How Electricity Pricing Works
Electricity in Europe is traded on a day-ahead market. Every day around noon, prices are published for each hour of the following day. These prices are determined by supply and demand — when there is plenty of wind and solar, prices drop. When demand peaks and generation is scarce, prices rise.
The main source for these prices is ENTSO-E, the European Network of Transmission System Operators for Electricity. ENTSO-E publishes transparent day-ahead prices for bidding zones across Europe.
This means electricity has a different price every hour of the day. The difference can be dramatic — from over 30 cents per kWh during an evening peak to near zero (or even negative) during a windy night.
Why Price Variation Creates Opportunity
Most electricity consumers pay a flat rate and never notice these hourly fluctuations. But if you have flexibility in when you consume electricity, you can take advantage of the price variation. EV charging is the perfect candidate:
- Cars are typically parked much longer than they need to charge
- A full charge might take 4-6 hours, but the car sits plugged in for 12-14 hours overnight
- That leaves 8+ hours of flexibility to pick the cheapest moments
This is exactly what Stekker does.
How Stekker Uses Day-Ahead Prices
Every day, Stekker imports the latest day-ahead prices for your market. These hourly prices are fed directly into the optimization engine as one of its key inputs, alongside grid limits, solar forecasts, and your departure targets.
The engine then solves for the optimal charging schedule: which hours should each charger deliver power, and how much? The goal is to minimize total electricity cost while ensuring every vehicle reaches its target charge level by departure time.
A Practical Example
You plug in your car at 6:00 PM on Monday. You need a full charge by 8:00 AM Tuesday. The car needs about 30 kWh, which takes roughly 3 hours at 11 kW.
The day-ahead prices for that night look like this:
- 6 PM – 9 PM: 28 ct/kWh (evening peak, everyone cooking and watching TV)
- 9 PM – midnight: 18 ct/kWh (demand dropping)
- Midnight – 4 AM: 8 ct/kWh (overnight low)
- 4 AM – 8 AM: 15 ct/kWh (morning ramp-up)
An uncontrolled charger would start immediately at 6 PM and charge through the most expensive hours. Stekker’s engine instead waits and schedules the bulk of charging between midnight and 4 AM — the cheapest window. Your car is still full by 8 AM, but at a fraction of the cost.
Supported Markets and Tariff Types
Stekker supports dynamic pricing in multiple European markets:
- Netherlands — ENTSO-E day-ahead prices (EPEX Spot NL)
- Belgium — ENTSO-E day-ahead prices (EPEX Spot BE)
- Germany and Austria — ENTSO-E day-ahead prices
- United Kingdom — Octopus Energy agile tariffs
Beyond dynamic day-ahead pricing, Stekker also supports:
- Time-of-use tariffs: fixed price schedules with peak/off-peak/shoulder periods (common in business contracts)
- Fixed rates: a single price per kWh — in this case, the engine optimizes for solar self-consumption and grid limit management instead
How Savings Are Calculated
After each charging session, Stekker calculates your savings by comparing two scenarios:
- Smart cost: what you actually paid, based on the optimized schedule and the hourly prices during those hours
- Baseline cost: what you would have paid if the charger had started immediately at full power and charged without any optimization
The difference is your saving. This is a fair comparison because it measures the value of smart scheduling against the most common alternative — plugging in and charging right away.
These savings are visible in your session history, so you can see exactly how much each session saved and during which hours the charging took place.
Negative Prices: Getting Paid to Charge
On days with very high renewable generation and low demand, electricity prices can go negative. This literally means producers are paying consumers to take their electricity. It happens more often than you might expect — especially on sunny, windy weekends.
When negative prices occur, Stekker’s engine prioritizes charging during those hours. You are essentially getting paid to charge your car — or at minimum, charging at zero cost.
Transparency and Control
Stekker provides full transparency into how pricing affects your charging:
- View the hourly price breakdown for each session
- See when charging happened relative to price peaks and valleys
- Track cumulative savings over time
- Compare smart charging costs against uncontrolled baselines
You always remain in control. Set your departure time and desired charge level, and the engine handles the rest — finding the cheapest path to a full battery.
