Decision 963/QĐ-BCT

What windows changed

Decision 963 keeps the three-tier TOU structure (peak, standard, off-peak) and the Sunday no-peak rule. What it changes is which clock hours fall into each tier. The morning peak window is abolished; the evening peak is now a single continuous 5-hour block; off-peak shifts from late-night/early-morning to early-morning only.

What stayed the same

Three things are explicitly unchanged. First, the VND/kWh rate levels at peak, standard and off-peak by voltage class and customer category remain those set by Decision 1279/QĐ-BCT (signed 9 May 2025, effective 10 May 2025) — a 22 kV manufacturing customer continues to pay roughly VND 3,398/kWh peak, VND 1,857/kWh standard, and VND 1,190/kWh off-peak. Second, the three-tier structure is retained — Vietnam has not moved to a two-tier or capacity-based structure with this decision (that change is governed separately by Decree 146/2025/NĐ-CP for the manufacturing pilot). Third, Sunday's no-peak treatment is preserved.

In practice: customers seeing higher monthly bills after 22 April 2026 are seeing the effect of changed time bands on their existing consumption profile, not changed rates. The rate card has not moved.

Why MOIT moved peak hours later

Vietnam's residential and commercial evening load has grown faster than its industrial load over the last decade, shifting the system peak from late-morning to early-evening. The legacy 09:30–11:30 morning peak window dates to a period when factory startup and morning industrial load drove the system peak; that profile no longer holds. Air-conditioning load in residential and hospitality, evening retail and food service, and the rapid build-out of urban data centres have all pushed peak demand into the 17:00–22:00 window. Decision 963 brings the regulatory peak window into alignment with the actual system peak, mirroring TOU restructures already implemented in Thailand, Singapore and Malaysia over the past five years.

In practice: load-shifting strategies that worked under the morning + evening split (run a process at 12:00 to escape the 09:30–11:30 peak) no longer apply. Strategies that worked against the 17:00–20:00 evening peak now need to extend coverage to 22:30.

What it means for solar PV

Solar PV generates between roughly 06:00 and 17:30 in Vietnam, peaking midday and tailing off through the late afternoon. Under the legacy windows, the 09:30–11:30 morning peak captured approximately two hours of solar generation at the peak rate, plus a sliver of the 17:00–17:30 evening peak before sunset — combining to roughly 24% of typical 22 kV C&I rooftop solar offtake at the peak rate. Under Decision 963, peak does not start until 17:30 — by which time most rooftop solar generation has ended. Operationally, solar daytime offtake at typical 22 kV C&I sites now splits roughly 95% standard / 5% peak.

The 5% peak slice is the residual late-afternoon overlap — varying by latitude, season and panel orientation. South-Vietnam summer-month sites with west-facing arrays may capture closer to 8% at peak; north-Vietnam winter-month sites with east-facing arrays may capture close to 0%. The 95/5 split is the operational mid-case used in all Arcus modelling; the 100/0 split (zero peak capture) is the worst-case used in the underlying briefing as an upper-bound revenue-cut framing.

In practice: blended realised tariff at 22 kV manufacturing drops from roughly $0.112/kWh pre-963 to roughly $0.0906/kWh post-963 — a revenue cut of about 19%. Self-invest payback periods extend by approximately 24%. The briefing's headline 24% revenue cut reflects the 100/0 corner case, not the median outcome.

What it means for BESS

BESS arbitrage gets materially better, not worse. Three changes drive the improvement. First, the peak window consolidates — pre-963 dispatch had to manage a morning peak (09:30–11:30) and an evening peak (17:00–20:00) separately, often requiring two charge–discharge cycles per day with mid-day recharging during standard rate hours. Post-963 dispatch is a single cycle: charge at off-peak (00:00–06:00) and discharge across the continuous 17:30–22:30 evening peak. Second, the dispatch window is wider — the pre-963 evening peak was 3 hours; the post-963 evening peak is 5 hours, an approximately 66% wider earning window. Third, the off-peak charging window is now early-morning rather than late-night, which simplifies dispatch logic and avoids the 22:00–04:00 schedule constraint.

All Arcus BESS modelling now defaults to single-cycle dispatch as the canonical assumption. The dual-cycle dispatch model, which optimised for the pre-963 morning + evening split, remains preserved as an Advanced-panel override on the calculator for legacy comparisons but is no longer the operational default.

In practice: BESS investments that pencilled out under the pre-963 framework are now more attractive, not less. The economic floor under arbitrage is supported by Decision 963; the ceiling rises further if Q2–Q3 2026 brings the next retail tariff revision under the pending Decree 72 amendment.