Sunnify's Solar Estimate Methodology, in Full

Every number behind a Sunnify solar estimate is published here, in full, specifically so it can be checked against the source rather than simply trusted. Nothing here is proprietary or hidden; it is the same set of assumptions applied consistently across every article and every project on this site.

• The core generation figure, 1,106 kWh per kWp per year, comes directly from Singapore's 4.33 peak sun hours and a 30% system loss factor, shown as a worked calculation below, not asserted as a black box.
• Self-consumption is assumed at a conservative 25% reference figure, a starting point for comparability across system sizes, not a measurement of any specific household.
• Tariff and export-credit figures are reviewed quarterly, tracking SP Group's own regulated revision cycle.
• 25-year projections apply 0.5% annual panel degradation and a 4% annual discount rate, so a future dollar of savings is not counted as equal to a dollar saved today.

What's the actual generation formula, worked through?

Singapore's reference solar resource is 4.33 peak sun hours a day, a standard irradiance figure already averaged across the country's real mix of sunny and cloudy days over a full year. Applied across 365 days, that is 1,580 equivalent full-sun hours a year. A 30% system loss factor, covering temperature derating, wiring and inverter conversion losses, and typical soiling between cleanings, reduces that to a realistic 1,106 kWh generated per kWp of installed panel capacity per year.

What does the 30% system loss factor actually cover?

Several real, compounding factors rather than one single cause: temperature derating from Singapore's consistently high ambient and roof-surface heat, wiring and inverter conversion losses, panel manufacturing tolerance, and typical soiling between cleaning cycles. See simulation versus real output for how these individual factors actually compound in practice, and why a realistic loss assumption produces a more trustworthy estimate than an optimistic one that ignores them.

Why 25% self-consumption specifically, not a higher or lower figure?

It is a deliberately conservative, mid-range reference point for a typical landed household's daytime usage pattern, chosen for comparability across different system sizes rather than as a claim about any individual home. A household with more daytime occupancy, a home office or retirees at home, genuinely self-consumes more than this reference figure; a household mostly empty during the day self-consumes less. The 25% figure exists so every size comparison on this site starts from the same baseline, not because every home actually matches it.

What tariff and export-credit figures does the methodology use?

The current Q3 2026 SP Group regulated retail tariff, S$0.3478 per kWh including GST, and the current Simplified Credit Treatment (SCT) export rate, S$0.2581 per kWh, both reviewed and updated quarterly to track SP Group's own revision cycle. See SCT and ECIS, how solar export credit actually works for why two separate schemes exist and which one applies to a specific household.

How quickly does the methodology actually update after a tariff change?

Every article and estimate on this site referencing a specific tariff figure is checked and updated as part of Sunnify's own quarterly tariff-sync process, tied directly to SP Group's own published revision schedule, not on an ad hoc or delayed basis.

What cost assumption does the methodology use for the upfront price?

A reference range of S$1,000 to S$1,600 per kWp installed, drawn from real quotes and Sunnify's own documented installations rather than a single manufacturer's price list. A specific quote landing well outside this range, in either direction, is worth a direct question to the installer rather than assumed to be simply a better or worse deal, covered fully in solar panel cost by system size.

How is a 25-year savings projection actually built from these inputs?

Four components compound together: annual generation (from the 1,106 kWh/kWp figure), split between self-consumption and export at their respective rates, reduced year by year by a 0.5% annual panel degradation rate, and discounted at 4% a year to reflect that a dollar saved in year 20 is worth less today than a dollar saved this year. See the total cost of ownership framework for how these combine with upfront cost, one assumed inverter replacement around S$1,500 to S$3,500, and roughly S$400 a year in maintenance, into a single lifetime figure.

Why apply a discount rate at all, rather than simply adding up 25 years of savings?

Because adding up undiscounted future savings overstates their real present value, a distortion that grows larger the further out the projection runs. A 4% annual discount rate is a standard, conservative approach for this kind of long-horizon projection, applied consistently rather than adjusted to make any particular scenario look more favourable.

What does this methodology deliberately not account for?

Anything specific to an individual property that a standardised formula cannot know in advance: actual roof shading, real household consumption timing, a specific installer's exact pricing, or a household's own electricity usage pattern. This is exactly why an estimate is a starting reference point, not a substitute for an actual site survey and a real quote, and why every estimate on this site is presented as a projection rather than a guarantee.

What's the actual next step?

Run the Sunnify solar estimate to see these exact assumptions applied to your own roof, and see is solar worth it in Singapore for the full economics this methodology feeds into.