Fact-checked by Grok 2 weeks ago

Merit order

Merit order is a foundational in competitive markets for dispatching resources, ranking available power plants by their ascending short-run marginal costs and activating them sequentially from lowest to highest until demand is met, thereby minimizing the total cost of production. This approach constructs an curve by stacking generator bids or offers, ensuring that low-cost units—often , hydroelectric, or renewables with near-zero variable costs—are prioritized over higher-cost plants. The merit order mechanism determines wholesale prices through uniform , where all dispatched generators receive the clearing set by the marginal (highest-cost) required to balance in real time. This incentivizes generators to bid close to their true marginal costs, fostering in markets like those in , , and parts of the , though deviations can occur due to constraints or ancillary requirements. A key implication is the merit order effect, whereby additions of low-marginal-cost capacity, such as intermittent renewables, shift the supply curve rightward, displacing costlier thermal plants and exerting downward pressure on prices during high renewable output periods. This dynamic has driven observed price reductions in markets with rising and penetration, underscoring the protocol's role in integrating variable generation while highlighting challenges for conventional plants' adequacy. ![German electricity production mid-December 2017 from BNetzA SMARD portal][center]
This illustrative snapshot from Germany's market reveals merit order in practice, with renewables dominating low-cost dispatch amid variable demand.

Fundamentals

Definition and Core Principles

Merit order refers to the ranking of electricity units by their ascending short-run marginal costs, determining the sequence in which they are dispatched to meet system while minimizing total production costs. Marginal costs primarily encompass expenses and operation and costs, excluding sunk fixed costs such as investments. This principle underpins economic dispatch in power systems, where the objective is to allocate across available units such that the incremental cost of serving the next increment of is equalized across dispatched resources. The core mechanism operates by stacking generation offers or bids from lowest to highest cost until is satisfied, with the marginal unit—the highest-cost needed—setting the uniform clearing price for all dispatched in competitive markets. In practice, dispatch follows this order to ensure operational efficiency, as lower-cost units like or renewables (with near-zero fuel costs) are prioritized over higher-cost plants. This approach assumes and focuses solely on variable costs, promoting cost minimization but potentially overlooking long-term capacity investments or network constraints unless explicitly incorporated. Key principles include the equality of marginal costs at the optimal dispatch point and the reliance on verifiable cost data or approximating true variables, which in centralized markets uses offer schedules to construct the merit order curve. Deviations from pure marginal costing can arise from strategic or regulatory interventions, but the foundational goal remains minimization for given . This framework has been standard in since the mid-20th century, evolving with to inform wholesale pricing dynamics.

Marginal Costs and Dispatch Ordering

In electricity generation, the marginal cost of a power plant refers to the incremental expense required to produce one additional megawatt-hour (MWh) of electricity, primarily encompassing variable fuel costs, operational maintenance, and any short-term variable inputs, while excluding fixed costs such as capital investments or depreciation. For conventional thermal plants like coal or natural gas facilities, marginal costs rise with output due to increasing fuel consumption and potential efficiency losses at higher loads, often ranging from $20–$50/MWh for efficient combined-cycle gas turbines during periods of moderate fuel prices in 2023. In contrast, renewable sources such as wind and solar exhibit near-zero marginal costs once operational, as they rely on free natural resources without ongoing fuel expenses, though they may incur minor variable costs for maintenance or curtailment. Nuclear plants similarly feature low marginal costs, typically under $10/MWh, dominated by fuel fabrication and handling rather than combustion. Dispatch ordering under the merit order principle arranges available generation resources in ascending order of their marginal costs to meet at minimum total system , a process known as economic dispatch. The system operator incrementally commits units starting with those offering the lowest —often baseload resources like or renewables—until demand is satisfied, with the marginal unit (the last dispatched) setting the uniform clearing price for all inframarginal producers in competitive markets. This approach ensures efficient by prioritizing low-cost generation, theoretically minimizing welfare losses from over-reliance on expensive peaking plants, which have marginal costs exceeding $100/MWh due to rapid-start capabilities for gas peakers or oil-fired units. In practice, security-constrained variants incorporate limits and reliability constraints, adjusting the merit order to avoid overloads while preserving minimization. The merit order dispatch mechanism underpins wholesale electricity markets by incentivizing generators to reveal costs through bids, though strategic bidding can deviate from true marginal costs, potentially leading to exercises in concentrated systems. Empirical data from U.S. independent system operators, such as , demonstrate that real-time dispatch follows this ordering, with resources offering below the marginal unit's bid cleared first, fostering and revealing signals through price spikes when high-cost units are needed. This framework, formalized in since the mid-20th century, relies on first-principles optimization: solving for the generation schedule that equates marginal costs across units subject to supply-demand balance, as deviations would increase total production expenses without necessity.

Historical Development

Origins in Traditional Utility Planning

In the early 20th century, as electric expanded into interconnected systems with multiple generating units, the need emerged for systematic methods to allocate among while minimizing costs, given the dominance of thermal generation reliant on , and gas. The economic dispatch problem, central to this allocation, was first formulated in the early to address the optimization of generation across units in these growing grids, prioritizing based on ascending marginal costs—primarily variable expenses per megawatt-hour produced. This approach, known as merit order dispatch, ranked available units by their incremental heat rates () adjusted for prices, loading the lowest-cost units first to meet forecasted while respecting technical constraints like limits and ramp rates. Under the vertically integrated, regulated structure prevalent in the United States and many other countries through much of the , utilities operated their own generation fleets to serve captive customers, with regulators approving rates based on recovered prudent costs. served as the core operational for short-term scheduling, enabling system operators to achieve least-cost dispatch without , as all generation was internally coordinated within control areas. Initial implementations relied on manual calculations or early analog computers, evolving with digital tools post-World War II to handle real-time adjustments every few minutes or hours, ensuring reliability while minimizing expenses passed through to ratepayers. This framework assumed stable demand forecasts and predictable fuel costs, focusing on variable operating expenses while treating fixed capital costs as sunk and recovered via regulated tariffs, rather than influencing dispatch order. By the mid-20th century, merit order had become standard practice across major utilities, underpinning unit commitment decisions and load following, though it occasionally incorporated non-economic factors like fuel diversity or reserve margins mandated by regulators. The principle's emphasis on marginal cost efficiency aligned with the public utility model's goal of cost-of-service pricing, predating wholesale market liberalization and providing a foundation for later competitive adaptations.

Evolution in Deregulated Markets

In the late and early , of sectors in several countries transformed the merit order from an internal planning tool of regulated utilities into the foundational mechanism for competitive wholesale markets. The United Kingdom's Electricity Pool, launched on April 1, 1990, following the Electricity Act 1989, required generators to submit sealed bids for energy supply, which were then stacked in ascending order of bid prices to determine the dispatch schedule and set a uniform clearing price equal to the marginal bid. This system, managed by the National Grid Company, aimed to replicate efficient economic dispatch while introducing , with initial bids closely reflecting short-run marginal costs such as fuel expenses. By 1998, the Pool had facilitated a shift toward gas-fired generation, displacing higher-cost plants in the merit stack, contributing to wholesale price declines from around £30/MWh in 1990 to under £15/MWh by 2000. Parallel developments emerged in the region, where 's 1991 Energy Act enabled bilateral trading and led to the creation of a power exchange in 1993, which expanded into the multinational in 1996. implemented a uniform-price where hourly bids from producers across , , and were aggregated into a merit order curve, with the marginal bid setting the price for all dispatched units. This cross-border integration, handling over 300 annually by the late , promoted hydro-dominated low-cost dispatch while accommodating variable supply through price signals. In the United States, the Federal Energy Regulatory Commission's Order No. 888, issued April 24, 1996, mandated to transmission grids, enabling the formation of Independent System Operators (ISOs) and Regional Transmission Organizations (RTOs) that centralized dispatch. These entities, such as PJM (operational as an ISO from 1997) and , adopted security-constrained economic dispatch algorithms that rank generator bids in merit order, incorporating transmission constraints to minimize total production costs while meeting demand. By the early , this framework covered regions serving over 200 million customers, with real-time and day-ahead markets clearing via locational marginal pricing derived from the marginal unit in each constrained area. Subsequent refinements in these markets addressed limitations of pure merit order bidding, such as strategic deviations from true marginal costs observed in the , leading to reforms like the New Electricity Trading Arrangements (NETA) in , which shifted to voluntary bilateral contracting supplemented by a balancing mechanism retaining merit order principles. In the and , integration of renewables and capacity markets evolved the stack to include zero-marginal-cost resources at the base, but the core dispatch logic persisted, influencing price volatility and signals amid growing .

Implementation

Economic Dispatch Mechanics

Economic dispatch mechanics involve the systematic allocation of among available units to satisfy forecasted at the minimum total , guided by the merit order principle of prioritizing units with the lowest short-run marginal costs. Marginal costs typically include expenses, variable and , and startup/shutdown considerations, excluding fixed costs like capital investments. In practice, system operators, such as independent system operators (ISOs) or balancing authorities, execute this hourly or in sub-hourly intervals to balance in real time. The core process commences with load forecasting, drawing on historical data, weather patterns, and -side predictions to estimate required generation. Generators submit bids reflecting their incremental , which are sorted in ascending order to construct a merit order . Dispatch proceeds by incrementally loading units from the base (lowest-, often or renewables with near-zero marginal costs) upward until supply meets or exceeds , with output adjustments to equalize the incremental ( lambda) across online units under ideal conditions. The marginal unit's bid establishes the clearing price in competitive markets, ensuring efficient resource utilization. Operational constraints refine this stacking: capacities enforce security-constrained dispatch to prevent overloads, modeled via DC optimal power flow; unit-specific limits account for ramp rates (e.g., 1-5% of capacity per minute for gas turbines), minimum run times (often 4-8 hours for coal plants), and reserve margins for contingencies (typically 3-15% of load). Algorithms like priority list or merit order loading approximate solutions by committing units sequentially while checking feasibility, whereas advanced methods employ to solve the full optimization: minimize ∑ C_i(P_i) subject to ∑ P_i = D and network constraints, where C_i is the and P_i output. In deregulated markets, such as those overseen by FERC in the U.S., economic dispatch integrates unit commitment decisions 24-48 hours ahead, transitioning to adjustments via , which fine-tunes outputs in seconds to maintain at 60 Hz. This mechanics enhances , with studies estimating annual U.S. savings of $10-50 billion from optimized dispatch compared to non-economic scheduling. However, deviations from pure bidding, due to strategic behavior or must-run units, can introduce inefficiencies.

Mathematical and Operational Formulation

The mathematical formulation of merit order dispatch corresponds to the economic dispatch problem, which minimizes total generation costs while satisfying and constraints. Formally, for n generators, it is expressed as: \min_{S_k} \sum_{k=1}^n C_k(S_k) subject to \sum_{k=1}^n S_k = D, $0 \leq S_k \leq \bar{S}_k \quad \forall k = 1, \dots, n, where C_k(S_k) denotes the cost function (often , C_k(S_k) = a_k S_k^2 + b_k S_k + c_k) for k, S_k is its output, D is , and \bar{S}_k is its . This ignores constraints and losses for simplicity, focusing on nodal or ; extensions incorporate flows via optimal flow models. Operationally, the solution approximates via merit order loading: generators are ranked by ascending marginal cost \lambda_k = \frac{\partial C_k}{\partial S_k}, forming a stepwise supply curve of cumulative capacity against \lambda_k. Dispatch proceeds by incrementally activating units from the lowest \lambda_k until \sum S_k = D, with the system marginal price set to the \lambda_k of the marginal (last) unit. For constant marginal costs per plant (common approximation for baseload vs. peaking units), dispatch is all-or-nothing up to capacity; linear programming or Lagrange multipliers enforce equality at the optimum, yielding \lambda_k = \lambda for inframarginal units. In competitive markets, this aligns with welfare maximization, dual to cost minimization, where uniform pricing equals the shadow price \lambda on the demand constraint. In practice, implementation uses merit order curves updated hourly with bids reflecting short-run marginal costs (, variable O&M), excluding fixed costs or capacity payments. For example, in markets as of 2023, this stacking yields locational marginal prices deviating from nodal optima by 5-15% due to omitted constraints, but it ensures efficient short-run allocation under assumptions. variants incorporate in D or renewables via expected costs, transforming to multi-period optimizations.

Impacts on Markets

The Merit Order Effect from Renewables

The merit order effect from renewables arises because and generators, with marginal costs approaching zero, are dispatched ahead of thermal plants in the merit order, effectively shifting the curve to the right and lowering the market-clearing wholesale price for all produced in that period. This displacement reduces the need to run higher-marginal-cost units, such as gas or , during periods of sufficient renewable output. Empirical analyses confirm this causal link, with the magnitude of price suppression scaling with renewable penetration and the steepness of the residual supply curve excluding renewables. In , one of the earliest and most studied cases, the effect was quantified using data and simulations, showing average wholesale reductions of 1.7 €/MWh in 2001, rising to 7.83 €/MWh in 2006 as renewable shares grew under the EEG feed-in system. The total annual savings from this effect reached 4.98 billion € in 2006, exceeding the net subsidies paid to renewables that year. Extending the analysis to 2008–2012, wind generation contributed average reductions of 3.59–7.80 €/MWh, while added 1.55–3.56 €/MWh, with the combined effect totaling 5–11.36 €/MWh; these estimates derive from models isolating renewable output from and confounders. Similar patterns appear in other markets, though magnitudes vary with system characteristics. In U.S. ISO/RTO regions from 2008–2017, each 1% increase in (VRE) penetration—primarily and —correlated with a , yielding average annual reductions under $1.3/MWh in most markets but $2.2/MWh from solar in CAISO due to midday output alignment with demand. In ERCOT (), empirical quantile regressions on 2010–2019 data indicate that a 10% rise in lowers median real-time by 1.04–1.47% in northern zones, with stronger effects at lower quantiles reflecting supply curve flattening. These findings hold across econometric approaches, including fixed-effects and instrumental variable methods to address from weather-driven renewable variability. The effect intensifies during high renewable output, often yielding negative prices when supply exceeds inflexible demand, as observed in (frequent sub-zero hours post-2010) and ERCOT (negative bids averaging -$2.6/MWh in high-wind periods). However, it diminishes at low penetrations or when renewables coincide with , and long-term estimates suggest partial offsets from capacity retirements or fuel switching, though short-run suppression remains dominant. This dynamic benefits wholesale buyers but erodes revenues for all inframarginal producers, including renewables themselves via price cannibalization.

Price Dynamics and Volatility

In electricity markets operating under merit order dispatch, price dynamics are shaped by the positioning of low-marginal-cost renewable sources at the front of the supply stack, which displaces higher-cost generators and reduces average wholesale . Empirical analyses in from 2014 to 2018 demonstrate that increased renewable generation lowered by 2.89 to 8.89 euro cents per , with the merit order effect accounting for the bulk of this reduction through systematic shifts in the supply curve. Across , this effect has persisted, with variable renewable energy (VRE) penetration exerting downward pressure on by flattening the merit order curve during periods of high output, though residual demand served by gas plants during peaks tempers the extent of the decline. However, these dynamics introduce greater price volatility, as VRE intermittency causes abrupt shifts in the effective supply curve: high renewable output correlates with near-zero or negative prices due to oversupply, while low output forces reliance on expensive peaking plants, triggering spikes. Studies of European markets from 2015 to 2025 show that rising VRE shares amplify short-term price variance, with renewable investments initially increasing volatility through merit order-induced fluctuations before potential long-term stabilization via scale effects. In 2022, amid high VRE penetration, European prices exhibited extreme swings, reaching 700 EUR/MWh in Spain during scarcity periods despite low-cost hydro availability, highlighting how merit order rigidity exacerbates oscillations between abundance and shortage. Price cannibalization further intensifies these patterns, as growing VRE erodes revenues for renewables themselves during their hours, compressing durations at low levels and widening the to scarcity-driven highs. This effect, observed in markets like and , stems from zero-marginal-cost bids saturating the merit order, reducing the frequency of mid-range prices and polarizing the distribution toward extremes. Empirical evidence from Iberian and German markets confirms that and integration heightens determinants, with hourly data revealing amplified standard deviations in prices tied to VRE variability, though interconnectors and flexibility measures can partially dampen spreads.

Criticisms and Limitations

Failure to Account for Capacity and Fixed Costs

The merit order dispatch system relies on short-term marginal costs for sequencing generation, systematically overlooking the fixed costs—such as capital expenditures for plant construction, maintenance, and decommissioning—that constitute the bulk of expenses for dispatchable technologies like , , and gas-fired plants. These costs must be recovered over the asset's lifetime, but under merit order , revenues are derived primarily from energy sales at marginal clearing prices, which fail to provide adequate signals for long-term when from low-marginal-cost renewables displaces higher-cost units. As a result, generators operate fewer hours, eroding their ability to amortize fixed investments, a dynamic exacerbated in markets with high renewable penetration where zero-marginal-cost output shifts the supply curve rightward, suppressing average wholesale prices. This oversight manifests as the "missing money" problem, wherein energy-only markets using merit order dispatch generate insufficient revenues to incentivize capacity additions or retention of reliable , as peak-period —essential for recovery—remains infrequent or capped by regulatory interventions. Empirical analyses of power markets with elevated shares of renewables demonstrate that the merit order correlates with declining generator profitability, leading to plant retirements without commensurate replacement ; for instance, in , wholesale prices fell by approximately 30-40% from 2010 to 2020 amid rising and deployment, contributing to the deactivation of over 10 of conventional by 2022. Without mechanisms to value recovery, such as uplift payments or separate capacity auctions, the system underprices the reliability attributes of firm , distorting investment toward intermittent sources that contribute negligibly to fulfillment. Capacity adequacy is further undermined because merit order treats all dispatched energy equivalently based on instantaneous costs, ignoring the distinct value of —the probabilistic ability to deliver power , particularly during . Dispatchable plants incur fixed costs to maintain readiness (e.g., spinning reserves or stockpiles), yet these are not compensated beyond margins, leading to chronic underinvestment; NREL modeling indicates that in scenarios with 30-50% , revenues cover only 60-80% of fixed costs for baseload units under pure marginal pricing. Critics, including analyses from the IEEE, argue this creates a reliability , as markets fail to internalize the societal cost of inadequate reserve margins, prompting ad-hoc interventions like out-of-merit dispatches that further erode price signals. In practice, jurisdictions like (ERCOT) have observed capacity shortfalls during high-demand events, attributable in part to merit order's neglect of fixed capacity investments, with 2021 winter storm Uri exposing vulnerabilities where pre-event retirements left the system with insufficient firm resources despite abundant intermittent capacity.

Reliability Risks and Backup Requirements

The prioritization of (VRE) sources such as and in merit order dispatch, due to their near-zero marginal costs, introduces significant reliability risks stemming from their and unpredictability. High VRE penetration levels—reaching 35-75% annually in systems like those in , , and —can reduce system by up to 30% for every 10% increase in VRE share, as converter-connected lacks the synchronous provided by traditional plants, heightening to and voltage . In the California ISO (CAISO), where contributed 11% of total in 2017 (up to 20% on peak days), rapid evening demand ramps—such as 15,000 MW increases—exacerbate risks when dispatchable capacity retires prematurely, driven by suppressed wholesale prices from midday VRE oversupply. Without adequate safeguards, up to 15% of projected global VRE (approximately 2,000 TWh by 2030) faces curtailment or integration delays, potentially increasing reliance on fossil fuels and undermining emission reductions by 20%. These risks manifest in depressed prices—often negative during high VRE output—which erode revenues for flexible dispatchable generators, diminishing incentives for in backup and leading to resource adequacy shortfalls during extended low-VRE periods, such as multi-day wind lulls. The merit order effect thus contributes to a "missing " problem in energy-only markets, where fixed costs of are not recovered through sales alone, prompting premature exits of baseload and peaker . System operators mitigate this through out-of-merit dispatch, where higher-cost units are activated for reliability despite economic signals, as seen in U.S. regional organizations (RTOs) maintaining target reserve margins. However, such interventions distort signals and incur additional costs, with U.S. expenses reaching USD 21 billion in 2022 amid rising VRE variability. Backup requirements intensify with VRE growth, necessitating flexibility across timescales: short-term (e.g., 50% increase needed by 2030 in for intra-hour balancing), weekly, and seasonal, met via batteries, pumped hydro storage (comprising most of the U.S.'s 25 grid-scale storage as of 2018), , and retained thermal capacity like flexible gas turbines. In high-penetration systems, reliability must-run contracts and capacity payments—implemented in markets like PJM and —ensure availability of dispatchable resources, while interconnections and synchronous condensers provide ancillary services. Curtailment rates of 5-10% in regions exceeding 30% VRE shares, such as and , underscore the operational trade-offs, often requiring compensatory mechanisms like Spain's strategic storage remuneration to avoid excessive waste. Global short-term flexibility demand is projected to double by 2030, primarily from solar PV variability, highlighting the need for approaches beyond pure merit order to sustain grid stability.

Market Distortions from Policy Interventions

Policy interventions, including subsidies for sources (RES), feed-in tariffs (FiT), and priority dispatch rules, modify the effective marginal costs used in merit order dispatch, often prioritizing intermittent generation over dispatchable plants regardless of system-wide . These mechanisms artificially lower the dispatch priority of subsidized RES by treating their variable output as having near-zero , displacing higher-cost plants and compressing wholesale prices through the merit order effect. However, this ignores externalities such as intermittency-induced backup needs and grid reinforcements, resulting in suboptimal where total system costs rise despite lower energy-only prices. Feed-in tariffs guarantee fixed payments to RES producers above market rates, decoupling their revenue from competitive bidding and incentivizing over-investment in low-capacity-factor assets that flood the market during peak output. In , solar FiT under the Sources Act led to a 7% average wholesale price reduction from 2008 to 2010, but amplified price volatility and daily maximum price drops by up to 20 euros per megawatt-hour on high-insolation days. dispatch mandates, requiring grid operators to accept RES output first, bypass merit order principles, forcing curtailment of cheaper conventional or inefficient ramping of backup plants, as seen in markets where RES exceeded 40% of supply, yielding negative prices in over 10% of trading hours in 2020. Such rules distort flexibility markets by favoring subsidized RES curtailment over cost-effective demand-side or options for relief. Capacity payments, introduced to address the "missing money" problem—where RES-driven price suppression erodes recovery for dispatchable capacity—further intervene by remunerating availability outside markets, potentially sustaining uneconomic plants and inflating total costs. In imperfect markets, these payments can exceed 20-30% of system expenses, as modeled in simulations for high RES scenarios, distorting signals toward overbuilding peakers while underincentivizing efficient baseload upgrades. Empirical analyses in European and U.S. markets show that combining capacity mechanisms with RES subsidies amplifies inefficiencies, with generators receiving dual payments that decouple dispatch from true marginal costs, leading to reliability risks during scarcity events like the 2021 Texas freeze or 2022 European gas crisis. These distortions compound under high RES penetration, where policies fail to internalize integration costs estimated at 1-2 euros per megawatt-hour for backup and balancing in systems by 2030, per modeling studies, often understated in academic assessments favoring rapid decarbonization. While proponents cite price suppression benefits, causal analyses reveal net losses from stranded assets and elevated consumer bills, as subsidies totaling over 100 billion euros annually in the by 2022 have not proportionally reduced emissions due to coal-to-gas leakage and import dependencies.

Alternatives and Reforms

Capacity Markets and Hybrid Approaches

Capacity markets address limitations in pure energy-only systems, such as those relying solely on merit order dispatch, by compensating generators for maintaining available rather than solely for dispatched energy. In these mechanisms, system operators procure commitments from resources to provide a specified amount of (typically in megawatts) during peak demand periods, ensuring resource adequacy and grid reliability over multi-year horizons. Auctions, often held annually or biennially, determine payments based on bids reflecting the cost of provision, with penalties imposed for failure to perform during scarcity events. This approach incentivizes investment in and , mitigating risks of underinvestment where marginal pricing alone fails to recover fixed costs like capital expenditures for peaker . Hybrid approaches integrate markets with energy markets that employ merit order dispatch for real-time operations, creating complementary revenue streams: energy payments for produced megawatt-hours via lowest-marginal-cost sequencing, and payments for availability assurances. For instance, in the PJM Interconnection's Reliability Pricing Model (RPM), implemented since 2007, forward auctions secure three years in advance across zones, with the 2024 Base Residual Auction clearing at $269.92 per megawatt-day in most areas—a nearly tenfold increase from prior auctions due to retirements and demand growth—while energy dispatch remains merit-order based. Similarly, the UK's , established under the Energy Act 2013, conducts competitive T-4 auctions (four years ahead) to contract up to 50 gigawatts of , blending with its energy-only wholesale market to support reliability amid . These hybrids aim to sustain incentives for flexible, reliable resources amid rising renewable penetration, where zero-marginal-cost intermittents suppress energy prices and erode scarcity signals. Such systems contrast with energy-only markets like Texas's ERCOT, where merit order dispatch prevails without dedicated capacity payments, relying instead on elevated scarcity pricing during shortages to signal investments; however, empirical evidence from periods of low price volatility suggests energy-only designs may underprovide , prompting reforms toward hybrids in jurisdictions facing adequacy risks. Capacity mechanisms have proliferated, with over 30 countries implementing them by 2016 per analysis, often to counteract distortions from subsidized renewables that depress wholesale prices and fixed-cost recovery. While critics argue capacity markets can foster over-procurement or inefficient resource mixes, proponents cite improved planning horizons and performance obligations—such as must-run provisions during tests—as enhancing causal reliability over reactive energy pricing alone.

Environmental and Multi-Objective Dispatch

Environmental dispatch modifies the traditional merit order by integrating environmental externalities, primarily emissions of CO₂ and other pollutants, into the assessment of generation units, thereby prioritizing lower- sources to reduce overall system impacts alongside economic costs. This approach typically augments the variable cost of and operations with a term representing the monetized environmental cost, such as λ × e_k, where λ denotes the emission penalty factor (e.g., derived from carbon pricing or estimates) and e_k is the rate per unit output for generator k. As a result, the dispatch sequence shifts; for instance, units may supplant coal-fired plants earlier in the stack if emission penalties elevate the effective cost of the latter sufficiently. Multi-objective dispatch advances this framework by formulating the to balance conflicting goals—most commonly minimizing total fuel costs and total emissions—subject to , capacity limits, and transmission constraints, without relying solely on predefined weights for environmental factors. Solutions often yield a of trade-off options, enabling decision-makers to select dispatch plans based on priorities, such as regulatory mandates or signals; for example, in a 30-unit test system, multi-objective algorithms have demonstrated reductions in emissions by up to 20-30% at modest cost increases of 5-10%, depending on the weighting scheme. Techniques like non-dominated genetic algorithms (NSGA-II) or are employed to navigate the non-convex solution space efficiently, particularly in systems integrating variable renewables where uncertainty in or output adds elements to the objectives. In practice, such dispatch has been proposed and simulated for integrated thermal-gas-renewable systems, where units serve as flexible bridges to renewables, yielding multi-objective improvements like 15% lower combined cost-emission metrics compared to single-objective economic dispatch. However, faces challenges including computational demands—solving high-dimensional problems can require hours for large grids—and to emission valuations, which vary widely (e.g., U.S. social cost of carbon estimates ranging from $50-200 per ton CO₂ in federal analyses, contested for over-reliance on integrated assessment models with uncertain parameters). Empirical applications remain limited to research or pilot microgrids, as real-time market operators prioritize speed and reliability, often approximating multi-objectives via carbon taxes rather than full optimization.

Recent Developments

Adaptations for High Renewable Penetration

In electricity systems with high penetration of (VRE) sources like and , the traditional merit order dispatch—prioritizing generators by ascending marginal costs—encounters challenges from frequent oversupply periods, resulting in zero or negative wholesale prices and underutilization of conventional capacity during scarcity. Adaptations focus on enhancing flexibility, integrating , and refining market rules to maintain without abandoning the core merit order principle. These include shorter dispatch intervals and improved VRE to minimize imbalances, as longer lead times exacerbate errors in intermittent output predictions, leading to inefficient curtailment or over-reliance on reserves. Energy storage systems, particularly batteries, are integrated into the merit order by allowing operators to bid negative prices during charging (absorbing excess VRE generation) and positive marginal costs during discharge, effectively extending the supply stack to price volatility. This adaptation mitigates the "" phenomenon observed in high-solar markets like , where midday oversupply depresses prices, by shifting energy to evening peaks; studies show storage can raise low-price troughs by up to 20-30% and reduce peak prices, improving overall system economics without subsidies in competitive settings. mechanisms further adapt the curve, enabling large consumers to curtail or shift loads in response to prices, acting as a virtual supply-side resource that complements VRE by aligning consumption with generation peaks. Separate flexibility and ancillary services markets address limitations of energy-only merit order by procuring ramping, frequency regulation, and reserves from sources like gas peakers or , decoupled from baseload dispatch to ensure grid stability amid VRE variability. In , post-2022 reforms preserved the merit order for markets while introducing two-way contracts for difference (CfDs) to provide revenue certainty for VRE investors, capping upside exposure during high prices but allowing pass-through of low prices to incentivize ; these were finalized in , aiming for 45% renewables by 2030 without inframarginal caps that distort dispatch. designs, such as co-optimization of and reserves, have emerged in markets like PJM and ERCOT, where algorithms jointly clear bids to minimize total system costs under uncertainty, reducing VRE curtailment by 10-15% in simulations compared to sequential dispatch. These adaptations collectively sustain merit order viability, though empirical data from 2020-2024 indicates persistent needs for grid expansions to handle spatial mismatches in VRE output.

Policy and Regulatory Changes Post-2022 Energy Crisis

The 2022 energy crisis, exacerbated by Russia's invasion of and subsequent reductions in supplies, exposed vulnerabilities in Europe's merit order-based dispatch systems, where gas-fired plants often set marginal prices during , amplifying cost into wholesale rates. Peak day-ahead prices in the EU reached €1,000/MWh in August 2022, driven by gas prices exceeding €300/MWh, prompting calls for redesign to enhance security and affordability without undermining dispatch efficiency. In response, the proposed reforms in March 2023, culminating in the adoption of updated Electricity Market Design (EMD) rules by the and Council in May 2024, effective from July 2024. These preserved the core merit order principle for short-term dispatch—ordering plants by ascending marginal costs to minimize system costs—while introducing mechanisms to buffer prices from gas dependency. Key additions include mandatory two-way Contracts for Difference (CfDs) for new renewable and capacity, where producers receive fixed premiums or pay back windfalls relative to a reference price, stabilizing revenues for inframarginal (low-cost) generators without altering real-time bidding or clearing. Further enhancements targeted flexibility and integration: transmission system operators must prioritize renewables in dispatch where feasible, expand intraday and balancing s for storage and , and implement tariffs to shift consumption from hours. Zonal reforms allow temporary market splitting in congestion-prone areas to reflect local supply-, potentially flattening effective merit curves by enabling cheaper cross-border flows, though uniform marginal persists within zones. Revenue from CfD adjustments and inframarginal rents is ring-fenced for rebates or investments, aiming to redistribute crisis-era windfalls from renewables. Nationally, extended and plant operations until 2024 via the 2022 Electricity Market Stability Act, injecting low-marginal-cost capacity into the merit order to avert shortages, while phasing out by April 2023; this temporarily depressed prices by €10-20/MWh on average but raised emissions. The , outside the , accelerated capacity market auctions post-crisis, awarding £2.3 billion in 2023 for reliable dispatch, indirectly supporting merit order by ensuring backup availability without direct intervention. These changes reflect a to retain merit order's cost-minimizing logic—evidenced by simulations showing efficiency losses from alternatives like pay-as-bid exceeding 5%—while layering safeguards against geopolitical shocks.

References

  1. [1]
    [PDF] Price Formation and Grid Operation Impacts from Variable ...
    In today's electricity markets, electricity resources are dispatched in merit order. When resources are bid into an electricity market, their supply offers are ...<|separator|>
  2. [2]
    [PDF] Price Formation in Zero-Carbon Electricity Markets
    In an electric power system, generation units are typically dispatched according to their economic merit order, which means that the system operator dispatches ...
  3. [3]
    [PDF] By StEVE CiCAlA - University of Maryland
    The central measure that makes this possible is what is known in the electricity sector as the “merit order.” This is an idealized power supply curve that ...
  4. [4]
    [PDF] COMPETITIVE ELECTRICITY MARKET DESIGN: A WHOLESALE ...
    Dec 17, 1998 · This merit order defines the short-run marginal-cost curve, which governs power supply. Similarly, customers have demands that are sensitive to ...
  5. [5]
    [PDF] The importance of adequate carbon prices
    May 5, 2021 · In uniform-pricing markets, power plant owners are incentivized to bid at their individual marginal cost. This merit order sorts all power ...
  6. [6]
    Long-term Equilibrium in Electricity Markets with Renewables and ...
    To summarize this issue, VRE may reduce Spot prices through the merit order effect, which in turn impacts other generators by increasing the “missing money ...
  7. [7]
    [PDF] Quantifying the "merit-order" effect in European electricity markets - KIT
    The supply curve, the so called merit order, is derived by ordering the supplier bids according to ascending marginal cost. The intersection of the demand ...
  8. [8]
    [PDF] Course notes for EE394V Restructured Electricity Markets
    More generally, economic dispatch means using generation with lower marginal costs whenever possible in preference to using generation with higher marginal ...
  9. [9]
    [PDF] the value of economic dispatch a report to congress pursuant to ...
    Nov 7, 2005 · In centralized markets, the merit order of available resources is determined using offer schedules for each resource rather than the variable ...
  10. [10]
    [PDF] Module E3 - Iowa State University
    Economic dispatch is the process of allocating the required load demand between the available generation units such that the cost of operation is at a minimum. ...
  11. [11]
    Marginal Costs of Power Generation & Merit Order - FlexPower
    Merit order is an economic model that explains the order in which power plants are used on a particular power market to cover electricity demand. Another term ...
  12. [12]
    Merit Order: How ancillary services get their price - Next Kraftwerke
    The merit order is based on the lowest marginal costs, ie the (operating) costs incurred by a power plant for the last megawatt hour produced.
  13. [13]
    [PDF] Overview of the Electric System - US EPA
    This theory of ―economic dispatch‖ predicts that any new resource shifts upward all resources above it in the dispatch order, reducing demand on the marginal ...<|control11|><|separator|>
  14. [14]
    [PDF] Study and Recommendations Regarding Security Constrained ...
    May 24, 2006 · For purposes of the joint boards' studies, the FERC adopted the following definition of security constrained economic dispatch: “the operation ...
  15. [15]
    How Resources Are Selected and Prices Are Set in the Wholesale ...
    As demand increases, higher-priced generators are dispatched with the highest-priced resources dispatched last. As demand decreases, higher-priced resources ...Missing: principles | Show results with:principles
  16. [16]
    Fifty years of power systems optimization - ScienceDirect
    May 27, 2025 · The ED problem was first formulated in the early 1920s when the need of new methods for optimizing the economic allocation of power generation ...
  17. [17]
    [PDF] A Primer on Electric Utilities, Deregulation, and Restructuring of U.S. ...
    Plants are generally dispatched (started and run) to serve loads based on production costs in what is called merit order, i.e., lowest production costs first.<|separator|>
  18. [18]
    [PDF] An Empirical Analysis of Bids to Supply Electricity in England and ...
    When the British government privatized and restructured its electricity industry in April 1990, one of the most significant steps it took was to introduce ...
  19. [19]
    [PDF] Why did British electricity prices fall after 1998? - mit ceepr
    In 1990, most of the generators' sales were hedged with three-year. “coal-related” contracts at relatively high prices, above the expected level of Pool prices.
  20. [20]
    The power market and prices - regjeringen.no
    Jul 26, 2016 · Following the liberalisation of the energy legislation in the other Nordic countries, the Nord Pool Spot power exchange was established in 1996.
  21. [21]
    Experience with the Nord Pool design and implementation
    The electricity industry of the Nordic countries went through a major restructuring during the 1990s. A wholesale market with significant competition has beenMissing: merit | Show results with:merit
  22. [22]
    Order No. 888 - Federal Energy Regulatory Commission
    Aug 5, 2020 · Order No. 888 Promoting Wholesale Competition Through Open Access Non-discriminatory Transmission Services by Public Utilities.Missing: merit | Show results with:merit
  23. [23]
    [PDF] Characterizing US Wholesale Electricity Markets - INL Digital Library
    Those resource owners with capacity submit bids to the ISO/RTO who then puts the bids into merit order, from smallest to largest, to form the capacity ...
  24. [24]
    Electric generator dispatch depends on system demand and ... - EIA
    Aug 17, 2012 · The exact order of dispatch varies across the United States, depending on such factors as fuel costs, availability of renewable energy resources ...<|separator|>
  25. [25]
  26. [26]
    The Merit Order - ETPA
    The merit order works by listing all available power plants in ascending order of their marginal costs. When there is a demand for electricity, the grid ...
  27. [27]
    (PDF) Economic Dispatch in power systems - ResearchGate
    Economic Dispatch Problems (EDP) refer to the process of determining the power output of generation units such that the electricity demand of the system is ...
  28. [28]
  29. [29]
    Economic Dispatch Optimization Strategies and Problem Formulation
    Economic dispatch problems (EDPs) represent a fundamental optimization challenge within traditional power systems. The principal aim of the EDP is to optimize ...
  30. [30]
    [PDF] Economic Dispatch and Introduction to Optimisation
    Problem Formulation. • Objective function. • Constraints. □. Load / Generation balance: □. Unit Constraints: A. B. C. L. C = CA (PA ) + CB (PB ) + CC (PC ). L = ...
  31. [31]
    [PDF] Modelling Network Constrained Economic Dispatch Problems
    A general mathematical formulation of the economic dispatch problem is then presented ... [PG PU ] = q, that the economic dispatch problem is in an equivalent ...
  32. [32]
    Real-Time Economic Dispatch and Reserve Allocation Using Merit ...
    Aug 9, 2025 · The method is based on the rules of Linear Programming and the classical method of merit order loading. The basis for the algorithm is shown as ...
  33. [33]
    Economic dispatch optimization using Lagrange multipliers as merit ...
    May 12, 2023 · The merit order strategy is needed to help power plant management define the most efficient and economical generators to be dispatch.
  34. [34]
    [PDF] The Merit Order and Price-Setting Dynamics in European Electricity ...
    In the merit order, the last accepted bid, the marginal bid, determines the market-clearing price. Gas plants set the price 55% of the time in 2022.
  35. [35]
    Comparison of Static, Dynamic, and Stochastic Economic Dispatch ...
    Aug 4, 2025 · This paper presents and compares four economic dispatch models: Static Economic Dispatch (SED), Dynamic Economic Dispatch (DED), Stochastic ...
  36. [36]
    A detailed analysis of the price effect of renewable electricity ...
    This paper seeks to analyse the impact of privileged renewable electricity generation on the electricity market in Germany.
  37. [37]
    [PDF] The Merit-order effect: A detailed analysis of the price of renewable ...
    If the difference is summed up according to Formula 3-1, the absolute volume of the merit-order effect can be estimated.Missing: mathematics | Show results with:mathematics
  38. [38]
    [PDF] The Merit Order Effect of Wind and Photovoltaic Electricity ...
    We estimate the merit order effect of both wind and photovoltaic (PV) electricity generation in Germany between 2008 and 2012. Our results indicate that for ...
  39. [39]
    [PDF] Impact of Wind, Solar, and Other Factors on Wholesale Power Prices
    Overall, the merit-order effect estimates reported in Table 1 are within the range of results for wind and solar in European countries. 2.2.2 Literature on ...
  40. [40]
    An empirical study of the merit order effects in the Texas energy ...
    Jan 21, 2022 · This research finds that when wind generation increases by 10%, median prices ($/MWH) in the North region of ERCOT decline by 1.47%, 1.04% and ...
  41. [41]
    On the long-term merit order effect of renewable energies
    Aug 6, 2025 · The merit order effect describes the lowering of the average wholesale electricity price due to increased capacity of renewable energies.
  42. [42]
    The impact of renewables on electricity prices in Germany
    Aug 6, 2025 · Results show that renewable energy sources considerably reduced electricity prices by between 2.89 ct/kWh in 2014 to 8.89 ct/kWh in 2017. This ...
  43. [43]
    [PDF] Energy Transition and Electricity Prices in Europe
    This negative impact, known as the merit-order effect in the literature, is attributed to the low marginal cost of renewables, which shifts the electricity.
  44. [44]
    Renewable Energy and Price Stability: An Analysis of Volatility and ...
    One of the most frequently cited mechanisms in explaining price formation is the merit-order effect. This principle describes how electricity generators are ...
  45. [45]
    Dynamics of Electricity Price Volatility and Its Impacts on Energy ...
    Sep 13, 2025 · Renewable energy investments increase short-term price volatility due to the Merit Order Effect, but in the long run, they enhance energy ...
  46. [46]
    [PDF] Potential limitations of marginal pricing for a power system - IRENA
    It explores how renewables can die of success (through cannibalisation and merit order effects), how price volatility may increase, and how socio-political ...
  47. [47]
    The cannibalization effect of wind and solar in the California ...
    The cannibalization effect is caused by the merit-order effect: for any given demand, zero marginal cost electricity technologies entering the market will ...
  48. [48]
    The “Merit-order effect” of wind and solar power - ResearchGate
    Aug 6, 2025 · In this study, we estimate the value of the Merit-Order Effect due to wind and solar power generation in the Iberian electricity market with ...
  49. [49]
    [PDF] Marginal Cost Pricing in a World without Perfect Competition
    Wholesale electricity markets employ marginal-cost pricing to provide cost-effective dispatch such that generators are compensated for their operational costs.
  50. [50]
    Empirical Analysis of the Merit-Order Effect and the Missing Money ...
    Aug 7, 2025 · In this paper, we show that both effects over-amplify the well-known merit-order effect of RES power feed-in, and indirectly also the missing- ...
  51. [51]
    [PDF] Revenue Sufficiency and Reliability in a Zero Marginal Cost Future
    Both of these VG impacts can be illustrated by the merit- order effect, which pushes more expensive resources up (or off) the dispatch stack. This is shown ...
  52. [52]
  53. [53]
    [PDF] Lessons from the Failure of U.S. Electricity Restructuring
    If the market were competitive, the peak generators would never recover their fixed costs and the baseload generators would be overpaid. More importantly, a ...
  54. [54]
    The new merit order: The viability of energy-only electricity markets ...
    An efficient new merit order emerges in electricity markets even when the grid is completely powered by intermittent sources with near-zero marginal costs.
  55. [55]
    [PDF] Challenges for Wholesale Electricity Markets with Intermittent ...
    Dec 18, 2018 · System operators have the flexibility to dispatch generators “out of merit order” if necessary to maintain reliability of the system and a ...
  56. [56]
    [PDF] Integrating Solar and Wind - NET
    This report aims to support policy makers on this issue by presenting an update of the IEA's phases of VRE integration framework, originally developed in 2017 ...
  57. [57]
    Market distortions in flexibility markets caused by renewable subsidies
    We show that subsidies can cause market distortions and lead to an inefficient selection of flexibility options to solve grid congestions.
  58. [58]
    (PDF) Revisiting the Merit-Order Effect of Renewable Energy Sources
    Energy-based power markets are, however, facing several market distortions, namely from the gap between the electricity volume traded at spot markets versus ...
  59. [59]
    Solar feed-in tariffs and the merit order effect: A study of the German ...
    The results show that the SEG has caused a 7% reduction in average electricity prices for this period. The average daily maximum price and daily price variation ...
  60. [60]
    [PDF] Quantifying the "merit-order" effect in European electricity markets - Ifri
    We present here a statistical analysis of the merit- order effect using the example of wind power in. Germany. The merit-order effect can be shown by analysing ...
  61. [61]
    A Capacity Market for the Transition towards Renewable-Based ...
    This shows the potential for distortions in a capacity market if subsidies for RES are not considered. However, Δ p t maybe overestimated due to inflated ...
  62. [62]
    Time to Double Down on Uniform Pricing in U.S. Energy Markets
    Oct 3, 2023 · Uniform Pricing Facilitates Merit Order Dispatch and Economic Efficiency; Non-Uniform Pricing Would Not. The RTO pricing mechanism story does ...<|control11|><|separator|>
  63. [63]
    Impact on Electricity Markets: Merit Order Effect of Renewable ...
    This chapter quantifies the merit order effect in 2030 and 2050 in European electricity wholesale markets by comparing electricity systems in a Reference and ...
  64. [64]
    [PDF] Do Renewables Drive Coal-Fired Generation Out of Electricity ...
    The mechanism under- lying the merit-order effect is renewable generation displacing higher-cost resources ... renewables-related policy can distort market ...<|separator|>
  65. [65]
    Understanding Wholesale Capacity Markets
    Jun 16, 2025 · A capacity market pays power suppliers for their commitment to meet future electricity needs. A capacity market does not pay for the energy produced.
  66. [66]
    Market and system operation - IEA
    Capacity markets are typically mechanisms where a system operator procures or imposes capacity requirements (in MW) to ensure system adequacy in the future.
  67. [67]
    [PDF] Capacity Market Fundamentals - Peter Cramton
    Electricity capacity markets work in tandem with electricity energy markets to en- sure that investors build adequate capacity in line with consumer ...
  68. [68]
    PJM's Electric Capacity Market: Background and Current Issues
    Jun 2, 2025 · PJM's capacity market saw its July 2024 auction clear at $269.92/megawatt-day (MW-day) in most parts of PJM, a nearly 10-fold increase from the previous ...
  69. [69]
    Energy vs. Capacity: How Teamwork Between Markets Supports a ...
    Jun 20, 2023 · The function of the energy market is to secure enough power supply for the system to meet demand in real-time;; The ancillary market maintains ...
  70. [70]
    The Capacity Market: everything you need to know | GridBeyond
    Aug 18, 2025 · In this article, we explore what the Capacity Market is, why it's needed, and how you can participate. What is the Capacity Market? The UK's ...<|separator|>
  71. [71]
    Capacity Market vs Energy Market
    Jul 6, 2023 · ERCOT in Texas is one example of an energy-only market. The market works with generators and retail electric providers in determining how much ...
  72. [72]
    Capacity Markets: The Way of the Future or the Way of the Past?
    Mar 27, 2020 · Capacity markets are used in some wholesale electricity markets to pay resources for being available to meet peak electricity demand.
  73. [73]
    Multi-Objective Environmental Economic Dispatch of an Electricity ...
    This paper presents a multi-objective economic-environmental dispatch (MOEED) model for integrated thermal, natural gas, and renewable energy systems
  74. [74]
    Multi-objective-based economic and emission dispatch with ...
    Sep 16, 2024 · In this work, a study of economic and emission dispatch issues based on the multi-objective optimization is solved, and generation costs and emissions are ...
  75. [75]
    Multi-objective economic and emission dispatch problems using ...
    This study aims to identify optimal strategies for power system networks, optimizing parameters like power flow equations and equipment limits to achieve ...
  76. [76]
    A multi-objective optimisation approach with improved pareto ...
    Jun 11, 2024 · We observed that our approach can reduce 6.4% of fuel costs and 9.1% of computational time in comparison to the classical PSO technique.
  77. [77]
    [PDF] Adapting market design to high shares of variable renewable energy
    Merit order effect: the displacement of thermal generation units from the generation economic dispatch during hours of high renewable production, driven by ...
  78. [78]
    Toward Sustainable Electricity Markets: Merit-Order Dynamics on ...
    The historical merit-order data were modified under the assumption that all hypothetical PV energy enters the market at zero marginal cost (0 CAD/MWh). This ...
  79. [79]
    Demand-based pricing stabilizes the electricity market of the future
    Feb 28, 2024 · The oversupply of electricity from renewables can be consumed flexibly during moments of high supply. For example, oversupply from renewables ...
  80. [80]
    Electricity market reform - consilium.europa.eu
    This mechanism is called the merit order principle. When high prices hit consumers in summer 2022, EU countries acted immediately to ease the burden on citizens ...Missing: VRE | Show results with:VRE
  81. [81]
    European Electricity Market Reform - Freshfields Transactions
    May 2, 2024 · The merit order principle which fixes electricity prices to the most expensive energy source sold at a given moment, will remain intact.
  82. [82]
    [PDF] Reforming the EU electricity market - European Parliament
    Mar 23, 2023 · In its 2022 position paper, WindEurope calls for maintaining short-term wholesale markets based on marginal pricing and merit order, boosting ...
  83. [83]
    Parliament adopts reform of the EU electricity market | News
    Apr 11, 2024 · The reform adopted on Thursday will make the EU electricity market more stable, affordable, and sustainable.
  84. [84]
    EPEX SPOT prepares implementation of European Electricity Market ...
    Next week, on 16 July 2024, the European Electricity Market Design (EMD) reform enters into force. EPEX SPOT welcomes the reform, as it globally confirms the ...
  85. [85]
    The New EU Electricity Market Design: The Main Me | Lexgo.be
    Jul 25, 2024 · There was no reform of the main principle underlying the short-term electricity market. The merit order principle will continue to apply, so ...
  86. [86]
    Phased European Union electricity market reform - Bruegel
    In this paper, we set out a framework for evaluating the many interrelated issues in the current EU electricity market reform.
  87. [87]
    Merit order shifts and their impact on the electricity price - FfE
    Sep 14, 2022 · The merit order has changed significantly due to the substantial rise in fuel prices, resulting in high market prices and high profits for ...
  88. [88]
    Reforming European electricity markets: Lessons from the energy ...
    Indeed, Europe has been updating its renewable energy targets up to 45% in order to meet the goal of reducing net greenhouse gas emissions by at least 57% by ...