> ## Documentation Index
> Fetch the complete documentation index at: https://docs.trlyr.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Wholesale Energy Markets: Trading Electricity

> Discover how BESS participates in day-ahead and intraday electricity markets to generate revenue from price differences.

Wholesale energy markets are where electricity itself is bought and sold. For a BESS, this is a primary revenue source — the asset charges when prices are low and discharges when prices are high, capitalising on the difference.

## The 15-Minute Heartbeat of the German Market

In Germany, the entire electricity day is divided into **15-minute settlement periods**. This is the fundamental unit of time for buying and selling electricity. All energy contracts specify a certain amount of energy to be delivered or consumed within each 15-minute block.

Electricity is traded on the European Power Exchange (EPEX) through two main mechanisms.

## The Day-Ahead Auction

**When it happens:** Every day, closing at 12:00 CET/CEST, for all 15-minute settlement periods of the following day.

**How it works:** Generators place offers to supply electricity at a given price, and consumers and traders place bids to buy it. The market is "cleared" for each 15-minute period, with a single **clearing price** determined at which all matched bids and offers are executed.

The day-ahead auction gives market participants a coarse-grained plan for how much electricity should be on the grid and at what price for the next 24 hours, ensuring supply and demand are matched in advance.

## The Intraday Market

**When it happens:** Continuously throughout the day, starting at 3:00 pm after the day-ahead auction closes and running right up until 30 minutes before physical delivery for each 15-minute period.

**How it works:** Participants make fine adjustments to their positions as new information emerges:

* A change in the weather forecast means wind farms or solar plants need to adjust their planned output.
* A home energy supplier gets a more accurate view of customer consumption.
* Equipment issues change what a generator can actually deliver.

The intraday market allows all of these adjustments to be made in real time, so the actual power bought and sold matches actual generation and consumption as closely as possible at the time of delivery.

## The 15-Minute Delivery Principle

An important aspect of the German wholesale market is that settlement is based on the **total energy delivered within each 15-minute period**, not the exact profile within that period.

* The exact second-by-second delivery profile does not strictly matter for wholesale settlement, as long as the **average** over the 15-minute block matches the contracted volume.
* However, to prevent grid instability, **ramp rates are limited** — so power cannot be injected or absorbed too suddenly.

<Info>
  Even when the 15-minute average is balanced, supply and demand can still be mismatched within that period on a moment-by-moment basis. This temporary mismatch is precisely what ancillary services — specifically aFRR and FCR — are designed to correct.
</Info>

BESS assets thrive in wholesale markets because their flexibility allows them to quickly charge when prices are low and discharge when they are high, capitalising on pricing differences across both day-ahead and intraday trading.