Decision 963 for factories: the 99.5/0.5 split, a revenue cut of up to 20%, and why BESS is the default response
Decision 963's headline impact on factory solar is a daytime revenue cut of up to 20%. Operational data from post-963 systems anchors the daytime offtake split at 99.5% standard / 0.5% peak. When 963 takes effect, pure-solar economics on 22 kV manufacturing compress meaningfully; pairing the array with a BESS overlay offsets much of the revenue impact and keeps solar attractive for factories with evening load.
Page current as of May 2026. Anchor regulation: Decision 963/QĐ-BCT, issued 22 April 2026; applies from the next EVN average retail tariff adjustment. See the full Decision 963 explainer.
Does Decision 963 hit factory solar economics as hard as the headline suggests?
The headline impact lands close to the briefing's framing — but the route through is clearer than the briefing suggested. Operationally, typical 22 kV factory rooftop solar sees a daytime offtake split of 99.5% standard / 0.5% peak. The headline solar revenue cut is up to approximately 20%.
The interesting question for a factory operator in 2026 is not whether Decision 963 reduces solar revenue — it does, when it takes effect. The interesting question is what to do about it: (a) defer the project, (b) build solar-only and absorb the revenue cut, or (c) build solar+BESS as an integrated configuration that captures the new 5-hour evening peak via stored generation. The right answer depends on factory load profile and BESS capex tolerance, but option (c) is the default rather than the upgrade going forward.
The thesis on this page is straightforward: pure-solar economics on the manufacturing tariff compress to roughly the briefing's headline impact when 963 takes effect. Operational data confirms the residual peak slice at typical sites is small enough (~0.5%) that the gap to the briefing's 100/0 framing is within ~1%. The 99.5/0.5 operational split is the locked Arcus baseline (per BESS Vietnam README §4 canonical). Solar+BESS offsets much of the revenue impact and keeps solar attractive; solar-only leaves material revenue on the table.
In practice: the right baseline for factory solar term sheets is the 99.5/0.5 split with a revenue cut of up to 20%. The financing case for BESS overlay has correspondingly strengthened — it is now the default response, not an optional upgrade, for factories with evening load.
What operational data shows about the post-963 split
Three reasons the 99.5/0.5 split is the operational baseline at typical factory sites, and what it means for the headline revenue impact.
4.1 · The 0.5% peak slice is the late-afternoon overlap, but it's small
Decision 963's new peak window starts at 17:30. South-Vietnam solar generation continues at meaningful output until roughly 18:00 on summer days with west-facing arrays — a small residual stream that lands inside the new peak window. In aggregate across the operating year, across orientations, across seasons, this residual is approximately 0.5% of total daytime offtake. North-Vietnam winter months produce effectively zero (sunset around 17:30 in December–January); east-facing arrays produce close to zero year-round. Even the most favourable south-Vietnam summer-month sites with west-facing arrays struggle to push much above 1%.
Operational data anchors the post-963 daytime offtake split at 99.5% standard / 0.5% peak. The residual peak slice is small, consistent across configurations, and within ~1% of the briefing's 100/0 framing. The headline revenue impact lands close to the briefing's framing.
In practice: the 99.5/0.5 operational baseline is the right starting point for every factory deal. The 100/0 framing remains useful as a directional check — operationally, the gap to 99.5/0.5 is below the noise floor of site-level modelling. Site-specific re-modelling still matters for orientation and shading, but the headline revenue impact is now within ~1 percentage point regardless.
4.2 · Revenue impact at the 99.5/0.5 split
At the 99.5/0.5 split, the math is: standard rate ~$0.085/kWh, peak rate ~$0.197/kWh at 22 kV manufacturing under Decision 1279/QĐ-BCT. Pre-963 blended realised tariff (76/24 split): (0.76 × $0.085) + (0.24 × $0.197) ≈ $0.112/kWh. Post-963 blended realised tariff (99.5/0.5 split): (0.995 × $0.085) + (0.005 × $0.197) ≈ $0.090/kWh. The drop in realised tariff is up to approximately 20%, and that flows directly through to annual solar revenue from EVN-export and self-consumption-displacement at the same proportion.
The cut applies only to the realised-tariff side of the equation. Tariff levels have not moved — only the windows have shifted. The asset still generates the same kWh and still displaces the same imported kWh; what's changed is the share of those kWh that earn the peak rate vs the standard rate. Self-invest factory rooftop solar remains attractive on most sites — the proposition shifts from "daytime self-consumption alone" to "still-good revenue, paired with a BESS overlay that captures the new evening peak". With a BESS overlay sized for the lunch-trough overspill window, combined revenue recovers around half of what would otherwise be lost.
In practice: the right pricing baseline for new factory solar deals is the 99.5/0.5 split with a revenue cut of up to 20%. Pricing should be set against operational data, not pre-963 assumptions.
4.3 · BESS overlay is the default response — it offsets much of the revenue impact
Pre-963, the integrated solar+BESS configuration was often deferred as a Phase 2 expansion — install solar first, see how the bills land, add BESS in year 3 or 4 if economics warrant. Post-963, the case is structurally different. With operational data confirming that virtually no solar generation lands in the new peak window, the 17:30–22:30 evening peak can only be served from a solar asset via storage. Any factory with material evening load (single-shift winding-down operations, second-shift continuing through 22:30, on-site cold storage, evening security and lighting) leaves substantial peak-tariff revenue on the table without a BESS overlay.
The dispatch logic also simplifies. Pre-963 BESS dispatch had to optimise across two charge–discharge cycles per day: charge overnight 22:00–04:00, discharge into the morning peak 09:30–11:30, recharge mid-day at standard rate, discharge into the evening peak 17:00–20:00. Post-963 dispatch is a single cycle: charge off-peak 00:00–06:00, discharge across the 5-hour evening peak 17:30–22:30. The earning window is approximately 66% wider than the pre-963 evening peak alone (5 hours vs 3 hours). All Arcus BESS modelling now defaults to single-cycle dispatch as the canonical assumption.
In practice: integrated solar+BESS is the default product configuration for factory sites with evening load post-963 — paradoxically, Decision 963 made BESS more attractive for factory operators, not less. Solar-only remains viable on sites with very low evening consumption (effectively dawn-to-dusk daytime operations) or where BESS capex is deferred for cash-flow reasons. Outside those carve-outs, building solar without BESS leaves a meaningful share of pre-963 revenue on the table.
Decision 963 terms most relevant to a factory operator
The anchor page covers the full Decision 963 framework. What follows is the narrow slice a factory operator actually uses when modelling solar, BESS, or solar+BESS economics.
- New peak window: 17:30–22:30 Mon–Sat (5h continuous) Solar generation has largely ended by 17:30 at typical south-Vietnam factory sites. The 5-hour continuous block is the BESS dispatch window, not the solar generation window. For factories with second-shift operations running through 22:30, every kWh consumed in this band that is not displaced by stored generation is billed at the peak rate (~VND 3,398/kWh at 22 kV manufacturing under Decision 1279).
- 99.5/0.5 daytime offtake split (operational baseline) Locked Arcus operational baseline for typical 22 kV manufacturing rooftop solar — replaces the pre-963 76/24 split. The 0.5% peak slice is the residual late-afternoon overlap (17:30–~18:00) before sunset, anchored on operational data. North-Vietnam winter and east-facing arrays produce effectively zero peak capture; south-Vietnam summer and west-facing arrays push marginally above 0.5%. The gap to the briefing's 100/0 framing is below ~1 percentage point.
- New off-peak window: 00:00–06:00 (6h early-morning) Shifted forward by 2 hours from the legacy 22:00–04:00 window. Total off-peak hours unchanged. For BESS dispatch this is the charging window — wider and simpler than the legacy late-night/early-morning split. For factories running 24/7 production, the off-peak window now overlaps with shift-change-and-clean-down periods rather than active production, which often improves the on-site self-consumption rate of grid-imported off-peak kWh.
- Single-cycle BESS dispatch (post-963 canonical) Charge once at off-peak 00:00–06:00, discharge once across the 17:30–22:30 evening peak. Simpler than the pre-963 dual-cycle model, with a wider dispatch window. All Arcus BESS modelling defaults to single-cycle dispatch as the canonical assumption from 22 April 2026 onwards. The dual-cycle model is preserved as an Advanced-panel override on the calculator but is no longer the operational default.
- Tariff-hedge thesis: standard-rate band rises fastest on next revision Decision 963 is windows-only — rate levels under Decision 1279 are unchanged. The next retail tariff revision (plausibly Q2–Q3 2026 if the pending Decree 72 amendment for 2022–2024 EVN loss recovery is enacted) is likely to lift all tier rates roughly proportionally. For factories with rooftop solar self-consumption, this means the standard-rate band rises fastest in absolute VND/kWh terms — and self-consumption rooftop solar effectively hedges that increase. The hedging value of solar PV grows under the next retail tariff revision; modelling against today's Decision 1279 levels understates the long-run case.
Worked example — a 22 kV factory rooftop solar PPA pre-963 vs post-963
A 1 MWp rooftop solar installation at a 22 kV manufacturing site in Binh Duong, single-shift operations
Setup
- Site typeManufacturing facility, 22 kV connection, Binh Duong province (South)
- Solar size1 MWp rooftop, ~1,500 kWh/MWp/yr specific yield → ~1,500 MWh/yr generation
- Self-consumption~80% of generation consumed on-site (1,200 MWh/yr), ~20% overspill (~300 MWh/yr — within Decree 58 cap)
- Tariff schedule22 kV manufacturing under Decision 1279/QĐ-BCT: ~$0.085/kWh standard, ~$0.197/kWh peak, ~$0.027/kWh off-peak
- Solar daytime splitPre-963: 76/24 (standard/peak). Post-963: 99.5/0.5 (operational baseline anchored on operational data)
- TOU window sourcePre-963: Circular 16/2014 (peak 09:30–11:30 + 17:00–20:00). Post-963: Decision 963/QĐ-BCT (peak 17:30–22:30)
The numbers — solar-only configuration
| Component | Pre-963 (76/24 split) | Post-963 (99.5/0.5 split) |
|---|---|---|
| Share of solar offtake at standard rate | 76% | 99.5% |
| Share of solar offtake at peak rate | 24% | 0.5% |
| Blended realised tariff | ~$0.112/kWh | ~$0.090/kWh |
| Solar revenue (annual) | ~$167,800/yr | ~$135,000/yr |
| Revenue cut vs pre-963 baseline | — | up to ~−20% (~$32,800/yr) |
Adding a BESS overlay — what it offsets
| Component | Solar-only post-963 | Solar + BESS overlay post-963 |
|---|---|---|
| BESS sizing | n/a | 200 kW / 400 kWh (sized to match the lunch-trough overspill window, when on-site load drops and solar generation is at midday peak) |
| Daily charging energy required vs available midday overspill | n/a | ~360 kWh/day required (400 kWh × 90% DoD) against ~500 kWh/day practical overspill (~50% of headline daily overspill, the lunch-trough portion realistically captured) — non-binding |
| BESS dispatched annually | n/a | ~99,000 kWh/yr (300 cycles × 90% DoD × 92% RTE) |
| Solar revenue (annual) | ~$135,000/yr | ~$135,000/yr (unchanged) |
| BESS revenue at peak rate | — | ~$16,400/yr (~50% of the ~$32,800/yr solar revenue lost to 963) |
| Combined annual revenue | ~$135,000/yr | ~$151,400/yr |
| Combined capex (1 MWp solar + 400 kWh BESS @ $190/kWh) | ~$900,000 | ~$976,000 |
| Effective recovery of revenue lost to 963 | 0% | ~50% |
Interpretation
Where the silver linings sit. Once Decision 963 takes effect, the headline revenue cut of up to 20% on solar-only configurations looks meaningful — but several factors reduce the impact in practice. First, tariff levels haven't moved — only windows. The asset still self-consumes against the same VND/kWh standard rate; the cut applies only to the share of generation that previously hit peak, not to the asset's underlying ability to displace grid imports. Second, a BESS overlay sized for the lunch-trough overspill window (sized in the table above at 200 kW / 400 kWh against a 1 MWp solar archetype) recovers ~50% of the annual revenue lost to 963 by capturing the peak tariff via stored generation rather than direct consumption. Third, sites with stronger evening load (single-shift wind-down, second-shift production, on-site cold storage, evening security and lighting) can sustain a larger BESS layer with more cycles per day, pushing recovery toward 70–80%. Fourth, the pending Q2–Q3 2026 retail tariff revision under MOIT's Decree 72 amendment, if enacted, would lift standard rates and offset a further share of the cut. Fifth, BESS capex continues to fall and operating costs are trending down, which improves the overlay economics on a forward-looking basis. Self-invest economics still pencil throughout — the proposition shifts but stays attractive.
Modelling Decision 963's impact for your factory?
Send us your last 12 months of EVN bills and a quick site description (voltage class, shift pattern, roof area available). We'll size a BESS overlay against your actual evening load profile, run the operational baseline (99.5/0.5 split, real BESS capex), and show you what the combined revenue picture looks like — typically a 1–2 day turnaround for a directional answer.
Source: Arcus Energy operational baseline as of May 2026, anchored on Decision 1279/QĐ-BCT rate schedule (May 2025) and operational data on the 99.5/0.5 daytime offtake split (BESS Vietnam README §4 canonical). BESS economics use 300 cycles/yr, 90% DoD, 92% AC-AC RTE, $190/kWh BTM C&I capex per Arcus benchmarks. USD/VND conversion at April 2026 reference FX. Site-specific modelling required for any live deal.
Three configurations a factory operator can run after Decision 963, ranked
Which response to Decision 963 gives a factory operator the strongest revenue outcome. The right configuration depends on factory load profile, BESS capex tolerance, and roof or land availability — not on the regulation.
- Solar + BESS integrated hybrid Default configuration for any factory with material evening load. Solar handles daytime self-consumption at the new 99.5/0.5 split; a small BESS sized to the lunch-trough overspill window captures peak-tariff revenue that pure solar can no longer earn. Typical sizing: BESS at ~40% of solar nameplate kWh, sized to match practical midday overspill availability (e.g. 200 kW / 400 kWh against a 1 MWp solar array — see worked example above). Recovers around 50% of the annual revenue lost to 963. Sites with stronger evening load can sustain a larger BESS layer with more cycles per day, pushing recovery toward 70–80%. Best post-963 economics where load profile and capex tolerance allow. Default for factories with evening load
- Solar standalone with C&I tariff hedging Viable where BESS capex is deferred for cash-flow reasons or the factory has only marginal evening consumption. Accepts the revenue cut of up to 20% on the daytime side. Hedge value sits in the next retail tariff revision: when Decision 1279 rate levels rise (plausibly Q2–Q3 2026 under the Decree 72 amendment), self-consumption solar effectively hedges the standard-rate-band increase. Best for factories with weak evening load or BESS-deferred capital plans. Viable for capex-constrained or daytime-only sites
- Solar standalone with no hedge or overlay Acceptable only for sites with very low evening load — effectively dawn-to-dusk daytime operations like daytime cold storage, daytime-only manufacturing without late-shift cleanup, or single-shift production winding down by 17:00. Such sites genuinely lose minimal economic value to Decision 963 because they have no evening load to benefit from BESS overlay regardless. Self-invest economics still pencil at the 99.5/0.5 split, often without meaningful difference from a BESS-overlay scenario. Defer the BESS conversation indefinitely. Niche — genuinely daytime-only sites
In practice: the first question to answer at any factory site post-Decision 963 is the evening load profile, not the solar capex budget. If evening consumption (17:30–22:30) is meaningful — even 20–30% of total load — configuration 1 is the default and will typically beat configuration 2 on combined revenue. If evening consumption is negligible, configuration 3 is honest and configuration 1 is over-engineering. Configuration 2 is the conditional middle path for capex-deferred decisions, not a permanent destination.
Frequently asked questions
How much does Decision 963 cut factory rooftop solar revenue?
At typical 22 kV manufacturing sites operating on the 99.5/0.5 daytime offtake split (99.5% standard, 0.5% peak — anchored on operational data), the headline solar revenue cut is up to approximately 20%. Operational data confirms the residual peak slice is small enough that the briefing's headline impact on revenue stands as the practical operational reality. The 99.5/0.5 split is the locked Arcus operational baseline.
What does operational data show about the post-963 split?
Operational data anchors the post-963 daytime offtake split at 99.5% standard / 0.5% peak. The residual 0.5% peak slice is the small late-afternoon overlap between solar generation and the new 17:30 peak start, primarily from south-Vietnam summer-month sites with west-facing arrays. North-Vietnam winter months and east-facing arrays produce effectively zero peak capture. The result sits within ~1% of the briefing's 100/0 corner case — close enough that the briefing's headline revenue impact lands as the practical operational baseline.
How much revenue can a BESS overlay recover from the Decision 963 cut?
Adding a BESS overlay sized for the lunch-trough overspill window (~200 kW / 400 kWh against a 1 MWp solar archetype) typically recovers around 50% of the annual revenue lost to Decision 963 by capturing the peak tariff via stored generation rather than direct solar consumption. Sites with stronger evening load can sustain a larger BESS layer with more cycles per day, pushing recovery toward 70–80% of the lost revenue.
Should a factory still install solar PV after Decision 963?
Yes, in most cases — but the configuration matters more than it did pre-963. Three configurations apply: (1) solar+BESS hybrid is the default for sites with evening load, with the BESS overlay offsetting much of the revenue impact and keeping solar attractive; (2) solar standalone with C&I tariff hedging remains viable where BESS capex is deferred or the site has very weak evening load; (3) solar standalone with no hedge is acceptable only for sites with very low evening load (effectively dawn-to-dusk operations like daytime cold storage). Pure solar without a hedge against the post-963 split underperforms its pre-963 case on most factory sites once 963 takes effect.
How does BESS close the gap from Decision 963?
A BESS overlay charges off-peak (00:00–06:00) and discharges into the new 17:30–22:30 peak window. This converts the kWh that would otherwise have been late-afternoon solar (lost to the post-963 standard rate) into stored kWh dispatched at the peak rate. The 5-hour continuous evening peak is approximately 66% wider than the pre-963 evening peak alone, giving BESS a longer earning window and simplifying dispatch to a single cycle per day. The result for solar+BESS hybrids is restoration of much of the revenue lost to 963 — and a more attractive financing case for BESS overlay than existed pre-963.