Fundamentals of electricity markets

From centralization to markets

For most of the 20th century, a single entity — usually a state-owned utility — decided who produced electricity, when, and at what cost. One operator, one plan, one bill.

Today, most countries have moved to a different model: many independent producers compete to sell electricity, and a market decides who wins. The system operator no longer dispatches plants by hand — it runs an auction.

Why the change? Markets push costs down through competition. They also make it possible to integrate thousands of small renewable producers — wind turbines, solar farms, batteries — that no central planner could schedule by hand.

But replacing a single decision-maker with a market raises a new question: how do you make sure the right amount of electricity gets produced at the right time, when nobody is in charge anymore?

The two organizational models

A centralized power system works like a top-down command chain. One operator owns or controls the plants, runs the grid, and decides everything. Most countries operated this way until the 1990s.

An electricity market works like an auction. Producers announce how much they can supply and at what price. Consumers (or their retailers) announce how much they want to buy and at what price. A market operator matches them.

Both models have to solve the same physics problem — supply must equal demand at every instant — but they reach the answer through very different mechanisms.

How a market clears

Forget electricity for a moment. Imagine an apple market. Sellers announce how many apples they have and the minimum price they'll accept. Buyers announce how many apples they want and the maximum price they'll pay.

Sort sellers from cheapest to most expensive — that's the supply curve. Sort buyers from highest bid to lowest — that's the demand curve. Where they cross is the market clearing price. Everyone trades at that price, no matter what they originally asked for.

The merit order see it

The rule of sorting sellers from cheapest to most expensive is called the merit order principle. It guarantees that demand is met at the lowest possible total cost.

In electricity, this means cheap renewables (wind, solar) clear first, then cheap thermal (nuclear, hydro), then more expensive gas, and finally — only if needed — the most expensive peaking plants.

Social welfare see it

The area between the supply and demand curves is called social welfare — the total value created by the trade. The market operator's job is to maximize it.

By maximizing welfare, the operator simultaneously minimizes the total cost paid by buyers and maximizes the total value received by sellers. Both sides win compared to no trade at all.

Uniform pricing see it

In a uniform price auction, all winning sellers receive the same price — the marginal one — even if they offered less. A wind farm that bid €5/MWh and a gas plant that bid €80/MWh both get paid €80/MWh, if gas was the last unit needed.

This sounds generous to the wind farm, but it's the design that makes producers truthful: bidding your real cost is optimal under uniform pricing. We'll see why in chapter 5.

Who plays in the market

A real electricity market has more than just buyers and sellers. Around the auction sit several roles, each with a specific job.

Producers see it

Conventional: coal, gas, nuclear, hydro, combined heat and power. Renewable: wind, solar, biomass. Many producers own a portfolio of plants spread across the grid.

Consumers see it

Large consumers are industrial plants that buy directly from the wholesale market. Retailers are intermediaries: they buy in bulk and resell to households and small businesses.

The referees

The market operator runs the auction and announces the clearing price. In the Nordics, this is Nord Pool; in Germany, EPEX SPOT.

The transmission system operator (TSO) keeps the grid stable in real time. In Denmark, this is Energinet; the equivalent in the U.S. is the Independent System Operator (ISO).

The distribution system operator (DSO) handles the low-voltage network — the wires that bring electricity from the high-voltage grid to your home.

The regulator writes the rules and enforces them. In Denmark, this is Forsyningstilsynet; in the U.S., it's the Federal Energy Regulatory Commission (FERC).

Why so many? see it

Each role exists because electricity needs both an economic decision (who produces, at what price) and a physical guarantee (that supply equals demand on every wire, every second). Markets handle the first; system operators handle the second.

When and where markets happen

One trade for tomorrow's 6 PM is not really one trade. It's a chain of markets that close at different times before delivery, each one fixing the deal a little more precisely.

The timeline

Futures markets trade years to weeks in advance. They are purely financial — used by producers and retailers to hedge against price swings. We don't cover them in this course.

The day-ahead market is the main one. Each day at noon, 24 hourly auctions for the next day are cleared in a single shot. This is where most volume trades.

The intraday market opens after the day-ahead and stays open until shortly before delivery. It lets producers and buyers adjust their positions as forecasts update — a wind farm that over-predicted output can buy back electricity here.

The balancing market closes the last gap, in real time. The TSO uses it to keep frequency at exactly 50 Hz, calling on fast-reacting plants and batteries when needed.

Three product types

Beyond timing, markets also differ by what they trade. Energy markets trade MWh (the actual electricity). Capacity markets pay producers just for being available, even if not used. Ancillary services cover the grid-stability products: reserves, voltage control, black-start capability.

Geography matters

Europe uses zonal pricing: one price per country or bidding zone. Some countries split into several zones — Denmark has two (DK1, DK2), Sweden four, Norway five, and Italy six. Within a single zone, the grid is assumed to have no internal constraints.

The U.S. uses nodal pricing: one price per substation, sometimes thousands of prices in a single market. Each node reflects the local cost of delivering one more MWh — including grid congestion.

Same fundamental auction, different geographic resolution. The consequences of this choice are the subject of chapter 3.