Collective Self-Consumption (CSC)

• Collective self-consumption (CSC) is a model where multiple consumers and prosumers jointly use locally generated renewable energy to maximize self-consumption and enhance economic savings.
• Mathematical and operational models like MILP and MPC optimize PV, battery sizing, and equitable energy allocations under varying regulatory frameworks.
• Real-world CSC implementations in Europe show improved self-consumption rates, fair energy sharing, and significant grid import reductions while informing policy reforms.

Collective self-consumption (CSC) denotes schemes in which multiple consumers and/or prosumers—entities that both generate and consume electricity—jointly maximize the local consumption of distributed renewable energy (especially photovoltaic) before resorting to grid imports or exports. Regulatory frameworks enabling CSC have proliferated in Europe, especially following the EU Clean Energy Package, and now underpin a variety of shared energy community models, local energy markets, and optimisation-based allocation protocols across Spain, France, Switzerland, and Italy. The principal objectives of CSC schemes include increasing self-consumption rates (SCR), achieving economic savings, promoting equitable energy sharing, and mitigating distribution grid impacts.

1. Legal and Regulatory Frameworks

CSC is defined and governed by national legislation shaped by European directives, with operational details varying by country and region.

• Spain: Royal Decree 244/2019 abolishes the "sun tax," establishes two main self-consumption categories—simplified net billing (≤100 kW) and direct sale (>100 kW)—and allows collective self-consumption for co-located prosumers sharing a transformer, cadastral registry, or within 500 m. Monthly net balances cannot be negative; surplus exports beyond credited amounts are unrated. Fixed sharing coefficients for each co-owner are permissible (Gallego-Castillo et al., 2020).
• France: Article 119 of Law 2015-992 and ensuing orders define CSC as local production sharing via the public grid, with maximum system size (3 MW) and perimeter (2 km diameter). "Keys of repartition" (KoRs) allocate production to consumers every 30 minutes, with allocation modes including static, default dynamic, and customized dynamic (Contreras-Ocaña et al., 2020, H. et al., 25 Jan 2026, Couraud et al., 22 Aug 2025).
• Switzerland: As of 2026, the Federal Electricity Supply Act enables Local Electricity Communities (CEL) in the same municipality and DSO service area. Participation requires ≥5% renewable connection capacity and smart metering. Internal exchanges attract reduced network-usage tariffs: 40% discount if on same LV feeder, 20% for shared transformer (Gonzalez et al., 19 Dec 2025).
• Italy: Implements EU directives via ARERA and GSE; "virtual self-consumption" incentives pay for the minimum of group import and export, with the group administrator optimizing battery management for cost savings (Awerkin et al., 10 Mar 2025).

CSC mechanisms commonly prioritize legal eligibility, transparent allocation of benefits, grid import/export minimization, and fairness.

2. Mathematical and Operational Models

Optimization frameworks, deterministic or stochastic, form the backbone of CSC sizing, allocation, and real-time control:

• Spanish CSC Model (annual/hourly):
  • Decision variables comprise PV installed capacity $P_{pv}$, battery capacity $E_{bat}$, hourly charge/discharge rates, and grid interchange $g^{in}_t, g^{out}_t$.
  • Objective: Minimize Equivalent Annual Cost (EAC) including capital expenditures and time-varying energy import/export, subject to technical, rooftop, and remuneration constraints.
  • Key constraint: monthly export remuneration is capped by import value, with the export-to-import remuneration ratio $\alpha \approx 0.46$ (can be raised to $\alpha \approx 0.63$ by including economic value of avoided losses) (Gallego-Castillo et al., 2020).
• French MPC-based CSC (rolling 30-min window):
  • Implements real-time allocation using Model Predictive Control; operation tracks long-term equitable supply references even under PV output uncertainty.
  • Settlement problem: ex-post convex QP reallocates realized generation to ensure annual supply adheres to the long-term fair reference (Contreras-Ocaña et al., 2020).
  • Keys of repartition $G(t)$ must respect instantaneous capacity and consumption feasibility: $$\sum_{i} g_i(t) = \min(g(t), \sum_i l_i(t)), 0 \leq g_i(t) \leq l_i(t)$$.
• Swiss Techno-Economic Model:
  • Objective: Minimize total cost of ownership (TOTEX), with annuity factor $R$ incorporating the discount rate and lifecycle.
  • SCR: $$\text{SCR} = E_{\text{local\_used}} / E_{\text{local\_gen}}$$; internal matching ratio $\eta_{match}$ quantifies supply-demand synergy.
  • Storage model: centralized batteries sized as the sum of individual optimal capacities, but grid impact strongly dependent on placement and operation (Gonzalez et al., 19 Dec 2025).
• Battery Management under Incentive Tariffs (Italy):
  • Stochastic optimal control of PV + battery system modeled as a Hamilton–Jacobi–Bellman PDE.
  • Virtual self-consumption quantified as $\min\{D_t, E_t\}$ for instantaneous demand $D_t$ and market-fed energy $E_t$.
  • The "bang-bang" optimal control policy operates in four modes: maximal charge, maximal discharge, rest, and matching group demand (Awerkin et al., 10 Mar 2025).
• Network-Flow MILP for Strategic Design:
  • Single- and multi-loop CSC design cast as mixed-integer LP optimizing loop formation, flow allocation, and grid exchange.
  • Benders and Dantzig–Wolfe decompositions enable tractable scaling to hundreds of actors and months-long horizons by separating discrete loop-selection from continuous flow allocation (Chasseray et al., 2024).

3. Energy Sharing and Allocation Mechanisms

Allocation of local renewable production is operationalized via time-resolved mechanisms, each with distinct fairness and efficiency properties:

• Static Allocation: Proportional, fixed KoRs (as in investment shares or forecasted consumption) (H. et al., 25 Jan 2026).
• Default Dynamic Allocation: KoRs recomputed at every interval to match proportional real-time consumption, maximizing SCR when total load exceeds production.
• Customised Dynamic Allocation: PMO can define prioritization rules, e.g., favoring buildings with higher tariffs or strategic loads; these maximize savings where tariff heterogeneity is significant.
• LEM Mechanisms (France):
  • Pro-rata: Each consumer/producer receives/exports proportionally to instantaneous demand/production.
  • Standard Glass-Filling: Iterative equitable allocation followed by redistribution of surplus.
  • Prioritized Glass-Filling: Historical cumulative benefit used for prioritization, favoring least-advantaged members.
  • Uniform-Price Double Auction: Real-time market clearing matches highest willingness-to-pay with lowest offer prices.

In practice, dynamic and customized sharing rules outperform static arrangements in SCR and financial savings, especially under variable load and generation (H. et al., 25 Jan 2026, Couraud et al., 22 Aug 2025).

4. Quantitative Performance and Sensitivity Analysis

Empirical and modeled analyses reveal how technical, economic, and regulatory parameters shape CSC outcomes:

• Spanish Case: At standard costs, net-billing with surplus remuneration increases optimal PV sizing (2.73 kW/household), rooftop use (45%), and ASR (22.8%) versus no-remuneration scenario (1 kW/household, ASR 16.2%). SCR rises to ≈47%. Simple payback ≈5–7 years at average retail prices. Battery uptake is conditional on major cost reductions (below 140 €/kWh) (Gallego-Castillo et al., 2020).
• Swiss Case: Optimal PV-to-load ratio $\alpha=1$–$2$ maximizes internal exchange. Grid imports drop 27–46%, DSO revenue loss is 17–36%. Batteries marginally improve profits (up to 5%) and LCOE (~2–3%), but technical grid relief is limited by optimal small sizing (Gonzalez et al., 19 Dec 2025).
• French PV-Sharing Experiment: Dynamic allocation methods improve SCR by 3.3 percentage points over static allocation in low-irradiation scenarios, with 100% SCR attainable when high-duty-cycle consumers (e.g., data centres) are included. Customised dynamic sharing boosts financial savings up to 41% over static allocation in certain scenarios (H. et al., 25 Jan 2026).
• Storage Management: "Match demand" control regime optimally utilizes CSC incentives, broadening the discharge region and enhancing group self-consumption under virtual exchange (Awerkin et al., 10 Mar 2025).
• MILP Scaling Insights: Benders decomposition excels for long time horizons; Dantzig–Wolfe benefits large actor sets in semi-rural contexts. Increasing installed capacity cap or actor density increases total cost savings but SCR plateaus beyond ≈85% (Chasseray et al., 2024).
• LEM Fairness Results: At 40% PV uptake in 20-household communities, average bill reduction is ≈12%. Prioritized glass-filling achieves best Jain index (≈0.99), pro-rata and double auction excel in meritocratic fairness. Savings are maximized at moderate PV uptake; equity and incentive alignment depend on allocation rule selection (Couraud et al., 22 Aug 2025).

Scenario/Parameter	Optimal PV Sizing	ASR/SCR (%)	Battery Adoption	Economic Savings
Spain, Net Billing	2.73 kW/hh	22.8/46.7	Very limited	≈0.03 €/kWh saved
Switzerland, CEL100	α = 1–2	≈45–65	105 kWh (modest)	5–9% bill drop
French PV-sharing, DC	N/A	100 (all)	N/A	Up to +41% vs stat.
LEM, 40% PV Uptake	3 kW/hh (simulated)	SCR ≈ 70	N/A	12% bill reduction

5. Fairness, Equity, and Community Design

The intersection of economic benefit, equity, and meritocracy is crucial to CSC scheme acceptance and sustainability:

• Fairness Metrics: Jain’s index (equality), min-max ratio (Rawlsian equity), and a meritocratic index (deviation from ideal proportional allocation) allow rigorous quantitative comparisons of sharing rules.
• Allocation Mechanism Trade-offs:
  • Prioritized glass-filling delivers maximum egalitarian and min-max fairness, favoring the least benefited but potentially disincentivizing high contributors.
  • Pro-rata and double auction excel in meritocratic fairness, rewarding active contributors but increasing utility disparity.
  • Standard glass-filling offers a compromise between equality and meritocracy (Couraud et al., 22 Aug 2025).
• Community Composition Guidelines: Maximizing internal exchange and economic gains requires diversity—mixed portfolios of producers, consumers, and flexible assets. Design should target PV-to-load ratios in 1–2 range and consider inclusion of high-duty-cycle loads.

6. Implementation, Scalability, and Grid Impact

CSC implementation leverages metering infrastructure, IoT, and distributed control platforms:

• Metering and Data Flow: Smart meters and dedicated IoT (e.g., Tecsol TICs, LoRaWAN, blockchain-backed registries) underpin transparent, auditable sharing, and billing (H. et al., 25 Jan 2026).
• Long-Term/Short-Term Integration: Rigorous MILP and MPC frameworks scale allocation from strategic design (loops, sizing) to real-time operation (ex-post settlement, dynamic allocation).
• Grid Impacts: Modest technical grid relief is typical; poorly sized batteries can create new power peaks. Placement and operation of storage assets must account for voltage and congestion management, and regulatory/tariff adaptation is needed to align cost recovery with the evolving distribution economics (Gonzalez et al., 19 Dec 2025).
• Scalability: Decomposition techniques (Benders, Dantzig–Wolfe) efficiently handle hundreds of actors and extended time horizons, especially in sparse, spatially clustered networks (Chasseray et al., 2024).

7. Policy Recommendations and Practical Outlook

CSC effectiveness depends critically on regulatory alignment, financial mechanisms, and ongoing innovation in community structure and sharing rules:

• Remuneration Design: Inclusion of avoided losses in export credit (as in Spain’s PERD) improves alignment and net incentives without extra subsidy (Gallego-Castillo et al., 2020).
• Financial Instruments: Promoting zero/low-interest loans and innovative on-bill financing can lower the discount rate, directly improving CSC economics.
• Legal Refinements: Time-varying KoRs and explicit support for mixed, heterogeneous load/generation profiles enhance operational fairness and matching (Gonzalez et al., 19 Dec 2025).
• DSO and Tariff Reforms: Distribution system operators require evolved cost-recovery frameworks and adaptive tariff structures to manage revenue risk and incentivize flexibility assets.
• Algorithmic Best Practices: Communities should select allocation mechanisms per their fairness priorities—prioritized glass-filling for social equity, pro-rata/double auction for investment incentive, standard glass-filling for balanced outcomes (Couraud et al., 22 Aug 2025).
• Future Directions: Integrating battery and demand-side flexibility into meritocratic metrics, scaling dynamic sharing algorithms, and performing full-year validation studies are recommended.

Collective self-consumption continues to advance as a principal paradigm for integrating distributed renewables, unlocking material economic, fairness, and grid benefits when implemented under rigorous optimization, scalable allocation, and adaptive regulation.