff escalation, and panel degradation rate. The calculator compounds the bill forward year-by-year, applies the saving net of degradation, and reports break-even year, monthly saving, 10-year saving, and 20-year saving.

The default assumptions (12% tariff escalation, 0.5% degradation, 80% coverage) are roughly conservative for a well-sized system in Gauteng or KZN. Coastal regions get slightly lower yields; the Karoo and Northern Cape get higher. Adjust coverage down 5-10% for east-west roofs vs north-facing.

• Eskom — Tariffs and Charges (current rate booklet)
• NERSA — Approved Electricity Tariffs and Decisions
• SARS — Section 12B (renewable energy capital allowance)
• PV GreenCard — installer accreditation and CoC standards