Why ROI Matters for Residential Solar
Unlike commercial installations that benefit from tax incentives in many countries, Singapore residential solar systems have no direct government subsidy as of Budget 2026. The return on investment is driven entirely by electricity bill savings and, for systems with net metering, revenue from excess generation sold to the grid.
This makes accurate financial modelling particularly important for Singapore homeowners considering solar. The figures below are based on 2026 SP Group tariff rates and current installation costs from multiple contractors.
Payback Period by System Size
| System Size | Upfront Cost | Annual Savings | Payback Period | 25-Year Net Return |
|---|---|---|---|---|
| 5 kWp | SGD 12,000–16,000 | SGD 1,800–2,400 | 5–7 years | SGD 32,000–44,000 |
| 8 kWp | SGD 15,000–20,000 | SGD 2,800–3,600 | 4.5–6 years | SGD 55,000–70,000 |
| 10 kWp | SGD 18,000–25,000 | SGD 3,500–4,500 | 4–6 years | SGD 69,500–87,500 |
| 15 kWp | SGD 25,000–35,000 | SGD 5,200–6,500 | 4–5.5 years | SGD 95,000–127,500 |
Net return figures account for one inverter replacement (SGD 3,000–5,000) at approximately year 12–15, panel degradation at 0.6% per year, and a conservative 2% annual electricity tariff increase.
How Savings Are Calculated
Residential electricity savings from solar come from two mechanisms:
1. Self-Consumption Offset
Electricity generated and consumed on-site directly reduces the monthly SP Group bill. The current low-tension tariff (Q1 2026) is approximately SGD 0.3185 per kWh. A 10 kWp system generating 13,000 kWh/year, with 70% self-consumption, offsets approximately SGD 2,898 annually.
2. Excess Export to Grid
Under the Simplified Credit Treatment (SCT) scheme administered by SP Group, excess solar electricity exported to the grid is compensated at the prevailing low-tension tariff. For the same 10 kWp system with 30% export (3,900 kWh), this adds approximately SGD 1,242 annually.
Combined: SGD 4,140/year — consistent with the SGD 3,500–4,500 range reported by multiple contractors.
Tariff Sensitivity Analysis
SP Group electricity tariffs have fluctuated significantly in recent years, from a low of SGD 0.2072/kWh in Q3 2020 to a peak of SGD 0.3580/kWh in Q4 2022. Payback periods are sensitive to tariff levels:
| Scenario | Tariff (SGD/kWh) | 10 kWp Annual Savings | Payback |
|---|---|---|---|
| Low tariff | 0.25 | SGD 3,250 | 5.5–7.7 years |
| Current tariff | 0.3185 | SGD 4,140 | 4.3–6.0 years |
| High tariff | 0.35 | SGD 4,550 | 4.0–5.5 years |
25-Year Projection: 10 kWp System
The following projection uses a 10 kWp system costing SGD 22,000, current tariff of SGD 0.3185/kWh, 2% annual tariff escalation, and 0.6% annual panel degradation:
| Year | Generation (kWh) | Cumulative Savings (SGD) | Net Position (SGD) |
|---|---|---|---|
| 1 | 13,000 | 4,141 | -17,859 |
| 3 | 12,844 | 12,713 | -9,287 |
| 5 | 12,690 | 21,703 | -297 |
| 7 | 12,538 | 31,125 | +9,125 |
| 10 | 12,314 | 46,028 | +24,028 |
| 13* | 12,093 | 61,870 | +35,870 |
| 15 | 11,949 | 73,218 | +51,218 |
| 20 | 11,597 | 101,342 | +79,342 |
| 25 | 11,254 | 132,648 | +106,648 |
*Inverter replacement cost of SGD 4,000 deducted at year 13.
Factors That Affect ROI
- Roof orientation: South-facing roofs in Singapore receive the most consistent irradiance. East/West orientations reduce generation by 10–15%.
- Shading: Even partial shading from trees or adjacent buildings can reduce output by 20–40% on affected panels (mitigated by micro-inverters or power optimisers).
- Self-consumption ratio: Higher self-consumption (homes occupied during the day, EV charging, pool pumps) accelerates payback since avoided tariff cost exceeds export compensation.
- Panel quality: Tier 1 monocrystalline panels with lower degradation rates (0.4–0.5% vs. 0.7–0.8%) produce measurably more energy over 25 years.
- Maintenance: Regular panel cleaning (3–4 times per year) maintains output within 2–3% of rated capacity.
Comparison: Solar vs. Grid-Only Over 25 Years
| Metric | Grid Only | 10 kWp Solar + Grid |
|---|---|---|
| 25-year electricity cost | SGD 195,000–240,000* | SGD 70,000–95,000* |
| Solar investment | SGD 0 | SGD 22,000 + 4,000 inverter |
| Total cost | SGD 195,000–240,000 | SGD 96,000–121,000 |
| Net saving | — | SGD 99,000–119,000 |
*Based on average household consumption of 600 kWh/month, 2% annual tariff escalation.