Glossary

Ancillary services are all services that grid operators procure to keep the power system secure and stable. They include balancing services, voltage control and black start capability.

Arbitrage is earning revenue from price differences over time. A battery storage system charges when prices are low and discharges when they are high.

Automatic frequency restoration reserve (aFRR) is a balancing services product that follows frequency containment reserve (FCR) and restores the grid frequency. The transmission system operator (TSO) activates it automatically, with full activation within five minutes. Providers are paid for holding capacity available (aFRR capacity) and for the energy delivered on activation (aFRR energy).

Backtesting is running a trading strategy against historical market data to estimate how it would have performed. Results depend on the assumptions behind the test. A backtest with perfect foresight assumes that all future prices are known, so it sets an upper limit for the revenue achievable in practice.

A balance responsible party (BRP) is the party financially responsible for keeping a balancing group balanced. It pays for imbalance energy or is paid for it when deviations occur.

A balancing group is a virtual account that balances all power fed in and taken out at its assigned market locations in every settlement period. Any difference between schedule and actual flow is settled as imbalance energy.

Balancing services are reserves that transmission system operators (TSOs) procure to keep supply and demand in balance and the grid frequency stable at 50 Hz. Providers are paid for holding capacity available and, for some products, for the energy actually delivered. Balancing services are one type of ancillary services.

Bankability is the degree to which a battery storage project can secure debt financing. It depends on factors such as how predictable the project's revenue is and how that revenue is secured.

A battery cycle is one full charge and discharge of a battery storage system's usable capacity. Manufacturer warranties often limit cycles per day, per year or within a rolling time window, because every cycle contributes to degradation.

A battery energy storage system (BESS) stores electricity and releases it when markets or the grid need it. Grid-scale systems connect to the public grid and give energy markets and grid operators flexibility, for example by shifting solar power into the evening.

A capacity market is a market mechanism that pays assets for being available to supply power when the system needs it, usually through long-term contracts awarded in auctions. Poland and Italy already run capacity markets. In Germany, the introduction of a capacity mechanism is under political discussion.

Co-location is the combination of a battery storage system with a renewable generation plant at the same site and behind a shared grid connection.

A commercial model defines how a battery storage system earns its revenue and how the price risk is shared between asset owner, trader and offtaker. Models range from the merchant model, in which the asset owner bears the full price risk, to tolling, in which the offtaker takes it on. Hybrid forms secure part of the revenue.

The Baukostenzuschuss (BKZ) is a one-off payment that grid operators in Germany can charge when a grid connection is established or expanded, as a contribution to grid expansion costs. Its amount depends on the connection power.

Curtailment is the reduction of a generation asset's output below the level it could produce. Grid operators order it to relieve congestion, and it also occurs when prices are negative.

The day-ahead auction is the market in which power for the following day is traded in hourly and quarter-hourly products. Bids close at 12:00 p.m. (CET) on the day before delivery, and the auction sets one clearing price for each period.

Degradation is the gradual loss of a battery storage system's usable capacity and performance over its lifetime. It depends on cycling, depth of discharge, temperature and time.

A distribution system operator (DSO) operates the regional and local distribution grid. It sets the technical conditions for connecting to its grid. These conditions can limit when and how much a battery charges or discharges.

Direct marketing is the sale of power from a renewable plant on the market through a direct marketer. Under the German Renewable Energy Sources Act (EEG), the plant operator receives a market premium on top of the market revenue instead of a fixed feed-in tariff.

An energy management system (EMS) monitors and controls a battery storage site. It receives control signals from the trader and turns them into charging and discharging commands.

EPEX SPOT is a European power exchange for short-term trading. It operates the day-ahead and intraday markets in Germany and other European countries.

Flexibility trading is the commercial use of an asset's ability to shift power consumption or generation in time. For battery storage, it means selling this flexibility on day-ahead, intraday and balancing markets.

A flexible connection agreement (FCA) is a grid connection agreement in which the grid operator connects a battery storage system earlier in exchange for limits on when and how much power the system may charge or discharge. The limits can be static or dynamic.

Frequency containment reserve (FCR) is a balancing services product and the grid's first response to frequency deviations. It is activated automatically within seconds to contain them.

Green co-location is a co-location in which the battery storage system charges only from the renewable generation plant.

Green power is electricity from renewable sources whose renewable origin is proven.

Grey co-location is a co-location in which the battery storage system can also charge from the grid.

Grey power is electricity without proof of renewable origin.

A grid booster is a large battery storage system operated by a transmission system operator (TSO) that works like a virtual power line. If a line fails, it reacts within seconds and feeds in power behind the bottleneck, so existing lines can be used more fully.

Grid congestion management covers the measures grid operators use to prevent or resolve overloads in the power grid. These include redispatch, curtailment and connection conditions that limit when and how much a battery storage system may charge or discharge. Grid-supportive operation of a battery storage system can relieve congestion.

Grid constraints are limits that grid operators set on when and how much power a battery may charge or discharge. They are caused by local grid congestion. Static constraints are fixed in advance, dynamic constraints are set shortly before delivery.

Grid fees are charges that grid users pay for using the power grid. They are determined under regulatory rules. In Germany, the rules are currently being reformed.

Imbalance energy is the amount of energy that corresponds to the difference between a balancing group's schedule and its actual flows.

Industrial storage, also called commercial and industrial (C&I) storage, is a battery storage system installed at a company site, behind the site's grid connection.

Inertia is the power system's ability to resist sudden frequency changes immediately after a disturbance. Rotating masses of large power plants provide it physically. Grid-forming batteries can provide it synthetically.

Intraday auctions are trading rounds in which power is traded in quarter-hourly products at one clearing price per period. They take place after the day-ahead auction, on the day before and on the day of delivery.

The intraday continuous market (IDC) is the trading of power on the intraday market until shortly before delivery, in Germany up to five minutes before. Prices form trade by trade in an order book.

Manual frequency restoration reserve (mFRR) is a balancing services product that takes over from frequency containment reserve (FCR) and automatic frequency restoration reserve (aFRR) during longer-lasting imbalances. It must be fully activated within 12.5 minutes. It is also called tertiary reserve.

The Marktstammdatenregister (MaStR) is the German register for installations and market participants in the power and gas markets. It is run by the Federal Network Agency (Bundesnetzagentur). Operators must register grid-connected battery storage systems there with their technical data.

A merchant model is a commercial model in which a battery earns its revenue solely from market prices, without fixed or guaranteed payments. The owner benefits fully from market upside and bears the full price risk.

Multi-market optimization is trading a battery storage system across several markets at once, such as frequency containment reserve (FCR), automatic frequency restoration reserve (aFRR), day-ahead and intraday. It continuously reallocates the system's capacity across these markets to maximize total revenue.

Negative power prices are prices below zero in a trading period. They occur when high solar or wind generation meets low demand. Sellers then pay to deliver power, and buyers are paid to take it.

An offtaker is a company, such as a utility, trading house or financial institution, that takes on part or all of the price risk of a battery's revenue under a contract with the asset owner.

Partial tolling is a form of tolling in which only part of the battery's revenue is fixed. The rest depends on market prices.

Peak load is the highest power demand that occurs in the power grid or at a single connection point within a given period.

Prequalification is the approval process a battery must pass before it may provide balancing services. The transmission system operator (TSO) reviews the technical documentation, validates the control setup and tests whether the battery follows dispatch requests as fast as required.

The price spread is the difference between the highest and lowest power prices within a period. Arbitrage earns revenue from this difference.

The ramp rate is the speed at which a battery may increase or decrease its power, usually stated as a percentage of its usable power per minute or per second. Slower ramps limit the energy a battery can deliver in a delivery period.

Recharge management keeps the state of charge of a battery storage system at the level its market commitments require, especially in balancing markets, while minimizing recharging costs.

Redispatch 2.0 is the German framework under which grid operators adjust the output of generation and storage assets to resolve grid congestion. Asset operators provide data, grid operators send curtailment instructions, and the resulting deviations are balanced in the balancing group.

REMIT (Regulation on Wholesale Energy Market Integrity and Transparency) is a regulation of the European Union (EU). It prohibits insider trading and market manipulation on wholesale energy markets and requires market participants to report trades and fundamental data to the Agency for the Cooperation of Energy Regulators (ACER).

A revenue floor is a minimum revenue secured by contract for a battery. Revenue beyond the floor depends on market prices.

A revenue share is a remuneration model in which the trader receives an agreed percentage of the revenue from marketing a battery. It can replace a fixed fee or be combined with one.

Revenue stacking is combining several revenue streams for one battery storage system, such as balancing services and arbitrage on day-ahead and intraday markets. Together, these streams form its revenue stack.

Round-trip efficiency (RTE) is the share of the energy put into a battery storage system that can be taken out again. Losses occur during charging, discharging and power conversion.

Route to market is the path by which an asset's power or flexibility reaches the market: who trades it, through which market access, under which commercial model and in which regulatory roles.

State of charge (SoC) is the current charge level of a battery storage system, shown as a percentage of its usable capacity. Manufacturers set upper and lower SoC limits to protect the cells and the warranty.

State of health (SoH) is the condition of a battery storage system compared to when it was new, usually measured as the share of its original usable capacity that is still available. SoH declines over time through calendar aging and cycle aging.

Storage duration is how long a battery can discharge at full power: energy capacity (MWh) divided by power (MW). It determines how a battery can split its capacity across day-ahead, intraday and balancing markets.

Tolling is a commercial model in which an offtaker pays the asset owner a fixed fee for the right to use the battery and keeps the trading revenue. The owner receives predictable income without market risk.

A transmission system operator (TSO) operates the power transmission grid and is responsible for the stability of the power system. It procures balancing services, prequalifies providers and settles imbalance energy. Germany has four TSOs: 50Hertz, Amprion, TenneT and TransnetBW.

A virtual battery is a digital model that replicates the behavior of a battery storage system based on market data, forecasts and trading strategies. It is used to test trading strategies. It can also be the basis of a commercial model in which a buyer receives the economic value of storage capacity without owning an asset.

Virtual cycling means opening and closing trading positions before physical delivery. The battery earns from price movements without physically charging or discharging, which saves cycles and reduces degradation.

A virtual power plant (VPP) is the aggregation of distributed assets that are controlled centrally, so that their power and flexibility can be traded on energy markets as one unit.

The wholesale market is where producers, suppliers and traders trade power with each other, among other channels on power exchanges. For battery storage, the Day-Ahead and Intraday markets are the most relevant segments.