Quick Panel Count Calculator
Enter your average monthly TNB electricity bill to get an instant recommendation.
3 Ways to Calculate Your System Size
Use whichever method you have data for. All three should give you a similar answer — if they don't, the roof-based method caps your maximum.
Method 1: Bill-Based (Quickest)
Divide your average monthly TNB bill by RM50 to get your approximate system size. Example: a RM300 bill ÷ 50 = 6kWp, a rough guide only; our savings engine sizes a RM300 bill at 5.58 kWp (9 panels).
The 105 Factor: Why We Use It
We size on 3.5 peak sun hours per day (about 360 days a year), so a 1kWp system generates roughly 3.5 kWh/day, or about 105 kWh/month (1,260 kWh/year). This is a deliberately conservative basis that allows for panel soiling, inverter losses, temperature derating, and cloudy-day reductions — typical for Malaysian conditions. Your own roof, orientation and shading will move the real figure.
Panel Count by TNB Bill Size
Find your typical monthly bill in the table below. Savings are our estimate on the RP4 domestic tariff (3.5 sun-hours a day, about 40% used at home, export credited at the Energy Charge, unused credit forfeited monthly) with Trexon catalogue prices (Jinko 620W panels, Solis inverter).
| Monthly Bill | System Size | Panels | Monthly Savings |
|---|---|---|---|
| RM 200 | 5.58 kWp | 9 | RM 143 |
| RM 300 | 5.58 kWp | 9 | RM 184 |
| RM 400 | 6.20 kWp | 10 | RM 230 |
| RM 500 | 7.44 kWp | 12 | RM 291 |
| RM 800 | 11.16 kWp | 18 | RM 418 |
| RM 1,000 | 11.78 kWp | 19 | RM 610 |
Panel Count by House Type
Malaysian house types have different typical electricity consumption, roof areas, and constraints. Find your home type below.
Apartment / Condo
RM 100-200/mo
Individual units cannot install their own rooftop system. A rooftop system for the common-area meter is arranged by the JMB/MC; Solar ATAP excludes multi-tenant premises, so eligibility is confirmed with TNB per building.
Single-Storey Terrace
RM 150-300/mo
Single phase (5 kWac cap, up to 7.44 kWp). Roof often has water tank and vent obstructions. Usually enough for a meaningful system.
Double-Storey Terrace
RM 200-400/mo
Single phase allows up to 7.44 kWp (12 panels) on a 5 kWac inverter. Larger systems need a three-phase supply. Larger south-facing slope available.
Semi-Detached House
RM 500-800/mo
Usually three-phase already. Ample roof for 7-11kWp. Check for shared wall setback requirements with adjoining unit.
Bungalow
RM 700-1,200/mo
Three-phase needed for systems above 7.44 kWp; it allows up to 15 kWac (19.84 kWp, 32 panels). Bungalows can fully offset their bills. Consider battery storage to capture overnight self-consumption.
Inverter selection matters too. For houses with complex multi-slope roofs (L-shaped, U-shaped), consider micro inverters or power optimizers. Each panel operates independently, maximising yield even when different slopes face different directions. Read our inverter comparison guide for details.
Don't Oversize Under Solar ATAP
Oversizing is a common and costly mistake under Solar ATAP.
The Solar ATAP Sweet Spot
Roof Area Requirements in Detail
The 10m² per kWp rule is a starting point. Here is how to calculate your real usable roof space.
Common Roof Obstructions in Malaysia
- 1Water tanks (1.5–3m² each, plus 1m clearance all around)
- 2Roof vents / ventilators (0.3–0.5m² each, 1m clearance)
- 3Solar water heaters (2–4m²)
- 4Satellite dishes (0.5m² + shadow zone)
- 5Ridge vents (full ridge length × 0.5m)
- 6Air conditioning condenser units (1–2m²)
- 7Chimney stacks (1m clearance all sides)
Pro Tip: When You Can't Fit Enough Panels
If your roof area is limited, switching from 400W panels to 620W Tier 1 panels (Trexon installs the Jinko Tiger Neo 620W; JA Solar JAM72D40 is a market reference, not stocked by Trexon) gives you about 55% more power per panel. A 5-panel roof that would have been 2kWp at 400W can now be 3.1kWp at 620W — without installing any extra panels.
Quick Roof Area Reference
Single Phase vs Three Phase: System Size Limits
Your home's electrical connection type determines the maximum system size you can install under Solar ATAP.
Max 5 kWac → up to 7.44 kWp (12 panels at 620W)
Most terrace houses, apartments, and smaller landed properties. Your meter box will have a single-phase MCB.
Max 15 kWac → up to 19.84 kWp (32 panels at 620W)
Semi-detached houses, bungalows, and most commercial premises. Your meter box has three-phase MCBs.
Can I Upgrade to Three Phase?
Yes. It needs a TNB application plus rewiring, a new meter and new MCBs; ask your electrician and TNB for the cost. For a home with a RM700+ bill that needs a system of around 10kWp, the extra generation capacity can justify the upgrade. Systems above 15 kWac on three phase need a TNB Connection Confirmation Check (RM1,000).
