Question 1

What is a capacity market, and why does it exist?

Accepted Answer

A mechanism that pays generators and other providers to **be available** when needed, rather than for the electricity they actually produce — addressing a problem that energy-only markets create.

**The problem it solves.** In an energy-only market, generators earn only when they sell electricity. A power station needed for a handful of hours each winter, during the coldest, stillest evenings, would earn almost nothing for the rest of the year — so nobody would build or maintain one, even though the system needs it for those hours.

This is the **missing money problem**: the market pays for energy but not for **reliability**, which is a distinct product.

Prices during scarcity could in principle rise high enough to fund it, but most markets impose price caps for political and consumer protection reasons — so the revenue never materialises.

**How a capacity market works.** The system operator forecasts peak demand plus a reserve margin, then runs an **auction** for capacity. Participants bid to be available, the price is set at the level that secures the required amount, and successful bidders receive a payment per unit of capacity per year.

**In return they must deliver** when instructed during system stress events, with penalties for failing to.

**Who participates:** conventional power stations, but increasingly also **batteries**, **interconnectors** and — significantly — **demand side response**, where large consumers are paid to reduce usage at peak. Demand reduction is treated as equivalent to generation, which is the economically correct treatment and is frequently the cheapest option.

**Auctions are held years ahead**, allowing time to build new capacity, plus a shorter-term auction closer to delivery.

**The criticisms:**

**It can subsidise existing fossil plant** that would otherwise close, which conflicts with decarbonisation objectives. Emissions limits have been introduced in response.

**Forecasting is imperfect**, and over-procurement means consumers pay for capacity that is never needed.

**Costs appear on bills**, and the mechanism is invisible to consumers who pay for it.

**Whether it is necessary at all** is genuinely contested — some argue a well-designed energy market with scarcity pricing would suffice, and several markets operate without one.

Question 2

What is demand side response?

Accepted Answer

Paying electricity consumers to change when they use power — reducing at peak or increasing when there is surplus — treated as an alternative to building generation, because avoiding a megawatt of

Question 3

Why is energy storage the hard problem for renewables?

Accepted Answer

Because electricity grids must balance supply and demand continuously and instantaneously, and the main renewable sources produce power when conditions allow rather than when it is needed. The

Question 4

What is curtailment, and why are wind farms paid to stop?

Accepted Answer

Curtailment is reducing generation below what a plant could produce — and wind farms are compensated for it because the grid physically cannot move the electricity to where it is needed, not because

Question 5

How does the electricity grid stay balanced second by second?

Accepted Answer

By matching generation to demand continuously, because electricity is consumed at the instant it is produced and the grid stores essentially none of it. The balance is visible in a single number:

Question 6

What is the environmental cost of streaming and data?

Accepted Answer

Real, frequently overstated in viral claims, and concentrated in places most people do not expect — the network and the device, not the data centre alone. Where the energy actually goes: data

Question 7

What is a renewable energy certificate, and does buying green electricity work?

Accepted Answer

A certificate proving that a unit of electricity was generated from a renewable source — and whether buying one changes anything depends on a concept called additionality, which is where most green

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