How to Size a BESS for Peak Shaving: A Worked Malaysian Factory Example

By: Progressture Solar | Last verified: 29 July 2026

Size a BESS for peak shaving from the factory’s interval load and billed demand events—not from monthly kWh consumption alone. First set a realistic kW reduction target, then find how long that reduction must be sustained, then convert delivered energy to nameplate capacity after allowing for usable state of charge, efficiency, degradation and reserve. Finally, simulate it against the tariff and operational constraints.

Start with 12 months of interval data

Use the same granularity TNB uses for billing where available, and identify each month’s actual maximum-demand event, its time, duration and recurrence. A battery that succeeds on a typical day can fail economically if a single unprotected spike establishes the month’s billed demand.

For an MV-ToU site, verify the current peak-period and demand-charge rules with TNB. The TNB tariff page lists MV-ToU peak energy of 31.32 sen/kWh, capacity of RM30.19/kW per month and network of RM66.87/kW per month, effective 1 July 2025. These published values support an illustrative calculation only; confirm the account’s actual tariff, billing rules and AFA.

Worked example — capacity and power are different

Assume a factory’s interval profile shows it can lower a recurring peak by 250 kW for two hours. The desired delivered energy is:

250 kW × 2 hours = 500 kWh delivered.

Assume the system is designed to use only 80% of nominal battery capacity and discharge-side efficiency is 90%. Required nominal energy is:

500 ÷ (0.80 × 0.90) = 694 kWh, rounded conceptually to about 700 kWh before adding degradation margin, minimum reserve, auxiliary loads, warranty limits and a dispatch contingency.

The battery also needs at least 250 kW of discharge capability at the relevant operating conditions. A 700 kWh battery with inadequate kW power capability will not meet this task.

Demand-charge value in the example

If the 250 kW reduction is achieved in the tariff-relevant monthly peak and holds every month, applying only the listed MV-ToU peak capacity and network charges gives:

250 kW × (RM30.19 + RM66.87)/kW-month × 12 = RM291,180/year.

This is a gross demand-charge illustration. It excludes energy used to charge, round-trip losses, AFA, control/availability shortfall, BESS capex, financing, maintenance, degradation, taxes and any tariff or billing-rule changes.

Why energy arbitrage can be much smaller than demand value

Using the same 500 kWh discharged per weekday, assume 90% round-trip efficiency, 260 operating days/year and only the listed MV-ToU energy prices. Peak energy avoided is 500 × RM0.3132 = RM156.60/day. Charging energy is 500/0.90 = 556 kWh × RM0.2723 = RM151.28/day. The nominal energy-price difference is roughly RM5.32/day or RM1,384/year, before AFA and other effects.

That does not mean all batteries lack value; it means the revenue stack must be simulated rather than assumed. Here, the proposed demand reduction dominates the simple energy-arbitrage line.

Design checks before procurement

• Test worst-month peaks, not annual averages, and include production changes and start-up loads.

• Reserve state of charge for the highest-risk peak window and define what happens after an unexpected second peak.

• Include PV shape, export restrictions, generator/UPS interfaces, transformer limits and protection coordination.

• Select warranty throughput, retained-capacity, availability and response-time terms consistent with the dispatch plan.

• Complete a site-specific safety, approvals, installation, testing and emergency-response plan under current ST requirements.

Internal-link opportunities

• Link “BESS safety” to the BESS Safety Guidelines 2026 article above.

• Link “solar + BESS savings” to article 1.

• Link “request load-profile analysis” to the BESS/commercial-solar enquiry page.

Sources and update warning

• Official: TNB tariff information: https://www.mytnb.com.my/business/understand-your-bill

• Official: ST BESS Safety Guidelines GP/ST/No.62/2026: https://www.st.gov.my/sites/default/files/2026-05/Guidelines-on-Battery-Energy-Storage-System-%28BESS%29-Safety_0.pdf

• Independent technical context: UL 9540A test-method overview: https://www.ul.com/services/ul-9540a-test-method

Staleness warning: tariff components and AFA are not static. Sizing and savings must be re-run on the customer’s current bill, interval data, equipment data sheets and current applicable rules.