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Glossary · Energy industry & energy transition

Arbitrage

Arbitrage electricity market storage Battery storage pumped storage price differences flexibility spot market

Arbitrage refers to the exploitation of price differences between different points in time, locations or products. In the power system, it usually means temporal arbitrage. When the price is low, electricity is stored, purchased or consumed in greater quantities. If the price is higher later, electricity is released, sold or consumption is avoided. The economic return results from the difference between the purchase price and the selling price. From this, technical losses, operating costs, grid fees, levies, taxes, financing costs and, where applicable, the ageing costs of a storage unit are deducted. Unlike in financial theory, where arbitrage is often defined as risk-free profit, electricity arbitrage is in practice always associated with risks. When charging, the later selling price is usually not yet known.

Prices are usually stated in euros per megawatt hour. Energy quantities are measured in kilowatt hours or megawatt hours, and charging and discharging power in kilowatts or megawatts. This distinction is essential for arbitrage. A storage unit with high power but small storage capacity can take up or release a lot of electricity in the short term, but it is quickly full or empty. A storage unit with a large energy content can shift electricity for longer, but for that it needs price differences over longer periods. An example: a plant with 10 megawatts of power and 20 megawatt hours of capacity can discharge at full power for two hours. Arbitrage therefore always depends on two variables at once: the size of the price spread and the quantity that can be shifted within the technical limits.

Temporal arbitrage in the electricity market

In the electricity market, price differences arise because generation and consumption must be balanced at every moment. The grid itself can hardly store electricity. When there is a lot of wind or solar power and demand is low, prices on the spot market fall. When demand is high, renewable feed-in is low or power plant capacity is scarce, they rise. The actors who engage in arbitrage respond to these price signals.

A battery storage system can buy electricity on the day-ahead market or the intraday market when the exchange price is low and sell it later at a higher price. Since the delivery day of 1 October 2025, the Europe-wide coupled day-ahead auction has been settled in quarter-hours instead of hours. As a result, price differences within an hour also become visible and tradable on the day-ahead market. A pumped-storage power plant uses cheap periods to pump water into a higher-lying reservoir and later generates electricity via turbines. Flexible consumers also engage in a form of arbitrage when they shift processes to cheaper times. Examples are cold storage warehouses, electrolysers, industrial heat generation, the charging of electric vehicles or heat pumps with buffer storage.

Arbitrage is closely linked to flexibility, but the two are not the same. Flexibility describes the technical ability to adjust feed-in, consumption or storage over time. Arbitrage describes the economic exploitation of price differences. A plant can be technically flexible without engaging in arbitrage, for instance when fixed tariffs, technical restrictions or regulations do not allow a reaction to prices. Conversely, arbitrage always presupposes flexibility. Without a shift in time, location or product, no price difference can be exploited.

Distinction from speculation, balancing energy and redispatch

Arbitrage is often equated with speculation. That is imprecise. Arbitrage exploits observable or expected price differences between points in time or products. Speculation generally means taking on price risks in anticipation of future price changes. In practice the two areas overlap, because a storage operator does not know for certain when charging what price it will achieve when discharging. Nevertheless, arbitrage in the power system primarily describes the ongoing exploitation of price spreads by physical assets, and not merely betting on rising or falling prices.

Arbitrage differs from balancing energy in its function. Balancing energy stabilises the grid frequency and is procured by the transmission system operators in order to offset very short-term deviations between generation and consumption. Arbitrage on the spot market follows market prices and shifts energy over quarter-hours, hours or days. Battery storage systems can provide both. However, revenue sources, technical requirements and responsibilities differ.

Redispatch is also not another word for arbitrage. Redispatch is an intervention by grid operators: power plants, storage units or consumers change their mode of operation in order to avoid or resolve grid congestion. The trigger is the physical limits of the power grid, not the market price alone. A plant can trade on the market for arbitrage reasons and subsequently be dispatched differently via redispatch if its planned feed-in or withdrawal would aggravate a congestion.

Why price differences are not automatically profits

The simple formula "buy cheap, sell high" leaves out several cost blocks. Storage units lose energy. The ratio of discharged to charged energy is called round-trip efficiency and is always below 100 percent. A simplified, purely illustrative example: a storage unit charges 100 megawatt hours at 40 euros per megawatt hour and has an overall efficiency of 85 percent. It can then sell only 85 megawatt hours. Merely to cover the purchase costs of 4,000 euros, it needs a selling price of a good 47 euros per megawatt hour. Only above that does the contribution margin for wear, operation and capital begin.

For batteries, degradation is added. Every charging and discharging process stresses the cells. Cycle depth, charging and discharging power, temperature and operating strategy influence ageing. An arbitrage transaction can look profitable on paper and still be unattractive if the additional wear eats up the price spread. Many operators therefore apply a minimum spread per cycle. For pumped-storage plants, other costs count, such as pumping losses, water management, maintenance and long-term capital costs.

Regulatory costs also change the calculation. Grid fees, levies, taxes and charges help determine whether a storage unit or flexible consumer responds to price signals. If costs are incurred several times for the same kilowatt hour when charging and later when consuming, arbitrage becomes less attractive. If, by contrast, fees are charged as flat rates or according to capacity, different incentives arise. Anyone who wants to understand the effect of arbitrage must therefore look at the pricing rules that trigger the behaviour.

Legal framework in Germany: grid fees for storage (as of November 2026)

In Germany, section 118(6) of the Energy Industry Act (EnWG) exempts newly built facilities for storing electrical energy from grid fees. The prerequisite is commissioning from 4 August 2011 within 18 years, i.e. by 4 August 2029. The exemption applies to the withdrawal of the electricity to be stored and runs for 20 years from commissioning. The first withdrawal of electricity during trial operation already counts as commissioning. Pumped-storage power plants whose capacity or storage volume has demonstrably been increased to a certain extent after 4 August 2011 can be exempted for ten years. Since the EnWG amendment of late 2025, the exemption applies insofar as the stored electricity is fed back into the same grid with a time delay. This means that mixed-use storage units and bidirectional charging points are also covered proportionately. Previously it applied only in the case of complete feed-back.

For the arbitrage calculation, the limits of this rule are important. It concerns only grid fees in the narrower sense and not, for example, levies or concession fees. In addition, section 118(6) EnWG allows the Federal Network Agency (Bundesnetzagentur) to lay down deviating rules, including on the temporal scope of application. With the procedure on the General Grid Fee Systematics for Electricity (AgNes), the authority is restructuring the fee system. On 6 August 2026 it put the draft determination out for consultation. The determination is to be issued at the end of 2026 and, from 2029, to replace the Electricity Grid Fee Ordinance (Stromnetzentgeltverordnung). According to the state of play presented in May 2026, new storage units are in future to pay a moderate capacity price, but no volume-based energy charges. Fee collection is to begin only after the special rules of section 118 expire. Dynamic grid fees for storage are envisaged at the earliest from 2030. Until the final decision, these points are provisional.

Systemic effect of arbitrage

Arbitrage can dampen price peaks. Storage units and flexible loads provide additional electricity or reduce demand in expensive hours. In cheap hours they increase demand or absorb surpluses. In this way they reduce price swings, as long as enough capacity is available and the plants respond to the relevant scarcity signals. This is not a side effect but part of the coordination function of electricity prices. With increasing competition among storage units, however, precisely the price spreads on which they live become smaller. Arbitrage revenues therefore tend to fall the more storage units are in the market.

In a power system with a lot of weather-dependent generation, arbitrage gains importance. Wind and solar plants have low variable costs but feed in depending on weather and time of day. As a result, there are more frequent hours with very low or negative prices and others with high prices when renewable feed-in is low. Arbitrage helps to shift energy over time. However, it does not replace firm capacity over arbitrarily long periods. A battery storage system designed for two or four hours can exploit short-term price spreads, but cannot on its own bridge a multi-day Dunkelflaute (prolonged period of low wind and solar output).

Arbitrage also shows that the value of electricity does not depend only on the quantity generated. A megawatt hour of solar power at midday has a different market value than a megawatt hour in a low-wind evening hour. The concept thus points to the relationship between electricity consumption, power, load profile and generation profile. For investments in storage, electrolysers, heat pumps or charging infrastructure, what counts is not only the annual energy quantity but also the time profile of prices and loads.

Spatial and product-related arbitrage

Arbitrage can also be spatial. If electricity is cheaper in one place than in another, trade between price zones can exploit this difference, insofar as transmission capacity between the zones is available. Within a uniform price zone, as Germany forms together with Luxembourg, however, the exchange price does not reflect regional grid congestion. The price is then the same in the north and the south, even though the grid situation differs. A storage unit can thus charge or discharge in a market-driven way and thereby trigger additional control needs on the grid side. The conflict arises where market price, grid physics and responsibility for congestion management diverge.

Product-related arbitrage exploits price differences between markets or delivery products, for example between the day-ahead auction and continuous intraday trading. A storage unit can earn revenues on the day-ahead market, on the intraday market, with balancing energy or through bilateral contracts. These revenues cannot simply be added up, because the same capacity is not fully available for several purposes at the same time. Anyone who reserves capacity for balancing energy can use it for spot-market arbitrage in the same period only to a limited extent. Optimisation consists in managing technical availability and market risks across several revenue channels.

Typical misunderstandings

A common misunderstanding is that arbitrage generates electricity. It shifts electricity quantities and changes dispatch decisions, but does not create additional energy. Because of storage losses, more electricity must be generated for the same later usable quantity of energy. The situation is different if the storage unit absorbs electricity that would otherwise have been curtailed. Energy then becomes usable that would otherwise have been lost. The benefit of arbitrage lies in the temporal adjustment to scarcities, not in an increase of energy. The emissions effect also depends on the individual case: it depends on which generation additionally runs during charging and which is displaced during discharging.

A second misunderstanding concerns negative prices. They do not automatically mean that arbitrage is profitable without risk. Negative prices can arise from high renewable feed-in, low demand, minimum output of conventional power plants, support rules or grid restrictions. A storage unit benefits only if it is allowed to charge, has free capacity, is not limited by connection or grid rules, and can later achieve a sufficiently high selling price.

A third misunderstanding sees arbitrage as purely private profit without benefit to the power system. Private revenue can coincide with a system-serving effect when prices indicate scarcities appropriately. But it can also reinforce wrong incentives if price zones conceal grid congestion or fees allocate costs incorrectly. Arbitrage is therefore neither automatically good nor automatically problematic. Its effect depends on which scarcity the price expresses and which costs remain outside the market price.

In summary, arbitrage in the power system translates temporal, spatial or product-related price differences into concrete operating behaviour. It connects storage, flexible demand, market prices and grid restrictions. Properly understood, it is not a trading trick but a coordination function. Electricity is absorbed or consumption is increased when prices indicate oversupply, and electricity is provided or saved when prices signal scarcity. Whether this helps the overall system depends on the technical losses, on the market and fee rules, and on whether prices reflect the actual limits of the power system.

Sources

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Edited by eCMS on 11.11.2026 14:28

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