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. Once it applies, the morning peak window will be abolished; the evening peak will be 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: when the new framework takes effect, customers will see higher monthly bills as a result of changed time bands on existing consumption profiles, 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 will not start until 17:30 — by which time most rooftop solar generation has ended. Operationally, when 963 takes effect, solar daytime offtake at typical 22 kV C&I sites will split roughly 99.5% standard / 0.5% peak.

The 0.5% 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 marginally more; north-Vietnam winter-month sites with east-facing arrays effectively zero. The 99.5/0.5 split is the operational baseline used in all Arcus modelling, anchored on operational data; operational data shows a small residual peak slice at less than 1% of total daytime offtake — close enough to 100/0 that the briefing's headline revenue impact lands as the practical operational baseline.

In practice: when Decision 963 takes effect, blended realised tariff at 22 kV manufacturing will drop from roughly $0.112/kWh pre-963 to roughly $0.090/kWh post-963 — a revenue cut of up to approximately 20%. Pure-solar economics on the manufacturing tariff compress meaningfully; pairing the array with a BESS overlay offsets much of the revenue impact and keeps solar attractive.

What it means for BESS

BESS arbitrage will get materially better, not worse, when Decision 963 takes effect. 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 will be 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 will be 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 post-963 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 for forward-looking projects.

In practice: BESS investments that pencilled out under the pre-963 framework will be more attractive when 963 takes effect, 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.