The single most important document for sizing your solar system is your TNB electricity bill. Yet most homeowners hand it to their installer without understanding what it says. This guide teaches you to read your bill like a solar engineer — and verify that your installer's recommendation actually makes sense for your usage.
The Key Numbers on Your TNB Bill
A standard TNB residential bill (Tariff A) contains three numbers that drive your solar system sizing decision:
1. Monthly kWh Consumption
Find this under the heading "Jumlah Unit Digunakan" or "Total Units Consumed". It appears in your Current Month column. This is your most critical number — the total kilowatt-hours of electricity your household consumed in that billing cycle.
Rule of Thumb: A properly sized residential solar system should generate 70–90% of your monthly kWh consumption. Aiming for 100% often means oversizing, which reduces your ROI.
2. Tariff Block Breakdown
Malaysia's TNB Tariff A is a tiered (block) tariff. The higher your consumption, the more expensive each additional unit becomes:
| Usage Block | Rate (RM/kWh) | What This Means |
|---|---|---|
| First 200 kWh (0 – 200) | RM 0.219/kWh | Your cheapest electricity |
| Next 100 kWh (201 – 300) | RM 0.334/kWh | 50% more expensive |
| Next 100 kWh (301 – 400) | RM 0.516/kWh | More than double the base rate |
| Next 100 kWh (401 – 500) | RM 0.546/kWh | High consumption penalty |
| Above 500 kWh | RM 0.571/kWh | Peak tier — highest savings from solar |
Why this matters for solar: Every unit of solar electricity you self-consume replaces a unit from TNB. If you are consistently in Tier 4 or 5 (above 400 kWh/month), each unit of solar is saving you RM 0.546–0.571 instead of RM 0.219. This dramatically improves your ROI compared to low-consumption households.
3. Minimum Monthly Charge
TNB charges a Minimum Monthly Charge (MMC) of RM 3.00 regardless of how much solar you generate. This is the irreducible minimum on your bill — you will always receive at least a RM 3 charge even if your net import is zero.
Step-by-Step: Using Your TNB Bill to Size Your Solar System
Step 1: Find Your Average Monthly Consumption
Pull out your last 12 TNB bills (or download them from the TNB website or myTNB app). Add up all 12 months' kWh consumption and divide by 12. This gives your average monthly kWh.
Using just one month can be misleading — bills spike in March–May and October–November during hot spells when air conditioning usage peaks.
Step 2: Calculate Daily kWh
Divide your average monthly kWh by 30. This is your daily energy consumption.
- Monthly average 600 kWh ÷ 30 = 20 kWh/day
- Monthly average 400 kWh ÷ 30 = 13.3 kWh/day
- Monthly average 900 kWh ÷ 30 = 30 kWh/day
Step 3: Apply the Solar Sizing Formula
Malaysia receives an average of 4.5 to 5.0 peak sun hours (PSH) per day, varying by state and season. Use a conservative estimate of 4.5 PSH for reliable sizing.
Formula: System Size (kWp) = Daily Consumption (kWh) ÷ Peak Sun Hours ÷ System Efficiency
System efficiency (accounting for inverter losses, cable losses, temperature derating) is approximately 0.80 for a well-designed system.
- 20 kWh/day ÷ 4.5 PSH ÷ 0.80 = 5.56 kWp → round up to 6 kWp
- 13.3 kWh/day ÷ 4.5 PSH ÷ 0.80 = 3.69 kWp → round up to 4 kWp
- 30 kWh/day ÷ 4.5 PSH ÷ 0.80 = 8.33 kWp → round up to 8–9 kWp
Step 4: Apply the Solar ATAP Cap
Under Solar ATAP, domestic system capacity is capped at 5 kW for single-phase and 15 kW for three-phase connections per §8 of GP/ST/No. 60/2025. Systems exceeding these limits require a Connection Confirmation Check (CCC). Confirm your phase type with TNB before sizing.
Example: Reading a Real TNB Bill for Solar Sizing
Let's say your bill shows:
- Month: January 2026, 31-day billing period
- Total kWh consumed: 587 kWh
- Bill amount before Solar ATAP: RM 285.20
- Tariff breakdown: 200 kWh × RM 0.219 + 100 kWh × RM 0.334 + 100 kWh × RM 0.516 + 100 kWh × RM 0.546 + 87 kWh × RM 0.571
Sizing calculation:
- Daily consumption: 587 ÷ 31 = 18.9 kWh/day
- System size needed: 18.9 ÷ 4.5 ÷ 0.80 = 5.25 kWp → recommend a 6 kWp system
- Why not 5kWp?: The extra 1kWp costs only ~RM 2,500 more but generates an additional 135 kWh/month, saving an extra RM 77/month in Tier 4/5 electricity.
Special Cases: What to Look For on Commercial TNB Bills
If you are sizing solar for a shop, office, or light industrial space (TNB Tariff B, C, D, or E), your bill includes an additional field: Maximum Demand (MD) in kVA. This is the peak power your premises consumed at any 30-minute interval during the month. TNB charges for this demand capacity regardless of whether you used it consistently.
Solar can reduce your MD charge if panels generate power during your peak demand period (usually 2–5pm). However, MD reduction requires careful system design — a topic for your solar engineer to address with a half-hourly consumption data analysis.
Three Situations Where Standard Sizing Rules Break Down
1. Night-Shift Households
If you work night shifts and most of your power usage occurs between 8pm and 7am, solar's daytime generation won't match your consumption pattern. Solar ATAP's export credit (RM 0.218/kWh) partially compensates, but ROI will be lower than a family home with daytime consumption. In this case, consider adding battery storage or sizing the system smaller.
2. EV Charger Owners
If you own or plan to own an EV, add 150–300 kWh to your monthly consumption estimate to account for charging. A Tesla Model 3 consuming 200km/month at 15 kWh/100km uses 30 kWh/month. A BYD Atto 3 driven 1,500km/month uses approximately 225 kWh/month in charging. Add these to your TNB bill baseline before sizing. See our guide on solar and EV charger combos.
3. Planned Upgrades
If you plan to add an air conditioner, pool, or EV within the next 3 years, size your solar system for your future consumption, not just today's bill. The marginal cost of adding 1–2 extra panels now versus installing a second system later is significant.
Use our Solar Savings Calculator to input your TNB bill figures and get an instant system size recommendation and ROI projection for your specific address and consumption pattern.