ACM 2028: the time-weighted kWmax and what it does to a Dutch battery case (draft decision of 8 October 2026)

Status: a draft, with dates

• Draft code decision ACM/26/200254 of 8 October 2026; comments are open for six weeks, until 18 November 2026 (ACM consultation page).
• Intended start: "Dit besluit treedt in werking met ingang van 1 januari 2028" — the decision takes effect on 1 January 2028 (ACM draft).
• Small connections (households and small businesses) would follow from 1 January 2029 under a separate draft (ACM draft, small connections); press reports in May 2026 said that date might slip to 2030 (Solar Magazine, 19 May 2026).
• Customers connected to TenneT's high-voltage grid already pay a time-dependent kWmax and no kWh tariff, according to the draft's explanatory note.

What changes

• kWmax becomes kWmax_gewogen: every quarter-hour's kW is multiplied by the weight for its moment, and the month's charge applies to the highest weighted quarter-hour (the week's, for customers with at most 600 operating hours a year).
• kWh becomes time-dependent in five price levels. Level 5 is the base price; the other levels are the base price times their weight, so a kWh in a weight-0.10 hour costs a tenth of a base-hour kWh.
• Tariff categories a to d: the transport charge is split 50% on contracted kW and 50% on kWmax_gewogen per month.
• Customers with at most 600 operating hours: 0.5 × the contracted kW, plus a weekly kWmax_gewogen priced at 18/52 of the monthly rate.
• Categories g and h with a connection above 3×80 A: 16% on contracted kW and 84% on the time-dependent kWh.
• Exemption: if at least 60% of a grid operator's annual kWh is drawn in category-1 and category-2 hours, all that operator's weights are set to 1.00.
• Overall, 50 to 75% of the transport tariff becomes time-dependent, and 84% in a few specific cases (explanatory note, paragraph 20).

The weight schedule

The draft gives two tables of 12 months × 24 hours, one for working days and one for non-working days (weekends and official Dutch holidays). Zorowatt's compression, by hour column 1–24:

• November–February, working days: 1–7: 0.58 · 8: 0.82 · 9–10: 1.00 · 11–12: 0.82 · 13–15: 0.58 · 16: 0.82 · 17–22: 1.00 · 23–24: 0.82.
• March–April and September–October, working days: 1–11: 0.58 · 12–16: 0.25 · 17–19: 0.58 · 20–24: 0.82.
• May–August, working days: 1–9: 0.58 · 10–13: 0.25 · 14–15: 0.10 · 16–19: 0.25 · 20–21: 0.58 · 22–24: 0.82.
• November–February, non-working days: 1–17: 0.58 · 18–21: 0.82 · 22–24: 0.58.
• March–April and September–October, non-working days: 1–9: 0.58 · 10: 0.25 · 11–16: 0.10 · 17–18: 0.25 · 19–24: 0.58.
• May–August, non-working days: 1–7: 0.58 · 8–9: 0.25 · 10–18: 0.10 · 19–20: 0.25 · 21–24: 0.58.

What a battery does differently

Illustrative arithmetic, not a real customer (hours read as in the note above):

• A winter working day with 400 kW at 09:00–10:00 (column 10, weight 1.00) and 450 kW at 13:00–14:00 (column 14, weight 0.58). Weighted: 400 × 1.00 = 400 and 450 × 0.58 = 261. Today the 450 kW sets the month's kWmax; under the draft the 400 kW does. A battery that shaves the early-afternoon peak earns nothing on the kW charge; one that shaves the morning peak does.
• A summer working day: the site draws 300 kW at 13:00–14:00 and the battery charges at 100 kW (column 14, weight 0.10): 400 × 0.10 = 40 weighted kW. A night hour at 200 kW counts 200 × 0.58 = 116. Charging at summer midday adds nothing to the month's charge.
• Where the time-dependent kWh applies, a kWh charged in a 0.10 hour and used in a 1.00 hour moves energy from a tenth of the base price to the full base price — a small arbitrage on the network charge itself.

So the battery's job changes from "cap the absolute monthly peak" to "cap the weighted peak": holding the import down in the weight-1.00 windows of winter working days, and charging when the weights are low.

What is not known

• The 2028 price per weighted kW. The battery coalition's response argues the draft does not make clear that the weighted rate will equal today's kWmax rate, and that it could rise (zienswijze Batterijcoalitie).
• Whether the final decision keeps the weights, the schedule, the split and the start date of the draft.
• How the hour columns map to clock time (see the note above).
• How the draft's 50/50 split for categories a to d relates to today's per-kWh transport charge in those categories; the research did not settle it. Read the final text.

How to model it now

1. Bill 2026 and 2027 on the current tariff, with its rates.
2. Bill 2028 onwards as a scenario: the weights and schedule of the draft, and a rate per weighted kW you enter and label as an assumption.
3. Show the case with and without the scenario, so the client sees how much of it depends on 2028.
4. Report a break-even rate: the price per weighted kW at which the battery still meets the client's payback or NPV target.

Illustrative: if the 2028 rate per weighted kW were R per month, one weighted kW held down in every month would be worth 12 × R a year. With today's Liander medium-voltage kWmax rate of €3.57 used only as a placeholder, 12 × 3.57 = €42.84 a year; at twice that, €85.68. The real value of R is the open question.

The Workspace carries the ACM 2028 draft as a scenario next to the 2026 tariff, with the rate left for you to set. Dutch large-connection tariffs: kW contract, kWmax and kWh explains today's tariff it would replace.

Related guides

• Dutch large-connection tariffs: kW contract, kWmax and kWh
• Netcongestie: growing within a connection you cannot enlarge
• Rule-based vs optimal dispatch

Sources

• ACM, draft code decision on time-dependent tariffs for large connections, ACM/26/200254, 8 Oct 2026
• ACM, consultation page
• ACM, draft for small connections
• Solar Magazine, ACM proposal for time-dependent tariffs, 19 May 2026
• Batterijcoalitie, response to the ACM draft
• Liander, tariffs for connection and transport, large consumers 2026

Last checked: 2026-10-30. Every figure in this guide comes from the source linked next to it, with the retrieval date Zorowatt's research recorded (28–30 October 2026), or from arithmetic shown step by step. This guide describes a draft decision under consultation; the final decision may differ.