Most solar calculators online quote you a payback that never matches reality. They assume you use every kilowatt your panels make, that prices stand still, that your battery lasts forever and that the cash you sank into it could not have earned a cent anywhere else.

So I built one that does not pretend. You put in your real numbers and it shows you two figures side by side - the rosy payback a salesman quotes and the realistic one you are actually likely to get - then it breaks down exactly what eats the gap. Wasted daytime generation, panel degradation, the battery you will replace once down the line, financing interest and the higher fixed charge some municipalities slap on solar homes.

It is free and there is no signup. Set your own tariff off your bill rather than the presets and be honest about how much you use in daylight and you will get a sensible answer.

Anyone interested can have a look here:

https://southafricafacts.co.za/solar-savings-calculator-south-africa/

Keen to hear if the numbers line up with what you are actually seeing. Share your own setup and payback if you are up for it.

1 hour ago, TheOracle said:

Keen to hear if the numbers line up with what you are actually seeing. Share your own setup and payback if you are up for it.

Nice, but there is one serious flaw in your calculations - TAX. Your "Interest you gave up" will be taxed at (say) 35% per year, whilst your saving for not paying for electricity is totally tax free. Run the numbers again with this taken into account and your investment will look much better.

1 hour ago, HennieL said:

Nice, but there is one serious flaw in your calculations - TAX. Your "Interest you gave up" will be taxed at (say) 35% per year, whilst your saving for not paying for electricity is totally tax free. Run the numbers again with this taken into account and your investment will look much better.

Good point, although the first R23,800 interest income per tax year is exempt from income tax, so it will not affect too many people.

Generally love it. Point of feedback, maybe a thought to display the SA map of daily peak sun hours, as an indication of how much sun hours one can expect in different parts of the country. And extend the inputs range to around 6.5 hrs to include major towns in the North-West part of the country like Upington.

Edited 4 hours ago4 hr by GreenFields

1 hour ago, GreenFields said:

Generally love it. Point of feedback, maybe a thought to display the SA map of daily peak sun hours, as an indication of how much sun hours one can expect in different parts of the country. And extend the inputs range to around 6.5 hrs to include major towns in the North-West part of the country like Upington.

Thanks for the feedback. The range is extended to 6.5. I also added a location dropdown so you can select your location.

Interesting Calculator

Thank you for creating and sharing this tool it’s a great idea and a much-needed step toward more honest solar payback calculations in South Africa.

I fully support the effort to show the difference between optimistic salesman figures and real-world outcomes.I’ve been completely off-grid for more than 5 years with older JA Solar all-black 365W mono panels that are still performing well.

Here’s some constructive feedback based on long-term practical experience:

Current market pricing example (June 2026) for reference: 24 × 460W JA Solar Bi-facial panels + mountings + accessories

2 × 6kW SOLIS Hybrid Tier-1 inverters

2 × 15.3kWh batteries (≈30.6kWh total)

Panels + inverters + batteries + delivery: R113,000 ex VAT

Installation: R30,000 VAT incl.

Batteries alone: ≈R58,000 VAT incl.

A few questions / suggestions on the assumptions:

Battery Replacement

The tool assumes a relatively high replacement cost (around R180k for a 30kWh bank). Current real prices are significantly lower. Would it be possible to allow users to input their own expected future battery prices?

Self-consumption percentage

The “you actually use only 44–61%” figure seems based on typical grid-tied homes. In a well-sized off-grid system this looks very different. After 5+ years off-grid I achieve close to 100% utilisation on a 24-hour cycle. In summer my batteries are often full by midday and all loads (including aircon) run directly off solar. An off-grid mode with higher utilisation options would be very helpful.

Hardware tiers, lifespan & losses

Equipment varies widely in quality and longevity, for solar panels inverters and batteries you have Tier 1 Tier 2 and Budget ratings. Have you considered adding options for different inverter/battery design lives, warranties, cycle counts based on actual loading, and system losses cables, conversion, etc? Cable sizing can factor in a 5% Plus loss or less than 1% loss on the overall system. Inverter efficiency converting PV to Load and Storing PV including conversion from LV DC to AC and battery conversion losses also varies between different manufacturers and voltage ranges LV vs HV.

Bi-facial gains & new technology

Many modern systems benefit from bi-facial panels (5–20%+ extra yield) and improving panel tech. Including these as optional inputs could add value. As an example simply having a reflective surface below a bi facial panel can mean the difference between 5% and 20% or more yield gain.

AI Optimisation

Premium inverters and aftermarket AI systems are already learning usage patterns, automatically switching loads, and improving over time. Does the model have room to factor in these efficiency gains?

Tariff Increases & Real Costs

With recent hikes already in effect and municipalities adding complex fixed/demand charges, your 10% default looks reasonable.

Opportunity Cost

The 8% discount rate is an important realistic factor. In strong off-grid cases it can be partly offset by high self-consumption, bi-facial gains, and rising utility prices.

Tax Incentives

Section 12B still offers companies 100% deduction in year one. A toggle for business vs private use could be useful.

Value of Reliable Power During Outages

Everyone claims load shedding is over, but in reality it continues under new names like “load shifting” and “maintenance”. Many small towns still face outages of 24–48 hours. For businesses, farmers, online workers and industry, the ability to keep operating can prevent significant income loss.

Factoring in the financial value of uninterrupted power (avoided downtime, spoilage, lost productivity, etc.) would make the calculator even more honest and realistic, especially for commercial and off-grid users.

Overall, this is already a very useful calculator that highlights important realities most tools ignore. Adding more flexibility (off-grid mode, hardware tiers, AI, system losses, and reliability benefits) would make it even stronger and applicable to a wider range of users.

My 2 cents

Edited 2 hours ago2 hr by Powerforum Store

Thanks, this is genuinely one of the most useful bits of feedback I've had, and coming from five years off grid it carries real weight.

A few quick responses. On battery replacement, the figure is actually a field you can edit, it just defaults high and tracks your bank size, but you're right that the default is steeper than today's pricing, so I'll bring it down closer to what you're seeing. The self-consumption point is fair too. The numbers lean toward a typical grid-tied home, and a properly sized off-grid setup like yours sits much higher, so an off-grid mode with a high utilisation option makes a lot of sense.

The Section 12B business toggle and the value of uninterrupted power are both great calls, especially for farmers and anyone running an income off the system. Bi-facial gains and hardware tiers I'll keep on the list, though I want to add them without making the thing a spreadsheet.

Really appreciate you taking the time. I'll work through these and post back when the next version is up.

That battery figure was the one that needed fixing first. I've dropped the default to about R2,500 a kWh, which is much closer to what you're actually seeing, and it's still a field you can edit to your own view. The off-grid self-consumption point is next on my list.