Small and medium businesses — restaurants, workshops, small factories, retail spaces — are often the sweet spot for rooftop solar economics. Daytime load, dedicated roof space, and commercial electricity rates usually stack up well. But the ROI figures in marketing materials often assume ideal conditions. Here's what a realistic breakdown looks like.
Our ROI calculator gives you a rough estimate of system size, cost range, and payback period based on your monthly bill and load pattern. Useful context before reading the detail below.
The four numbers that drive small-business ROI
1. Self-consumption ratio
This is the percentage of solar production you actually use on-site versus export to the grid. Self-consumed energy offsets your full retail electricity rate. Exported energy is typically compensated at a lower feed-in tariff or net-metering credit.
For a business operating 8am–6pm, Monday–Friday, self-consumption is often 70–85% for a properly-sized system. A 24/7 operation approaches 100%. A weekends-closed operation drops to 50–60% without changes.
2. Electricity rate structure
Commercial tariffs in Asia often include:
- Energy charge (per kWh) — the most obvious component.
- Demand charge (per kW peak) — based on your highest 15- or 30-minute demand in the billing period. Solar can reduce this if your peak happens during daylight.
- Time-of-use rates — higher rates during peak hours (often 11am–3pm, exactly when solar produces most).
- Power factor penalties — separate from solar but worth understanding.
The actual savings per kWh depend on which combination of these the solar is displacing.
3. System cost and financing
Small commercial systems (50–200 kWp) in Asia typically cost in a range that, with favourable local conditions, produces payback in 4–7 years. Cash purchase gives best long-term return; loans extend payback but preserve capital; PPAs (power purchase agreements) give you zero-capex access but take most of the benefit.
4. System lifetime and O&M
A 25-year design life is the standard. But realistic ROI models must account for:
- Inverter replacement at year 10–12 (typically 5–10% of system cost).
- Annual O&M: cleaning, inspection, minor repairs (typically 0.5–1.5% of system cost per year).
- Gradual panel degradation: ~0.5% per year for tier-1 panels.
A realistic example
Let's walk through a hypothetical small factory, 100 kWp system:
Annual production: ~140,000 kWh (at 4.5 peak sun hours, 85% system efficiency)
Self-consumption: 75% → 105,000 kWh offset at retail rate
Exported: 25% → 35,000 kWh at feed-in rate
Annual savings: depends on local tariffs, but typically strong enough for a 5–6 year payback
Over 25 years, after accounting for one inverter replacement, 0.5%/yr panel degradation, and 1%/yr O&M: the system pays for itself several times over.
What the overselling usually looks like
Marketing-heavy quotes often inflate ROI by:
- Assuming 100% self-consumption when your actual pattern is 60%.
- Ignoring inverter replacement costs.
- Assuming your utility rates will rise faster than they realistically will.
- Using a production figure based on ideal orientation and no shading, when the actual site has both.
- Ignoring O&M and panel degradation.
A 3-year payback promise for a small commercial system should make you suspicious, not excited. A 5–7 year payback with conservative assumptions is a healthy outcome.
The questions to ask your installer
- What self-consumption ratio did you assume, and why?
- Did you include an inverter replacement in the 25-year cost?
- What panel degradation rate did you use?
- Can I see the annual cash flow table — not just payback period?
- What happens to the ROI if electricity rates stay flat instead of rising?
If the installer can't walk you through these quickly and clearly, they're selling you a number rather than an analysis.