Korea Redrew Its Time-of-Use Bands After 49 Years. The Grace Period Is Ending

A structural change 49 years in the making has begun in factory electricity bills. From 16 April, the time-of-use bands changed for the Industrial (B) tariff, and for the sites that put off applying them, the grace period ends on 30 September.

What changed

The core of the government's explanation is that it is drawing electricity consumption into the daytime. The intent is to use the tariff to encourage electricity use during the day, when solar generation is concentrated, and to press down the evening peak, when generation drops away.

A separate discount also applies during daytime hours on spring and autumn weekends and public holidays.

Why there was a grace period

While the reform was being drafted, industry argued that it needed time to prepare, and the government took grace period applications from 23 March to 10 April. As a result, 514 sites applied to defer the change.

These sites will go through preparations such as adjusting operating hours by 30 September and will have the reformed rates applied from 1 October.

It affects your RE100 plan too

This part is frequently left out. When daytime rates fall, the saving you get from rooftop solar on the factory falls with them.

The economics of self-consumed solar are calculated from "the charge on the electricity you no longer have to buy in that hour". The hours when solar generates the most are exactly 11:00–15:00 in the middle of the day, and because the unit price for that band has come down, the same generation now produces a different saving.

Before you move your operating hours — the basic charge trap

If you move operations looking only at the time-of-use charges, you will miss something. The basic charge moves separately.

The industrial basic charge is not set by the current month's consumption. It is fixed for a year at the largest of the maximum demand values from summer (July to September) and winter (December to February) over the preceding 12 months and from the current month.

What that means is this: a single peak recorded in some 30-minute interval last August is setting your basic charge all through this year. However carefully you save after that, the figure does not come down.

So responding to the reform is not "move into the daytime" but "move into the daytime while spreading the peak out". Simply starting equipment in sequence instead of all at once already makes a difference.

The optional tariff — an opportunity that comes once a year

The industrial tariff includes an optional tariff you choose according to your load factor. The advantageous option differs between a site that operates for short hours and one that runs 24 hours.

What matters here is that once you choose, you cannot change it for a year.

There are quite a few cases where the pattern of operations has changed but the old choice has been left in place. If you are adjusting operating hours because of this reform, you also need to check whether your optional tariff is still the right one. If you make the adjustment but the tariff is still matched to the old operating pattern, the saving is cancelled out.

You can check which side is advantageous for your site using the tariff comparison function on 한전ON (KEPCO ON, KEPCO's online service).

Something you can look at without investing in equipment — the power factor

Talk about charges usually moves on to replacing equipment, but there is one thing to check before that.

Article 41 of KEPCO's Terms of Electricity Supply requires the customer to maintain a lagging power factor of 90% or above across all their consuming equipment. Article 43 then adds to or discounts the basic charge according to the power factor.

To maintain the reference power factor, the terms require capacitors of appropriate capacity to be installed on each individual piece of equipment and to be switched on and off together with that equipment. When capacitors operate independently of the equipment, the power factor wanders.

Where should you look up the tariff table

One point of caution. Among the KEPCO tariff table pages that come up in search results, some have stopped being updated. Parts of the tariff tables on the Cyber Branch (사이버지점) have not been updated since the November 2023 edition.

When you check unit prices, look at the current tariff table on 한전ON, or the authoritative text of the Basic Terms of Supply on the information disclosure board. The current terms are the edition in force 1 August 2026.

When does it start for other contract types

This reform applied first to Industrial (B) and to electricity for electric vehicle charging. The other classes to which time-of-use rates apply, such as General and Educational, took effect from 1 June.

If your site also holds contracts other than industrial, the effective dates differ, so you need to read the bills separately.