The most common question we get at Trexon is: "How many solar panels do I need?" The honest answer depends on your electricity bill, roof space, and energy goals. This guide gives you two reliable methods to size your solar system correctly — and explains the costly mistakes to avoid.
Method 1: Bill-Based Sizing (Fastest & Most Accurate)
Your TNB electricity bill is the single best indicator of your energy consumption. Malaysian households consume energy at roughly consistent rates per ringgit spent, which makes bill-based sizing surprisingly reliable.
The rule of thumb used by Trexon's engineers for grid-connected Solar ATAP systems:
| Monthly TNB Bill | Recommended System Size | Est. Monthly Savings | Approx. Price Range |
|---|---|---|---|
| RM 200–350 | 3–4 kW | RM 130–200 | RM 12,000–18,000 |
| RM 350–650 | 5–6 kW | RM 220–350 | RM 18,000–26,000 |
| RM 650–1,000 | 8–10 kW | RM 380–520 | RM 28,000–38,000 |
| RM 1,000–1,500 | 12–15 kW | RM 550–750 | RM 38,000–55,000 |
| RM 1,500+ | 18–25 kW+ | RM 800–1,200+ | RM 60,000–90,000+ |
Why this works: In Malaysia, a 1 kW solar system generates approximately 100–120 kWh per month under typical Peninsular conditions. At an average blended TNB tariff of RM 0.52–0.57/kWh, that is RM 52–68 in monthly savings per kW installed. Divide your bill by RM 75 for a quick estimate of the kW system you need.
Quick Bill-Based Formula
System size (kW) ≈ Monthly Bill (RM) ÷ 75
- RM 300 bill → 300 ÷ 75 = 4 kW system
- RM 500 bill → 500 ÷ 75 = 6–7 kW system
- RM 800 bill → 800 ÷ 75 = 10–11 kW system
- RM 1,200 bill → 1200 ÷ 75 = 15–16 kW system
Use our solar savings calculator to enter your exact bill and get a personalised estimate including ROI projections.
Method 2: Roof Space Method
If you want to maximise your roof's potential (rather than just offsetting your current bill), start from available roof area instead. This approach is popular for new homeowners expecting electricity usage to increase.
Malaysia Solar Panel Space Requirements
A standard 450W–550W solar panel measures approximately 2.1m × 1.1m = 2.3 m². In Malaysia's climate, accounting for row spacing to avoid self-shading:
- 1 kW of solar requires approximately 5.5–7 m² of usable roof space
- A 6 kW system needs roughly 36–42 m² of south/west-facing roof
- A 10 kW system needs roughly 60–70 m² of usable roof
Roof Space Calculator
Measure your available south or west-facing roof area (avoid areas with shade from trees, water tanks, or neighbouring buildings). Then:
Maximum system size (kW) ≈ Usable roof area (m²) ÷ 6.5
For example: a 50 m² rooftop → 50 ÷ 6.5 ≈ 7.7 kW maximum. You would then select a 6 kW or 8 kW system depending on your bill and budget. Browse our 6 kW system packages and 8 kW system packages to compare options.
The Recommended Approach: Combine Both Methods
The most robust sizing strategy uses both methods together:
- Calculate the bill-based size (what you need)
- Calculate the roof-based maximum (what fits)
- Choose the smaller of the two — or add battery storage if you want to capture excess generation
Example: Bill suggests 10 kW, roof fits 8 kW maximum. In this case, install 8 kW and offset your bill by roughly 80%, with the remaining 20% from the grid. This is a perfectly common and economical outcome.
Common Solar Sizing Mistakes in Malaysia
These are the errors our survey team sees most often — each one costs homeowners money:
Mistake 1: Oversizing the System
Installing a larger system than you actually need wastes capital. Under Solar ATAP, excess electricity exported to the grid earns only RM 0.218/kWh — far less than the RM 0.52–0.57/kWh you save by self-consuming. An oversized system sends too much electricity to TNB at a discount instead of offsetting your own bill at full tariff value.
Rule: Target 70–90% self-consumption rate. Size to offset, not to export.
Mistake 2: Undersizing the System
Conversely, a system that is too small leaves significant savings on the table. If your bill is RM 800 and you install only 4 kW, you are capturing less than half the potential savings — and your payback period stretches unnecessarily. The incremental cost of adding more kW during initial installation is much lower than upgrading later.
Mistake 3: Ignoring Future Load Growth
Planning to buy an EV? Adding air conditioning to a new room? Installing a heat pump water heater? Factor these in when sizing. A 6 kW system for a current RM 400 bill may be undersized within 2 years if you add an EV charger drawing 7 kW. Panel quality also affects long-term output — understand how panel degradation affects your system's lifetime yield when deciding on system size.
Mistake 4: Not Accounting for Roof Shading
Shading from a single obstacle can reduce total system output by 20–40% if microinverters or power optimisers are not used. Always conduct a proper shading analysis before finalising system size. Our surveyors use Solargis irradiance data for every Trexon installation.
Mistake 5: Using Total Roof Area Instead of Usable Area
Not all roof space is usable. Deduct area for: water tanks, A/C compressors, skylights, access hatches, shaded zones, and required setbacks from roof edges (typically 0.5m). Many homeowners overestimate usable area by 30–40%.
Quick Reference: System Size by Bill Range
| Monthly Bill | System Size | Panels Needed | Roof Area Required | Monthly Savings | Price Range | Payback Period |
|---|---|---|---|---|---|---|
| RM 200–350 | 3–4 kW | 6–9 panels | 20–28 m² | RM 130–200 | RM 12k–18k | 6–8 years |
| RM 350–650 | 5–6 kW | 10–13 panels | 32–42 m² | RM 220–350 | RM 18k–26k | 5–7 years |
| RM 650–1,000 | 8–10 kW | 16–22 panels | 50–65 m² | RM 380–520 | RM 28k–38k | 5–6 years |
| RM 1,000–1,500 | 12–15 kW | 24–33 panels | 75–100 m² | RM 550–750 | RM 38k–55k | 4–6 years |
Professional Survey: What Happens During a Trexon Site Visit
Beyond the calculator, every Trexon installation begins with a comprehensive site assessment:
- Roof structural check: Load-bearing capacity for panel weight (10–14 kg per panel)
- Shading analysis: Using Solargis irradiance maps and on-site measurement
- TNB meter inspection: Confirming bi-directional meter compatibility for Solar ATAP
- Wiring audit: Ensuring existing DB box and earthing meet safety standards
- Inverter location planning: Ventilation, cable routing, and monitoring access
The RM100 priority site visit typically takes 45–60 minutes, and the full RM100 is credited when you proceed. Book the visit online or view our full pricing and package options.
Battery Storage: When Does It Make Sense?
If your roof is already maxed out but you want to capture more value from your solar system, battery storage is the next step. Batteries store excess daytime generation for use at night — effectively raising your self-consumption rate from 70% to 90%+.
Battery systems typically add RM 15,000–35,000 to system cost (10–15 kWh capacity). They make strongest financial sense for households with:
- Evening-heavy electricity usage (air conditioning running until midnight)
- Planned EV ownership (charging overnight from stored solar)
- Frequent power outages (battery provides backup power)
Ready to find the right system size for your home? Use our solar calculator or browse our complete package pricing to get started today.