For years, the day-ahead electricity market worked in hours. Each hour of the next day had a single price, and companies on spot-indexed contracts planned around it. That changed on 1 October 2025: the European day-ahead market, including the Czech market run by OTE, now trades electricity in 15-minute periods.
What changed on 1 October 2025
The day-ahead market is an auction held the day before delivery, which sets a price for each period of the following day. That period used to be an hour; now it is a quarter-hour. Every quarter-hour has its own price, and prices can differ within a single hour.
This brings the market in line with how larger sites are metered, which is also in 15-minute intervals. For businesses, the price signal is sharper: you can see exactly when power is cheap and when it is dear. The flip side is that there are many more prices to follow, and planning around them is harder.
Why prices swing during the day
The day-ahead price reflects supply and demand in each quarter-hour. Around noon on sunny days, solar plants across the region all produce at once, demand cannot absorb that much supply and the price falls close to zero. Sometimes it drops below zero, and buyers are in effect paid to take electricity.
In the evening the picture reverses. The sun sets, solar output disappears and household demand rises. More expensive sources fill the gap, and evening prices are often several times higher than at midday. Quarter-hour prices also capture fast changes within the hour, typically as demand ramps up in the morning and evening.
A simplified sunny day looks like this. Real prices vary from day to day.
| Time of day | Price on a sunny day | What controlled storage does |
|---|---|---|
| Night | lower than in the evening | recharges or waits, as planned |
| Morning ramp | rising | discharges in the dearest quarter-hours |
| Midday | near zero, sometimes negative | charges |
| Evening | several times the midday level | discharges |
How a business can benefit
Price swings affect you directly only if your supply contract is linked to the spot market. On a fixed price, the supplier carries both the risk and the opportunity. If you are on a spot-indexed contract, there are three ways to benefit.
Shifting consumption
Some loads can move into cheaper quarter-hours: water heating, pre-cooling, charging forklifts and electric vehicles, and some batch processes. Production has its own fixed rhythm, though, and only what does not disrupt it can move.
Charging and discharging storage
Battery storage separates the moment you buy electricity from the moment you use it. It charges in the cheapest quarter-hours and discharges in the dearest, so the site draws more from the grid when power is cheap. You can use the stored energy on site or sell it.
Efficiency matters because every cycle has a cost. Only spreads that cover both losses and battery wear are worth trading.
Ancillary services
Where market rules allow, storage can also offer flexibility to the grid as aFRR and FCR through an aggregator. Availability itself is paid for, so storage can earn even on days when price spreads are narrow.
Why manual control falls short
Day-ahead results are known the day before. In theory, someone could check prices every day and plan when to charge and discharge. In practice it does not work: a day has far too many quarter-hours, prices change daily, and the plan must also account for battery charge, expected demand, solar output and your reserved capacity limit.
A fixed timer will not do it either. One day the cheap period falls at noon; the next, under cloud, it does not come at all. Automated control fetches next-day prices, builds a plan from them and adjusts it through the day as actual demand comes in.
Our energy management system works with data from the market operator, OTE, plans charging around next-day prices and keeps watch on demand peaks at the same time. Why those peaks matter is covered in peak shaving and reserved capacity.
What to work out first
The benefit depends on how your supply contract is set up, how wide the daily price spreads are and how much energy you can shift. Storage that only trades the spread is assessed differently from storage that also shaves peaks or stores your own solar output. We cover the latter in solar plus storage.
Prices also shift from year to year with the weather, new generation and changes in demand. That is why we do not model a single sample day, but work from your 15-minute metering data and historical price patterns.
See how price-driven storage works across a sample day on our energy storage page.