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Capstone: Read and Reduce Your Electricity Bill
A worked exercise to finish the course. Aina reports to the owner of our example office tower: sort the September 2026 TNB bill by what drives each line, value a saved kWh at the marginal rate, and price three options against a shoplot's LV bill.
Tan Kok XinUnderstanding Your Electricity Bill
Part 7 of 7 in Cobler's Understanding Your Electricity Bill course. New here? See the course page.
Aina has the tower's September 2026 TNB (Tenaga Nasional Berhad) bill on her desk again. It's the same RM310,532 bill the owner handed her in her first week, with two questions. "Why is it so high, and what can we do?" This time there's a blank page next to it for her answer, and we'll write it with her.
The method is simple to say. To read and reduce an electricity bill, we sort each line by what drives it. Then we value each option only by the lines it really changes. For the tower, on the MV (medium voltage) non-domestic General tariff, a saved kWh is worth 33.50 sen. A kW taken off the month's highest half hour is worth RM89.27. For the café owner in the shoplot, on LV (low voltage) non-domestic General, only kWh matter.
The tasks below use both buildings' September 2026 bills, and they value three options for the tower:
- lowering its maximum demand by 100 kW
- moving a load out of the 2pm to 10pm Time-of-Use window
- keeping the power factor above 0.85
How to use this exercise
Each task gives you some information and asks a few questions. Try the questions first, with a calculator and a notepad. Then open the worked answer under each task to check your working.
Both buildings are made up, and their numbers are consistent across Cobler's courses. Tariff figures are the RP4 rates (the TNB tariff structure in force since July 2025) for Peninsular Malaysia. The Automatic Fuel Adjustment (AFA) figure is for September 2026. All ringgit figures are before the KWTBB levy and tax, as in Part 3.
You'll need four ideas from earlier parts:
- Energy (kWh) is what most lines charge for, and power (kW) is the rate. From Part 1.
- Each bill line is a meter reading multiplied by a price. From Part 3, Your TNB Bill, Line by Line, which holds both bills in full.
- Maximum demand (MD) is the highest 30-minute average kW in the month, and on MV General it counts at any hour. From Part 4.
- The ToU peak window and the power factor surcharge. From Part 5 and Part 6.
Task 1: What drives each line
Let's start with the two September 2026 bills from Part 3, line by line.
- Office tower (MV General): energy RM149,150, capacity RM47,088, network RM95,744, retail RM200, AFA RM18,350. Total RM310,532 for 500,000 kWh and an MD of 1,600 kW.
- Shoplot (LV General): energy RM2,162.40, capacity RM706.40, network RM1,185.60, retail RM20.00, AFA RM293.60. Total RM4,368.00 for 8,000 kWh.
- For each building, sort the lines into three piles: kWh lines, maximum demand lines and fixed lines. How much is in each pile?
- Which piles can Aina influence, and which can the café owner influence?
Show the worked answer
1. For the tower:
- Follows kWh: energy and AFA, RM149,150 + RM18,350 = RM167,500 (54% of the bill).
- Follows maximum demand: capacity and network, RM47,088 + RM95,744 = RM142,832 (46%).
- Fixed: retail, RM200 (under 0.1%).
For the shoplot:
- Follows kWh: energy, capacity, network and AFA, RM2,162.40 + RM706.40 + RM1,185.60 + RM293.60 = RM4,348.00 (99.5%). On LV, capacity and network are charged per kWh, so they sit in this pile.
- Follows maximum demand: nothing. An LV bill has no per-kW charge.
- Fixed: retail, RM20 (0.5%).
2. Aina can influence two piles. She can shrink the kWh pile by using less energy, and the demand pile by lowering the month's highest half hour. Together they're all but RM200 of the bill. The café owner can influence only the kWh pile, which is nearly the whole bill. The retail charge doesn't change for either of them.
So the answer to "why is it so high?" has two parts. The tower used 500,000 kWh, and nearly half the bill came from a single half hour at 1,600 kW. As Part 4 showed, the tower's load factor is about 0.43. Its peak stands well above its average, and that makes the demand pile large.
The tower's bill has two piles that Aina can influence, and the shoplot's bill has one.
Task 2: What a saved kWh is worth
So what is a saved kWh actually worth on each bill? Let's take one floor of the tower. The level 12 east office floor uses 7,392 kWh a month, for its lighting, its sockets and the supply fan of air handling unit AHU-12A. That figure comes from Read a Building's Electrical Story, the capstone of our Electricity Fundamentals course.
- What do those kWh add to the tower's bill? Use the lines that follow kWh.
- Aina's first draft divided the bill by the kWh to get an average cost of 62.1 sen/kWh. She multiplied the floor's kWh by that. What answer did she get, and why is it wrong for valuing a saving?
- What is one saved kWh worth to the café owner?
Show the worked answer
1. On MV General, a kWh adds to the energy line (29.83 sen) and the AFA line (3.67 sen in September 2026). That's 33.50 sen for each kWh, the marginal rate, which is the change in the bill for one more or one fewer kWh.
- Energy: 7,392 × 29.83 sen = RM2,205.03
- AFA: 7,392 × 3.67 sen = RM271.29
- Together: 7,392 × 33.50 sen = RM2,476.32 a month.
2. The average rate is RM310,532 ÷ 500,000 kWh = 62.1 sen/kWh, or 62.1064 sen more exactly. At that rate, 7,392 kWh comes to about RM4,590.91, which overstates the answer by about RM2,114.59.
That's because the average includes the capacity and network lines, and those fall only if the month's highest half hour falls. If the floor used fewer kWh, the MD would fall only if the saving cut the load in that one 2:30pm half hour. And only the bill's MD reading can confirm that. So Aina values kWh savings at 33.50 sen, and adds a demand saving only when the peak really falls.
3. For the shoplot, every line except retail follows kWh. So a saved kWh removes 27.03 + 8.83 + 14.82 + 3.67 = 54.35 sen from the energy, capacity, network and AFA lines. The shoplot's average of about 54.6 sen/kWh (RM4,368 ÷ 8,000) is only slightly higher, because only the RM20 retail charge is left out.
Worth knowing: The average cost of a kWh on a bill doesn't tell you what a saved kWh is worth. On the tower's bill the average is 62.1 sen, but a saved kWh removes only 33.50 sen, because nearly half the bill follows the peak. On the shoplot's LV bill the two are almost the same.
Task 3: The half hour that sets the demand charge
Now for the demand pile. The tower's monitoring system logs the energy used in each half hour. So let's look at part of Thursday 17 September 2026, a hot weekday afternoon. The month's highest reading falls on this afternoon.
Half hour | Energy in the half hour (kWh) |
|---|---|
12:00 to 12:30 | 710 |
12:30 to 13:00 | 695 |
13:00 to 13:30 | 725 |
13:30 to 14:00 | 755 |
14:00 to 14:30 | 785 |
14:30 to 15:00 | 800 |
15:00 to 15:30 | 790 |
15:30 to 16:00 | 770 |
16:00 to 16:30 | 745 |
16:30 to 17:00 | 715 |
- Turn each reading into an average demand in kW.
- What is the maximum demand, and when was it set?
- What does this MD cost for the month on MV General?
Show the worked answer
1. Each reading is energy over half an hour. Average power = energy ÷ time = kWh ÷ 0.5 h, which is the same as kWh × 2. For example, 710 kWh in half an hour is an average of 1,420 kW. The ten averages are 1,420, 1,390, 1,450, 1,510, 1,570, 1,600, 1,580, 1,540, 1,490 and 1,430 kW.
2. The highest half hour is 2:30pm to 3:00pm at 1,600 kW (800 kWh × 2). No other half hour in September is higher, so the month's MD is 1,600 kW. For this exercise, assume the logged half hours line up with the periods the TNB meter uses. The TNB meter's own MD register is what appears on the bill.
3. On MV General, the capacity and network lines together are RM89.27 per kW. So 1,600 kW × RM89.27 = RM142,832, the demand pile from Task 1.
The tallest half-hour bar sets the maximum demand. On the tower's General tariff a half hour at any time of day counts, so the shaded ToU peak window doesn't matter here.
Task 4: Option one, a lower peak
So the peak is the 2:30pm half hour, and that gives Aina her first option. She'd hold the tower's highest half hour to 1,500 kW. Part 4 put a figure on this, and here she checks it against the peak-day log and the bill lines.
The building management system (BMS) would briefly hold off flexible loads as demand nears the limit. Those are the car park ventilation fans, the water transfer pumps that refill the roof tanks, and a small reset of the chilled water temperature. The loads run a little later instead, so the load is moved, not removed.
- Look at the peak day in Task 3. Which half hours are above 1,500 kW, and how many kW must be held off in each?
- Which bill lines change, by how much, and what is the new total?
- What would it be worth over a year, and what has to be true for that figure to hold?
Show the worked answer
1. Five half hours are above 1,500 kW: 1:30pm (1,510 kW), 2:00pm (1,570), 2:30pm (1,600), 3:00pm (1,580) and 3:30pm (1,540). The BMS must hold off 10, 70, 100, 80 and 40 kW in those half hours. Held for half an hour each, that's (10 + 70 + 100 + 80 + 40) × 0.5 = 150 kWh, which is used later in the afternoon instead.
2. Only the two per-kW lines change:
- Capacity falls by 100 × RM29.43 = RM2,943, to RM44,145.
- Network falls by 100 × RM59.84 = RM5,984, to RM89,760.
- The saving is RM8,927 for the month, the same as 100 × RM89.27. The new total is RM310,532 − RM8,927 = RM301,605, about 2.9% lower.
The energy and AFA lines stay the same, because the kWh were moved, not saved. Retail stays at RM200.
3. If the peak is held 100 kW lower every month, the saving is 12 × RM8,927 = RM107,124 a year. That holds only if no half hour in any month goes above the target. One hot afternoon that the BMS misses sets that month's MD, and the saving for that month is lost.
Holding the tower to 1,500 kW means trimming five half hours. The 150 kWh held off are used later, so only the demand lines fall.
Task 5: Option two, moving a load
Aina's second idea came from Part 5. She could move a flexible load, such as the water transfer pumps, so that it runs before 2pm or after 10pm on weekdays.
- The tower is on MV General. What does moving the load save on the energy and AFA lines?
- When would the move save anything at all?
- Part 5 found that ToU would cost the tower about RM6,172 more a month. Would switching to MV ToU make moving loads worthwhile?
- The café owner asks the same question about the shoplot, which is open from 8am to 10pm every day. What would you say?
Show the worked answer
1. Nothing. On a General tariff every kWh costs the same at every hour, which on the tower's bill is 29.83 sen energy plus 3.67 sen AFA. So moving a kWh from 3pm to 11pm leaves both lines unchanged.
2. Only if the move lowers the month's highest half hour. Then it saves RM89.27 for each kW taken off the peak, but that's option one again. Aina counts it once, in Task 4, not twice.
3. No. On MV ToU, each kWh moved from the peak window to off-peak saves 31.32 − 27.23 = 4.09 sen. In September 2026, ToU would have cost the tower RM12,464 more on demand and RM6,292.40 less on energy, so RM6,171.60 more in total.
Just to break even, the tower would have to move about RM6,171.60 ÷ RM0.0409 ≈ 150,900 kWh a month out of the window. That's over nine-tenths of the 164,000 kWh it uses there, while its offices are occupied until 6pm. The demand line would also stay RM7.79 per kW higher on ToU for whatever peak is left in the window. So the tower stays on General, and option two is worth nothing on its own.
4. On LV General, moving a load saves the café owner nothing either, and there's no demand line to lower. On LV ToU, the capacity and network rates per kWh are the same as on LV General, so only the energy rates differ. The LV ToU rates sit 1.49 sen above and 2.60 sen below the LV General rate, the same gaps as on MV.
So Part 5's break-even applies, and ToU lowers the bill only if more than about 36% of the shoplot's kWh fall outside the window. Weekday mornings until 2pm and all of Saturday and Sunday are off-peak, but the café's evenings are inside the window. The café owner needs a month of half-hour data from the meter to check the share before switching.
Task 6: Option three, the power factor
The tower's September bill shows a power factor of 0.92 and no surcharge. Aina's third option is to keep it that way. She'd check the power factor on every bill and have the capacitor banks maintained, so that a failed step doesn't go unnoticed.
- What is this option worth on the September 2026 bill?
- What would each 0.01 below 0.85 cost the tower in a September-sized month?
- Does the same apply to the shoplot?
Show the worked answer
1. Nothing on this bill. At 0.92, the tower pays no surcharge, so there's no line to reduce. The option protects against a charge rather than reducing one.
2. Below 132 kV, the surcharge is 1.5% of the energy, demand and AFA charges for each 0.01 below 0.85 (Part 6). Those charges are RM149,150 + RM142,832 + RM18,350 = RM310,332. So each 0.01 below 0.85 would cost 1.5% × RM310,332 = RM4,654.98 a month. Part 6 worked out the cost at a power factor of 0.80.
3. TNB's published rule doesn't say how the surcharge applies to LV accounts, and the shoplot's September bill has no power factor line. So the café owner should check the bill rather than assume either way.
Aina's report
So now Aina can write her report, and it answers the owner's two questions in plain terms. The bill is high because the tower used 500,000 kWh, worth RM167,500 at 33.50 sen each. And one half hour at 2:30pm on 17 September set RM142,832 of capacity and network charges. Of the three options, only lowering the peak changes this month's bill. She also adds the shoplot as a contrast, because the café owner asked her the same question.
Option | Office tower (MV General) | Shoplot (LV General) |
|---|---|---|
Lower the highest half hour by 100 kW | RM8,927 a month, or RM107,124 a year if held every month | Nothing, because there's no per-kW charge |
Move a load out of 2pm to 10pm | Nothing on its own. It counts only if it lowers the peak, and then it's option one. ToU would cost about RM6,172 more a month | Nothing on LV General. On LV ToU, only if more than about 36% of kWh are off-peak |
Keep power factor above 0.85 | Nothing today (PF 0.92), but it avoids RM4,654.98 a month for each 0.01 below 0.85 | No published LV rule, so check the bill |
Use fewer kWh | 33.50 sen per kWh saved, plus RM89.27 per kW if the peak also falls | 54.35 sen per kWh saved |
That's the answer we set out to write with her in Part 1, with a ringgit figure against each option. Her recommendation has four parts:
- Start with demand limiting through the BMS.
- Keep the monthly power factor check.
- Stay on the General tariff.
- Look for kWh savings, valued at 33.50 sen each.
All these savings are before KWTBB, which is 1.6% of the kWh and kW charges (Part 3), so the real saving would be slightly higher. For how a BMS holds a demand limit in practice, see Load Shedding and Demand Limiting with a BMS.
Where to go next
If one task gave you trouble, go back to the part it draws on:
- Task 1: Your TNB Bill, Line by Line
- Task 2: Power vs Energy: What You Actually Pay For
- Tasks 3 and 4: Maximum Demand: Why One Bad Half-Hour Costs So Much and How Electricity Meters Work
- Task 5: Time-of-Use, Green Tariffs and Avoidable Penalties
- Task 6: Power Factor Correction: What Capacitor Banks Do
If all six tasks made sense, you've finished the course, and Aina's report is with the owner. The owner's next question is easy to guess. Is demand limiting worth what it costs? That's the subject of our Energy Management: The Economics of Saving Energy course. It takes the tower's options further, to measuring a baseline, proving a saving, and judging a project with payback and discounted cash flow.
Check your understanding
1. A tenant's lighting upgrade in the tower saves 2,000 kWh a month, and the bill's MD doesn't change. What does the bill fall by?
Show the answer
2,000 × 33.50 sen = RM670 a month, from the energy and AFA lines. Valuing it at the 62.1 sen average would give about RM1,242. That wrongly counts capacity and network charges that didn't change.
2. The café owner hears that the tower could save RM8,927 a month by lowering its peak. Would staggering the café's air conditioners to lower its peak save money in the same way?
Show the answer
No. The shoplot is on LV General, which has no per-kW demand charge, because capacity and network are charged per kWh. Its bill falls only if it uses fewer kWh, at 54.35 sen for each kWh saved.
Recap
- Sort the bill by what drives each line. On the tower's MV General bill, RM167,500 follows kWh, RM142,832 follows the month's highest half hour and RM200 is fixed.
- On the shoplot's LV General bill, everything except RM20 follows kWh.
- Value a saved kWh at the marginal rate, not the bill's average. That's 33.50 sen for the tower and 54.35 sen for the shoplot. Add RM89.27 per kW only when the peak really falls.
- Holding the tower to 1,500 kW saves RM8,927 a month.
- Moving a load out of the 2pm to 10pm window saves nothing on a General tariff unless it lowers the peak. ToU would cost the tower about RM6,172 more a month.
- Keeping the power factor at 0.92 costs nothing on today's bill. But it avoids RM4,654.98 a month for each 0.01 below 0.85.
This is Part 7 of 7 in Cobler's Understanding Your Electricity Bill course. Previous: Power Factor Correction: What Capacitor Banks Do.
Cobler builds CobiNeural, a platform that shows a facility team its building's energy, water and indoor air data as live numbers across the whole site. To see how your building performs, talk to us.
FAQ
Frequently asked questions
It depends on the tariff. On MV non-domestic General, a saved kWh removes the energy charge (29.83 sen) and the AFA (3.67 sen in September 2026), 33.50 sen in total. The capacity and network charges fall only if the month's maximum demand falls. On LV non-domestic General, capacity and network are charged per kWh, so a saved kWh removes 27.03 + 8.83 + 14.82 + 3.67 = 54.35 sen. Do not use the bill's average cost per kWh to value a saving on an MV bill. For our example office tower the average is 62.1 sen, which overstates a kWh saving by about 85%.
On MV non-domestic General, the capacity and network charges total RM89.27 per kW, so 100 kW less maximum demand saves RM8,927 in that month. For our example office tower, that takes the September 2026 bill from RM310,532 to RM301,605 before KWTBB and tax. The saving holds only in months where no half hour goes above the new target. On an LV bill there is no per-kW charge, so lowering the peak saves nothing.
Only on a Time-of-Use tariff, or if the move lowers the month's highest half hour. On a General tariff every kWh costs the same at every hour, so moving load saves nothing on the energy and AFA lines. On MV ToU each kWh moved off-peak saves 4.09 sen, but ToU also charges RM7.79 per kW more for demand in the peak window. For our example office tower, whose peak is at 2:30pm on a weekday, ToU would cost about RM6,172 more a month.
Nothing on a bill that already has no surcharge, but it avoids one. Below 132 kV, TNB adds 1.5% of the energy, demand and AFA charges for each 0.01 below 0.85. For our example office tower, whose energy, demand and AFA charges were RM310,332 in September 2026, each 0.01 below 0.85 would cost RM4,654.98 a month. Check the power factor on every bill and keep the capacitor banks maintained.
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