The jargon, explained.
Every term the game uses in its tooltips and modals, written out in full — plus the acronyms you'll see all over real UK energy news and data, and a couple more for the bigger picture. If you're mid-game, tap any underlined term to get the short version; come back here whenever you want the longer one.
- Merit order
- The queue plants are dispatched in to meet demand, ordered from cheapest marginal cost to most expensive. The grid works down this queue, switching plants on as demand rises, until enough capacity is running — so the cheapest generation runs almost all the time, and the most expensive only runs on the highest-demand half-hours.
- Marginal cost
- What it costs a plant to produce one additional megawatt-hour — mostly fuel, plus a carbon cost for anything that burns fossil fuel. It's the number that decides a plant's position in the merit order: low marginal cost means it's dispatched early and runs often.
- Clearing price
- The single price every dispatched plant is paid for a given half-hour, set by the most expensive plant still needed to meet demand — the marginal plant. This is a real feature of how the GB electricity market prices, not a simplification for the game: a cheap wind farm and an expensive gas plant running in the same half-hour both get paid the same clearing price.
- Marginal plant
- The most expensive plant still needed to meet demand in a given half-hour — the last one the merit order has to call on. It sets the clearing price for every plant running alongside it, which is why which plant is "on the margin" matters so much to profitability.
- Spot price
- The live clearing price for power right now, as opposed to a price agreed in advance through a hedge. If you haven't locked anything in, this is the price you're exposed to.
- Settlement period
- The 30-minute slot Great Britain's electricity market is priced and accounted for in — 48 of them a day. That's exactly why the game's clock runs 48 ticks a day: each tick is one settlement period.
- Settlement price
- The official, final price for a settlement period once it's closed out — the real-world figure the game's clearing price is modelled on.
- Hedge
- A forward position: you agree a price today for a volume of power you'll actually deliver tomorrow, rather than taking whatever the spot price happens to be on the day. It trades away upside for certainty — useful when you'd rather know your revenue in advance than gamble on the market moving in your favour.
- Forward position
- The volume and price a hedge locks in ahead of time. At the end of the day it's settled against what you actually generated — any gap between the two becomes an imbalance.
- Imbalance
- The difference between what a forward position promised and what you actually generated, settled separately at the spot price. Generate less than you hedged and you have to buy the shortfall at the spot price; generate more and you sell the surplus at it.
- Reserve price
- The price a battery running in Auto mode privately sets for itself before it will discharge, based on a rolling average of recent prices. It only sells into the market when the price on offer clears that bar — the mechanism that lets a battery buy low and sell high without you managing it tick by tick.
- Balancing mechanism
- How the system operator makes last-minute adjustments to keep supply and demand matched in real time — paying some plants to generate more, and others to back off. It's a real, active part of how Great Britain's grid is run every single day, not a game invention.
- Constrained-off
- Being paid to switch off, or turn down, because the local part of the grid can't physically carry your power right now — usually a transmission bottleneck rather than a lack of demand nationally. It's a real, and increasingly common, feature of the UK's balancing mechanism, especially for wind farms in areas with limited grid capacity.
- Biomass
- Power stations that burn organic material, such as wood pellets, to generate electricity. Like coal or gas they can be switched up or down on demand, but under most carbon-pricing rules sustainably sourced biomass is treated as carrying no carbon cost, which is why it can compete when carbon prices are high. In the game it's a dispatchable plant you can build, hold back or hedge.
- Demand response
- Paying large consumers to shift or cut their electricity use at peak times, instead of switching on another power plant to cover the shortfall. It's often cheaper and faster than building or running extra generation, and is a growing part of how modern grids balance supply and demand.
- Capacity market
- A separate system that pays generators just to be available when called on — insurance against a shortfall on the tightest days of the year — on top of whatever they earn from the energy they actually sell. It exists because a market that only pays for energy delivered doesn't, on its own, guarantee enough spare capacity exists for the worst-case day.
- Interconnector
- A high-voltage cable linking Great Britain's grid to a neighbouring country's — France, Belgium, the Netherlands, Norway and others. It lets GB import power when it's cheaper abroad, or export when it's cheaper here, effectively adding capacity from outside the national system.
- National Grid ESO / NESO
- The organisation responsible for balancing electricity supply and demand across Great Britain's grid, second by second. It was renamed from National Grid ESO to NESO — the National Energy System Operator — in 2024, when it became a fully public body. NESO also publishes the live carbon intensity and generation-mix data this site's live grid widget uses.
- Demand
- How much power, in megawatts, the grid needs to supply at any given moment. It follows a predictable daily shape — low overnight, rising through the morning, peaking in the early evening — with day-to-day variation layered on top from weather and season.
- Reliability
- A running score of how well you've kept the lights on. Blackouts and plant breakdowns hurt it; steady, well-covered days rebuild it slowly. It's a deliberate trade-off against pure profit — running lean and cheap is more likely to leave you exposed when demand spikes.
- State of charge
- How full a battery is right now, expressed as a share of its total energy capacity in megawatt-hours. It's the number that decides whether a battery has anything left to sell, or room left to buy.
- Charge cycle
- One full trip from empty to full and back again — or the equivalent in smaller partial charges and discharges added up. It's the standard way battery wear is measured, not calendar time: a battery cycled hard every day wears out faster than one doing the same job once a week.
- Depth of discharge (DoD)
- How far a battery is drained on a given cycle, as a percentage of its full capacity — running from 100% down to 20% is an 80% DoD cycle. Shallower cycles are gentler on a battery than deep ones, which is part of why real operators rarely run one all the way to empty.
- Round-trip efficiency
- How much of the energy put into a battery comes back out when it's discharged — never 100%, since some is always lost as heat. A battery with 90% round-trip efficiency that charges on 10 MWh only has 9 MWh left to sell, which eats into the profit from any buy-low-sell-high spread.
- Battery degradation
- The gradual, permanent loss of a battery's usable capacity over its lifetime, driven mainly by cycle count and depth of discharge — cycled hard and deep every day, a battery wears out faster than one used gently. It's why real battery operators think in lifetime cycles, not just today's profit.
- Blackout
- What happens when demand outstrips available supply and some of it goes unmet. It's the costliest outcome in the game — and in reality — and a direct hit to reliability, which is why keeping some spare capacity in reserve on tight-margin days is usually worth the cost.
- Generation mix
- The share of total electricity generation coming from each fuel type — gas, wind, nuclear, solar, and so on — at a given moment. It shifts constantly through the day and the year as weather, demand and plant availability change; the live widget on this site's homepage shows Great Britain's actual mix right now.
- Carbon intensity
- How much CO₂ is emitted per unit of electricity generated, measured in grams of CO₂ per kilowatt-hour. It falls when more of the generation mix comes from wind, solar, nuclear or hydro, and rises when more comes from gas or coal — a live, minute-to-minute number, not a fixed figure for a fuel type.
A unit of power — the rate energy is generated or consumed. Run 1 MW for an hour and you've produced 1 MWh.
A unit of energy — how much power was delivered over time. This is what actually gets priced and traded in the market, not raw megawatts.
1,000 MW or MWh. National demand and total generation capacity are usually quoted at this scale — GB's demand peaks at around 45–60 GW.
The common, efficient gas plant design: burns gas in a turbine, then uses the leftover heat to drive a steam turbine too — squeezing more power from the same fuel.
A simpler, cheaper, less efficient gas plant that starts up fast. Used to cover short demand spikes rather than run continuously like a CCGT.
Elexon's public data platform (now branded Elexon Insights Solution) publishing real GB prices, volumes and balancing actions — the dataset behind this game's Live UK Data days.
The rulebook governing how GB electricity trades are balanced and financially settled, administered by Elexon.
Balances GB's grid second by second. See the full National Grid ESO / NESO entry above.
The regional company running the local wires that carry power the last stretch to homes and businesses — distinct from the national transmission grid.
Owns the high-voltage cables and pylons that move bulk power around the country. NESO operates the system, but TOs own the physical wires.
An older UK subsidy scheme requiring suppliers to source a growing share of power from renewables — largely replaced by CfDs for new projects.
The main UK renewable subsidy scheme today: a generator gets a fixed price for its power, topped up when the market price is lower and paid back when it's higher.
A long-term contract where a generator sells its output directly to a buyer — often a company or supplier — at an agreed price, instead of relying purely on the open market.
Great Britain's independent energy regulator, setting price controls and market rules for the industry.
Fees generators and suppliers pay for using the local (DUoS) or national (TNUoS) grid infrastructure.
Go deeper with the real data
Everything above is modelled on how the actual UK electricity market works. These are the public data sources it's built on — free to browse, no sign-up required.
The best way to understand any of this is to run a day yourself.